Intake Closing Point vs Cylinder Pressure
12-20-2018, 01:38 PM
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Car: 1983 Camaro Z28
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Intake Closing Point vs Cylinder Pressure
Every engine is different, but has anyone seen any studies done on the optimal intake closing point to maximize peak engine power or torque? The general idea behind it can be seen here:
https://www.hotrod.com/articles/inta...g-performance/
https://www.hotrod.com/articles/inta...g-performance/
12-20-2018, 01:55 PM
#2
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Re: Intake Closing Point vs Cylinder Pressure
That's what goes on when you select a camshaft using the dynamic compression ratio. The intake valve closing point for the most part controls cylinder pressure. And that's why I say always choose and buy your camshaft last when building an engine for performance.
The reality is you optimize cylinder pressure for the octane of the fuel you use. That meaning use the intake valve closing point that keeps your cranking pressure below the 210psi to 220 psi range for premium fuel. Lower cranking pressure is leaving power on the table.
Good luck.
The reality is you optimize cylinder pressure for the octane of the fuel you use. That meaning use the intake valve closing point that keeps your cranking pressure below the 210psi to 220 psi range for premium fuel. Lower cranking pressure is leaving power on the table.
Good luck.
12-20-2018, 01:58 PM
#3
Re: Intake Closing Point vs Cylinder Pressure
Yeah lol race teams with unlimited budgets do this all the time
its just getting cam grinds and testing them. All the calculations in the world establish a baseline. A cam is made and tested. Results tabulated and new theories developed. New valve events are tried. Iteration iteration iteration then final result
eventually find the best for the application
you can also see it in modern day vvt motors. Variable cam timing advances or retards the cam centerline which changes all 4 valve events on an ls motor lets say, but the coyote ford 5.0 has a separate cam for intake and exhaust lobes so you can control 2 events separately. It works fantastic. Advance it at low rpm really makes low end power. Retard as rpm climbs make more top end
its just getting cam grinds and testing them. All the calculations in the world establish a baseline. A cam is made and tested. Results tabulated and new theories developed. New valve events are tried. Iteration iteration iteration then final result
eventually find the best for the application
you can also see it in modern day vvt motors. Variable cam timing advances or retards the cam centerline which changes all 4 valve events on an ls motor lets say, but the coyote ford 5.0 has a separate cam for intake and exhaust lobes so you can control 2 events separately. It works fantastic. Advance it at low rpm really makes low end power. Retard as rpm climbs make more top end
12-20-2018, 02:04 PM
#4
Re: Intake Closing Point vs Cylinder Pressure
And dynamic compression aka cranking doesnt necessarily mean much. Its very losely correlated with fuel octane, a guideline but not end all be all. Volumetric efficiency changes how much mass is trapped in the cylinder when its running, it could be much more or less mass than whats trapped in a cranking test lol meaning effective comp ratio is higher or lower than calculated by intake closing. Guideline but i wouldnt design around it
12-20-2018, 02:42 PM
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Re: Intake Closing Point vs Cylinder Pressure
Yea, so the cranking compression may not mean much at all once VE gets high since when the engine is running the effective compression is actually higher than static compression, and dynamic compression. Cranking compression would be a linear correlation to dynamic compression, I'd imagine. But once the engine is running, especially at high rpms, that all changes.
So the goal is to maximize cylinder pressure without causing detonation (through all rpm ranges), and tune the intake closing point to peak power, or just before. If that is known (say 80 ABDC), then I could tune my static CR to achieve 8.0:1 Dynamic CR since that seems to be an agreed number to prevent detonation?
I am trying to decide what the best method/theory would be to go in setting compression to cam before I am locked into either.
Cam manufacturers seem to not be on the same page when speaking with them. Any recommendations on who to use?
So the goal is to maximize cylinder pressure without causing detonation (through all rpm ranges), and tune the intake closing point to peak power, or just before. If that is known (say 80 ABDC), then I could tune my static CR to achieve 8.0:1 Dynamic CR since that seems to be an agreed number to prevent detonation?
I am trying to decide what the best method/theory would be to go in setting compression to cam before I am locked into either.
Cam manufacturers seem to not be on the same page when speaking with them. Any recommendations on who to use?
12-20-2018, 02:54 PM
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Re: Intake Closing Point vs Cylinder Pressure
There is no "one" "optimum" number for any of those things. Everything is a trade-off. Give up something you don't want or need to get something else.
Best you can do is, select results that give the compromise you can best accept. Trade off low-end grunt for high-end HP, trade off "max power" for pump gas compatibility, etc.
If you use Pat Kelley's DCR calculator, the one everybody talks about, you should generally choose a cam that gives somewhere in the low 8's of DCR, for a typical street build. Any lower than that, you have no low end; much higher, you have pinging problems that end up requiring race gas or other special accommodations.
Beyond that, there are any number of other cam properties you can manipulate to get the desired results for YOUR combo. Int/exh split is one: generally, the better the exh ports flow, the less split you need. Another is LSA: generally, the lower the LSA, the closer to the same RPM the peaks in torque & HP are, and the more of a peak they produce; higher LSA tends to give lower peaks but the HP peak moved upward in RPMs, kinds "smearing" the curves down and to the right with the area under the curve staying about the same; the "optimum" choice for YOUR situation depends on things like gearing and vehicle weight. And so forth.
If there was "one" "optimum" cam, there wouldn't be about 10 million grinds available. Everybody would just buy the ONE and be done with it. But it just doesn't work that way.
Best you can do is, select results that give the compromise you can best accept. Trade off low-end grunt for high-end HP, trade off "max power" for pump gas compatibility, etc.
If you use Pat Kelley's DCR calculator, the one everybody talks about, you should generally choose a cam that gives somewhere in the low 8's of DCR, for a typical street build. Any lower than that, you have no low end; much higher, you have pinging problems that end up requiring race gas or other special accommodations.
Beyond that, there are any number of other cam properties you can manipulate to get the desired results for YOUR combo. Int/exh split is one: generally, the better the exh ports flow, the less split you need. Another is LSA: generally, the lower the LSA, the closer to the same RPM the peaks in torque & HP are, and the more of a peak they produce; higher LSA tends to give lower peaks but the HP peak moved upward in RPMs, kinds "smearing" the curves down and to the right with the area under the curve staying about the same; the "optimum" choice for YOUR situation depends on things like gearing and vehicle weight. And so forth.
If there was "one" "optimum" cam, there wouldn't be about 10 million grinds available. Everybody would just buy the ONE and be done with it. But it just doesn't work that way.
12-20-2018, 03:11 PM
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Re: Intake Closing Point vs Cylinder Pressure
Yes - trade-offs. So my trade-off is low end torque for high end, say 7000-7500 power on 93 octane. Definitely not saying "what is the perfect performance cam for sbc"... thats why I prefaced with "Every engine is different". Now, using that DCR calculator, or the one on UEM pistons (both very similar) I can easily set DCR to 8:1. Where I am kind of stuck trying to decide what is better, 8:1 DCR, 11.5:1 SCR, and 80* Intake Closing Angle - OR - 8:1 DCR, 10.7:1 SCR, and 75* Intake Closing Angle. In my opinion, these should be the starting point of the cam design and work around that, no? Or knowing the IVC angle, I can set the compression to that. It seems like I would want closer to the 80* range?
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12-22-2018, 12:42 PM
#9
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Re: Intake Closing Point vs Cylinder Pressure
And dynamic compression aka cranking doesnt necessarily mean much. Its very losely correlated with fuel octane, a guideline but not end all be all. Volumetric efficiency changes how much mass is trapped in the cylinder when its running, it could be much more or less mass than whats trapped in a cranking test lol meaning effective comp ratio is higher or lower than calculated by intake closing. Guideline but i wouldnt design around it
12-22-2018, 06:57 PM
#10
Re: Intake Closing Point vs Cylinder Pressure
For most hobbiest guys who arent gonna be generating super high ve, dcr and cranking compression can be used. Just saying its not the end of all be all number.
there are 9:1 comp circle track motors with cams designed to generate/trap high cyl pressure. They make good power and have torque. theres compromises
imo on 93 gas and a good aluminum head motor, 11:1 is fine with a cam thats gonna get you cranking compression 200 psi or less. Some guys have run higher just fine. My personal 383 was around 11:1 with a dcr of 8 i believe. 93 oct just fine, lots of power to 6800.
consider the whole induction system from cubic inches/ cylinder size, to valve size to port area to runner length to your rpm peak target. A well balanced system sized for typical street 6000’s rpm range,, 230 deg and .550-.600” lift on a 383 will get you a strong 6000-6300 rpm peak and can carry power abit past 6500-6600 depending on exhaust lobe. 100-200 rpm higher peak easily with a 350. Lsa’s typically end up 107-112 depending what you want. Better the heads and well balanced top end you can go wider. More stable smooth idle likes wider. All rules of thumb
there are 9:1 comp circle track motors with cams designed to generate/trap high cyl pressure. They make good power and have torque. theres compromises
imo on 93 gas and a good aluminum head motor, 11:1 is fine with a cam thats gonna get you cranking compression 200 psi or less. Some guys have run higher just fine. My personal 383 was around 11:1 with a dcr of 8 i believe. 93 oct just fine, lots of power to 6800.
consider the whole induction system from cubic inches/ cylinder size, to valve size to port area to runner length to your rpm peak target. A well balanced system sized for typical street 6000’s rpm range,, 230 deg and .550-.600” lift on a 383 will get you a strong 6000-6300 rpm peak and can carry power abit past 6500-6600 depending on exhaust lobe. 100-200 rpm higher peak easily with a 350. Lsa’s typically end up 107-112 depending what you want. Better the heads and well balanced top end you can go wider. More stable smooth idle likes wider. All rules of thumb
12-22-2018, 07:03 PM
#11
Re: Intake Closing Point vs Cylinder Pressure
Yes - trade-offs. So my trade-off is low end torque for high end, say 7000-7500 power on 93 octane. Definitely not saying "what is the perfect performance cam for sbc"... thats why I prefaced with "Every engine is different". Now, using that DCR calculator, or the one on UEM pistons (both very similar) I can easily set DCR to 8:1. Where I am kind of stuck trying to decide what is better, 8:1 DCR, 11.5:1 SCR, and 80* Intake Closing Angle - OR - 8:1 DCR, 10.7:1 SCR, and 75* Intake Closing Angle. In my opinion, these should be the starting point of the cam design and work around that, no? Or knowing the IVC angle, I can set the compression to that. It seems like I would want closer to the 80* range?
12-22-2018, 08:31 PM
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Re: Intake Closing Point vs Cylinder Pressure
I recently went through a learning curve while trying to select a cam for an engine I have. I read many articles about camshafts, discussions on forums, etc, etc. My conclusion: I'm not qualified to choose a cam without help. The topic is too complex and requires iteration of experiment. Effort and money I'm not willing to expend.
So I changed my strategy and decided to look at engine builds similar to mine and see what works and what doesn't. I spent weeks searching the forums and found engines like mine with 23 different cams with dyno curves, many backed up with time slips. Basically I ran a large experiment without spending a dime of my own money.
One thing I noticed is all the cams that worked really well, whether big or small, had the same Intake Centerline Angle as installed in the engine, and had the same Dynamic Compression Ratio. Intake closing events varied. So ICA and DCR became a key characteristic that I hunted for since it was demonstrated what values my engine likes.
Then I started paying closer attention to torque curves, driving characteristics that people described, whether easy or difficult to tune.... anything that would help me narrow the list. I noticed one particular shop was exceptionally good at making killer torque curves with excellent throttle response and good drivability. So I picked up the phone and had that shop spec out a custom cam for me. The results ended up right where I figured it would be, based on my "23 cam test".
Anyway, that's how I chose a cam without having to know a whole lot about the subject.
So I changed my strategy and decided to look at engine builds similar to mine and see what works and what doesn't. I spent weeks searching the forums and found engines like mine with 23 different cams with dyno curves, many backed up with time slips. Basically I ran a large experiment without spending a dime of my own money.
One thing I noticed is all the cams that worked really well, whether big or small, had the same Intake Centerline Angle as installed in the engine, and had the same Dynamic Compression Ratio. Intake closing events varied. So ICA and DCR became a key characteristic that I hunted for since it was demonstrated what values my engine likes.
Then I started paying closer attention to torque curves, driving characteristics that people described, whether easy or difficult to tune.... anything that would help me narrow the list. I noticed one particular shop was exceptionally good at making killer torque curves with excellent throttle response and good drivability. So I picked up the phone and had that shop spec out a custom cam for me. The results ended up right where I figured it would be, based on my "23 cam test".
Anyway, that's how I chose a cam without having to know a whole lot about the subject.
Last edited by QwkTrip; 12-22-2018 at 09:02 PM.
12-23-2018, 09:42 AM
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Re: Intake Closing Point vs Cylinder Pressure
maybe some more details on your setup is needed to understand what you are looking to do? If you believe intake lobe needs to close in the 75-80 range then i assume you considered your induction system, the cubic inches, and rpm target and determined how much duration you need and lift to support your rpm goal? I would figure duration and lift then set comp to what you feel comfortable with on pump gas...which leads us into dcr as a guideline again. 8-8.3 i suppose is a starting point, but as i mentioned earlier, i would generally keep most alum headed sbc’s at 11:1 or under, if cranking comp is calc’d under or around 200 psi
I don't have pistons, rods and cam, so I am free right now to set CR and cam wherever I'd like. I would like to have a very good understanding of cam events and their effect on power in order to make the best decision, or know what NOT to do or listen to when calling cam grinders.
I recently went through a learning curve while trying to select a cam for an engine I have. I read many articles about camshafts, discussions on forums, etc, etc. My conclusion: I'm not qualified to choose a cam without help. The topic is too complex and requires iteration of experiment. Effort and money I'm not willing to expend.
So I changed my strategy and decided to look at engine builds similar to mine and see what works and what doesn't. I spent weeks searching the forums and found engines like mine with 23 different cams with dyno curves, many backed up with time slips. Basically I ran a large experiment without spending a dime of my own money.
One thing I noticed is all the cams that worked really well, whether big or small, had the same Intake Centerline Angle as installed in the engine, and had the same Dynamic Compression Ratio. Intake closing events varied. So ICA and DCR became a key characteristic that I hunted for since it was demonstrated what values my engine likes.
Then I started paying closer attention to torque curves, driving characteristics that people described, whether easy or difficult to tune.... anything that would help me narrow the list. I noticed one particular shop was exceptionally good at making killer torque curves with excellent throttle response and good drivability. So I picked up the phone and had that shop spec out a custom cam for me. The results ended up right where I figured it would be, based on my "23 cam test".
Anyway, that's how I chose a cam without having to know a whole lot about the subject.
So I changed my strategy and decided to look at engine builds similar to mine and see what works and what doesn't. I spent weeks searching the forums and found engines like mine with 23 different cams with dyno curves, many backed up with time slips. Basically I ran a large experiment without spending a dime of my own money.
One thing I noticed is all the cams that worked really well, whether big or small, had the same Intake Centerline Angle as installed in the engine, and had the same Dynamic Compression Ratio. Intake closing events varied. So ICA and DCR became a key characteristic that I hunted for since it was demonstrated what values my engine likes.
Then I started paying closer attention to torque curves, driving characteristics that people described, whether easy or difficult to tune.... anything that would help me narrow the list. I noticed one particular shop was exceptionally good at making killer torque curves with excellent throttle response and good drivability. So I picked up the phone and had that shop spec out a custom cam for me. The results ended up right where I figured it would be, based on my "23 cam test".
Anyway, that's how I chose a cam without having to know a whole lot about the subject.
Care to share more of your engine combo? CR and cam? Also, what shop was it?
I've called a few cam grinders and you can really get different recommendations from different guys. Some said that static CR should be 9.5 to 1 to produce the most power in order to have the ideal timing. One recommended a 80 degree intake closing angle. One said forget about everything because I need 2" headers not 1 3/4 which will shut the motor off at 4500 rpm. So really, it is me who needs to be intelligent enough to at least know what to look for and to understand if I am getting good or bad advice. Once I feel comfortable, then I can call a place and spec a cam with them, generally knowing what I want. I am not there yet, but getting there!
12-23-2018, 12:52 PM
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Re: Intake Closing Point vs Cylinder Pressure
I don't think any of my build examples will be helpful to you. My engine is a LS7 with EFI style longitudinal intake and it wants different valve events than a SBC engine.
12-24-2018, 10:39 AM
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Re: Intake Closing Point vs Cylinder Pressure
Ohh yup. I didn't realize it was a LS. Heard a lot about him though and intake/head porting.
12-24-2018, 10:57 AM
#17
Re: Intake Closing Point vs Cylinder Pressure
What size valves in the head? What stroke crank? Solid roller or hyd roller?
Might need alot more carb than that. 1 7-8 header be better but 1 3/4 could work for now
i can run it thru my cam software to see where it ends up
else you can likely talk to bullet cams, straub technologies, or Jones racing cams.
Might need alot more carb than that. 1 7-8 header be better but 1 3/4 could work for now
i can run it thru my cam software to see where it ends up
else you can likely talk to bullet cams, straub technologies, or Jones racing cams.
12-24-2018, 04:37 PM
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Re: Intake Closing Point vs Cylinder Pressure
What size valves in the head? What stroke crank? Solid roller or hyd roller?
Might need alot more carb than that. 1 7-8 header be better but 1 3/4 could work for now
i can run it thru my cam software to see where it ends up
else you can likely talk to bullet cams, straub technologies, or Jones racing cams.
Might need alot more carb than that. 1 7-8 header be better but 1 3/4 could work for now
i can run it thru my cam software to see where it ends up
else you can likely talk to bullet cams, straub technologies, or Jones racing cams.
12-24-2018, 09:07 PM
#21
Re: Intake Closing Point vs Cylinder Pressure
Well they seem similar in flow to my old speier 245’s so using similar data and making a few assumptions
cam around a 300/309 at .020” advertised, 269-276 at .050 188/190 at .200
.421/.410” lobe lift. Assuming 1.6 rockers and .020/.022 lash, net lift of .653/.634. Lsa 111. Install on a 108.
should get you close to a 6800 rpm peak and carry power to well over 7000. Get you close to 650 hp i’d say
more drag race only,
303/313 at .020
274/280 at .050
.453/.441 lobe lift
.704/.683 with 1.6 rockers
111 lsa again
but you gotta watch cam to rod clearance at 4” stroke. Base circle gets small so with shaft rockers go more ratio, 1.7-1.75 if you can
cam around a 300/309 at .020” advertised, 269-276 at .050 188/190 at .200
.421/.410” lobe lift. Assuming 1.6 rockers and .020/.022 lash, net lift of .653/.634. Lsa 111. Install on a 108.
should get you close to a 6800 rpm peak and carry power to well over 7000. Get you close to 650 hp i’d say
more drag race only,
303/313 at .020
274/280 at .050
.453/.441 lobe lift
.704/.683 with 1.6 rockers
111 lsa again
but you gotta watch cam to rod clearance at 4” stroke. Base circle gets small so with shaft rockers go more ratio, 1.7-1.75 if you can
12-24-2018, 09:16 PM
#22
Re: Intake Closing Point vs Cylinder Pressure
Pipemax thinks the higher lift above .660 is ideal for that rpm range. 650 hp def doable based on head air flow if manifold and carb support it
intake close at 62.5 deg based on .050” duration specs
1 7/8 header ideal. Could even go 2”
assuming 11.5:1 comp, cranking compression would be between 180-200 depending on starter rpm. May be ok on 93.
But i would lean toward 11:1 or so.
900 or so cfm carb be good. 1000 wouldnt hurt
intake close at 62.5 deg based on .050” duration specs
1 7/8 header ideal. Could even go 2”
assuming 11.5:1 comp, cranking compression would be between 180-200 depending on starter rpm. May be ok on 93.
But i would lean toward 11:1 or so.
900 or so cfm carb be good. 1000 wouldnt hurt
Last edited by Orr89RocZ; 12-24-2018 at 09:20 PM.
12-24-2018, 10:00 PM
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Re: Intake Closing Point vs Cylinder Pressure
The solid rollers seem to carry power really well, like 1000 rpm within 20 hp or so. So yea 6800 would be great. Now going to the more drag race only, what am I losing for driveability? Just low end power or the extra lift killing springs? I think over 0.660 would be smart to do. Surprised that the 62.5 is all it is looking for, although I haven't found any real engines with data including intake close. On a comp cams cam card is the ABDC @ 0.050"? Makes sense with the header size. I have a do have a dominator adapter, so I will have options with the carb.
12-25-2018, 09:24 AM
#24
Re: Intake Closing Point vs Cylinder Pressure
Drag race lobe might be tougher on springs. Depends which lobe type you go with if you have comp grind it. Bigger duration would be abit less driveable but both cams are pretty decent in size.
Going up in rocker ratio will help keep lobe size down. I assumed a 5.85” rod to get a decent piston in there.
comp cams usually are .050 specs but some are .006. Mine was .050” on last few
on the seat duration, the 62.5 becomes more like 89
Going up in rocker ratio will help keep lobe size down. I assumed a 5.85” rod to get a decent piston in there.
comp cams usually are .050 specs but some are .006. Mine was .050” on last few
on the seat duration, the 62.5 becomes more like 89
12-26-2018, 08:26 AM
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Re: Intake Closing Point vs Cylinder Pressure
I won't want to be changing springs every year, so I will factor that into the decision. Not as concerned with idle/low end power. Most 4.125/4.155 bore, 4" stroke are actually 6" rods. doesn't leave much room for the piston, but on the brighter side... its lighter lol.
So, either cam, the right choice would be to push my SCR up to 11.5 using a 15cc dish. Depending on what my actual chamber volume comes out to.
Using Pat Kelly DCR Calculator:
With the drag race cam: 11.55 SCR and 8.11 DCR
With the 1st cam............11.55 SCR and 8.24 DCR
Now, it seems like the DCR has a higher role in detonation, so 11.5 should be fine right? I've reaf of a few engines that run high SCR as long as DCR is in the appropriate zone for pump gas... sketchy though to push the limit.
So, either cam, the right choice would be to push my SCR up to 11.5 using a 15cc dish. Depending on what my actual chamber volume comes out to.
Using Pat Kelly DCR Calculator:
With the drag race cam: 11.55 SCR and 8.11 DCR
With the 1st cam............11.55 SCR and 8.24 DCR
Now, it seems like the DCR has a higher role in detonation, so 11.5 should be fine right? I've reaf of a few engines that run high SCR as long as DCR is in the appropriate zone for pump gas... sketchy though to push the limit.
12-26-2018, 09:18 AM
#26
Re: Intake Closing Point vs Cylinder Pressure
Yeah that would be abit less tuning window. You would need to keep it cool, get the right heat range plug as always, and keep an eye on timing as it might become pretty sensitive quickly. Also may want to run it much richer than normal during part throttle stuff.
11:1 would be safer imo. And still get the power you seek. In fact you probably can get there with a 260 deg cam. Peak closer to 6300-6500. 434 is alot if cubes and you have the airflow to make closer to 680-700
good spring like a pac, psi, or manley nextek they will last a little while. Comp has some lobes that will last a decent while too. Rx lower lift 420-430 lobes are good.
12-26-2018, 09:56 AM
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Re: Intake Closing Point vs Cylinder Pressure
But if I go 11:1 I should scale back the cam to get the 8.1:1 DCR, correct? Heard of Tool Room springs? The heads were assembled with those and XcelDyne valves too. Seems like he used good stuff.
01-22-2019, 07:54 AM
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Re: Intake Closing Point vs Cylinder Pressure
Shooting for high compression obviously increases the risk of detonation. Looking into the J&S Safeguard ignition box for the higher spark energy and automatic timing retard/detonation sensing. Anyone else interested in the group buy?
https://www.thirdgen.org/forums/grou...safeguard.html
https://www.thirdgen.org/forums/grou...safeguard.html
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