Adverse affects to high fuel pressures?

[forcefed86]

My fuel setup is in my sig.

These are what my DC's are looking like at 30lbs of boost with 45 base fuel pressure.

RPM...DC
3600 66%
4000 73%
4400 80%
4800 85%
5200 90%
5600 95%
6000 100%
6400 105%


These are the ratings for my fuel pump.

ProTuner 750 MP-4303
2,000+ HP (na std fuel)
20 to 120 psi
14A @ 45psi


Did some pressure research.

I'd need 97lb injectors for 600 crank HP on e85. This calculations seems a little high to me, but I used the RC inj. Calculator at 99% DC .65BSFC to get these figures. Then multiplied the injector size needed by 1.47 for e85 requirement.

I'd need to run 60psi base pressure to get my 83's to flow like 97's. While I don't think I'll be doing that, is there any adverse effects to this? MAx real world pressure folks have run on similar low-z injectors?

At 30lbs of boost I'd be at 90psi head pressure. Still well within the 120psi max of my pump. Will this kind of pressure destroy injectors? I know the dead times would be way off with that much head pressure.

 

[GNVYUS 1]

Ya most can't pull this off due to pump volume at say 90psi, but in your case that's not an issue so you could achieve this if you had a FAST.

Your issue will be everything other than WOT tuning wise, you're better off just going to 120's and having the chip deal with the Injector dead time for idle/cruise.

I've seen multiple E85 injector calculators, 1.47 is pretty liberal, that's for those who need plenty of room to grow.

 

[forcefed86]

I thought the same on the fuel calc. The DC numbers are straight from eric and programmed into the chip though. I'm sure I could get by with adding some fuel pressure at the track. I have a MAFT as well so I can change the idle settings leaner if need be. Could always throw the meth injection back on as well.

 

[87GN_70GS]

Its possible. The issue with the injectors at high pressure is that the pintle is opening against fuel pressure. So the high pressure may slow down the opening and make operation lazy. The plus side is that pressure is helping to close the pintle. "They say" not to run injectors above 100 psi because they might not open at all.

While the dead-head (zero flow or 0 gph) pressure of the pump is 120 psi, by no means will it flow it's full amount near that pressure. That pump flows 138 gph at 60 psi and 120 gph at 75 psi. Extrapolate that out to 90 psi, and the number is about 100 gph (if you assume the relief valve has not started to open and bypass fuel). 6 of 83# injectors at 30 psi boost and 100% dc will require about 100 gph. So the pump supply of 100 gph is roughly equaled by the injector demand of 100 gph (assuing a perfect world, no losses, etc) - it's gonna be close as to whether your fuel pressure will start dropping at WOT and static dc.

But all that aside, the only true test is to crank up the base fpr, monitor dc and afr and go from there.

 

[Chuck Leeper]

So, why would one use a DC of 99% to calculate the size requirement??

"The issue with the injectors at high pressure is that the pintle is opening against fuel pressure." And, they are also seeing boost psi at the nozzle end. Therefore, delta psi is 100-30.

 

[forcefed86]

Its possible. The issue with the injectors at high pressure is that the pintle is opening against fuel pressure. So the high pressure may slow down the opening and make operation lazy. The plus side is that pressure is helping to close the pintle. "They say" not to run injectors above 100 psi because they might not open at all.

While the dead-head (zero flow or 0 gph) pressure of the pump is 120 psi, by no means will it flow it's full amount near that pressure. That pump flows 138 gph at 60 psi and 120 gph at 75 psi. Extrapolate that out to 90 psi, and the number is about 100 gph (if you assume the relief valve has not started to open and bypass fuel). 6 of 83# injectors at 30 psi boost and 100% dc will require about 100 gph. So the pump supply of 100 gph is roughly equaled by the injector demand of 100 gph (assuing a perfect world, no losses, etc) - it's gonna be close as to whether your fuel pressure will start dropping at WOT and static dc.

But all that aside, the only true test is to crank up the base fpr, monitor dc and afr and go from there.

Thanks for the input! Since the DC is programmed into the chip by RPM, boost won't affect the DC. So I know at 6k RPM I'm at 91% DC no matter what boost I run. I can adjust the DC with chip settings, but it will never change with boost. I can tune the rest with fuel pressure/meth inj etc.

Spoke with eric a bit and he thinks the trims will be ok up to 45-50psi base FP range. I have a little to play with idle wise on the MAFT as well. I can always crank it to 55-60psi base FP at the track when running 30lbs of boost and turn it back down to 45ish for my usual street 23-25lbs of boost.

So, why would one use a DC of 99% to calculate the size requirement??

"The issue with the injectors at high pressure is that the pintle is opening against fuel pressure." And, they are also seeing boost psi at the nozzle end. Therefore, delta psi is 100-30.

You wouldn't want to use 99% DC. But I'm not calculating size requirements to purchase injectors. I already have 83's and I want to see how close to the edge I am now, and how far I can push them.

My Chip tuner has found 1.27 to be a better modifyer for e85 calculations. ( I used 1.47) I'm already around the 600 crank HP going by weight and trap speeds. 30psi out of the old pt-68 may be to much power for this $600 short block to handle...:biggrin: