1990hondaHF

Right now I have a d15b vtec with 9.3:1 compression. If I raisied the ratio to 10:1, how different would the engine perform? Would there be more low end and high end power or just more high end? I'm a bit uneducated when it come to compression....so if anyone has a link or could explain how it affects engine HP and torque, I would appreciate it.

Downey

by raising the compression i would expect so more power out of the engine. for each point, how much horsepower.. no idea.

i look at it like this.
US B16A PR3 pistons = 10.2:1 compression = 160hp
JDM B16A P30 pistons = 10.4:1 compression = 168hp

US B18C5 AO P73's = 10.6:1 c/r = 195hp
JDM B18C R OO P73's = 11.1:1 c/r = 200hp

JDMlyfestyle

^^^^^^^ doesnt make sense.
b16 compression was raised .2 and got 8 HP
The Type R raised .5 and only got 5.
Since the type R has a bigger displacement shouldnt the up in compression give it more than 5 HP?

Downey

all im trying to point out is that power was raised a small bit with the slight bump in compression.

JDMlyfestyle

i know but i still want to know why the difference with the 2 changes.. got me stumped..lol

carsaregood

hmm well i think the only thing you can really conclude from that info is that there is some correlation between cr and hp output. But its hard to say anything more than that, because the b16 and b18c5 are different motors. there are other factors that effect the power output, like manifold design, cam profile, engine geometry, fueling systems, etc etc.

it'd be interesting though to see two identical engines, the only difference being the cr, and compare how the output differs. does anyone know a decently accurate way to quantify this??