Tuning Suggestions/Help

[Scrymerr]

I have a GST, stock 7 bolt, 50 trim @20psi, 91 octane, 3" GM MAF blowthru, 720cc inj. 255pump, tuning with AFC2, GM MAFT, logger.

I am able to get a decent tune by doing a 3rd gear pull, starting at 30mph and going to redline. By 4000 rpm, I am at app. 10psi of boost, and my AFC value at that point is -18. This is all good, O2s are in order, and nothing is too bad.

The problem happens when I downshift and go WOT. I will be cruising at ~40mph, and put it in 2nd and gun it. Because there is a small moment of lag before boost hits, the fuel pressure at that point is ~10psi lower than it was when I made my pull. Because of this the car runs extremely lean for a while, sputting until it finally builds boost, bumps the FP up to where it should be, and picks up.

What should I do about this problem?

Thanks in advance.

--Dan

 

[BreathinHeavy]

i dont see a fuel pump in your list of mods? if you dont have one i would say that is your problem. you might also want to look into rewiring your fuel pump if you have done the upgrade already.

sorry i see your fuel pump look into rewire.

 

[Scrymerr]

My fuel pump is rewired. I can supply plenty of fuel under boost when necessary, just during boost lag is when it runs lean.

 

[slickster]

How about uping your low afc settings in the higher rpm bands(3500-7500) to be more in line with what your highs are at that point. I'm sure your running closer to your lows at that point, because you are off gas. IMO, your lows in those ranges should mimmick your highs, since i never slowly rev my car past 4k or so when normal shifting at low throttle.
Hope it helps,
-Slick

 

[chrisdob30]

I'd look into a fuel pressure regulator. I see you have a gauge but still running the stock regulator which is probably being overrun.

Chris

 

[Scrymerr]

I am sorry for forgetting to mention the FPR in my brief list of mods, I do have one.

As far as the low settings, I agree, I do not take it over 4k unless I am 50% throttle or more pretty much, so I can try that. I have a few other problems that need to be addressed before I can test your idea out, but I will report back when I do so.

Thank you.

Also, I have my fuel pressure set at 48psi with the line off. Should I increase or deacrease the fuel pressure, or does it matter? What are the determining factors of fuel pressure? Obviously, more airflow might make increasing the FP beneficial, but if it does not NEED to be at 48psi, are there any benefits gained by trying to lower it down a bit??

Again, thanks for the help.

Dan

 

[Quazz209]

fuel pressure should be at 43.5 for a 2G so 48 is a little high, then with injectors as large as 760cc you are getting alot of fuel to begin with combined with the high fuel pressure means even more fuel. I would say you can turn that down a little and might help an overly rich condition that you could be having.