Remember, when this dyno run was done, the compression ratio had been dropped from 9.5:1 to 8.5:1. This equates to a huge loss of power.
I have received so many e-mails saying how I must be disappointed with minimals HP gains. No, I am not. Running 4 psi boost AND LOWERING THE COMPRESSION RATIO a full point would net a slight gain. This is to be expected. The reason for lowering the CR was to be able to run a higher boost level.
Even though I have fought with the formatting of the image, I cannot get it so it's legible. The stats are:
This was after installing 8.5:1 compression ratio pistons, plasma moly rings and running 4lbs. of boost. The overall gain is not hugely impressive if you just look at the numbers. The lower compression pistons and a fairly low boost pressure presented a better power curve (comes up quicker and stays longer) but the max numbers are not as better as may have been expected.
With the lower CR pistons (and that they're forged), I will be increasing the boost pressure to 10 or 11 lbs. If money allows, another dyno run will then be done.
During the run below, the AFR (air/fuel ratio) remained constant at around 12 to 12.5 to 1 while above 4400 RPM.
I went for another run on the dyno to measure the setup with the compression ratio back to 9.5:1 and running 8psi of boost. I don't have an intercooler yet and there is one issue with the air-fuel ratio as seen in the graph below:
As you can see, the boost control is working nicely. The max boost was held pretty well at 8psi. Kind of surprising to see that the manifold didn't go to positive pressure until about 2700RPM.
The max power was achieved at right about 4400-4600RPM. This is also where the AFR began to go too rich achieving a little worse than 10:1. Up until that point, the AFR looked great. This brings about the next mod...an S-AFC from Apexi to fine tune that AFR.
The numbers:
130.33 HP at 4600 RPM
148.15 ft/lb at 4500 RPM