high or low comp pistons
 

as you know we are building a b16 and it is sleeved, it will also be turbod, now i know low comp pistons are good for turbo 8.5-9.0 but why cant I use high comp pistons say 10.0-10.5-1 in this build and get better results on hp & tq. any input will be greatly taken in consideration

Re: high or low comp pistons
 

I all depends on who is tuning it. There is no reason you can't go 10:1 and boost, as long as it is tuned right.

Re: high or low comp pistons
 

your forcing pressurized air into a cylinder, the more dome on the piston, the less air can be forced through there , meaning you cant run as much boost as safely look at like you can run 28 psi on 8.5:1 and 24 psi on 10:1 obviously the 8.5:1 c/r with more boost will be faster ;)

Re: high or low comp pistons
 

i would do 10:1 if i had a sleeved B16A... but im crazy too... and have a great tuner...

Re: high or low comp pistons
 

10:1 isnt that high, i'd do it, i've seen 12.5:1 c/r boosted/sleeved b20

Re: high or low comp pistons
 

its about octane and retard...

if you have lots of octane, you can have lots of comp and lots of boost

do you wanna run it on street gas? if so, you will make more power on the lower compression because you will be able to have it advanced correctly without detonation.

if you wanna run it on some funky ---- like i currently run mine on, go ahead and keep it high.

with high comp on pump gas, you will be limited to lower boost with good advance, and less gains as you increase the boost. however, for track use, chucking some high octane at it and upping the boost is a real possibility...

hope that helps you. if not, there are acres of reading material out there to mull over.

read this :

http://www.sdsefi.com/techocta.htm

and also these if you are bored...

http://www.sdsefi.com/meltdown.htm
http://www.sdsefi.com/tech400.htm

Re: high or low comp pistons
 

JG was a huge fan of high compression motors and high boost. I also saw them spit out motors at the track alot too but those 700 whp passes looked nice while they lasted. Low compression allows for errors in tuning mechanical failure etc. FWD cars cant lay down huge #'s so follow what has worked

Re: high or low comp pistons
 

:y

Re: high or low comp pistons
 

thanx for some input, being here in Denver were already have low compression so that is the reason for ?'s. havent decided yet if we are going
to use 91 oct. or set it up for e-85 and we do have a excellent tuner

fe3tcourier-- those are some goor reading material you found thanx. even though I'm an old bastered I can still be taught new tricks
and that is why I keep coming back here

I LOVE THIS PLACE!!! There are great pros and cons on this matter and they just about equal out so now we have to decide how far we want to take it.
I just want to get this thing done and get it on the road
More input Please Mark

Re: high or low comp pistons
 

i dont know the pros and cons, but i bought 8.7:1 supertech pistons for my 2.0L focus.

they should handle 500hp, 30psi FTW.

Re: high or low comp pistons
 

Yes, it's all about the octane and timing.

With pump gas you'll want go with a lower compression, with race gas or e85 you can use a higher compression.

If you try to use low octane with high compression and high boost you'll have to pull a ton of timing, that will cause high EGT's and it will be inefficent at making power.

Re: high or low comp pistons
 

Good points brought up... One more thing, as far as I know a lower CR would make it feel more sluggish when not in boost - which would bug the hell out of me in a street car. Just something to think about... I probably wouldnt go below 9:1 in my car

Re: high or low comp pistons
 

I wouldn't go lower than 9 to1 it wouldn't have power off boost. :8

Re: high or low comp pistons
 

my friend has 7.1 in his dsm and it hits 36 psi no problem not laggy

Re: high or low comp pistons
 

i'm running 9:1 cr pistons with a .074 cometic gasket which is probably bringing it down to 8.8-.8.9:1. it's not SO bad n/a once it gets going, but you can definitely feel it struggling down low if you dont rev it out to at least 3500+ in first and second.

Re: high or low comp pistons
 

I'm running 8.5-8.6ish:1 and Now that I'm driving it I realized it was a mistake, Its pretty doggy out of boost have to rev it up to about 4k out of boost to keep up with traffic.

Re: high or low comp pistons
 

yeah but once you start running 30psi you wont care about that anymore.

Re: high or low comp pistons
 

Low comp Cast piston's is the way to go until sumones proves me otherwsie!

Re: high or low comp pistons
 

yup, its about volume of gasses much less than comp ratio.

you dont loose that much torque my dropping compression ratio, and you still poke out the same sized flames to spool it... theres more to it than that, but its not the big deal ppl make of it...

as for the altitude...

you will need more turbo to produce 15psi, but 15psi is still 15psi. and the pistons wont know any different when in boost.

when out of boost, yes, it might be a bit sluggish if you go on the low side, as it will be effectively lower than what they are again...

i'd still go low though. there are plenty of torquey 7:1 motors around...

Re: high or low comp pistons
 

im running 9.0 Cp and lag owns me dont build boost till 35k full boost by 4500-5000

Re: high or low comp pistons
 

and what is full boost, and what sized engine is it, and what turbo is it? those could be key ;-)