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Tech / General EngineIs your car making a strange sound or won't start? Thinking of adding power with a new combination? Need other technical information or engine specific advice? Don't see another board for your problem? Post it here!
I just wanted to ask for some opinions before I pull the trigger on a cam. This is an OEM Roller block. Specifics are as follow.
CID: 355
Compression: Approximately 9.9:1 (I have not CC'd chambers to verify they are indeed 64cc. If they are, it's 9.9:1)
Crank: Stock, polished
Rods: Stock, new bolts
Pistons: KB 4v Relief 7cc flat top Pistons
Heads: Pro Topline 906 Vortec Heads. 2.02/1.6 Valves (stock is 1.94/1.5), 1.6" Roller Rockers, 170cc Intake Runner, 64cc chamber. Minor port work to open throat to seats and blend bowl area. Removed casting flash\imperfections from Exhaust runners.
Intake: Vortec Professional Products Crosswind
Exhaust: Doug's 1.75" Primary, 3" Collector long tubes. 3" Y-Pipe. Haven't purchased or fabbed anything beyond that.
Carb: Edelbrock 1407 750CFM
Ignition: HEI
Transmission: 700R4
Stall: 2600-ish
Rear Gear: 3.73
This build is roughly based on a build by David Vizard. The cam that Vizard specs is as follows:
Comp Cams Magnum 280HR
LSA: 108, 4 degrees of advance
Advertised Duration: 280/280
Actual Duration @ .050: 224/224
Lift (with 1.6RR): .560/.560
However, knowing that Vortec style heads usually have issues on the exhaust side, I figured I'd ask to see if anyone had any different ideas, or confirm that I'm on the right track.
According to Vizard, he made 437hp at 5500 RPM and 435ft/lb of torque at 4300 RPM using ported OEM 906 heads. However, he suggests using any similar head from EQ, Dart, or RHS (specifically mentions CH350C, which if I'm correct, is the same as my Pro Topline heads).
Key differences between the builds: I have almost a half point more static compression, I'm using flat tops instead of the stock dish pistons, mildly ported heads, in the article they use the stock 1.94/1.6 valves (vizard uses 2.02/1.6 valves on an OEM 906 head) I have an Edelbrock 750 rather than a 3310, I'm running dual springs rather than the beehives, and 1 3/4 primaries rather than the 1 5/8s.
Good lord that's a lot to type out. Let me know if I forgot anything. At any rate, I appreciate any advice you have to offer about the cam, and I thank you for taking the time to read all of this.
That cam should run fine. If you wanted power to hang on alittle longer after peak, usually alittle more exhaust duration will help, but sacrifice alittle trq on the lower end and midrange
Those are dyno engines. By that I mean they won't suffer from the limiting exhaust system you still have to attach to your chassis. That said, a little extra exhaust duration will help to mitigate that. As Orr points out, there are compromises.
Here's the other thing that stands out in Vizard's build, and trust me, I've followed his work, the cam he spec'd is an outdated profile (and so is what you've been reading). If you want to recover some of that lost torque by extending the exhaust profile, the same came be done with a more modern intake lobe that has quicker action on the ramps. The .050" value of 224 can be had with an adv. duration of 276. That'll build some low engine speed torque, help driveability and mileage.
For what it's worth, I've built a more or less identical engine to your spec before and it performed nicely. Keep in mind that you're not going to get 450 hp once it's installed in your chassis. Those dyno numbers are free from losses due to accessories and they have optimum exhaust by way of the headers and nothing more.
Those are dyno engines. By that I mean they won't suffer from the limiting exhaust system you still have to attach to your chassis. That said, a little extra exhaust duration will help to mitigate that. As Orr points out, there are compromises.
Here's the other thing that stands out in Vizard's build, and trust me, I've followed his work, the cam he spec'd is an outdated profile (and so is what you've been reading). If you want to recover some of that lost torque by extending the exhaust profile, the same came be done with a more modern intake lobe that has quicker action on the ramps. The .050" value of 224 can be had with an adv. duration of 276. That'll build some low engine speed torque, help driveability and mileage.
For what it's worth, I've built a more or less identical engine to your spec before and it performed nicely. Keep in mind that you're not going to get 450 hp once it's installed in your chassis. Those dyno numbers are free from losses due to accessories and they have optimum exhaust by way of the headers and nothing more.
I understand that there will be accessory losses. My hope was around 350 to the rear wheels, so if I can get around there I'll be happy.
So, I asked Comp Cams for their recommendation, and someone finally got back to me today. The individual recommended an 08-502-8, which is an XR269HR-12. Which seems... Tame to me.
Compared to the 280HR, it has overall less lift and duration, but it ramps much faster. I compared the two via Desktop Dyno, and sure enough, the XR269HR makes more torque and power from 2000 RPM to 6000RPM.
You've followed Vizard's work and he states that the effects of a longer duration cam or more specifically, a cam with more overlap, can largely be overcome with an appropriate increase in compression ratio.
I'm going through this exact same scenario with my move up from my custom spec'd cam (274/282, 224/230 @ .050", .574/.569, 110/106) to Comps XR288HR (288/294, 236/242 @ .050", .555/.576, 110/106).
DynoSim results show torque is considerably less, about 35 ft\lbs @ 2500, 25 ft\lbs @ peak comparing the two with the same SCR of 9.9:1. DCR is 8:1 with the short cam and 7.6:1 with the 288. When the SCR is bumped up to 11:1, a considerable amount of that lost torque is recovered.
I've attached DynoSim charts to illustrate.
So, all of that said, it comes down to what you have planned for the car and what other modifications you're prepared to make to the engine.
I've found that in a street application, you'll have more satisfying results with an engine that has more low engine speed torque. This is all things being otherwise equal. Specifically the torque converter.
The old and outdated Magnum cam notwithstanding, (and you know there a better grinds out there that will give you the lift values your heads need without too much overlap and the resulting loss of torque), running a bigger cam doesn't necessarily mean you have suffer if you have a converter that will keep the engine RPMs closer to peak torque when you have your foot in it. That's the approach I'll have to take as I can't get my engine to 11:1 with the current pistons, heads, etc. I'll have to rely on a properly spec'd converter to get the engine up to it's operating RPM quickly.
If you're looking for an opinion, check out Comps XR276HR. I ran that with my Vortecs and 9.9:1 (basically your engine specs) and had excellent results. It moved my 3700 IROC into the 12's at 106+ mph. Good gas mileage too.
As you'd expect, there's more power (although slightly less torque), but driven higher into the RPM range. I tried tightening the LSA to 108 as well, but it just fell on its face losing both torque and power over the 110 LSA.
Keeping the same duration values but tightening up the LSA will increase the overlap. It also moves the intake valve closing event further away from TDC. That's where the torque goes.
If you want to try an interesting experiment with your DynoSim, go into the cam manager and check the overlap of the 269. Use the seat to seat numbers rather than the .050" values. Then check the overlap of the 276 with a 110 LSA and a 108 LSA. Keeping the 108 LSA, try and design a cam that will match the overlap of the 269 and/or the 276 (at 108). That's one of the major points that Vizard touches on when he is specifying a cam. Select the overlap first, then get the duration as a result.
Last edited by skinny z; 06-02-2016 at 09:29 AM.
Reason: Additional information
So I made a mistake earlier. I forgot to add 4 degrees of advance to the Magnum, which obviously drives the powerband down, netting more torque but a loss of power. Not that it really matters. It's still completely overshadowed by the XR269HR.
Just saw the 112 LSA on the XR269HR.
Seeing as you're running a carb, why would you consider that wide a separation angle? The trend is to tighten up the LSA on a 350 (from the typical 110 to a 108).
And another question: When you're in DynoSim, what do you input for your exhaust spec? I see your torque and horsepower numbers are really high in comparison to my results. I select a small tube header w/ mufflers as this more closely replicates the results of the exhaust that it's my chassis. The numbers go through the roof when I select an open header for the exhaust input field.
As I had mentioned earlier, I have direct experience with the XR276HR (with 1.6 ratio rockers) and the unported/stock valve size Vortec top end. It was by most accounts, an excellent choice. Pulled 12-13" of vacuum (at 600' elevation), idled at 650 RPM, sounded great and offered decent performance and mileage. The just less than 10:1 SCR and that cam installed straight up resulted in cranking pressures in the 190 PSI range.
so how low do you think an engine can idle before it starts to have bouts of bearing damage?
Do high volume pumps help or exacerbate the low rpm situation?
What are the oil system modifications we can do to an engine that help with oil flow, discuss porting an oil pump, filet radius, chamfer, slotted bearings, tight 0.0008" and loose 0.0022" clearances with respect to idle, oil viscosity, and max rpm performance?
what roles does a camshaft have in all of this, including engine durability long term?
As I had mentioned earlier, I have direct experience with the XR276HR (with 1.6 ratio rockers) and the unported/stock valve size Vortec top end. It was by most accounts, an excellent choice. Pulled 12-13" of vacuum (at 600' elevation), idled at 650 RPM, sounded great and offered decent performance and mileage. The just less than 10:1 SCR and that cam installed straight up resulted in cranking pressures in the 190 PSI range.
I'm not doubting you and I'm not trying to be difficult. I just like exploring all possibilities... And it's sort of fun to see what puzzle pieces fit better than others.
I'm not taking offence or anything like that. I appreciate exactly what you're doing. I have pages of dyno files from past builds and the one I'm currently involved in. That's the XR288HR with the RHS Pro Torker heads that have spent some time on the porter's bench.
As for the 276, it was excellent in all categories. Idled well, pulled away from a stop with no hesitation. Keep in mind that I have a 10" TCI converter. Nothing special but it does allow the RPMs to advance quickly and I would spend very little time below 2000. That said, when I would be creeping along in traffic, the engine was well behaved. It did have a nice sound too.
so how low do you think an engine can idle before it starts to have bouts of bearing damage?
Do high volume pumps help or exacerbate the low rpm situation?
What are the oil system modifications we can do to an engine that help with oil flow, discuss porting an oil pump, filet radius, chamfer, slotted bearings, tight 0.0008" and loose 0.0022" clearances with respect to idle, oil viscosity, and max rpm performance?
what roles does a camshaft have in all of this, including engine durability long term?
That's a lot of territory to cover however I can say this: In all of my experiences building Gen 1 SBCs, some with flat tappet cams but most with hydraulic rollers, oiling has never been an issue. Idling oil pressure with a fresh engine is about 30 PSI. Higher RPMs sees the pressure top out at 60-65 PSI. Even at 10-15 PSI at idle, there's sufficient pressure to keep the bearings alive.
Now don't do what I did and that's tow a trailer cross-country with the lock-up converter on the Fritz. Engine temps were a consistent 240 F for about a 40 hour trip. End result: I took a couple of rod bearings out.
I have a Circle-D 2600 that's going to be used. I don't recall the diameter, but I doubt I'll spend much time that low also, but I figured it was worth asking.
I'm wondering what sort of difference we'll see. At the time, you were running stock vortec heads, while I'll be running pocket ported aftermarket vortec heads, with 2.02/1.6 valves. I should probably just pay a few bucks to flow the heads to see exactly what I'm getting into before I buy a cam.
... I should probably just pay a few bucks to flow the heads to see exactly what I'm getting into before I buy a cam.
I wouldn't waste your time and money doing that. Unless somebody ruined those Vortec heads, we already know their characteristics, and any flow numbers you get should not influence your cam decision.
It's pretty clear to me the XR276 is right for you.
I wouldn't waste your time and money doing that. Unless somebody ruined those Vortec heads, we already know their characteristics, and any flow numbers you get should not influence your cam decision.
It's pretty clear to me the XR276 is right for you.
$50 doesn't seem like too much of a waste of money to know what I'm working with in the grand scheme of things. It'll also help to document it in case I ever sell the car or motor. IMO, God is in the detail.
Interestingly, I had my RHS heads flowed for a couple of reasons. One: The specs issued by the manufacturer used a 4.20" fixture bore and the thinking is those numbers are inflated. Two: I had those heads ported and wanted to know the results. This helped my computer modelling. Funny thing about flow numbers (including the Vortecs) there are just about as many different results as there are tests. It can be maddening at times.
There's also the possibility that the heads have been messed up. This is especially true when someone, with the best of intentions, moves up to the 2.02 intake valve from the 1.94. A lot of the excellent qualities that the Vortecs have, that is their exceptional low lift flow (.050" - .300" +/-), can be attributed to the valve seat. Cut that up with the larger valve and those that don't pay attention can ruin those low lift numbers. I would trust that any manufacturer would take this into consideration.
Interestingly, I had my RHS heads flowed for a couple of reasons. One: The specs issued by the manufacturer used a 4.20" fixture bore and the thinking is those numbers are inflated. Two: I had those heads ported and wanted to know the results. This helped my computer modelling. Funny thing about flow numbers (including the Vortecs) there are just about as many different results as there are tests. It can be maddening at times.
There's also the possibility that the heads have been messed up. This is especially true when someone, with the best of intentions, moves up to the 2.02 intake valve from the 1.94. A lot of the excellent qualities that the Vortecs have, that is their exceptional low lift flow (.050" - .300" +/-), can be attributed to the valve seat. Cut that up with the larger valve and those that don't pay attention can ruin those low lift numbers. I would trust that any manufacturer would take this into consideration.
Precisely why I'm going to have it done. I'd rather know ahead of time rather than kicking myself in the **** for not doing it later. Better safe than sorry.
The bore being used to test them is 4.070 if I remember correctly, which should be a bit closer to the 4.030 actual than whatever the factory used (which like you said, is probably 4.2, or in the best case 4.1)
Check out Stan Weiss.com.
There are hundreds of Gen 1 SBC heads represented with all kinds of critical data. Maybe a half dozen or more Vortecs. I think are a couple of Pro Topline heads there too.
My heads are also based on the 350C castings ( judging by the casting number between the valve guides).
Bowls blended into the 5 angle valve job and some work on the short side:
.100 63/59
.200 124/108
.300 179/142
.400 229/167
.500 254/176
.600 247/179
.700 250/185
.800 250/190
Despite being ported there's still the classic .550" "Vortec stall". Louie at AMS Racing Engines attributes that to short side turn. I would have it was the 170cc intake runner but he says no. I'll agree with his expertise.
I have both the "906" and the "350C" stamped on the castings of mine as well.
Still, your numbers look pretty good. I'm guessing that for us to get beyond the .550 stall, we'd have to open up the runners quite a bit. But then it's a trade off, velocity vs volume, I would think. I'm not sure if it would help or not.
Yes. 2.02/1.60. As prepared by RHS. Basically they're an RHS ported Vortec head with bigger valves and were sold as cast. I went a step further when I redid the guides and had some porting done. Despite being small, I hope they're capable of working with the 288 cam up to 6500-6800 RPM.
If your intention is daily driving / street car. You will want the lowest lift you can get away with, with the slowest/most gradual camshaft ramps you can find, with the weakest spring that will still do the job.
This will ensure valvetrain longevity will be as high as possible. You do NOT need big lift/cam profiles to make big power, even a stock OEM camshaft with an OEM spring and 6000rpm redline can net 600 horsepower to the flywheel, in a wide variety of 5.XL applications. I am not saying do not upgrade; only to use the gentlest upgrades possible. Duration is whatever you want it to be. Lift and fast ramps is what breaks and wears out parts.
I'll agree with you on the lift and fast ramps breaking parts. My experiment with Comps XFI series of lobes has proved a little problematic in the longevity department. Despite having a few issues with the valvetrain geometry (as in failing to readdress the pushrod lengths after swapping short blocks and lifters), valves and guides both suffered although I will say that was after a considerable number of cruising miles and hundreds of redline passes.
Now if you're pushing the most from the least approach and are considering parasitic losses due to a heavy valve springs and aggressive profiles (that necessitate a heavier valve spring), sure, I can agree. However, for a given cylinder head, that is one who's flow increases proportionately with lift, then getting the valve opened as far as possible, as quickly as possible within the confines of the overlap selected (and the resulting duration and various lobe angles) is the way to not only build power but also preserve qualities that make the engine workable on the street. That is, more torque production with less duration (or again more specifically, overlap). This does mean a more aggressive ramp and unless the builder is careful in the selection of the supporting parts, most notably, the valve spring, and strict attention to the geometry, valvetrain stability and longevity will suffer.
Now, BIG is relative. And what the OEMs produce now compared to what they used to produce are different things altogether. As far as the Gen 1 SBC is concerned, (and I won't stray too far from that as it's where the bulk of my experience is) I can't think of any valve spring that I would rely on to consistently keep a 6000 RPM valve under control. As for camshafts from the heady days of the SBC, sure, there were many produced that made power. And many designed to make power while keeping the top of the engine alive long enough to finish whatever variety of racing was involved (I'm taking endurance road racing here). But I think it would be safe to say, that if we were able to go back in time and present one of today's camshafts to the engineers of yesterday, they would take the modern offering in a heartbeat.
The intent of the car is fun. It's not a daily driver, but more of a fun weekend car that I'll probably take to the track a few times per season. Being in Minnesota, the season is relatively short. The car won't be driven during the cold months unless there were an emergency of some sort.
That's the purpose of my vehicle as well. Although my weekends tended to be the entire driving season (with a climate similar to yours). Visits to the track tend to be addictive. Then the desire to go faster becomes a little stronger. I was pretty happy with a mid 12 second "all street" car until the modern OEMs started keeping pace and then going quicker. That's why I'm stepping up my game with ported heads and a bigger cam. The converter is next and while I can't say I'd swap out rear end gears, that would be the next logical step in making it more race than street.
Looking back at your first post, about the only thing that stands out from a balanced combination perspective is the 1 3/4" headers (the carb may be a little on the large side too). My experiences with a larger tube didn't produce the results I had hoped. In the street category, I thought that the torque was down somewhat. If the build had been more drag race orientated, the bigger pipes (and a better converter) would probably have led to better top end charge but on the street it felt lacking by comparison.
And as for your compression ratio, I didn't see any mention of your piston height relative to the block deck. You also didn't specify what head gasket you wanted to go with.
If the block is undecked and you have a standard compression height piston, anything other than a steel shim gasket will leave you short of your 9.9:1 target. The shim gaskets tend to be temperamental in that the surface finish of the block and heads has to be suitable for the gasket to seal properly.
I agree the 1.75” primaries might be kind of iffy, but I think they’ll probably be fine. I actually had to port the primary ports slightly to get them wide enough so that the exhaust flow wouldn’t be inhibited. I actually need to check it again after I get the heads back again. I’m not a professional engine builder, but I’m guessing .125” probably won’t be too big of a deal. We want completely free flowing exhaust, but going too large reduces velocity, which could inhibit overall flow. The goal then, to me, is to use the largest diameter primary, collector, and exhaust pipe that allows the exhaust to flow freely without reducing velocity. There are various calculators on the internet that would help you decide what it should be, but everyone has their own formula. For instance, Vizard would say I should use 1.625" primaries, while using various calculators say the primaries should be anywhere from 1.40-1.75". Honestly, the bottom line is that I got a good deal on them, so it made sense from a budget perspective.
I feel similarly about the carburetor. Since it has vacuum secondaries, it’ll only open up as much as needed. As such, it makes it really difficult to over-carb.
I need to measure the deck height after the align hone to make sure I don’t need to deck the block, but in the event that it doesn’t need to be decked, with the higher compression height of the pistons, we’re looking at a range of .020-.023 in the hole. With a Victor Reinz head gasket, with a .026 compressed thickness, quench distance will be .046-.049. If I deck the block, it’ll obviously thin out the quench distance. The heads have a 64cc combustion chamber, and the pistons have a 7cc worth of valve cuts. With a 4.1” fire ring on the gasket, we’re looking at 9.9-10:1 compression as is.
I'll agree with you on the lift and fast ramps breaking parts. My experiment with Comps XFI series of lobes has proved a little problematic in the longevity department. Despite having a few issues with the valvetrain geometry (as in failing to readdress the pushrod lengths after swapping short blocks and lifters), valves and guides both suffered although I will say that was after a considerable number of cruising miles and hundreds of redline passes.
Now if you're pushing the most from the least approach and are considering parasitic losses due to a heavy valve springs and aggressive profiles (that necessitate a heavier valve spring), sure, I can agree. However, for a given cylinder head, that is one who's flow increases proportionately with lift, then getting the valve opened as far as possible, as quickly as possible within the confines of the overlap selected (and the resulting duration and various lobe angles) is the way to not only build power but also preserve qualities that make the engine workable on the street. That is, more torque production with less duration (or again more specifically, overlap). This does mean a more aggressive ramp and unless the builder is careful in the selection of the supporting parts, most notably, the valve spring, and strict attention to the geometry, valvetrain stability and longevity will suffer.
Now, BIG is relative. And what the OEMs produce now compared to what they used to produce are different things altogether. As far as the Gen 1 SBC is concerned, (and I won't stray too far from that as it's where the bulk of my experience is) I can't think of any valve spring that I would rely on to consistently keep a 6000 RPM valve under control. As for camshafts from the heady days of the SBC, sure, there were many produced that made power. And many designed to make power while keeping the top of the engine alive long enough to finish whatever variety of racing was involved (I'm taking endurance road racing here). But I think it would be safe to say, that if we were able to go back in time and present one of today's camshafts to the engineers of yesterday, they would take the modern offering in a heartbeat.
Yes, all good for those of us who know what parts to use, and have experience with them. We can increase lift and play with camshaft profiles because we already know enough to avoid the biggest mistakes. The comment about Vizard is also very nice to see, the exhaust system should fit the range of RPM the engine duty will see mostly, even if it means a loss of top end power, the vehicle could be faster on the street with more area under the curve. But that is getting off topic slightly.
My advice was directed towards novices with daily drivers mostly, who may be taking notes from online sources, and recommendations from other novices online. They seem to think bigger is better, you know the drill. All complicated details aside, the way I look at things these days is: if the OEM engine can support 500~bhp with an OEM camshaft/head/spring for 200k.... then there is absolutely no reason to use anything "larger" or "stiffer" for anything making less power. I realize this cuts out the 450rwhp N/A options for the most part because it limits RPM: I think this way on purpose since the OEM clearance is often not up to the challenge of a 6000+rpm redline. Sure, you can do it, the engine will tolerate it. But this is not going to get you to 200k anymore, something is going to fail before then, probably a rod bearing. Due simply to the nature of tight clearance, and oiling character, has nothing to do with valvetrain longevity at that point. In other words, even if you DO manage to get the big lift cam/spring hardware and run it 'safe' you still stand a reasonable chance to wreck the OEM bearing due to it's distaste for the lofty RPM regions, where again, many a novice thinks that just because the engine "feel good up there" that it isn't toasting and roasting its rotating assembly little by little with each pass. I am strongly in favor of minimal RPM passes, using other methods to improve output besides RPM is more acceptable daily driver behavior, since we rarely spend time there anyways driving it around.
Rpm is nothing imo. Proper machine work and bearing clearances will still keep a motor happy and little to no bearing problems. A nascar motor can run 500 miles at 8000 rpm wide open. They dont fail often. For us street strip guys that would equate to 2000 1/4 mile passes! If you saw 200 passes a year which unless you bracket race, you'll never see, would still last you 10 years!
Most guys seem lucky to get 20 passes a year
Only place rpm really matters to a point is valvetrain, you cant have a heavy valve train and aggressive lobe if you want it to get some life. High spring loads will require parts inspection from time to time. Good thing is, light valves and titanium retainers can make it possible for most small blocks to hit 7000-8000 rpm and not hurt parts
I got 6 years of my two bolt main spinning to 7100 rpm. The last two years saw road course duty too. I did have main cap walk. Even though the mains were affected, a broken stock piston was its demise. I have no doubt I'd have gotten 10 years out of it strictly drag racing and street use.
Post mortem: http://ls1tech.com/forums/lt1-lt4-mo...alvetrain.html
Its not the 20 passes a year at the track that take their toll on an engine, its the 20 passes a DAY that really put the wear and tear on the parts. Mine is more street than race for sure but that doesn't stop me from red-line shifting dozens of times on any given day. That said, those short duration bursts are definitely easier on parts than keeping it pinned for the flying mile or an open road event. That's another reason why I ditched my cast rotating assembly.
As long as the oil film is doing its job, and oil is clean, and detonation is avoided, there shouldnt be any bearing to metal contact so virtually no wear.
Its the start ups when no oil pressure is present and dirty oil over time that will wear a bearing down
Rpm is nothing imo. Proper machine work and bearing clearances will still keep a motor happy and little to no bearing problems. A nascar motor can run 500 miles at 8000 rpm wide open. They dont fail often. For us street strip guys that would equate to 2000 1/4 mile passes! If you saw 200 passes a year which unless you bracket race, you'll never see, would still last you 10 years!
Most guys seem lucky to get 20 passes a year
1. I am referring to strictly OEM bottom ends and daily drivers wanting to find 200k miles. I thought that was fairly clear. I realize engines can be built to do anything you want, 999999rpm etc... every limit is always tested. While testing limits, remind me what is the limit for the oem bottom end? And keep in mind that just because the engine will turn 8200rpm and make a good dyno output, does not mean that rod bearing #1 is happy doing it. The only way to actually answer this question is to go on a per-engine basis, as each engine has its own limit from the OEM (Still discussing OEM engines until I say otherwise), and the only way to really find it is to build a record of as many engines as you can find and record their use/mileage/environment and so forth. Every bit of data you collect can be compared, and THEN you can justify some kind of baseline, "yes 47% of engines which are kept below 6200rpm and 400bhp survive to 150,000 miles with a myriad of other factors also being compared, this was the most common trend." as an example.
Originally Posted by Orr89RocZ
As long as the oil film is doing its job, and oil is clean, and detonation is avoided, there shouldnt be any bearing to metal contact so virtually no wear.
Its the start ups when no oil pressure is present and dirty oil over time that will wear a bearing down
2. Another great point you made, lets emphasis this with a real world example with which I am familiar. The 2.0L made by Nissan called sr20det has an OEM main around 0.0012", and a rod with a minimum of 0.0008" yes my decimal is correct. The OEM engine calls for 5W-30 in Japan climate and 10W-30 in Florida. These engines will reach 200k and beyond like this. In many performance applications, however, a much larger clearance is used with thicker oils. They will open the mains to 0.0022" and use 40W or even 50W oil. An engine ran like this for brief period, upon inspection after just 6000 miles will show pitting of the rod bearing number one, most likely due to the reason you just mentioned, startup dryness. The human body experiences the same thing, walk at an include on a treadmill at a quick pace with enough include you will experience joint dryness in the ankle region, if you had not warmed it up prior. After a couple more minutes the joint will become lubricated (as chondrocytes respond to the stimulus) and pain will subside. In both cases, engine and ankle, what they really call for is an accumulator, a pre-oiling system to prevent startup associated wear. However, keep in mind the OEM engine requires no such thing- because the space and oil thickness is ideal for startups, and less ideal for max performance/high RPM. It is a trade, and if you believe that your engine was built properly for startup / thin weight oils then you should alsobe careful and cautious when increasing the OEM redline without having data that proves the engine will tolerate it, as with #1.
3. Another great point you made was the cleanliness, overlooked in my opinion. An engine spends its life hurtling towards the filthy end. Street cars are built around better filtration, blankets and temp control.
4. here is the meat and potatoes. it all comes down to cost/horsepower. If anyone of us can grab a 5.3 off the shelf for $800 or $1200 and make 550 to 600bhp with it for 50k, doesn't that completely obliterate any other option? Just a set of heads costs more than buying a complete spare engine. The money goes into the transmission, and the turbocharger configuration. The engine is just a throw away, your chances pushing a built engine at the same output to 50k are worse than pushing a stock engine to 150k (from 100k).
Even with the decent E/I ratio, unless you have the best designed exhaust system attached to those ports, the exhaust side still ends up being crippled to some degree.
Skinny, when you were running the 1.6RR, were you running flat tops? I was chatting with my machinist today and he's concerned about Piston to Valve clearance if I go with the 1.6 rockers.
1.6 ratio rockers. Flat top pistons .014" down and .026" head gasket. Running the larger XR288HR cam was a non issue as far a P/V clearance was concerned. 288/294, .550" intake, .570" exhaust. Smaller cams (on the same ICL) will have even more room.
Always check. I'll be revisiting this as I intend to run 4 degrees advanced on my cam and the intake valve might start getting close.
05-06-2016, 11:55 AM
At any rate, I appreciate any advice you have to offer about the cam, and I thank you for taking the time to read all of this.
