1fastVETTE

I have my fuel pressure set at 70lbs but under 100% throttle in high gear I notice that my fuel pressure starts dropping to about 65!!!! Very Scarry especially since Iam boosting about 10.5# but luckilly the weather is pretty cool.

My car is tuned to what I believe is ideal performance for my standards. except for the 70lbs fuel line pressure. I have ls1 Edit and I would like to scale my injectors so that I could turn down my fuel rail pressure to 60lbs but still maintain the same effects as if the fuel pressure was at 70lbs.

How can I modify my injector scaling to achieve this goal in ls1 edit?

1fastVETTE

The difference from 70lbs to 60lbs is about a 16 percent decrease so should I just multiply the current injector scale values by -16 percent????

Someone please help my car runs great at idle were it is I just want to decrease the fuel rail pressure and have the engine run the same by adjusting the injector scaleing.

horist

I don't believe you can modify fuel pressure on LS1 cars via the PCM... I believe some big boost guys run booster pumps that kick in as the boost rises so that it keeps the pressure up...

stock LS1 runs at 58psi which is 4 bar, running 70psi is almost 5 bar ... unfortuanetly injector scaling isn't as easy as just the percent difference

Scaling the injectors will let you add ore remove fuel but wont' have an effect on the fuel pressure (unless you're running rich right now and lean it out, then it may keep higher fuel pressures)

You really only want to modify your injectors though to get them where they should be mathmatically...

to do this you would want to scale your IFR table... I believe since you're running non stock Fuel Pressure what you can do is this:

Whatever injector you're running now... it was prolly rated at 3 bar... unless you're using stock injectors then they're 4 bar

We'll use the assumptions of 4 bar = 58 and 3 bar = 43.5

the equation is Square Root ( New PSI /Old PSI)
Example if you have 32lb injectors... Squrt(70/43.5) is 1.26 so your injector would flow 126% more fuel than the rated value... so that 32 lber would behave like a 40.6lb injector

Now load your stock IFR table ine

If you went from 28s to these new injectors, the difference is 40.6/28 = 145%

so you'd scale your Stock IFR table 145% .. this should put that table inline where it should be... at which point you don't want to mess with it much ... as it should be mathmatically correct

1fastVETTE

Horist, thanks for your reply. It seems you might be able to help but you might have misunderstood my question or problem.

I dont have a stock fuel rail its a costum made billet rail with an adjustable fuel pressure regulator.

My car was tuned by a local tuner and was tuned enough to make it run but I still had some detonation and a very rough idle. So I bumped up my fuel rail pressure from 60 to 70 lbs cause I was afraid of the detonation and wanted to drive it safely to another tuner in another city.

When I took my car to to the other tuner they tuned it but left the fuel rail pressure at 70lbs even though I asked them to turn it down to 60lbs. When I saw they had left it at 70lbs I asked them to retune it at 60 then they wanted to charge me for another tune. I was a bit upset but they assured me that the car was tuned perfectly at the 70lbs and just to leave it at that.

Iam not so convinced with that. Even though the car does run great and idle great, I still feel weary seeing my fuel pressure gauge come down from 70lbs to 65 lbs at WOT.

So what Iam trying to do is manually,at the fuel presure regulator, turn down the presure to 60lbs and compensate the loss of fuel by adjusting the injector scaling so that the injectors would behave as if they were being fed 70lbs although they are really getting 60lbs.

For your information I have 42# SVT injectors. Maybe that helps.

Basically what Iam trying to do is lower the fuel pressure to 60 but have the injectors spit out the same amount of fuel as if it were recieving 70lbs by adjusting the injector scaling in LS1 Edit.

I hope Iam not confusing you.

horist

ok... i see what you're gettin at... I'm about to head off to bed... but I'll reply in the morning....

basically all you need to do is turn your fuel pressure back down to 60psi and adjust your injectors as appropriate based on the formula above (sqrt(58/43.5)*42) then deivide by your stock injectors... then scale your stock IFR by that percent....

Then to feel extra safe you could richen your PE vs RPM table (higher values = richer... ideally those values represent 14.7/PE Value at specific RPM) and bring it back down to a level you feel safe at

I'll further clarify/explain in the morning ... soooo tired heh

Some useful info may also be to post your stock PE table values and your modified ones (I doubt the tuner touched the VE table... generally only the PE table is modified)

Also post up your stock vs modified IFR table values if you have them... just to see what percent they increased them by to see if they are mathmatically sound w/what I derived above ... if not we can use this to derive approximate IFR values given the drop in fuel pressure

1fastVETTE

Horist, I re-read your post carrfully and I think you might have already answered my question.

square root of (new psi/old psi) so square root of (60/70)=.9258

So I should multiply my IFR Tables by 92.58%

Is this right?