Which is better?-Lower or higher forged compression piston. - Honda Forum / Acura Forum

jap-spec · 01-17-2003, 02:12 AM

From what I have noticed Honda engines make more horsepower from higher compression pistons and a few other things, that's why a Type R has more horsepower than the GSR engine. I am going to buy forged pistons to put in a GSR engine that I plan on adding turbo to. I am having a hard time deciding on what compression pistons to get. I want to put higher compression pistons but I keep reading about how higher compression engines can't handle alot of boost. Wouldn’t getting lower compression pistons mean I am going backwards in horsepower? Lets say that I was going to race the same GSR engine with the same PSI of boost.
I have 8.5:1 pistons and he has 11.0:1 compression pistons. Wouldn’t he win because he’s got the higher compression pistons?

95dx4dr · 01-17-2003, 02:41 AM

do you know anything about engines and turbo???...i see you are a noob but some people know alot of stuff comming in......if you are staying N/A as in no turbo or supercharger or nitrous then higher compression is good because that is how you make power....now with a turbo appilcation you need to know how much boost you want to run and build your motor to handle it....if you only want 7 or 8 psi then stock internals are good...if your looking for 12 get some aftermarket pistons at 8.5 compression as that is a good C/R for turbo and get some nice rods and rod bolts and make sure the sleeves can handle it........now if you lowered compresion without a turbo youd lose hp but when you add that turbo and get to boost 2-4 more psi for lets say 1 or 2 lower compression youd gain much more power from that extra boost as opposed to the compression.....i hope you understood that but talk to the guys at the shop doing your work and they should know what you need....good luck

jap-spec · 01-17-2003, 03:01 AM

Ok , I see we have a smartass. No i'm not a newbie to 4 cylinders engine and yes i' new to this site. LoL if you want me to school you on honda motor's, ask me anything you want. I just wanted to see what people think about higher compression vs lower compression.

Kilika2k · 01-17-2003, 03:23 AM

Its basically a compromise between the turbo and the engine. Lowering the cr means that you will be more dependant on the turbo for your power. Which causes less response and more turbo lag, but of course, gives a larger margin of error when tuning. High cr means its more difficult to tune and you have a smaller window for error but won't require you to be so dependant on boost as the engine can pick up some of the slack thus better response. Basically, it all goes down to how much do you wanna pay for tuning. Most people pick a low cr because they are probably gonna install a bolt-on turbo kit and not go in depth with the tuning. Higher cr is usually where the big boys play and takes a ton of resources to make it right. Sure it will be harder but the dividends pay much better in the end. Now, I myself would pick a mid point as I don't have the resources to go all out nor do I want just want to a slap a turbo kit on go off. I would probably say a 9:1 cr is good for me. Not too high where it takes lots of tuning and not too low where there is no power in the low revs. Turbo sizing should be taken into consideration as the bigger the turbo, the more time it takes to spool up. Basically think about what kind of powerband do you want. You have to make some compromises here as you just can't have it all.

Plan ahead and forsee what your future setup will be when its done. Ask for other people's experiences and advice for what is the best setup. As just modding without looking at the big picture could get less than desired results. Also look for dyno plots for different setups as it will tell you what kind of results you can expect.

jap-spec · 01-17-2003, 04:00 AM

Thanks for the reply. Thats the reason i posted up,so i can hear what other people thought on this topic.

PM-Performance · 01-17-2003, 10:00 AM

dude, i would rather have the higher compression and lwoer boost . I rather say i do 300whp on 8psi than 300whp on 18 psi . just mkes more sence to me . plus the motor will make the turbo spool quicker. . . i think if i ever do lower my compression i wont lower it less than 10:1 im at 10:6 now and runs great

b16ahybrid · 01-18-2003, 12:26 PM

Depending on your desired hp ..and tuning capabilities
For a mild street set-up (250hp - 300hp) i would run 9.5:1 - 10.0:1.
I'm runing 10.2:1 compression and 9psi of boost, hopefully i'll be getting it on the dyno this next week or two to find out how much power it's making and make sure the air/fuel ratio is in check.
I wouldn't recomend runing lower then 9.5:1 (unless a stock engine)

uoboarder · 01-22-2003, 06:20 AM

Yep... I'm all for slightly high compression and low boost.

If I built and engine I'd settle for a compression between 10:1 and 10.5:1, and then run lower boost. Why... the engine will produce better torque numbers down low and off boost. Also the more boost you run with nearly any turbo the more inefficient it'll get. If it gets close to being outside its efficiency range then the compressed air the turbo produces heats up to a temp. a lot higher than desired.

Lets say 20psi from turbo X before it hits the intercooler is at about 300F. Now lower the psi to something like 12 on the same turbo and your air temp before it hits the IC is closer to 225F. (these are just examples). If the air temp is lower before it hits the IC then after it passes through the IC you'll still produce more power cause the air in not at hot. I love dense air!

As for doing a better job with tuning with high compression... Yep, its true, but get yourself a Hondata and let the Hondata dealer and the dyno guys get you taken care of.

Kilika2k · 01-22-2003, 08:45 AM

Hmm...I'm surprised people run such high boosts in comparison to factory turbocharged cars. Maybe because Honda engines are so tiny hehe. Ya, the WRX uses a 8:1 cr which is extremely low for any Honda. But I guess other factors should be taken account like stroke and bore. Hmm...I'm thinking if its a good idea to stroke the motor (as in increase the displacement and lengthen the stroke) to better increase spool up thus improving the powerband. Hondas have such narrow powerbands and turbocharging them just makes them even narrower.

kommon_sense · 01-22-2003, 03:34 PM

As others have said, I would take high comp w/low boost anyday over low comp w/high boost.

For example :

10psi @9:1CR yields the same power as 6.5psi @10.5:1

And the higher compression will give you more torque off boost as well as spool the turbo faster. Also, as someone else explained, you will have a cooler intake charge because the turbo won't be heating the air as much.

95PRELUDEVTEC · 01-23-2003, 10:35 PM

As for me i dropped from 10:1 to 9.6:1 with a 20 overbore in my H22.....still feels the same to me. But i would rather go with high CR than low. my .02

T4 60-1 · 01-24-2003, 01:52 PM

Quote:

Originally posted by 95dx4dr
do you know anything about engines and turbo???...i see you are a noob but some people know alot of stuff comming in......if you are staying N/A as in no turbo or supercharger or nitrous then higher compression is good because that is how you make power....now with a turbo appilcation you need to know how much boost you want to run and build your motor to handle it....if you only want 7 or 8 psi then stock internals are good...if your looking for 12 get some aftermarket pistons at 8.5 compression as that is a good C/R for turbo and get some nice rods and rod bolts and make sure the sleeves can handle it........now if you lowered compresion without a turbo youd lose hp but when you add that turbo and get to boost 2-4 more psi for lets say 1 or 2 lower compression youd gain much more power from that extra boost as opposed to the compression.....i hope you understood that but talk to the guys at the shop doing your work and they should know what you need....good luck

haha, i'm a noob too, but from your post count(152) your still a noob. First off, you can run high compression on a honda turbo motor. The type r is a awesome motor to turbo. It's all in the tuning. I know about 5 people that are really getting into turboing the type r motors and making well over 450hp to the wheels reliably.

Kilika2k · 01-24-2003, 04:15 PM

Quote:

Originally posted by T4 60-1
haha, i'm a noob too, but from your post count(152) your still a noob. First off, you can run high compression on a honda turbo motor. The type r is a awesome motor to turbo. It's all in the tuning. I know about 5 people that are really getting into turboing the type r motors and making well over 450hp to the wheels reliably.

But not with stock internals right? Turbocharging a b18c5 to 450 HP with stock internals is damn near impossible. So 5 guys with turbocharged ITR motors with that much output huh? I find that a bit hard to believe. I only know one and he has about 400 HP with internals. Well..I may believe you, but I don't really think you know them personally.

T4 60-1 · 01-24-2003, 04:19 PM

personally no, but i do talk with them on **********. Not qoute stock internals. What they have done is used stronger rods and pistons with stock compression though. I'd rather have low comp than high comp on a FI motor, but it is very possible of having a high comp FI motor push high hp numbers and run reliably.

sweet · 01-24-2003, 11:04 PM

it's a compromise basically. higher C/R=more precise tuning, more HP/TQ per psi of boost, quicker spool up time and more overall potential for power as the boost is raised (as long as the proper fuel and tuning is used).

the good range to be in is 9.8-10.6:1 C/R with pump gas and low to moderate boost levels. of course more tuning is needed including ignition retard. if something goes wrong with the high C/R motor the results are gonna be even worse than the low C/R motor. but if you go lower with the C/R to be safe don't go below 9:1.

i currently have 11:1 C/R in my B18C1 and will be adding a turbo system when i finally get the $$ together. the smart thing would be to get the thicker HG and lower it closer to 10:1 C/R so tuning won't be a pain in the ass. if anything goes wrong it won't be as bad either. so that's the route i'll prolly go when the time comes.
i don't really want to go below 10:1 C/R though.