10.5:1? or lower?


I told him the lower the better.

 

depends on the application. FI or NA?

if your friend has a SC, then running lower comp will allow more boost, however many have decided that since power is limited by the amount of boost we make (cant over rev the SC), that a higher comp ratio with less boost will yield more power

its really your call...but traditionally, FI uses lower ratios, and NA uses higher ratios

 

hes got a 06 sc and he wants to build his bottom end like i did.. i did 9:5:1 ratio on mine but im also running alot of boost. 21psi

 

FI engines tend to do better with under 10:1 compression due to issues with detonation.
My 2.4L has 10.4:1 and I can't run safely much over 8psi of boost.

 

Yeah but with 8psi at 10.4:1 compression, you'd be making a lot of power

 

If he is staying with the stock blower I would keep the compression ratio the same. If he is going with an aftermarket compressor in the future I would go as low as possible. If he plans on camming it in the future, keep it the same or very slightly higher than stock depending on your compressor.
Air > Timing

 

High compression plus high boost, if you can keep it all together.

 

Oh yeah, she does alright for only 8psi!

Thats the hard part! If we only had 100 octane fuel at every pump!

 

They call it E85, but it's not at every pump yet

 

why not run meth injection, couldnt ya run higher compression and higher boost?? from what i saw if you run 91 octane with meth its like around 103-110 octane..

 

Yay! To bad you'll need like 100 lb/hr injectors for that.

 

Shhhhhhh

 

Because what happens when you run out of meth and you hit boost. Bye bye pistons.

 

keep an eye on the meth

I dont no of any other ways

 

in the GM build book they go up to 10:1 compression pistons, i'd say thats the furthest you want to go on the cobalt SS/SC. I've heard at even that level some people got knock, but it was most likely from overboosting our supercharger, i bet at stage 2 size pulley's with as much cooling as possible and full exhaust that it would work alright.

 

Jw but are you trying to say i shouldnt have did a 9:5:1 ratio?

 

no hes not saying that from what it looks like.. hes basically saying going up to 10:1 would cost more money and work..

 

Ok so my friend should do the same9:5:1 ratio as right? cuz hes wanting to get all the preformance parts i have.

 

^thats fine. im assuming your gonna dump the heat pump at some point for some better F/I. i hope you didnt just build your engine overspin the stock s/c.

 

10:1 pistons are just fine and dandy with meth injection that'll fix the problem right there. I myself don't like meth, so i don't usually condone usage, but for other's their own.

 

It doesnt matter at the moment because its been in the shop for the past 3 weeks for a custom turbo kit that would probably make me close to 400+hp

 

i dont know honestly which one you should go with..

Me personally i am going 8-9ish in compression somewhere in there when i run turbo.. I want to run higher boost with a medium high compression and meth with a really good tune