What kind of psi could I run with 10:1 cr? This is the work I was planning to do to the bottom end:
1) Golden Eagle sleeves
2) Forger pistons
3) Balance and Micro-Polished Crankshaft
Newb question>>> What would happen if you ran high boost with high compression? I know you'd "blow your engine up" but HOW exactly? What blows up? Does it blow the head gasket, piston rigns, what??? Thanks guys!
Too many factors to give a specific answer to that. Intercooling, turbine/blower efficiency, fuel & ignition tuning, piston design . . . to name a few.
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It's not a matter of max psi. What are your power goals?
Don't really have a goal in mind yet. My personal power goals will depend on what is necessary to reach them.
I'm just trying to get a better understanding of what causes an engine to fail when it is exposed to pressure levels it's not designed to handle. What is the first thing to go? I've heard stories of valve covers blowing off the head, but that could be total BS, dunno. I would think that too mush boost would cause detination, no matter how much you retard the timing. Is that the limiting factor for how much boost an engine can take, if it experiences detination?? Maybe detination doesn't occur, but the engine just overheats
In summary, how do you determine a "safe" level of PSI for a motor? I plan on using 10:1 compression pistons for better low end torque (daily driver, not a track car) Thanks guys!!
Guys are making 500 whp on built H22 engines. If you are getting it sleeved and throwing in forged pistons, psi isn't going to matter. The components will be able to handle much more pressure than you can ever throw at them. psi is going to be relative to your choice of turbo and other components, anyway. Pressure is nothing more than a measurement of airflow restriction.
You need to first decide what your power goal is. It doesn't have to be a specific number, it can be a range. What will determine your reliability at a given power level is your fueling components, engine management and the tuning.
Thanks for the great info. I do have another question. Why do guys put lower compression pistons (9:1) into their engines? I thought it was to allow for higher boost levels, so they don't "blow up" their engines, but then you said this...
Quote:
Originally Posted by sharkcohen
If you are getting it sleeved and throwing in forged pistons, psi isn't going to matter. The components will be able to handle much more pressure than you can ever throw at them.
Is this true? Can I have high boost levels with 10:1 pistons? Is there a reason why I shouldn't do this? Thanks!
Lowering the compression is done not so much to run more boost, but to make it less difficult to tune. Of course, to get the same amount of power, you would need to run more boost on lower compression.
Also, don't misunderstand what I'm saying. It's not cylinder pressure that destroys a built motor, it's poor tuning that will melt a forged piston or crack a sleeve. But you need to get away from focusing on the amount of boost. The amount of boost pressure doesn't matter. It's how much power you want the motor to put out that matters.
Sure you can boost on 10:1. The margin of error in the tuning is narrower than with 9:1, but a good tuner can do it if you have well chosen engine management. Personally, I'd run 10:1, but that's me.
IIRC, the higher the CR the more power down low; If I was building a sleeved block for low-medium boost applications, I'd consider upping the CR to 11:1 to increase low end pull and to reduce turbo lag... if you're going medium-high apps, 10:1 is best. If you are going sky high with your boost, or using a huge turbo, reduce it to 9:1.
yea based off of the origional question. shark you said what parts you get depends on how much power you want to make. so i'm asking what would it take to get 300 to the wheels.
first, you should NEVER run 11:1 or 11.5:1 on a motor you want to run boost on. The second thing to keep in mind is turbo efficiency and octane levels where you live. for example, the same size turbo will not have the same efficiecy in the desert as it would in colder weather. octane almost dictates compression levels when you have a power goal in mind. The size and trim of the turbo also comes into play. For 300 wheels, on 91 octane in cali you would need a built block running on 9.0:1 compression. for 250 wheels you could PROBABLY get away with 10:1.
why not go 9.0:1 to give some tuning room and space in case you want to run higher levels at the track?
Boost psi and compression really have nothing to do with one another if you build it right and have a good tuner. Lower compression is easier to tune, it's that simple. DPR had many daily driven motors (as they were one of the few builders that believed in good tuning) that saw 12-14:1 compression ratios. You can EASILY get away with 10:1 compression, just note that your room for error will be reduced. Though also keep in mind that if you run higher compression you can run lower boost and get the same results. If that's what you have, don't worry about it. Low compression is just the way to get around mediocre tuning.
While octane is important, it's not insanely critical. All the DPR steet motors that were running 10:1 - 14:1 ~8 psi motors were running on sunny California 91 octane for the street. A toulene mix for the track, but then the psi levels were turned up as well. If you're worried about getting a bad tank of gas, invest in a J&S to prevent hurting the engine.
Interesting, I never realized that you lower compression to make it easier to tune. I was thinking about what keahi said about detonation, and worrying about octane, but I don't think that would be much of an issue. If our motors are 10.6:1 or something already, and we can push to 7800 safely, it wouldn't make a difference if you boosted. All you'd be doing is adding more air, and compensating it with the correct amount of fuel. And as long as this balance was achieved (by the tuner), you would be fine.
Am I right, or wrong here?
EDIT: I just realized that combustion properties would change under higher pressures.
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Last edited by Emerald99 : 05-18-2005 at 09:21 AM.
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