psi up the wazoo
 

okay, so me and my brother were talking about this, but we weren't to sure about the outcome, so i came here. heres the back-drop

okay, most people usually get lower compression pistons after a turbo. but doing that makes your car slower then what it was before the turbo. so basicly they up the turbo even more figure that they can and it won't hurt the engine as bad.

so what im trying to get at is. will less pounds of boost with a higher compression gonna make your car last any longer then a car with higher pounds oh boost with lower compression?

hey, thanks in advance to anyone that has the answer =)

well now... that depends.

how high are you talking with regard to compression or boost? i think the answer, in a nutshell, is that as long as the fuel map is correct, and everything is done correctly for the application, they can last just as long. of course, you asked how long the car would last, and that has nothing to do with the set up of the engine... ;)

the main thing to worry about with high performance engines- fuel delivery. if you run lean, forget about it.

if you supply more details, i can give an attempt at a more detailed answer.

okay, thanks for answering faster than light =) let me try to rephrase this.

Lets say you have 2 motors.
MOTOR A:
10.0:1 static compression ratio, boosting 10psi

MOTOR B:
8.5:1 static compression ratio, boosting 10psi

now, for MOTOR B to be as fast as MOTOR A, MOTOR B would have to up the psi 3 pound, thus being 13psi.

so my question, if that cleared it up any is; lowering your compression ratio and adding more psi gonna make your car engine life last any longer then if you did not lower your compression ratio while having less psi.[b]

It's all about how they're tuned.

The purpose of lowering the CR when turning up the boost is to prevent detonation. If you can tune the car to run 10 psi at 10:1 compression without detonation, it will run just as long as a motor running 10 psi at 8:1 compression, and be faster.

However, all things being equal, the engine running more psi is under more stress. So if both motors are well tuned (not detonating), motor B at 13 psi and 8.5:1 CR will not last as long as motor A at 10 psi and 10.0:1 CR.

FTL was on the right track, since running lean causes detonating because it raises the oxygen content. Other things that can cause detonation: advanced ignition timing, a high CR, and burred pistons, among others. Whatever the setup, know when to say when with boost, and make sure it's tuned to get the most out of the setup while maintaining the integrity of the motor.

so... i was thinking about how to reply to this in a way that isn't too convoluted. i don't want to lose the original poster, but then again, i can't boil this down too far either... here goes:

motor A @ 10/10... that's 10:1 compression and 10psi boost. well (here's where i don't want to lose anyone) atmospheric pressure at sea level is around 14psi. a naturally aspirated(non-forced induction) "sees" 14 psi of air pressure. 10 psi of boost is the equivalent of 24 psi (from the perspective of the inside of the cylinder.) so, if you take the ambient air pressure (14 psi) and add the 10 psi of boost, you get 24 psi. multiply that by the compression ratio, and you get 10*24, or 240 "psi". now one more thing- there are too many variables here to count. the higher the boost, the higher the air temperature, unless there's intercooling going on. like i said, a lot of variables. remember the "240"...

motor B @ 8.5/13... 8.5:1 and 13 psi. add the 14 atmospheric psi to make 27 and 229.5 is the result. apparently this combo will make less power... but not in the real world. you have to take totally different approaches from the ground up in your engine design depending on what you want the outcome to be.

of course, if you aren't trying to squeeze every drop of performance from an engine, things don't have to be that optimized, but why not spend the extra time?

You'e on the right track- the "10/10" motor will be more prone to detonation, because of the amount of pressure the contents of the cylinder are under. Think static CR, but to say the cylinder is under 240 psi is inaccurate.

Absolutely- there are a ton of variables- but that's part of the tuning- controlling all the variables you can to get the most power out of the setup, and (once again), maintain the integrity of the motor.

8.5:1 compression and 13psi will not yield more power. maybe i read your post wrong, wverything sounded good until you said even though 8.5:1 @13psi only yeilds 229.5 but it really makes more power... 1psi dose not make up for 1cr of a piston.

okay, thanks for everyone that answered =)

here is an article that kinda explains he static compression and the effective compression. i think dr. drew does a very good job at explaining stuff.