Low compression B16 question??

[steve1178]

Hi,

When i get my 9.0:1 Forged pistions how much will i need to boost to get the same power as i had before when i had the stock pistons (I think 10.8 : 1.). Before i was running 7PSI. I have also got Eagle rods (rated upto 600HP) comming with the pistons.

The motor will be tuned after i have broken in all the new parts, but will anything major need to be done to the fueling or will the Vortec 12:1 FMU do all the work for me.

If it is properly tuned what is the max PSI i can run the motor at and what sort of power do you think that i would be able to reach

It is a B16a2, with revhard stage 2 kit. FMU, extra fuel pump, intercooler, BOV etc.

Thanks very much guys

Steve

[MatT3T4]

I think your compression is 10.4:1...so follow this simple expression:

((boost psi / 14.7) + 1) x motor compression = effective compression

Stock motor on 7psi:
7psi/14.7psi = .47
.47 + 1 = 1.47
1.47 x 10.4 = 15.288 effective CR

Built motor (9.0:1 CR) on 7psi:
7psi/14.7psi = .47
.47 + 1 = 1.47
1.47 x 9 = 13.23 effective CR

You will lose 2.058 points from your effective compression ratio, this translates to a significant power loss.

In order to gain back that power, you have to do this:

Built motor (9.0:1 CR) on 10.5psi:
10.5psi/14.7psi = .71
.71 + 1 = 1.71
1.71 x 9 = 15.39 effective CR

Add 3.5psi to what you were boosting before, and you should be able to make around the same power as before, granted you haven't done any other kinds of modifications port/polish, cams, etc...

[steve1178]

You are a Star!!!! Nice one.

Sorry, i have another question. Is boosting 10.5psi on a low compression motor safer than boosting 7psi on a 'higher' compression engine.

[MatT3T4]

Originally posted by steve1178
You are a Star!!!! Nice one.

Sorry, i have another question. Is boosting 10.5psi on a low compression motor safer than boosting 7psi on a 'higher' compression engine.

No, it's roughly the same. If you look at the effective compression expressions, you can see that the motor is pretty much taking the same pressure as it was before.

[steve1178]

The motor will be tuned after i have broken in all the new parts, but will anything major need to be done to the fueling or will the Vortec 12:1 FMU do all the work for me.

If it is properly tuned what is the max PSI i can run the motor at and what sort of power do you think that i would be able to reach

Thanx Mat for your help. Can anyone help with the other Q's too.

thanks