increased compression

[skeeterone2]

Okay. the 3.1 that is in my car has a compression ratio of 8:1... i was wondering if anybody knows any information about how to rais this... if its via domed pistons or new seal... i dont know how close the pistons get to the valves... but it would be sweet to get 10:1 pistons... i know about needing a higher octane gas... but how sweet would it be to get a better compression ratio... i bet that would be good for a drastic horsepower and torque gain. well if anyone has any input of companies or people, that information would be much apriciated.

[z284pwr]

1. Its actually ~8.9:1 compression....
You won't really gain much HP/TQ from raising the compression that much, it'll give you better throttle response, but without support mods, its not really going to help out.

Anyways, you can contact just about any Piston manufacture, tell them your specs, and they can probably set you up with what you need.

[SappySE107]

It will increase low end torque a lot if you go 12:1, but the rest of the engine needs mods to really get some power with the new compression.

[robby1870]

Yeah, the motor also needs to breathe a lot better to safely run 12:1. A nice cam is basically a requirement.

[ikessky]

How high can you go on a stock engine before you risk hurting it? How are you guys getting the higher compression, milling heads or new pistions?

[Anonymous]

I bumped the C/R in my cxar from 9.5:1 to 10:1 and I noticed it a lot. the low end tq is unbelievable(for a 3.4). But this isn't with just the new cr, this is with corrected cam timing, so I was used to a crappy low end.

[geoffinbc]

Well to answer your question... People do the following: Use a head gasket from an IRON head motor. They are thiner increasing compression. Use a full 3X00 top end with the pistons or swap then entire motor. Use a combination 1.5/1.6 roller rocker combo to help increase combustion pressure. This does not increase compression ratio. Or finally just buy the compression you want through custom pistons.

But like it was said above you need to make the engine breathe a whole lot more so doing a 3X00 swap may be the best answer.

[ikessky]

Ah, I see. It is the 3.1 MPFI. What is the CR on a 3x00?

[bszopi]

Depending... its either 9.5:1 or 9.6:1. Varies between models and years.

[RacerX11]

People do the following: Use a head gasket from an IRON head motor. They are thiner increasing compression. Use a full 3X00 top end with the pistons or swap then entire motor.

Don't use an iron head gasket with the 3X00 pistons. The compression height of the 3x00 pistons put the top of the pistons above the top of the cylinder deck at TDC to increase quench. If you combine this with the thinner head gasket, you are risking problems.

Basically, use the stock gasket with 3X00 pistons. Only use the iron head gasket with either stock 3.1 pistons, or iron head 3.1 pistons.

Marty

[v6h.o.]

People do the following: Use a head gasket from an IRON head motor. They are thiner increasing compression. Use a full 3X00 top end with the pistons or swap then entire motor.

Don't use an iron head gasket with the 3X00 pistons. The compression height of the 3x00 pistons put the top of the pistons above the top of the cylinder deck at TDC to increase quench. If you combine this with the thinner head gasket, you are risking problems.

Basically, use the stock gasket with 3X00 pistons. Only use the iron head gasket with either stock 3.1 pistons, or iron head 3.1 pistons.

Marty

yup. you end up with only .020 or less Piston to Head clearance with the 3X00 pistons and the Iron head gasket. the pistons will be hitting the head under higher rpm due to piston/rod stretch. you genrally want about .030 or more clearance between the piston/head.

i used iron head gaskets on my mpfi engine and also milled the heads a bit.

[Compufreek]

So can you use the iron head gaskets in a 3100? I already took .015 of the heads but want to do whatever I can to get more compression.

[v6h.o.]

So can you use the iron head gaskets in a 3100? I already took .015 of the heads but want to do whatever I can to get more compression.

No. re-read martys and my post right above yours. it explains why.

[Compufreek]

LOl, yeah what he said. Read it too fast didn't catch the jist

[skeeterone2]

so basicly im looking at reworking my top end with a valve job a throttle body and then getting a more aggresive cam... and possibly ignition... and then this is crazy... i need a much better paying job for this... i cant wait to get outta college. it would be nice to run a higher compression... but to get any type of respectable gains a package deal is needed.