uberstang1

Well here we are, currently im sitting on 42# injs and a 155lph walbro in stock tank with a return style 97 system. Starting to get my ducks in a row for a new engine/blower combination and needless to say I'm going to need a fuel system to support 650ish rwhp. I only want to do this one time. What kind of options am I looking at, could I go with a weld in sump and elimator pump from aeromotive and be done? Any better options?

cliffyk

None of this is intended as a solution, just a FWIW look at where you are...

At 40psi the 42lb/h injectors will be pretty much tapped out (95% duty cycle) by 525HP at the flywheel--you'd need to pump the fuel pressure up to 75psi to get 650fwHP out of the 42's; 105psi to get 650 to the wheels.

I assume you meant a Walbro 255lph pump, is it the standard or high pressure model?

I ask because the standard pressure model won't make 100psi. and the HP model only flows 32gal/h at 13.5V and 100psi; that's 192lb/h, only enough for 320fwHP or so (I ran the 255lph HP pump on my M55 Eaton '92 Miata, at 100psi fuel pressure to get 255rwHP at 18psi boost--a bunch in a 1800lb car).

72lb/h injectors at 40psi would get you up to the 650rwHP with some head-room (they'd be running 80% duty cycle). And the Walbro standard pressure pump can deliver 68gal/h at 40psi. That's 405lb/h, good for about 680HP at the flywheel...

uberstang1

Yes that was a typo it is indeed a 255lph, but the standard version not FI. So are you saying with 72# or bigger injectors I can squeeze by with a 255lph HP walbro.

cliffyk

Here are the flow rates in lb/h for the Walbro 255lph pumps:



You cans see that at 40 psi the HP model has only a 12lb/h advantage. Using the typical BSFC (Brake Specific Fuel Consumption) of 0.6lb/h for forced inductions applications the standard pump would max out at 408/0.6 = 680fwHP; the HP model at 700.

Note that these are both flywheel HP, and that they are "maxed out" capacities based on Walbro's specs. Using an 85% design ceiling they work out to and 575 and 595 flywheel HP respectively.

Using injectors larger than 72lb/h would add nothing as the pump would be flat out anyway.

Here is the formula for estimating fuel injector fwHP capacity:



BSFC for n/a is typically 0.5lb/HP, 0.6lb/HP for f/i.

And how to recalculate injector capacity as fuel pressure is changed:

jlc41

Very interesting thanks for sharing.

uberstang1

Cliff your knowledge overwhelms me.

cliffyk

Been doing this stuff for too many years now...

jlc41

That maybe, but look at all the uninformed you are helping, like me. Again thanks for sharing your knowlegde.