l98 cylinder head question
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l98 cylinder head question
ok i have some cast iron 350 tpi heads casting number 083 now i have ported and cc measured the intake slots but have yet to blend the bowls. My question however is about the exhaust runners. I have cleaned them up and i am wanting to gasket match and port them out but im afraid of hitting a water jacket or something so i was wondering how much clearance i have
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Re: l98 cylinder head question
well i cant find my sheet from the flow bench number but the ratio was like 59% which id rediculous the exhaust should be closer to 70-75% of the intakes flow i can open up the throat and blend the bowl but in all honesty i dont think its gunna matter cause there is so much metal inside of my header gasket which just shows i could port them out but i just wanted some clearance info
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Re: l98 cylinder head question
Exhaust port flow IS horsepower potential. Look at AFR. They alone are proof enough.
OP, Go read my sticky thread on porting SBC heads. It's in the engine swap sub-forum. Your exhaust ports are slightly different, but even so, just follow the instructions for the Vortec exhaust ports. You can get huge improvements without removing much iron, you just have to remove it in the right places.
Re: l98 cylinder head question
What are you smoking?
Exhaust port flow IS horsepower potential. Look at AFR. They alone are proof enough.
OP, Go read my sticky thread on porting SBC heads. It's in the engine swap sub-forum. Your exhaust ports are slightly different, but even so, just follow the instructions for the Vortec exhaust ports. You can get huge improvements without removing much iron, you just have to remove it in the right places.
Exhaust port flow IS horsepower potential. Look at AFR. They alone are proof enough.
OP, Go read my sticky thread on porting SBC heads. It's in the engine swap sub-forum. Your exhaust ports are slightly different, but even so, just follow the instructions for the Vortec exhaust ports. You can get huge improvements without removing much iron, you just have to remove it in the right places.
Sprint cars and other engines, REAL performance engines, have 900HP and exhaust ports that flow 240ish.
I don't need a lecture from you about SBC heads. I have forgotten more than you'll ever know and have written on the subject extensively. I know more about what goes on behind the scenes of this industry than you'll hope to know. Now get off your high horse and go read this months addition of popular hodrodding and come back with some more garbage.
Last edited by InjectorsPlus; Sep 17, 2010 at 07:19 PM.
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Re: l98 cylinder head question
Ha Ha Ha Ha Ha ! Good one. You think that being a sponsor is gonna add you any credibility? Heck NO!
Atilla's stuff is all proven, everyone here respects his facts, even if they hate his personality, because he's never yet failed to prove his claims, so far as I can tell.
When Atilla says you need good exhaust flow to make good power, you better believe him.
This isn't sprint crap. This is mostly street, with some drag racing, and the rare autocross or whatever. We don't give a rat's butt what works in sprint.
You didn't tell the lift of that 240 cfm, you didn't mention intake flow, you didn't give cam specs, you didn't give bore or stroke. This proves you have nothing but a desire to prove yourself right. You're barking up the wrong tree.
Yes, tree. Like a good tree, Atilla has stood through many passing storms like you, they're all gone now.
Take a word to the wise, and apologize. It's your only hope for saving face. Otherwise, you'll find yourself unwelcome here.
Atilla's stuff is all proven, everyone here respects his facts, even if they hate his personality, because he's never yet failed to prove his claims, so far as I can tell.
When Atilla says you need good exhaust flow to make good power, you better believe him.
This isn't sprint crap. This is mostly street, with some drag racing, and the rare autocross or whatever. We don't give a rat's butt what works in sprint.
You didn't tell the lift of that 240 cfm, you didn't mention intake flow, you didn't give cam specs, you didn't give bore or stroke. This proves you have nothing but a desire to prove yourself right. You're barking up the wrong tree.
Yes, tree. Like a good tree, Atilla has stood through many passing storms like you, they're all gone now.
Take a word to the wise, and apologize. It's your only hope for saving face. Otherwise, you'll find yourself unwelcome here.
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Re: l98 cylinder head question
lol torquer you just torqued his *** xD but yeah my ;ocal machine shop told me just simply blening bowls and a mirror finish on the exhaust that i would be flowin really good but hell i know that when i had these flow benched the ratio between exhaust and intak was trash the exhaust was i think 57% of the intake so i set out to fix that number closer to 70% but like i said dont know how much to port and i will take a look at that sticky thread atilla
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Re: l98 cylinder head question
Post your flow data would you?
Don't listen to the machine shop about the blend and polish the real gains will be around the valve guide and short side radius in the exhaust port. The port is small and the valve guide is huge and right in the middle of the highest flow area and shaped in a way that would create a LOT of turbulence all around it. Thinning and blending all the sharp edges will help a lot.
When I do exhaust I only grind for very short periods of time and constantly check work. You don't want to make them larger you want them to be more efficient.
Don't listen to the machine shop about the blend and polish the real gains will be around the valve guide and short side radius in the exhaust port. The port is small and the valve guide is huge and right in the middle of the highest flow area and shaped in a way that would create a LOT of turbulence all around it. Thinning and blending all the sharp edges will help a lot.
When I do exhaust I only grind for very short periods of time and constantly check work. You don't want to make them larger you want them to be more efficient.
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Re: l98 cylinder head question
if and when i find my read out of the bench test i will :S the place where i was doing all my porting work got the electricity turned off cause they printed the bill wrong but today when it is restored i will look for it i need to find it anyway for the before and after if i do get them flowed again :S 10 dollars a cylinder is ridiculous in my books
Re: l98 cylinder head question
There's lots of reasons these AFR builds show more dyno power...none of which have anything to do with exhaust flow.
Tell ya what, I'll read up more on Attilla's stuff, maybe this is just a blip. Words like used in this thread such as "efficiency" have no place in head design, so I'm just suspect as to the information is all. I have less than 200 posts, so in deference I'll read up a little.
However, I think as a community rather than attack me, perhaps consider that another point of view can be discussed, and the facts laid out as to how this stuff works instead of just just blindly accepting what someone tells you.
I'm all for civil discussion, but to dismiss my point out of hand, I think the membership deserves an apology.
I still stand by my point, most heads come with exhaust ports that flow enough, perhaps some gasket matching, and clean up would help, but what comes from the factory is adequet.
I know, I have sat with the R&D guys in their factory for no less than 3 major head manufacturers. And in each case, I was invited. I know what goes into it designing a head and what matters. Now, I'm no expert on all things engine, but I do know what makes a head work, and what a fuel system needs. On those topics I will be accurate.
I can be an asset, if you choose to listen. Why dismiss me before proving I'm a crackpot?
Last edited by InjectorsPlus; Sep 21, 2010 at 09:14 AM.
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Re: l98 cylinder head question
Given everything else equal a 65cc port and a 70cc port with the same peak flow the 65cc port will make more power everywhere under peak HP and yield a flatter power-band. That's physics at play there, the smaller port obviously has better velocity.
Re: l98 cylinder head question
I think I'm the one who was talking about efficient port designs. Why do you think it has no place in head design? If that was the case wouldn't we all be using 230cc heads? I'm interested in what you've learned to the contrary of that.
Given everything else equal a 65cc port and a 70cc port with the same peak flow the 65cc port will make more power everywhere under peak HP and yield a flatter power-band. That's physics at play there, the smaller port obviously has better velocity.
Given everything else equal a 65cc port and a 70cc port with the same peak flow the 65cc port will make more power everywhere under peak HP and yield a flatter power-band. That's physics at play there, the smaller port obviously has better velocity.
First of all 65CC and 70CC refer to the chamber size not the port size. Ports are typically measured in three digit numbers such as 215, 225, 180, 195, etc... A larger combustion chamber WILL HELP FLOW as will a larger valve, like a 2.05 vs. a 1.95.
The one element you forget to consider is called CSA, or cross sectional area. A bigger port has more CSA by definition. Think of it this way, a paper towel insert (cardboard thing) can flow XXX air. IF you increase the diameter, hence the CSA or AMMOUNT OF AREA the air comes in contact with, you will SLOW DOWN the port.
I believe your definition is that a smaller port that provides as much flow as a bigger port, is a "more efficient" port and will make more. There is no place in science, research and development, or head design that supports that theory. It is all marketing bulls**t.
A small port that has high flow will produce what I term a "dumptruck" motor. Tons of torque to pull stumps, but times that basically suck at the track. Is the goal to pull stumps or be fast? If the goal is to be fast, RPM equals HP and you have to let the motor spin up, and small ports, no matter what they flow, will not make power at higher RPMS, they will fall on their face too soon.
Head manufacturers have to balance flow with port speed, with fuel suspension. A flow number off a flow bench is essentially useless to do that. Too many people put too much emphasis on flow numbers, see below:
Re: l98 cylinder head question
Here's a little diddy from Reher Morrison, one of the most famous engine builders of all time:
http://www.rehermorrison.com/blog/?p=275
http://www.rehermorrison.com/blog/?p=275
#70- Airflow Fallacies: Avoiding the Pitfalls of the Flow Bench
Category: Tech Talk —
Published in National Dragster
Written by David Reher
“What’s it flow?”
Whenever a conversation about cylinder heads begins with that question, I cringe. I know where this discussion is going, and it’s not good. When a racer wants to distill the performance of a highly developed cylinder head down to a single number, I know I’m dealing with someone who is fixated on the flow bench.
I can speak from hard-earned experience, because there was a time when the flow bench was the center of my universe. When my partners Buddy Morrison and Lee Shepherd constructed our first flow bench in the ’70s, it was a revelation – or so we believed. We were addicted to airflow, and like three flow bench junkies, we convinced ourselves that big flow numbers translated to quicker elapsed times. But that was more than 30 years ago, and since then I’ve learned to avoid the pitfalls of flow bench testing.
Unfortunately many racers coming into the sport haven’t been taught the lessons that Buddy, Lee and I learned the hard way. Cylinder head manufacturers, porting shops, and engine builders constantly advertise flow numbers – and I confess that I’m sometimes guilty as well. In this environment, it’s understandable that some racers think it’s all about maximum airflow. They shop for the biggest cfm number at the lowest price, like finding a screaming bargain on a 52-inch TV at WalMart.
The strategy to win the “Biggest CFM Contest” is simple: Grind the largest port that will physically fit in the head, use the biggest valves that will fit the combustion chambers, and test it on the biggest fixture you can find. That head might win the prize for airflow, but it won’t win on the dyno or on the race track.
The factors that determine the performance of a cylinder head are complex. A head that is ported without considering air speed, the size of the engine, the rpm range, the location of the valves, and a dozen other parameters isn’t going to be the best head, regardless of its peak airflow. And yet I see racers who are seduced by big cfm numbers bolt a pair of 10,000 rpm cylinder heads on a 7,000 rpm short block and then wonder why the engine won’t run.
The most critical area in a competition cylinder head is the valve seat, and the order of importance works its way out from there. There are many questions that are much more important than airflow: How far are the valve heads off the cylinder wall? What’s the ratio of valve size to bore diameter? What’s the ratio of the airflow to the size of the valve? What’s the size of the port, what’s its taper, how high is the short-side radius? The answers to these aren’t as simple as comparing a flow number, but they are what really make a difference in an engine.
Airflow is simply one measurement among many that influence engine performance. With the availability of affordable flow benches and computer simulation programs, it’s easy to fall into the airflow trap. A builder works on a cylinder head, sees some bigger cfm numbers, and keeps working for more flow. But if he doesn’t stop and test the engine on a dyno and on the drag strip, it’s very likely he’s gone down a blind alley. What the manometer on a flow bench sees at a steady 28 inches of depression is not at all what the engine sees in the real world. The pursuit of a big cfm rating has ruined countless cylinder heads in terms of what will actually run on an engine.
I put more faith in dyno pulls and time slips than I do in flow benches. I’ll cite an example from back in the day when Buddy, Lee and I were winning Pro Stock championships. Lee came up with an idea for a tuliped exhaust valve. He filled in the back of the valve with Bondo, and tested the new design on our flow bench. It was killer. We instantly saw a tremendous improvement in airflow with a small exhaust port, a nice tight radius below the seat, and much more stable flow. So we had some titanium tulip exhaust valves made and tested them on the dyno – and the engine didn’t run well at all. We had great airflow on the bench, but the engine didn’t care.
We were working late one night, and Buddy decided to yank the heads off the block and have Lee open up the exhaust throats. Well, Lee kept grinding and Buddy kept taking the heads on and off, and eventually we picked up 30 horsepower that night. We were porting from the dyno and not from the flow bench. When Lee finally flow tested the heads the next day, they were down 30 or 40 cfm, but that’s not what that engine saw.
The final test of a cylinder head is on the track. Frank Iaconio was our chief Pro Stock rival, and he was a smart racer. Frankie used to change valves at the track — he’d make a run, come back to the pits and switch from valves with a 30-degree back angle to a 20-degree back angle. We did similar tests on the dyno, but he did it at the track. I was impressed.
I’m not dismissing flow benches. In fact, we use them daily at Reher-Morrison Racing Engines. But a flow bench is a tool, and it’s really not much different than a micrometer. A micrometer can measure the diameter of a piston, but you have to run the engine to learn the correct piston clearance. Knowing the sizes of the piston and cylinder bore doesn’t tell you if the piston is going to gall or collapse a skirt until you run it. And knowing the airflow of a cylinder head doesn’t tell you whether it will make good power on a given engine until you race it.
Experience is the most important tool in cylinder head development. A person with extensive dyno and track experience has been through it all before, and knows how to avoid the flow bench fallacies.
Category: Tech Talk —
Published in National Dragster
Written by David Reher
“What’s it flow?”
Whenever a conversation about cylinder heads begins with that question, I cringe. I know where this discussion is going, and it’s not good. When a racer wants to distill the performance of a highly developed cylinder head down to a single number, I know I’m dealing with someone who is fixated on the flow bench.
I can speak from hard-earned experience, because there was a time when the flow bench was the center of my universe. When my partners Buddy Morrison and Lee Shepherd constructed our first flow bench in the ’70s, it was a revelation – or so we believed. We were addicted to airflow, and like three flow bench junkies, we convinced ourselves that big flow numbers translated to quicker elapsed times. But that was more than 30 years ago, and since then I’ve learned to avoid the pitfalls of flow bench testing.
Unfortunately many racers coming into the sport haven’t been taught the lessons that Buddy, Lee and I learned the hard way. Cylinder head manufacturers, porting shops, and engine builders constantly advertise flow numbers – and I confess that I’m sometimes guilty as well. In this environment, it’s understandable that some racers think it’s all about maximum airflow. They shop for the biggest cfm number at the lowest price, like finding a screaming bargain on a 52-inch TV at WalMart.
The strategy to win the “Biggest CFM Contest” is simple: Grind the largest port that will physically fit in the head, use the biggest valves that will fit the combustion chambers, and test it on the biggest fixture you can find. That head might win the prize for airflow, but it won’t win on the dyno or on the race track.
The factors that determine the performance of a cylinder head are complex. A head that is ported without considering air speed, the size of the engine, the rpm range, the location of the valves, and a dozen other parameters isn’t going to be the best head, regardless of its peak airflow. And yet I see racers who are seduced by big cfm numbers bolt a pair of 10,000 rpm cylinder heads on a 7,000 rpm short block and then wonder why the engine won’t run.
The most critical area in a competition cylinder head is the valve seat, and the order of importance works its way out from there. There are many questions that are much more important than airflow: How far are the valve heads off the cylinder wall? What’s the ratio of valve size to bore diameter? What’s the ratio of the airflow to the size of the valve? What’s the size of the port, what’s its taper, how high is the short-side radius? The answers to these aren’t as simple as comparing a flow number, but they are what really make a difference in an engine.
Airflow is simply one measurement among many that influence engine performance. With the availability of affordable flow benches and computer simulation programs, it’s easy to fall into the airflow trap. A builder works on a cylinder head, sees some bigger cfm numbers, and keeps working for more flow. But if he doesn’t stop and test the engine on a dyno and on the drag strip, it’s very likely he’s gone down a blind alley. What the manometer on a flow bench sees at a steady 28 inches of depression is not at all what the engine sees in the real world. The pursuit of a big cfm rating has ruined countless cylinder heads in terms of what will actually run on an engine.
I put more faith in dyno pulls and time slips than I do in flow benches. I’ll cite an example from back in the day when Buddy, Lee and I were winning Pro Stock championships. Lee came up with an idea for a tuliped exhaust valve. He filled in the back of the valve with Bondo, and tested the new design on our flow bench. It was killer. We instantly saw a tremendous improvement in airflow with a small exhaust port, a nice tight radius below the seat, and much more stable flow. So we had some titanium tulip exhaust valves made and tested them on the dyno – and the engine didn’t run well at all. We had great airflow on the bench, but the engine didn’t care.
We were working late one night, and Buddy decided to yank the heads off the block and have Lee open up the exhaust throats. Well, Lee kept grinding and Buddy kept taking the heads on and off, and eventually we picked up 30 horsepower that night. We were porting from the dyno and not from the flow bench. When Lee finally flow tested the heads the next day, they were down 30 or 40 cfm, but that’s not what that engine saw.
The final test of a cylinder head is on the track. Frank Iaconio was our chief Pro Stock rival, and he was a smart racer. Frankie used to change valves at the track — he’d make a run, come back to the pits and switch from valves with a 30-degree back angle to a 20-degree back angle. We did similar tests on the dyno, but he did it at the track. I was impressed.
I’m not dismissing flow benches. In fact, we use them daily at Reher-Morrison Racing Engines. But a flow bench is a tool, and it’s really not much different than a micrometer. A micrometer can measure the diameter of a piston, but you have to run the engine to learn the correct piston clearance. Knowing the sizes of the piston and cylinder bore doesn’t tell you if the piston is going to gall or collapse a skirt until you run it. And knowing the airflow of a cylinder head doesn’t tell you whether it will make good power on a given engine until you race it.
Experience is the most important tool in cylinder head development. A person with extensive dyno and track experience has been through it all before, and knows how to avoid the flow bench fallacies.
Re: l98 cylinder head question
So basically it's not true that a head with more flow will make more power everywhere...
here's more..in my own words:
If you are looking for a set of heads, you are going to hear a lot of noise on the internet and marketing information packaged as technical information. Typically you're going to hear about flow numbers and port size. You are going to be told that the ideal head is the one with the biggest flow and the smallest port. Like all urban legends, there is some truth to that but also like urban legends, has little basis in fact. Port size and flow are not the “be all to end all” in head selection.
You're going to hear a lot of noise from the self appointed "experts", many who probably need help tying their shoes. Their expertise will be based on sweeping the floors at a high performance shop in the middle of nowhere while some have even read a brochure or two. You will find even more who went to the track once or twice, with many who know a guy who did something a few years back. So I recommend you consider the sources relative expertise as it relates to the subject matter at hand when weighing such advice. I am no such technical expert. I'm just a guy who likes to learn about this stuff, so I go to the experts in the field and ask the questions, and listen to the answers (and learn what I can when I can). Marketing brochures have little value. For example, I wanted to know about disc injectors so I called Lucas and talked directly to the engineer who designed them, for over an hour....now, that does not make me an expert, however, I try to relay the information I gained since we all can't talk to the guy (this is the best one can do in this situation).
And finally, never trust an opinion from someone who has an interest in the outcome. I betcha Dodge would love to come here and tell you how much better their Viper is than the new ZR-1, would anyone take that as a valid opinion? No, that would be ridiculous wouldn't it?
I find value in engineering. I find little value in people going through a catalog and picking out the coolest most expensive parts in the consumer realm, screwing them together and calling themselves experts. I look to racing as the arbiter of quality, process, and results. BILLIONS of dollars a year is spent on R&D in racing circles so it's a good place to reference, even for a street build...An example I like to use is kinda like a guy bragging about his Sony receiver to a guy who has a wall full of tube MacIntoch equipment. Two different worlds and two different levels of equipment, but doesn't mean you can't learn from the higher end, when building the lower end.
So let's cut through the crap you're going to hear:
here's more..in my own words:
If you are looking for a set of heads, you are going to hear a lot of noise on the internet and marketing information packaged as technical information. Typically you're going to hear about flow numbers and port size. You are going to be told that the ideal head is the one with the biggest flow and the smallest port. Like all urban legends, there is some truth to that but also like urban legends, has little basis in fact. Port size and flow are not the “be all to end all” in head selection.
You're going to hear a lot of noise from the self appointed "experts", many who probably need help tying their shoes. Their expertise will be based on sweeping the floors at a high performance shop in the middle of nowhere while some have even read a brochure or two. You will find even more who went to the track once or twice, with many who know a guy who did something a few years back. So I recommend you consider the sources relative expertise as it relates to the subject matter at hand when weighing such advice. I am no such technical expert. I'm just a guy who likes to learn about this stuff, so I go to the experts in the field and ask the questions, and listen to the answers (and learn what I can when I can). Marketing brochures have little value. For example, I wanted to know about disc injectors so I called Lucas and talked directly to the engineer who designed them, for over an hour....now, that does not make me an expert, however, I try to relay the information I gained since we all can't talk to the guy (this is the best one can do in this situation).
And finally, never trust an opinion from someone who has an interest in the outcome. I betcha Dodge would love to come here and tell you how much better their Viper is than the new ZR-1, would anyone take that as a valid opinion? No, that would be ridiculous wouldn't it?
I find value in engineering. I find little value in people going through a catalog and picking out the coolest most expensive parts in the consumer realm, screwing them together and calling themselves experts. I look to racing as the arbiter of quality, process, and results. BILLIONS of dollars a year is spent on R&D in racing circles so it's a good place to reference, even for a street build...An example I like to use is kinda like a guy bragging about his Sony receiver to a guy who has a wall full of tube MacIntoch equipment. Two different worlds and two different levels of equipment, but doesn't mean you can't learn from the higher end, when building the lower end.
So let's cut through the crap you're going to hear:
Re: l98 cylinder head question
1. It's all about flow....true and false...
Looking at cylinder head flow on a flow bench represents simply how restrictive the intake tract is. In other words, are you breathing through a straw or a garden hose… Unfortunately for everyone that develops engine combinations; air isn’t simply sucked through the intake tract. As we have all seen at some point or another, things like the intake valve closing, pressure bleeding through the ever so slightly opened intake valve cause what is commonly referred to as reversion. This is a result of your average Joe’s putting a name on something they see and don’t quite understand. The “reversion” is actually a pulse of pressure that is part of the longitudinal wave traveling back up the intake track. You see it push back through the carburetor when the timing of the event (actually the tuning of the intake tract) is off and the pulse is passing too far up the intake tract. Now this brings us a little bit into this notion of tuning this longitudinal wave to force air into the cylinder. This can be done but physics requires that the cross sectional area, length, and velocity of the pulse, be precisely matched to achieve this affect (and it will not be throughout a broad range). Another important point is that air cannot compress (at any velocity we will find inside an intake tract) so it must speed up or slow down with changes in cross sectional area. This represents the biggest shortcoming of the flow bench. The bench does not measure velocity, nor does it attempt to predict or model any of the increases or decreases encountered throughout the intake tract and how they are affecting flow. This means that all too often an intake tract is ineffective at controlling intake velocities throughout the entire operating range for the particular engine, throughout the entire intake tract (both are a big issue). This also leads to problems when working with the wet flow development. The concept of wet flow makes sense to most people; fuel is atomized into the intake tract and needs to stay evenly distributed all the way into the combustion chamber. Many experienced designers have found the all too common problem associated with converting a design from gasoline to alcohol (so say, taking a large circle track head that was designed for alky and trying to run it on a gasoline engine). Since we have different mixtures associated with the fuels the density and overall saturation changes as well. An even bigger problem is once airflow becomes a problem upstream the entire tract is not designed in an effort to correct this (it simply stays somewhat messed up and depending on how the rest of the tract is design can potentially get worse as it flows through another area). The typical result is that irregular airflow causes problems with the mixture and subsequently, causes problems with the proper air/fuel mixture getting into the cylinder.
These are all just the tip of ice burg so to speak; if you wish to test your ability to stay awake I would do what I did, talk with a few engineers that work with these concepts. They will shoot you straight and give you all (sometimes more) that you can handle. Now, the problem is testing on a flow bench does not give any insight into any of this, causing many to reach out for other possibilities.
Looking at cylinder head flow on a flow bench represents simply how restrictive the intake tract is. In other words, are you breathing through a straw or a garden hose… Unfortunately for everyone that develops engine combinations; air isn’t simply sucked through the intake tract. As we have all seen at some point or another, things like the intake valve closing, pressure bleeding through the ever so slightly opened intake valve cause what is commonly referred to as reversion. This is a result of your average Joe’s putting a name on something they see and don’t quite understand. The “reversion” is actually a pulse of pressure that is part of the longitudinal wave traveling back up the intake track. You see it push back through the carburetor when the timing of the event (actually the tuning of the intake tract) is off and the pulse is passing too far up the intake tract. Now this brings us a little bit into this notion of tuning this longitudinal wave to force air into the cylinder. This can be done but physics requires that the cross sectional area, length, and velocity of the pulse, be precisely matched to achieve this affect (and it will not be throughout a broad range). Another important point is that air cannot compress (at any velocity we will find inside an intake tract) so it must speed up or slow down with changes in cross sectional area. This represents the biggest shortcoming of the flow bench. The bench does not measure velocity, nor does it attempt to predict or model any of the increases or decreases encountered throughout the intake tract and how they are affecting flow. This means that all too often an intake tract is ineffective at controlling intake velocities throughout the entire operating range for the particular engine, throughout the entire intake tract (both are a big issue). This also leads to problems when working with the wet flow development. The concept of wet flow makes sense to most people; fuel is atomized into the intake tract and needs to stay evenly distributed all the way into the combustion chamber. Many experienced designers have found the all too common problem associated with converting a design from gasoline to alcohol (so say, taking a large circle track head that was designed for alky and trying to run it on a gasoline engine). Since we have different mixtures associated with the fuels the density and overall saturation changes as well. An even bigger problem is once airflow becomes a problem upstream the entire tract is not designed in an effort to correct this (it simply stays somewhat messed up and depending on how the rest of the tract is design can potentially get worse as it flows through another area). The typical result is that irregular airflow causes problems with the mixture and subsequently, causes problems with the proper air/fuel mixture getting into the cylinder.
These are all just the tip of ice burg so to speak; if you wish to test your ability to stay awake I would do what I did, talk with a few engineers that work with these concepts. They will shoot you straight and give you all (sometimes more) that you can handle. Now, the problem is testing on a flow bench does not give any insight into any of this, causing many to reach out for other possibilities.
Re: l98 cylinder head question
2. Smaller port size, the better for same flow
Looking above we see that there is a great deal of effort put into not only how much air could be pulled through the port, but mostly, how it will get through the port (that’s what we are really working on, getting air into the engine during actual operation). You must always remember that a flow bench is only measuring how easily air can be pulled into the cylinder, not how much WILL be pulled into the cylinder during operation. This means that when comparing cylinder head sizes the most important aspect as the SHAPE of the port and how that shape relates when viewing flow all the way to the combustion chamber. Airflow must be controlled, and hence the shape and measurements of the port are far more important that just looking at restriction versus runner size. Again; a flow bench does not measure how much air will be pulled through the port during operation, it measures how easily it can be pulled though in isolation. When looking at a port design one must look to see what the airflow demands will be; they also must look to what type and how much fuel will be induced into the mix, what RPM the engine will be operating at and lastly, must look past the port into the combustion chamber and into the intake manifold. Significant hp can be gained or lost with or without the proper entrance and filling of the cylinder. A cutting edge cylinder head not only has low restriction, a proper shape for tuning purposes (has to control the velocity along with cutting back irregular flow), a combustion chamber to promote flow (how a cylinder is filled is as important as how much is filled); it has all of the above working together and then promote proper flame travel once the cylinder is ignited (another very complicated aspect of how the engine makes its power, valve and spark plug placement and combustion chamber shape have to consider this as well as how much air can pass through it)!
Looking above we see that there is a great deal of effort put into not only how much air could be pulled through the port, but mostly, how it will get through the port (that’s what we are really working on, getting air into the engine during actual operation). You must always remember that a flow bench is only measuring how easily air can be pulled into the cylinder, not how much WILL be pulled into the cylinder during operation. This means that when comparing cylinder head sizes the most important aspect as the SHAPE of the port and how that shape relates when viewing flow all the way to the combustion chamber. Airflow must be controlled, and hence the shape and measurements of the port are far more important that just looking at restriction versus runner size. Again; a flow bench does not measure how much air will be pulled through the port during operation, it measures how easily it can be pulled though in isolation. When looking at a port design one must look to see what the airflow demands will be; they also must look to what type and how much fuel will be induced into the mix, what RPM the engine will be operating at and lastly, must look past the port into the combustion chamber and into the intake manifold. Significant hp can be gained or lost with or without the proper entrance and filling of the cylinder. A cutting edge cylinder head not only has low restriction, a proper shape for tuning purposes (has to control the velocity along with cutting back irregular flow), a combustion chamber to promote flow (how a cylinder is filled is as important as how much is filled); it has all of the above working together and then promote proper flame travel once the cylinder is ignited (another very complicated aspect of how the engine makes its power, valve and spark plug placement and combustion chamber shape have to consider this as well as how much air can pass through it)!
Re: l98 cylinder head question
3. Exhaust flow has real meaning.
This is one that every professional I talk to gets a real hoot out of; the idea that a cylinder head has to flow a ton on the exhaust side to make good power. When I ask this question I usually get a response like “a 900hp race engine has an exhaust port that flows 250cfm, so why would you feel that a street engine needs one to support 500hp?”. I have been urged to think about this in terms of airflow demand just as I would the intake side. Again, the shape and tuning of the exhaust is what pulls the last bit of exhaust out and first bit of intake charge in, not the flow number. This, again only shows how easy airflow can be moved through, it doesn’t imply how all the parts are going to come together and how much flow will actually occur during operation. As with the intake tract, simply pulling air through the port in isolation will not model what is happening during operation and should not be solely relied upon. Also, exhaust gases are forced out of the chamber; unlike the intake charge that has to be drawn in. Therefore, a few engine builders have expressed that they do not feel that restriction in the exhaust port is anything to really look at (the flow bench number); to them it’s all about tuning that tract to do the above. Many will cite how unimportant cylinder head flow numbers become when a supercharger is added to the intake side as some of the reasoning they feel that exhaust port flow numbers are not the hot ticket.
This is one that every professional I talk to gets a real hoot out of; the idea that a cylinder head has to flow a ton on the exhaust side to make good power. When I ask this question I usually get a response like “a 900hp race engine has an exhaust port that flows 250cfm, so why would you feel that a street engine needs one to support 500hp?”. I have been urged to think about this in terms of airflow demand just as I would the intake side. Again, the shape and tuning of the exhaust is what pulls the last bit of exhaust out and first bit of intake charge in, not the flow number. This, again only shows how easy airflow can be moved through, it doesn’t imply how all the parts are going to come together and how much flow will actually occur during operation. As with the intake tract, simply pulling air through the port in isolation will not model what is happening during operation and should not be solely relied upon. Also, exhaust gases are forced out of the chamber; unlike the intake charge that has to be drawn in. Therefore, a few engine builders have expressed that they do not feel that restriction in the exhaust port is anything to really look at (the flow bench number); to them it’s all about tuning that tract to do the above. Many will cite how unimportant cylinder head flow numbers become when a supercharger is added to the intake side as some of the reasoning they feel that exhaust port flow numbers are not the hot ticket.
Re: l98 cylinder head question
I have also learned other things about engine design and they are also important. There are aspects of engine design such as:
A modern camshaft like one produced by CompCams will utilize a very aggressive lobe design. The idea here is simple, cylinder heads used in racing classes often have to sacrifice low lift airflow (.100-.300) in order to get the very high flow at high lift numbers. Now many will talk until they’re blue in the face that a good head has superior low and mid lift numbers and that is not entirely correct. If for example, you are going to use a 1.7 rocker to achieve .675 lift and you are utilizing a new CompCams solid roller you are wasting your time with a low lift numbers and here’s why. The aggressive lobe was designed to get the valve quickly (very, very quickly actually) into the .500 lift and higher range. You also sped the process up a bit by using a higher ratio rocker. The end result here is simple, you have a package that is designed to get the valve open quick, and stay open for as long as possible (when the valve spends most of it’s measurable time at high lift, it’s best to get your flow there). There’s also another issue with small intake valves and low lift in high airflow demand situations. Above I mentioned the idea that airflow can not reach a compressible velocity inside the intake tract (I had a nice long talk with an engineer that explained how this principle is used in the F22 and F35 jet intake inlets) and the main reason for this is that once the air inside the intake tract reaches a set speed it will begin to form a shock wave. When air passes through such a thing it slows down…making for a bad situation when you are trying to fill a cylinder faster and faster. Now, since the air cannot compress the most likely place for this to happen is in “pinch” points. Points where the airflow has to flow through a reduced cross sectional area. Now a 2.02 intake valve hanging around at 0.400 lift sounds pretty pinched to me and hence why larger valve sizes and lift amounts go hand in hand with an increase in airflow demand.
Your turn....mention items such as:
1. Flame travel.....explain what it is and why it's important
2. Valve position in the chamber....again....explain what it is and why it's important
3. Gas vs. Alcohol.....again...what and why
As many as you can come up with.
As I have learned these things listed above can have a drastic effect on performance. The only way to measure those designs and the effectiveness of such would be to engineer heavily with computational fluid dynamics, modeling, and then demonstrate R&D on the wet flow bench. Major manufacturers such as Dart and Brodix use wet flow technology to refine their combustion chambers to best perform in the operational environment which they were designed to work in. This is key to validating what the numbers say during the design process; it’s not used to rate the effectiveness of said cylinder head, but to analyze and improve upon the theories being utilized.
A modern camshaft like one produced by CompCams will utilize a very aggressive lobe design. The idea here is simple, cylinder heads used in racing classes often have to sacrifice low lift airflow (.100-.300) in order to get the very high flow at high lift numbers. Now many will talk until they’re blue in the face that a good head has superior low and mid lift numbers and that is not entirely correct. If for example, you are going to use a 1.7 rocker to achieve .675 lift and you are utilizing a new CompCams solid roller you are wasting your time with a low lift numbers and here’s why. The aggressive lobe was designed to get the valve quickly (very, very quickly actually) into the .500 lift and higher range. You also sped the process up a bit by using a higher ratio rocker. The end result here is simple, you have a package that is designed to get the valve open quick, and stay open for as long as possible (when the valve spends most of it’s measurable time at high lift, it’s best to get your flow there). There’s also another issue with small intake valves and low lift in high airflow demand situations. Above I mentioned the idea that airflow can not reach a compressible velocity inside the intake tract (I had a nice long talk with an engineer that explained how this principle is used in the F22 and F35 jet intake inlets) and the main reason for this is that once the air inside the intake tract reaches a set speed it will begin to form a shock wave. When air passes through such a thing it slows down…making for a bad situation when you are trying to fill a cylinder faster and faster. Now, since the air cannot compress the most likely place for this to happen is in “pinch” points. Points where the airflow has to flow through a reduced cross sectional area. Now a 2.02 intake valve hanging around at 0.400 lift sounds pretty pinched to me and hence why larger valve sizes and lift amounts go hand in hand with an increase in airflow demand.
Your turn....mention items such as:
1. Flame travel.....explain what it is and why it's important
2. Valve position in the chamber....again....explain what it is and why it's important
3. Gas vs. Alcohol.....again...what and why
As many as you can come up with.
As I have learned these things listed above can have a drastic effect on performance. The only way to measure those designs and the effectiveness of such would be to engineer heavily with computational fluid dynamics, modeling, and then demonstrate R&D on the wet flow bench. Major manufacturers such as Dart and Brodix use wet flow technology to refine their combustion chambers to best perform in the operational environment which they were designed to work in. This is key to validating what the numbers say during the design process; it’s not used to rate the effectiveness of said cylinder head, but to analyze and improve upon the theories being utilized.
Re: l98 cylinder head question
And finally, some thoughts from:
Jon Kaase:
" I hate flowbenches. As you may know, most of our work is with 815" Pro Stock engines. On these heads the flow bench is almost totally worthless. I think it's misleading at best. We can port an older aluminum A-429 CJ head to flow 400 & 250. Then we can have a P-51 head that flows the same. The P-51 will dyno75HP better than the CJ. It's all about sizes, areas, shapes, and valve placement in the bore. I think you'll find that the more an engine builder uses the dyno, the less he trusts or even uses the flowbench. There are so many flowbenches out there in use that almost everybody thinks he's an expert.
One of our main goals when engineering these heads was to be able to deliver them with 400 cfm intake ports. We have reasonably well achieved that goal. In high flowing intake ports with the port opening positioned down close to the head gasket surface, the air often breaks away from the port floor and results in turbulence. This usually occurs above .600" valve lift when the air flow is high. With the P-51 head, some of the intake ports will be smooth and quiet all the way to .800" lift. Those ports will usually flow over 400 CFM. Some of the ports will go turbulent at .550"-.650" lift. When it happens, the sound changes and the airflow will drop off about 20CFM. The flow will be the same or better than the well behaved port right up to the lift where it goes turbulent. There are several ways to fix this, all of which are not a good idea. If we raised the port entry about 1" at the manifold, it would be a big help because the air would not have to make such a sharp turn. Of course none of the manifolds would fit. If we made the port a lot wider or taller at the short turn, that would fix the problem because the air speed would be much slower. But slow is not what you want in a good performance or race engine. When flowing one of these problem ports, sticking a butter knife or blade in the floor of the port will usually straighten it out to flow 400. We have dyno tested engines with heads that flowed 400 and then changed to heads where every port went turbulent to flow 375. They both made the same power. Now, if you ran a set of heads that flowed 375 because of improper porting or seat work, and then reworked them to flow 400, they would for sure make more power"
" I hate flowbenches. As you may know, most of our work is with 815" Pro Stock engines. On these heads the flow bench is almost totally worthless. I think it's misleading at best. We can port an older aluminum A-429 CJ head to flow 400 & 250. Then we can have a P-51 head that flows the same. The P-51 will dyno75HP better than the CJ. It's all about sizes, areas, shapes, and valve placement in the bore. I think you'll find that the more an engine builder uses the dyno, the less he trusts or even uses the flowbench. There are so many flowbenches out there in use that almost everybody thinks he's an expert.
One of our main goals when engineering these heads was to be able to deliver them with 400 cfm intake ports. We have reasonably well achieved that goal. In high flowing intake ports with the port opening positioned down close to the head gasket surface, the air often breaks away from the port floor and results in turbulence. This usually occurs above .600" valve lift when the air flow is high. With the P-51 head, some of the intake ports will be smooth and quiet all the way to .800" lift. Those ports will usually flow over 400 CFM. Some of the ports will go turbulent at .550"-.650" lift. When it happens, the sound changes and the airflow will drop off about 20CFM. The flow will be the same or better than the well behaved port right up to the lift where it goes turbulent. There are several ways to fix this, all of which are not a good idea. If we raised the port entry about 1" at the manifold, it would be a big help because the air would not have to make such a sharp turn. Of course none of the manifolds would fit. If we made the port a lot wider or taller at the short turn, that would fix the problem because the air speed would be much slower. But slow is not what you want in a good performance or race engine. When flowing one of these problem ports, sticking a butter knife or blade in the floor of the port will usually straighten it out to flow 400. We have dyno tested engines with heads that flowed 400 and then changed to heads where every port went turbulent to flow 375. They both made the same power. Now, if you ran a set of heads that flowed 375 because of improper porting or seat work, and then reworked them to flow 400, they would for sure make more power"
Re: l98 cylinder head question
I know I know what I'm going to hear....that's racing....blah blah blah blah...
Gents, the laws of physics do not descriminate between racing and street. The very same principles apply, and should be considered.
DO NOT BUY THE MARKETING BULLS**T.....
I hope this work and dedication has been helpful to someone.
Now, you all can refer to this as the ultimate discussion of heads.
Thank you for your time.
Oh, and before I go if you REALLY want to learn something, the thread I stole this from is here:
http://www.yellowbullet.com/forum/sh...ghlight=G+Code
There's some good reading there on the topic.
Gents, the laws of physics do not descriminate between racing and street. The very same principles apply, and should be considered.
DO NOT BUY THE MARKETING BULLS**T.....
I hope this work and dedication has been helpful to someone.
Now, you all can refer to this as the ultimate discussion of heads.
Thank you for your time.
Oh, and before I go if you REALLY want to learn something, the thread I stole this from is here:
http://www.yellowbullet.com/forum/sh...ghlight=G+Code
There's some good reading there on the topic.
Joined: Sep 2003
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Re: l98 cylinder head question
Many will cite how unimportant cylinder head flow numbers become when a supercharger is added to the intake side as some of the reasoning they feel that exhaust port flow numbers are not the hot ticket.
For frame of reference, 083 heads have been ported to 270cfm intake and I believe 190cfm exhaust with 2.02/1.6 valves. Just information on how much you can take out. May or may not mean much.
Re: l98 cylinder head question
This will be argued by some people depending on who you talk to. I was reading on this abit the last few days because I'm in a situation with a small head on a large motor and under boost. I think I can get alot of hp out of my setup with a better intake tract from a larger head/valve. Some say air is being forced in but others say the motor is still pulling air in, its just that there is just a greater pressure differential across the valve so the motor can get more air in on the same intake stroke, hence more power under boost. I guess thats just "forced" in but there are some interesting thoughts on the intake port design for boosted motors. I would say port design is just as important under boost as it is n/a.
For frame of reference, 083 heads have been ported to 270cfm intake and I believe 190cfm exhaust with 2.02/1.6 valves. Just information on how much you can take out. May or may not mean much.
For frame of reference, 083 heads have been ported to 270cfm intake and I believe 190cfm exhaust with 2.02/1.6 valves. Just information on how much you can take out. May or may not mean much.
Now let me say something about forced air.
IT MAKES NO DIFFERENCE IN TERMS OF ANYTHING I SAID AND CHANGES NOTHING IN TERMS OF CYL HEAD CHOICE.
All forced air does is put pressure behind the charge, it does nothing to change the characteristics of the head.
Basically it changes the VE of the combination. If you can get over 100% VE you're doing good.
Re: l98 cylinder head question
lol torquer you just torqued his *** xD but yeah my ;ocal machine shop told me just simply blening bowls and a mirror finish on the exhaust that i would be flowin really good but hell i know that when i had these flow benched the ratio between exhaust and intak was trash the exhaust was i think 57% of the intake so i set out to fix that number closer to 70% but like i said dont know how much to port and i will take a look at that sticky thread atilla
So many myths so little time....
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Joined: Oct 2004
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Car: '86 Z28, '91 RS
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Transmission: TH200c (no kidding), TH700r4
Axle/Gears: 2.73, 2.73
Re: l98 cylinder head question
I'm glad you asked doom...
First of all 65CC and 70CC refer to the chamber size not the port size. Ports are typically measured in three digit numbers such as 215, 225, 180, 195, etc... A larger combustion chamber WILL HELP FLOW as will a larger valve, like a 2.05 vs. a 1.95.
First of all 65CC and 70CC refer to the chamber size not the port size. Ports are typically measured in three digit numbers such as 215, 225, 180, 195, etc... A larger combustion chamber WILL HELP FLOW as will a larger valve, like a 2.05 vs. a 1.95.
Better CSA is generally the cause of a smaller port flowing the same as a larger port. That's usually where the wasted volume lays. From what I've seen just looking into the intake runners of well performing heads (LSX, AFR, ect) you can't go tall enough unless you find sun-light. The taller the port the more gentle the long turn can be which increases velocity.
I agree with some of the Great Wall of Text but too much to type. Some of it though defies simple physics.
Re: l98 cylinder head question
In the context that I'm using it the 65cc and 70cc are referring to the exhaust runner volume, just generalizing typical SBC volumes.
Better CSA is generally the cause of a smaller port flowing the same as a larger port. That's usually where the wasted volume lays. From what I've seen just looking into the intake runners of well performing heads (LSX, AFR, ect) you can't go tall enough unless you find sun-light. The taller the port the more gentle the long turn can be which increases velocity.
I agree with some of the Great Wall of Text but too much to type. Some of it though defies simple physics.
Better CSA is generally the cause of a smaller port flowing the same as a larger port. That's usually where the wasted volume lays. From what I've seen just looking into the intake runners of well performing heads (LSX, AFR, ect) you can't go tall enough unless you find sun-light. The taller the port the more gentle the long turn can be which increases velocity.
I agree with some of the Great Wall of Text but too much to type. Some of it though defies simple physics.
If you think it's too long and didnt read it, how do you come to the conclusion that it's wrong? Big time engine builders, and engineers seem to support my position, as do engineers at head manufacturers themselves.
My points fall directly into the realm of physics. There is no argument about that. It can not be disproven via physics..
Sounds to me like you're buying the small port big flow argument. If you want to that's fine, but please don't distribute it as fact. It is marketing, no more, no less.
Bottom line is anyone that wants to go fast will read this and learn something from it. Anyone that is too lazy and content with marketing as information, can lose to the former.
Last edited by InjectorsPlus; Sep 21, 2010 at 10:55 PM.
Joined: Sep 2003
Posts: 25,895
Likes: 429
From: Pittsburgh PA
Car: 89 Iroc-z
Engine: 555 BBC Turbo
Transmission: TH400
Axle/Gears: MWC 9” 3.00
Re: l98 cylinder head question
I think port velocity is a good thing and there is a happy medium. From what I know I believe that to be 260 fps. Too little and you are losing out on torque. Too much you choke the port. Have to find the medium for the engine combo and desired rpm range. On certain combinations I think there can be some good benefit to a smaller port with good flow compared to others but like discussed there are alot of variables.
Re: l98 cylinder head question
I think port velocity is a good thing and there is a happy medium. From what I know I believe that to be 260 fps. Too little and you are losing out on torque. Too much you choke the port. Have to find the medium for the engine combo and desired rpm range. On certain combinations I think there can be some good benefit to a smaller port with good flow compared to others but like discussed there are alot of variables.
The port locks up at .6 mach and small ports with big flow do not have enough CSA to manage port speed, which is how you wind up with a "dumptruck" motor.
It's about getting the highest VE you can get with good fuel suspension and not locking up the ports at high RPMs.
Show me the times, not the dynos.
I've seen too many people build motors that felt good SOTP, but ran **** for times..... We do this to be fast, whether it be on the track, or in the street. No point in being slower than you have to for the buck.
Last edited by InjectorsPlus; Sep 21, 2010 at 10:56 PM.
Senior Member
Joined: Oct 2004
Posts: 965
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From: SE, Ohio
Car: '86 Z28, '91 RS
Engine: 305ci, 305ci
Transmission: TH200c (no kidding), TH700r4
Axle/Gears: 2.73, 2.73
Re: l98 cylinder head question
With all out racing motors the valves are open so long it probably doesn't suffer from lower lift restrictions like a street motor would. I'm not going to repeat others information as fact, just theorizing of course, I don't build circle track motors.
Re: l98 cylinder head question
Velocity has to be higher on the smaller port to do this. You agree that valve velocity/acceleration is critical but don't see how this is as well? The action this would produce goes hand and hand doesn't it?
With all out racing motors the valves are open so long it probably doesn't suffer from lower lift restrictions like a street motor would. I'm not going to repeat others information as fact, just theorizing of course, I don't build circle track motors.
Now what is interesting on that comment, is many manufacturers post flow numbers at .600 and .700, points "street motors" will never see. If you have incredible flow at .600 and your cam never gets there, what's the point. The other trick is to put in 2.05 valves and compare them to .194 valves. Apples to oranges. Pay close attention when looking at numbers.
Thanks for the nice conversation, and not getting argumentative. It's not my intent.
Last edited by InjectorsPlus; Sep 21, 2010 at 11:24 PM.
Senior Member
Joined: Oct 2004
Posts: 965
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From: SE, Ohio
Car: '86 Z28, '91 RS
Engine: 305ci, 305ci
Transmission: TH200c (no kidding), TH700r4
Axle/Gears: 2.73, 2.73
Re: l98 cylinder head question
Right, and at some point the smaller port will lock up. What you get is a torquey engine that falls on its face at lower rpms than a properly sized head. This is the difference between the L98 and the LT1. If this is what everyone wanted, there wouldn't have been an LT1 or a LSX. The L98 would fit the bill
I own a L03 though I know EXACTLY what you are talking about with the dump truck effect. For the first 2000rpm it pulls hard, it feels like it could actually break drive-train parts, then it falls right on it's face.
And I did read all of what you posted before I didn't want to reply to all the points it made is all.
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Re: l98 cylinder head question
For a guy that claims to know SBC heads so well... One would think you'd know more about the EGR valves used on SBC's. I guess you must have forgot, huh? Or maybe you just learned a couple (actually 5) days ago about it.
Re: l98 cylinder head question
The fact that I didn't know about an EGR provision on a stock head means what exactly? I'm trying to understand how that is even relevant.
I'm going to run over to Yankee Stadium tonight and give Jeter a trivia test on baseball. If he can't answer every single questoin, clearly he sucks.
You're talking about something so insignificant and specialized I betcha outside of this board, there are few people who know about it. Hell, I called head manufacturers on this issue and they didn't know.
Last edited by InjectorsPlus; Sep 22, 2010 at 07:07 AM.
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