Tuning for higher base fuel pressure

[cman3000]

I am currently running PTE 880s with e85 at 18psi, and I am getting high IDCs. Is it acceptable to raise fuel pressure to take some of the work off the injectors? I am running a 255 pump, and I was only flowing around 170 lph while my injectors were maxing out.

From my understanding, If I were to run, say, 50 psi, I would have to decrease global by about 15% (1-sqrt(50/37.5)=-.15) Are there any other factors I would have to worry about, such as changing deadtime or MAFcomp?

[carltalon]

This is exsactly what I did when I first switched to E85. My 850s at 100% duty cycle at 480 HP uncorected on a dyno dynamics. I used that same formula to adjust for fuel pressure. I dont think I did anything with deadtime but the higher fuel pressure might rais it a little but probly not enuf to change anything. MAFcomp shouldnt change.

[niterydr]

Just make sure your fuel flow (volume) is acceptable at the higher baseline pressure. As fuel pressure increases, fuel pump volume decreases and if you are in fact at the limit of your pump AND your injectors, you will be pissing into the wind.

[way2fastalon]

having same issue but it dont matter what i have for base pressure car runs the same ... ? 37to 55 psi it dont really change. runs lean think the pump is dying its a 255 i get 12.5 to 13.5 in boost but i don't run it or use boost at this time cause of the afrs are too high im on gas right now for safety reasons only a year old pump ?

[Pushit2.0]

It could be, I would check your fuel pressure under boost and your wide band at the same time. Does the car run like its going lean and into knock retard?

As said above if you raise your base fuel pressure and your fuel pressure drops with boost/rpm or you injector duty cycle stays high you might be on a 2+ front wall, and that is no fun, ask the Axis.

~John

[bertrenolds5]

Sounds like you need bigger injectors, if you have a 1g the base fuel pressure for e85 is 37psi, adding more fuel will really do nothing since your injectors are maxed. I might waste more fuel if anything.

[way2fastalon]

so on to fuel .. i have a single 255 in the tank im wondering if i got the aeromotive stealth pump 340lph would that just be good or do i just get a bosh 044 run it inline with my 255 ?
upping my feed line to -8 for e85

[niterydr]

Sounds like you need bigger injectors, if you have a 1g the base fuel pressure for e85 is 37psi, adding more fuel will really do nothing since your injectors are maxed. I might waste more fuel if anything.

Raising the baseline fuel pressure increases the size of the injector, assuming the fuel pump volume is adequate and the injector spray pattern is sufficient. I've been using that trick for 10 years now when the injectors are correctly sized, just the idc's are higher than I'd like, and I have enough fuel pump volume to compensate for the increased fuel pressure. Typically when your baselines get over 50psi and you are running more than 20psi, you really see diminishing gains.

Factory fuel pressure is 36-38psi, most I've seen are around 36psi, but anyone running E85, larger injectors, and a stock fuel pressure regulator, is an idiot. This is because the stock regulator is hardly adequate to control a basic drop in fuel pump, let alone a hardwired Walbro 255hp or anything larger.

Most injectors flow (as well as fuel pumps) advertised levels at 43psi fuel pressure, unless noted elsewhere.

[way2fastalon]

well my 255 is hard wired and still outa fuel at 15 psi boost . i turned it back down to 40 psi still goes up to 13.2 and still unsure on the pump i should get it sounds like 2x 255s are still not enough for 500-600 hp on e85 ..

again im getting a tune here for e85 in a month or so and shooting for 400+ hp until i get my new head done thinking about getting an intake made from john gota pm him about it

[niterydr]

What are the IDC's on your 880's? Sounds like your pump isn't keeping up, is the pick-up sock clogged? I would think a single walbro could come close to supporting 400whp on E85 dependant upon the BSFC of the engine.