[mbtoloczko]

Originally Posted by Chiketkd

Interesting results Mychailo. I guess that graph explains a lot of my findings with the Impreza fpr as well. However, based on my dyno runs with the stock fpr last December, the richest the afr ever got was ~13.4:1-13.3:1 at WOT above 5000rpms.

It's interesting that the afr centers around 12.5:1 and then becomes even richer in the upper rpms! Per an article in SubieSport Magazine a few months back (when Huck369 was first featured), an afr of 11.6:1 or richer is needed to safely run an extra 5* of timing advance... Maybe I know what my next mod will be!

-Chike

P.S. I was doing some calculations the other day and realized just how much more fuel our engines would get in open loop by raising the fuel pressure by ~7psi.

Our injectors flow 275cc/min at a fuel pressure of 36.3psi
If the max fuel pressure is raised to 43.5 psi, then our injectors will effectively be able to flow: 329.5cc/min

Moreover, if people have estimated that 275cc/min can support 250hp on the motor, then 329.5cc/min should be able to support 295hp (assuming a linear relationship).

Hi Chike,

When you did the dyno runs in your car, I would guess that the shop simply put a wide-band O2 sensor in the tailpipe of your car. If that's the case, the afr reading is not going to be terribly accurate because its taking a reading of the exhaust after it goes through catalytic converters. From what I've read, dyno systems add a generic correction factor to the afr reading to attempt to compensate for the exhaust gas composition being altered by the cats. Bottom line is that the afr readings from your dyno runs are only approximate.

Be careful about running too rich. Running too rich can also cause detonation. 11.6:1 is probably not the optimum afr for timing advance.

I have not been able to understand why, but fuel flow from a fuel injector is not linearly proportional to the fuel pressure. Its proportional to the square root of the fuel pressure. I've talked with RCEng about it several times. Its what they see when they measure the flow rate of injectors. So going from 36.3 psi to 43.5 psi will only raise the max fuel flow by 9.5%.

I'd like to throw the SVX fpr back in the car, but I don't think I'm going to have time for about a month.