Sash

guys what is a max hp on 42 lbs injectors,what did you made?

mrtstang

Sash, i wanna say around high 400's with a blower, but don't quote me. I thought i remember Lidio telling me that.

lizzyfan

I ran 440rwhp and that's about the limit

cliffyk

where:

• HPmax = flywheel HP
• lb/h = injector capacity
• Dutycycle = % as a decimal fraction (E.g 95% = 0.95)
• Cyls = # of cylinders
• BSFC = Brake Specific Fuel Consumption (0.5 hp/lb for n/a, 0.6 hp/lb for f/i)

So for 42 lb/h injectors in a V8, flat out at 95% duty cycle, running f/i:

42 * 8 * 0.95 / 0.6 = 532 at the flywheel, take out 15% drivetrain loss = 452 rwHP; pretty close to lizzyfan's 440...

lizzyfan

Can't be anymore precise than that^

cliffyk

Yup, and that is theoretical--when actually running over 90% DC fuel control is quite imprecise and could easily account for the 12 rwHP difference...

Sash

Rod,IIRC Chris with the black cobra told me he is pushing over 500 with terminator 39 lbs injectors

mrtstang

Wow, i didn't realize Chris was running 39's. If he truly is then it might have something to do with the fact that he's running a built HCI 4 valve with only 12 lbs. of boost.

BTW, what does Lidio say about all this? I would just go off his recommendation. Besides you don't have a intercooler or meth right now anyways, so maybe just have it tuned to work within the capabilities of the 42's. When the time comes for meth then bump both both the injectors and psi, then get a retune.

Just a thought.

cliffyk

It depends on the fuel pressure, which affects the delivery rate of the injectors--I should have been more clear about this in the formula I presented above, where lb/h represents the injector capacity when operated at the actual pressure drop across the injector.

Fuel injector capacity is normally specified at a pressure of 3 bar (43.5 psi), though as Ford runs 39.15 psi differential FRPP injectors are specified at that pressure. That is why the FRPP 24 lb/h injectors can be found listed as 26 lb/h capacity, which they would be if run at 43.5 psi.

The formula for recalculating injector capacity is:



So, 39 lb/h (FRPP spec) injectors operated at 80 psi would become:

((80.0/39.14)^0.1) * 39 = 55.7 lb/h injectors

55.7 lb/h injectors running f/i at 90% DC could support 55.7 * 8 * 0.8 / 0.6 = 594 fwHP.

On my old '90 to '93 Miatas I ran the stock 24 lb/h injectors at 115 psi to get enough fuel to support 12 psi boost, this "turned them into" 39 lb/h injectors.