Ok, I installed a Walbro 255lhp fuel pump in preparation for running 24-25psi on race gas this coming weekend at the E-town Shootout. Things went smoothly with only a little unexpected fuel spillage , but the car ran perfectly right after I finished, so I was happy. I drove the car normally for a day, then went out for some tuning to see if there was an immediate change in low-throttle/idle readings as well as hi-throttle AFRs.

My idle did not change at all, which was good, so I didn't make any fuel adjustments at low rpm or low-throttle. When checking my LTFTs, I was at -1, which was fine. It was always right at 0 before, but anywhere within -3 to +3 is fine. -1 is well within expectations.

When I did a 3rd gear pull, I saw my AFRs had risen quite a bit all across the rpm range under boost (4-7.5k rpm), so I started my adjustments. I don't like doing many 3rd gear pulls, so I kept it to 2 and ended up pulling out about 4% fuel at every RPM point between 4000 and 7500 rpms. The result was an AFR curve that was pretty linear right around 11.5 while still having a beautiful timing curve that peaked at 20 around 7100-7200 rpm. This is a good thing, because I was spiking just below 22psi in 3rd and holding around 20 most of the way to redline. With this much boost, an 11.5 AFR, and 95 degree heat, I was getting no knock as is evident by my timing curve, so I'm happy.

I'm curious as to what adjustments others have made when JUST adding a fuel pump. I know that with injectors, there would be a SIZEABLE change, so I only expected a slight change with the fuel pump, and that's what I got. I'm happy that I now no longer have to add fuel from 4-5k like I used to, because that would always make my timing bottom out at 0. Now it's staying in the positive and should help with both spoolup and the quicker onset of torque/hp.

 

Actually, i've seen two cases where the fuel pump overruns the stock fpr, thus needing to take away fuel. Actually it benefitted a few cars since i got to pull so much fuel out. The settings i usually see are definately in the -20's near the top end. Usually with a fuel pump, i no longer have to add fuel anywhere, but basically leave 3500 at 0 and go down with a continuous slope from there.

 

All across I'm in the negative's also. When I switched to the walboro I took out about -3% to -5% in the upper rpm's. (4000 and up)

 

Great, that's right in line with what I experienced and with how I have mine setup now, except that I only max out at -13 at the top end due to the heat and increased boost. I will go into the -20s across the board when I toss in leaded race gas this weekend at E-town...

It's nice not having to add fuel in the peak torque area...I can feel a difference in spoolup and the onset of torque, since my timing doesn't hit 0 anymore.

 

-20 across the board sounds harsh. I'd be careful, even on leaded race gas.

 

I was at -15 when on the 104/93 unleaded mix, so I was just guessing on the -20. I work my way up to whatever my final settings are gradually, though, so I won't know until I start seeing knock.

 

Sounds like the extra bit of fuel pressure was perfect to get the proper midrange timing you need.

Im really curious to see how your times will change with more power. Seeing as you pretty much redlined 4th crossing the traps on your 12.22 run (which was perfect, for that power level) I want to know how the extra shift will play into your time.


Boltz- posting as eve-slow

Also, this is slightly off topic but I'm just curious if you guys know the difference in 4th gear between the 5 and 6 speed. If I remeber correctly, my brother trapped 111mph around redline in 4th, but Im not sure what he considers redline on his car (7k, or 8k)

 

yea be careful on stock injectors. -20 sounds very aggressive, my 7000 and 7600 is set at -26 with 720cc injectors on 91 octane. 11.1 AFR. I believe I am at -23 at 6800 and -19 at 6200.

 

yea race gas changes afr

 

I am curious how do you tune for race gas with only an afc? I always thought that timing needs to be adjusted to take full advantage of race gas since it allows you to run more timing. Are you using some secondary method of changing your timing settings under boost?