What is the Maximum Effective Compression Ratio, for B18A motor??

[teh_mugen18]

I was looking on a Honda Compression calculator, and i entered a number in it as if i was running my engine on 12psi. It gave me an Effective Compressionratio of 18.25:1.

What can the block and head, etc. handle as far as effective compression ratios go? How much can be safe for dailydriving? I know that, stock it come with a 9.6:1 ratio, but when boosting? How much can it handle on stock internals? How much can it handle when its fully built?

[teh_mugen18]

....Is this one of those Q's that belongs on HondaTech??

[FasTech]

....Is this one of those Q's that belongs on HondaTech??


well considering you haven't had a response yet! I guess so.....:D

[green91]

Youre going to run into fuel and clearance limitations long before you get to 18:1. And why are you asking how strong a high compression b18 would be with stock internals???? LOL.

[Motivation]

You mentioned boosting too... Think you might wanna try to get your compression lower...

[teh_mugen18]

You mentioned boosting too... Think you might wanna try to get your compression lower...

Well, i dont neccesarily want to lower my compression any more, since running more boost on lower CR = running less boost on higher CR. Id rather stick with more motor power than turbo power, but either way its the same in the end.

[Motivation]

... umm.... Boosting+high compression (especially + stock Internals)= not a very good day...

[teh_mugen18]

Youre going to run into fuel and clearance limitations long before you get to 18:1. And why are you asking how strong a high compression b18 would be with stock internals???? LOL.

I just wanted to know, thats all. B/c i was planning on going fully built, and then boosting. But i just had to know how much the most was that the block and all that could take safely

[IndianStig]

You are missing some basic concepts.

The static compression ratio of your motor is 9.6:1 with twelve PSI the effective ratio would be 18.25:1 I guess according to your calculator. You cannot change the static compression of 9.6:1 w/out changing your pistons so thats not stock internals right there. I guess you can change the effective compression ratio by varying the amount of boost though.

Sounds to me like you are asking the wrong question or just trying to act smart. A simple, "how much boost on stock internals can a B18A take?", would have sufficed.

The answer to this question, I cannot give you. If I were to guess, I'd say 10psi is safe. Feel free to correct me if wrong anyone.

[teh_mugen18]

Lets add into the equation, the fact that ill be boosting on a milled head, taken down .020" with forged internals. That gives me a 10.6:1 Static CR. Then, with 12psi, it gave me 18:1 Effective CR.

[teh_mugen18]

You are missing some basic concepts.



Sounds to me like you are asking the wrong question or just trying to act smart. A simple, "how much boost on stock internals can a B18A take?", would have sufficed.



Well, in that case, how much boost can a built B18a take?:D

[slostang]

12psi on a stock LS is ok. just dont run 12 daily

[bRiAnMcIvIcS]

HaHa! A healthy b18a/b can handle around 230whp not any more than that. Focus on the power not the psi. Turbo's flow differently. What turbo are you refering to?
A garrett t3/t4 57 trim ar.63 would be ideal.:goodjob:

[IndianStig]

HaHa! A healthy b18a/b can handle around 230whp not any more than that. Focus on the power not the psi. Turbo's flow differently. What turbo are you refering to?
A garrett t3/t4 57 trim ar.63 would be ideal.:goodjob:

True!

[Vteckidd]

you are missing the point completely.

There is DYNAMIC Compression and STATIC COmpression.

your LS motor is around 9.5:1 STOCK. If you were to boost it, on STOCK internals, you can run up to around 15psi with good tuning and the motor should be pretty reliable. The problem with stock pistons is the ringlands, they collapse and are the weak link.

If you decide to do forged internals, youll want around 9.5 or 10.0:1. At that point the pistons and rods are good for 1000whp, but your sleeves are not. The stock sleeves become the weak link at this point and will break past the 400whp mark.

Effective compression ratio is kind of pointless unless you are all motor. SInce turbo cars dont run big cams, your static and dynamic compression is pretty close to the same number.

WIth an NA engine, you can get away with a HIGH compression ratio (12.5 or 13.0+:1 if you run a very big camshaft,. like a PRO3. And all that means is you can push the limits of pump gas on the higher compression motor because the overlap from the cams "bleeds" compression off. so your 13.0:1 STATIC motor is more around 11.5: Dynamic or while the engine is running.

On a turbo car, in most cases, the difference in your compression is so small between static and dynamic, that its not really taken into account. Youll want to look at WHP and PSI more than compression

[Vteckidd]

Lets add into the equation, the fact that ill be boosting on a milled head, taken down .020" with forged internals. That gives me a 10.6:1 Static CR. Then, with 12psi, it gave me 18:1 Effective CR.
dont mill your head, kind of pointless.

But if you do, it only changes your compression maybe .3 at the most. So you may go from 9.5 to 9.7is

not that big of a deal

[RWD164]

Lets add into the equation, the fact that ill be boosting on a milled head, taken down .020" with forged internals. That gives me a 10.6:1 Static CR. Then, with 12psi, it gave me 18:1 Effective CR.

Don't forget, compression ratio is a physical measurement of a piston at bottom dead center versus top dead center. Example, a cylinder w/ 500cc volume at BDC and 50cc at TDC has a compression ratio of 10:1. Boost changes overall pressure, but not compression ratio.

[teh_mugen18]

Okay. Well, since ill have to worry about WHP and PSI, im looking to run ~250 - 300WHPmotor with forged rods/pistons and stock everything else, on XX psi with a t3/t4 turbo. Whatever that psi number may happen to be, is what i'd like to have to make my motor put out that much power.

[Vteckidd]

again, 250-300whp is pushing the stock limits of the pistons. They are the weak link .

If you want it to be safe, put rods an pistons in it, shoot for a compression ratio of 9.5 or 10.0:1, somewhere in there

[Echonova]

again, 250-300whp is pushing the stock limits of the pistons. They are the weak link .

If you want it to be safe, put rods an pistons in it, shoot for a compression ratio of 9.5 or 10.0:1, somewhere in thereLOL, why does everyone refuse to listen to you?:lmfao: You know more about Hondas than anyone else I've seen on here...

[Vteckidd]

cause they read some dumb**** information on the internet and they think that some guy who has never done anything knows more than anyone else.

They also like to LOOK for the answer they WANT TO HEAR .

No amount of information will help someone if they arent willing to listen.

But thanks for the compliment :)

[IndianStig]

So an LS motor with rods and pistons can handle upto 400whp?

How about the GSR? No sleeves, just rods and pistons.

[Z0_o6]

So an LS motor with rods and pistons can handle upto 400whp?

How about the GSR? No sleeves, just rods and pistons.


400-450 is about the limit for a B18 on stock sleeves. LS block or GSR block, they are similar on the sleeves.