L67 and Bigger compression?
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when my car is up we will soon find out!
I believe a slight increase in piston (mechanical) compression ratio, or a thinner head gasket allows you to run a larger pulley and keep the M-90 closer to its optimum performance range, yet still get similar cylinder pressure of someone who overdrives the M-90 (smaller pulley).
Overdriving the M-90 creates even more heat, and a charge that is less dense because of extreme heat, and more likely to cause KR.
The best scenario would be to lower the compression ratio and run and overdriven M-90 (or M-112) on top of an intercooler. That way you would get a large volume, a cooler (dense) charge, and lower the danger of detonation.
Overdriving the M-90 creates even more heat, and a charge that is less dense because of extreme heat, and more likely to cause KR.
The best scenario would be to lower the compression ratio and run and overdriven M-90 (or M-112) on top of an intercooler. That way you would get a large volume, a cooler (dense) charge, and lower the danger of detonation.
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238 Posts
from what i have heard the only time its ok to run higher compression with the M90 is when your basically maxing it out, and the only way to make more power out the M90 is to rise compression, but other than that it might be good to leave it alone until you do get to the point of maxing it out, but i will let someone with more experience in this chime in
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1,158 Posts
This is my understanding of it as well. When I rebuilt mine, it was recommended to me, (where I was going to be keeping my M90, and NOT running an intercooler), to increase the compression and continue to run my 3.4" pulley to prevent 'Over-driving' the blower and heating up the air TOO much.MikeGS said:
I'd still love to hear more on this from anyone out there, as i'm considering an intercooler next.
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134 Posts
This was recommended to me as well.
9.5:1 compression, M90, no IC and you can even go way down lower on the pulley size of the M90. I could get away with a 3.0 for sure I would imangine, but a scan would tell me for sure.
I also opened up the intake, custom job to be done on the M90 inlet and out let,port and polished intake manifold, stage 3 INTENSE heads so on and so on...lots of air flow now baby!
~Farnsworth~
9.5:1 compression, M90, no IC and you can even go way down lower on the pulley size of the M90. I could get away with a 3.0 for sure I would imangine, but a scan would tell me for sure.
I also opened up the intake, custom job to be done on the M90 inlet and out let,port and polished intake manifold, stage 3 INTENSE heads so on and so on...lots of air flow now baby!
~Farnsworth~
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134 Posts
My main thing was to try to NOT run an intercooler.
Every intercooler that I have seen...out of the box looks like a rigged set up. I think I have only seen two that looked sweet, because they spent the extra time and money to make it look good. No bashing here, but intercoolers...aftermarket are just uggly.
By raising the compression you do not over work the M90, causing extra heat wearing out your fluid in your blower and so on. M90's that are running like a 2" pulley is just sick man. They can handle it...but just wasnt really designed to be ran XX,XXX RPM's.
Ya, high KR and a chance of preignition is what those high RPM blower spinners are looking at with no scanning done. They have to spend an additional $1,000.000 odd some dollars in supporting mods, intercooler...machined snouts...additional scaners and what not. Lot more work than its worth. But if your not tearing apart a motor...and just plan on adding mod after mod after mod...spend more to get about the same gains in my opinion.
In building my engine...this was more cost efficent to me.
My second idea I had for a build was to lower the compression, and run a Animul/Whipple set up. But the idea of setting some good times at the track and good numbers on the DYNO....most everyone would say "it just because you added a different blower". I think the M90 isnt a bad blower...untill you start the additional spinning. But it does sound cool.
~Farnsworth~
Every intercooler that I have seen...out of the box looks like a rigged set up. I think I have only seen two that looked sweet, because they spent the extra time and money to make it look good. No bashing here, but intercoolers...aftermarket are just uggly.
By raising the compression you do not over work the M90, causing extra heat wearing out your fluid in your blower and so on. M90's that are running like a 2" pulley is just sick man. They can handle it...but just wasnt really designed to be ran XX,XXX RPM's.
Ya, high KR and a chance of preignition is what those high RPM blower spinners are looking at with no scanning done. They have to spend an additional $1,000.000 odd some dollars in supporting mods, intercooler...machined snouts...additional scaners and what not. Lot more work than its worth. But if your not tearing apart a motor...and just plan on adding mod after mod after mod...spend more to get about the same gains in my opinion.
In building my engine...this was more cost efficent to me.
My second idea I had for a build was to lower the compression, and run a Animul/Whipple set up. But the idea of setting some good times at the track and good numbers on the DYNO....most everyone would say "it just because you added a different blower". I think the M90 isnt a bad blower...untill you start the additional spinning. But it does sound cool.
~Farnsworth~
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