I know 3.1s came with 8.5:1 compression and only had like a 5 bhp 20 ft/tq over previous mpfi 2.8l with compression of 8.9:1. Assuming bone stock 3.1, how much more power would be gained from going from 8.5:1 to 9.5:1 compression?

 

you'd probably gain a few hp but i don't really have a number to give ya. what are your plans for a motor and how do you plan to raise compression? new pistons or what?

 

I don't currently have plans to raise compression. I just don't understsand the point of raising compression if it doesn't gain much power?

 

the motor typically will rev quicker if you've got higher compression. if i hold mine at 1500 rpms, i can 'stab' it for a second and hit about 4,000...almost instantly (out of gear). that's with about 10.75:1 compression. it will pull harder normally when its in gear. but, with high compression, you can't run boost (easily) and you have to run higher octane gas.

 

how did u get urself to 10.75 compression?

 

I'm currently going over this topic with my brother and his 95 camaro 3.4. So this is what I told him, although $10 says I go over to just help but it's going to be like his wifes 74 camaro and I get no help or money.

Honestly not much power will be gained. From my experience, mostly V8's the raise in compression 1 full point usually generates between 15-20 hp. That’s only if the pistons are designed well enough to allow good flame travel and the heads flow well. In a V6 application it is probably worth the effort to raise the compression in a N/A engine since every little bit does help. A trick when building a smaller engine is to think of its stock form like a race engine that has to be X bore X stroke to run in X class. From this point what can I do to make a few extra ponies? Raising the compression helps, getting the entire rotating assembly (professionally) balanced helps and no I’m not talking the average machine shop down the street. Good components like moly rings, decent valve springs, undercut valves and a list of other (non Autozone) type parts will help quite a bit. From there pick your cam modify your induction burn a chip and slap it on a dyno. When you add all of these up then you will notice a huge power gain, shoot for alot but only expect a little.

 

custom domed pistons.

 

If your gonna go through the work of changing compression. I would go to atleat 10:1. skip 9. Fast car have high compression.

 

how much the pistons run you?

 

Raising the C:R 1 full point (going from like 8:1 to 9:1) will increase hp by about 7%.
All it does is mix the a/f better, burn the A&F hotter and faster and push more exhaust out and suck more fresh a/f in with higher c/r.

 

i got the pistons out of another motor i bought then my dad and I did the custom work on them where he works. so, i didn't really have anything in them, to speak of.

 

Simply, most engine builders agree that you will gain about 4% per point of compression increase. So 9.5:1 to 10.5:1 with yield a 4% increase and so on and so on. But just remeber, 9.5:1 to 11.5:1 would not be 8%, rather 4% of whatever 10.5:1 is.