compression ratio
 

Hello people, tell me please what i need to make compression ratio 10 or 9.5? What parts i must to buy? Are there kits aviable for this action? (sorry for my english)

If you want to lower your CR you have to get a new set of pistons.

Your power goal should be known if you want to lower your CR.

What about connecting rods?

there are a few ways... even a thicker head gasket can lower compression... pistons are the way to go.

definitely replace the rods too
the stock items are weak and very variable in strength as they are a sintered part

Does anyone know how lower compression pistons affect emissions? I think I'd like to use lower compression pistons but I'm concerned that I'll no longer be able to pass a smog. California CARB is a PITA.

You shouldn't lower your compression ratio without first consulting your tuner on the benefits and cons for both keeping stock compression or lowering it, also for the amount of power you want to push out of the engine.

Personally for my build i'm staying with the stock compression with some (Custom CP Pistons, and Carrillo H Beam rods) because I don't think the trade offs you get with lowering your compression is worth it.
i.e. Lower gas mileage, lower grade fuel(usually), and etc.

But if you want to lower it, all you need is some low compression pistons from either (CP, JE, Arias, Manley, and etc just to name a few) just to name a few.

Or you can just run a stock internals with not a shitty tune and be fine to 450whp with e85 and 18psi. You should be blowing trannies before blowing blocks.

450whp won't last forever, no matter how good your tune.

200 won't last forever either.
@Reaper

13:1 or gtfo.

We have 2 cars locally racing time attack and still street drive. One is stock rods 13.5-1 at 400+whp and the other is all stock 450whp for 27,000 miles. Lots and lots of broken transmissions right now. Not much racing until sequentials come in.

Dont do it, unless you want to lose power.

Any CARB legal supercharger kits/tunes don't need lower C/R, and doing so will just cost you power.

I won't be running a CARB tune, I'll be running a custom tune. I am up for changing CR if it makes the engine more reliable so long as there are no adverse affects to emissions when ON a CARB tune, which would only be used during emissions testing.

Wait, you are asking how to reduce compression which one would usually only ask if you are going for major FI.

THEN you say that you are concerned about violating CA CARB laws?

How about you tell us WHY you want to reduce CR FIRST instead of leaving us guessing?

You want to use the highest compression your fuel will allow you to use, for your target boost level, to result in the most power. If that power is more than your target, then lower your target boost level.

The CARB tune is meant for the stock C/R, so it won't run right on a lower C/R.

What are your power goals? Building with lower C/R when you don't need it is a huge expense and hassle for CARB testing.

I realize I didn't mention that specifically.

I'm already supercharged. Apologies, I figured that my signature showing several different forced induction setups was sufficient. I realize that that assumes a) that you saw the signature, and b) that forced induction is still a consideration for that question. I'll be more explicit next time.

Something to be said for living up to your username though. :clap:

Replied inline...

stock CR and forged con rods. 110 or E85 for 400whp and CARB legal, youll shred transmissions. Not if, just when.

Stock rods are good for 600. Stock pistons not so much.

I do not now what you are talking about since I see no signature and zero mention of anything FI at all in your posts. Maybe my browser is omitting something?

http://i366.photobucket.com/albums/o...psludqfbsz.png

You would need to go further back, to post #6:

http://i.imgur.com/l2BJSyr.png

Lets get back on topic though :bonk:

The tune required for a supercharged setup capable of 400whp is going to be VERY different from the CARB legal one supplied with the kit. You're looking at different injectors, pump, S/C pulley, etc. Add lower c/r into the mix and I doubt it would run well at all on the CARB tune unless you were to swap all the fuel system and pulley back to stock for the testing, and even then it'll probably run rough with the lower C/R. If it's rough enough to fail the test would depend on how strict the test is, but I wouldn't bet on it passing.

Thanks, I'm aware of this. I have only had custom tunes with this kit up to this point.

Thanks, I do have all of this.

The point wasn't that you would need them, the point was how different the setup would be from a CARB legal setup, and how the CARB tune wouldn't run well at all with the other supporting mods.

The only way the car will last for ever is not using it.

Actually that will ruin it even faster!


http://assets.nydailynews.com/polopo...a20n-1-web.jpg

Hahaha! Not exactly what I have in mind.

Sir your statement is true but your didn't answer. It will continue to be carb until you adjust the tune.

Heat that's the enemy, you have to keep fluids in operating temps at all times if you really desire the car to last. But I can't help more due to tha lack of info about your car and goal... A good tune could help a lot, but is only part of the equation.

You're in Cali...
 

You should be more worried about what F/I solution you'll be using than what compression ratio you're running..

Also, I believe that our cars won't have a sniffer test when they start getting tested, so you would only need to pass the OBD-II test and the visual inspection.

If you plan on using a non CARBed turbo or other F/I solution, you'll have to remove it for inspection, which means you'll have to change the tune.

With lower compression, you'll just have a different tune that makes less power, but if the tune is right it should still pass.

Jaden

No. Modifying the engine internals (unless the new internals also have a CARB approval) will make it not CARB legal.

It'll also run way less than ideally on a lower c/r on the tune meant for stock c/r.

Nop.

Agree, but to clarify.

The only thing that you should do different on tune with same everything except from cr, is timing, no need to touch fuel.

You'll never tune my car, that's for sure :D

If you think the only thing you'd need to change after dropping the C/R like 3 full points is timing, you're in for a world of pain.

That much of a change is going to drastically alter the volumetric efficiency of the engine, and would require a full re-tune.

Sir today is your lucky day!

I am not a tuner (not professional and the ones I have done were finish by real professional tuner).

But what is volumetric efficiency? How can it be changed or altered? :bellyroll:

Volumetric efficiency, is the amount air (CFM) that gets to the "air chamber" to be used to produce the controlled explosion...
So it could be altered with modifications to the intake, heads (port, valves # and size) cams (duration and lift) exhaust, also and more dramatic with FI but no with cr. Sorry.

:cheers: