hoggy

I read about people saying that lowering compression does not affect spool time since displacement is not changed. I'm not sure if I agree with that or not. The same amount of air exhaust is being passed through the turbo, but with lower compression less power is created, which I believe also means less heat. From what I understand heat is what actually provided the energy for the turbo to spool. In that senario if I am correct, lower compression would affect spool time. Can anybody explain this better or tell me why my belief is wrong. I hear people say this so much and it doesn't make sense I would like to see more good info on here.

MachAF

I have no dyno's or anything else showing that it effects it..

like you said it makes sense. Less compression = less power = less heat.

Heat is used to spool the turbo. So less heat = less spool.

hoggy

to the top....i'm sure somebody has to have some info on this

11psiTurboSI

Higher compression will make the turbo spool faster then lower compression being the same bore

earl

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by 9psiTurboSI &raquo;</TD></TR><TR><TD CLASS="quote">Higher compression will make the turbo spool faster then lower compression being the same bore</TD></TR></TABLE>I have never seen that proven anywhere. Experience turbo people will always say it is the size of the exhaust that dictates spool time. High compression could make a micro second of difference but nothing you can feel or measure. High compression, however, will certainly help you to detonate quicker.

Lsos

From my understanding of turbos, higher compression will definately affect spool time because of the exact logic you went through. If I remember correctly from reading Maximum Boost, Corky Bell specifically pointed out how he feels about low compression/ high lag turbo setups (he didn't feel very good about them).

blundar

for the same reason that high compression NA motors make more power than low compression NA motors (more compression = more work), high compression boosted motors spool faster (assuming all other things held equal).

Higher compression means the motor is pulling more air in (greater difference in initial / final cylinder volume - differential creates pressure differential, pressure differential fills cylinder) and pushing more air out. The larger difference in initial/final cylinder volume alone is enough to create higher velocity on exhaust gas, which is in itself enough to spool a turbo faster. Remember, the "leftovers" from the combustion cycle (pressure, heat) are used to spool the turbo.

RyanEJ8

Higher compression will create more exhaust gas energy and have an effect on spool time. Exhaust sizing (like earl mentioned) and displacement will play a bigger role on spool time though. With the right gasoline and good tuning detonation can be avoided on high compression boost applications.

Lsos

It seems that way, but it's not really that the higher compression motor is pulling in more air (it isn't, the difference in initial/final cylinder volume, or the displacement is the same no matter what compression), but that it gets more energy out of the air because the higher the compression the more efficient the burn. However it all works, more energy made means more energy to spin the turbo....

blundar

you forget that time is a factor.
the volume difference creates a pressure difference between the "empty" cylinder and the intake manifold while the intake valve is open.
The rate of airflow into the cylinder is related to the pressure differential - larger pressure differential means higher air velocity.
as air fills the cylinder, the pressure difference approaches zero.
especially at high RPMs, unless your portwork was done by jesus ******* christ himself, you are going to run into limitations about how full your chambers can get due to portflow restrictions and TIME restrictions from the motor spinning fast.
Higher compression helps offset these pumping losses by increasing the air velocity (and thereby increasing cylinder filling) when portflow restrictions have come into play.

Higher compression motors will suck a little more air, but I guess the effect is probably less important for turbo spool than for other places.

You are 100% right - more energy coming out of the motor means more energy to spool the turbo.

h22 civic

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by 9psiTurboSI &raquo;</TD></TR><TR><TD CLASS="quote">Higher compression will make the turbo spool faster then lower compression being the same bore</TD></TR></TABLE>
im going to have ta agree