SpoolnG2

Lets say we have 2 identical b18c1's. with the same turbo, pushing the same amount of boost. however one has a 9:1 C/R and one is j-spec and has a 10.8:1 C/R. About how much more power will the higher compression motor make? like how much does almost 2 points of compression raise your hp?

ee8T

TURBOCHARGERS & COMPRESSION: THE MYTH!!!
There has been a long-standing myth with turbocharged Honda cars. For as long as I can remember, people have been quite concerned about having too high of a compression ratio, on their turbocharged Honda. The myth is: the lower the compression...the better. Well, this is not entirely true.

Why is a low compression motor good to turbocharge?

In essence, a low compression motor is good to turbocharge, because it is just easier to do so...and not worry about it. But is that what we really want to do as enthusiasts? Do we want to just slap a turbocharger on a car, and call it a day? Absolutely not. With turbocharging, comes the responsibility of tuning and care. If you are just going to turbocharge your car, and call it a day, then frankly, you don't deserve the luxery of boost! As well, might I add...that simply because it is easy to slap a turbocharger on a low compression motor and not worry about it, does not mean that it is right. I can guarantee you, that if you turbocharge a low compression motor, and fail to tune it correctly, you will end up on the side of the road, with blue smoke coming from your exhaust pipe.

Generally, a lower compression motor affords you more margin of error, when tuning. A slightly imperfect a:f ratio probably won't lead to the demise of your motor...unless you drive like a total jerk.

Why should I consider a higher compression motor, while making my decision of what motor will suit my needs?

Different from a low compression motor, a higher compression motor will not give you a large margin of error, when tuning. As stated before, if you expect to slap on a turbocharger, and call it a day, well then stay away from the higher compression motors all together. A higher compression motor demands slightly more TLC than a lower compression motor. But oh, the rewards are plenty.

Bottom line...a higher compression motor, pound for pound, will make more power, than a low compression motor. This works along the same lines as naturally aspirated Honda motors. You never see an NA enthusiasts spouting off about low compression do you? No, one of the keys to NA performance is high compression. So, why should it be any differnt for turbocharged applications? Of course, the routes to high compression are different (NA uses lightweight rods and pistons, that a turbocharged application would simply tear to shreds), but the end goal is the same.

Let's make an observation here. I am going to throw a scenerio for you...

Car A:
B18B (stock 9.2:1 CR)
Rev Hard Stage II
Thermal 3" exhaust
MSD 6AL
MSD Pro Cap
MSD Blaster 3 Coil
Holley 255lph in-tank fuel pump
AEM fuel rail
RC440cc injectors
A'pex S-AFC

Car B:
B18B (JE pistons, 10.5:1 CR)
Rev Hard Stage II
Thermal 3" exhaust
MSD 6AL
MSD Pro Cap
MSD Blaster 3 Coil
Holley 255lph in-tank fuel pump
AEM fuel rail
RC440cc injectors
A'pex S-AFC

Now for the sake of argument, let's say that both cars are well tuned, by the same tuner, both have an identical weight, both have the same slicks, both are boosting 1.0bar, and both are being driven by the same guy...at the same time (yeah, yeah, yeah...just roll with me here)! Now, which one do you think is going to come across the finish line first? Mythological thinking says that the guy with the low compression is best suited to win...right? Wrong. The guy with the 10.5:1 compression ratio is going to smoke the guy with the low compression.

Another point I would like to bring up is the misuse of the term "high compression" when it comes to Honda motors, and turbocharging them. In all honesty...10.6:1, 11.0:1, etc...aren't even really that high. Most NA monsters utilize 12.5:1 or higher...and some even as high as 14.0:1, in cases of extreme race. If you do some snooping around, you will realize that most of the really fast Hondas, and I'm talking sub-10 second monsters, utilize high compression setups, to achieve enourmous horsepower goals. Most of these guys won't openly discuss it though, so you are likely to come across terms such as "undisclosed compression", or something along that line. As I stated before, the myth is that low compression is key...so these guys want to stay on top, and the way to do it is hide the fact that they are using high compression, turbocharged motors...to propel themselves into sub-10's.

Thx to Matt3t4

SpoolnG2

i appreciate your reply, but my real question was how basically how much more power will the motor make with higher compression. i knew that higher compression makes more power, i just was curious if there was a guestimate. like say 9:1 c/r 10psi=300whp
then how much would a
11:1 c/r 10psi=? (same turbo and motor)

rioninja

Way to cut and paste....


And im curious also, i'm sure there is someone on here that dyno'd before an after a piston or headgasket install...

PM-Performance

i think it will depend on a few things. but i would like to see some before and after with the same car and motor also , just to get an idea, im sure it will make quite a bit of difference though