JDM_208

4 every 1 pound of boost u put into a motor how much will your compresion rasie?

RXSevenSymphonies

iTrader: (2)

For every 14.7psi (atmosphere) compression ratio is doubled?

So if you have 8.5:1 compression + 1lb that would be 1/14.7 of 8.5=.578

.578+8.5=9.078:1?

So it depends on base compression ratio if I'm thinking correctly.

digitalsolo

iTrader: (2)

Boost adjusts your dynamic compression ratio (as I understand it).

I know my GTP makes about 17.3:1 dynamic compression (I have the formula here somewhere) at maximum boost (15 psi), and it's 8.5:1 compression static. So following his theory, that'd be about right. I'm not sure of the actual formula though. Hopefully someone chimes in with it soon, else I'll find it.

edit: You also have to consider your volumetric efficiency, as your dynamic compression is effected by this. e.g., if your ve is 95%, then your calculation would be 1/14.7 of (8.5 * 95%) = dynamic compression.

I'm sure that's still rudimentary though.

NZConvertible

Effective compression ratio = static compression ratio x manifold pressure ratio

where manifold pressure ratio = (atmospheric pressure + boost pressure ) / atmospheric pressure

So for stock S4 TII (~6.6psi max boost, CR 8.5:1), the effective compression ratio is:

8.5 x (14.7 + 6.6) / 14.7 = 12.3:1

And for a stock S5 TII (~8.3psi max boost, CR 9.0:1), the effective compression ratio is:

9.0 x (14.7 + 8.3) / 14.7 = 14.1:1 (~15% more than the S4)

RXSevenSymphonies

iTrader: (2)

yay I was right, I'm gonna go pleasure myself to my rightness!