Injector Size for 500 HP engine?

Alright, I am getting an adjustable fuel pressure regluator from 30-65 psi and I got a walbro 255lph fuel pump. I was wanting to know if 36# is enough to support 500hp. I heard 36# can only support up to 450hp @ 45 psi. You can boost the injectors with pressure but that also makes ur pump put out less. So does a bigger injector like a 42# support 500+ hp @ 45 psi? Just wanted to clarify before I bought some 36# injectors. Thanks

Is that 500 Flywheel horsepower or 500 RWHP??

That will make a difference. If it is 500 flywheel horsepower - than I would think 36's would do it - as long as you are NA

If that is 500 RWHP - then the 36's may not cut it

500 RWHP NA (actually 480 or so)

Are these good injectors?

GM Bosch 36 LB # Injectors LS1 LT1 Ford 24508208

http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&ih=013&sspagename=STRK%3AMEBI%3AIT&viewitem=&item=230110101933&rd=1,1


Good Regulator?

HOLLEY ADJ FUEL PRESSURE REGULATOR LT1 LT4

FWHP = ([INJECTOR SIZE (LB/HR) X DUTY CYCLE] / BSFC) X (# OF INJECTORS)

For NA cars use a BSFC of 0.50, for blown cars, use 0.55. Assume a duty cycle of 0.85.

For 500RWHP, the minimum I'd use is 42's. Use Ford SVO inj. or better yet, get some 50's from Racetronix.

So, FWHP= ((42Lb inj)x 0.85/0.55) x 8 = 520 FWHP
To get RWHP assume a 15% drivetrain loss ~ 600 RWHP

www.iroczone.com/calcs/injectorsize.htm

Yea, I was thinking 42lbs.

I would calculate but dont know all the variables to put in.

See my edit post above.

No one can tell you the exact answer. First, we have to convert from rear wheel HP to flywheel HP. Since it appears you have an M6, your 500rwHP is about 575 flywheel HP. Then we would have to know the actual brake specific fuel consumption (BSFC) for your engine. That will be a factor of how efficient the combustion chamber configuration is, and how good the tune is. BSFC of 0.50 #/HR/HP is an OK number to use for a pretty much stock engine on a factory tune. But a well-designed combo, with an efficient tune should be able to approach 0.45 #/HR/HP.

Without knowing the specifics of your setup, and assuming our estimate of your drivetrain losses is correct, I feel you can use a "guideline" of multiplying flywheel HP by 0.07 to get a rough idea of the correct injector size. That actually reflects a BSFC of 0.476 and an 85% DC.

575 x 0.07 = 40.25 #/HR

That means a 36#/HR injector, running at its flow rated fuel pressure is not going to meet the needs of your engine. A 42 #/HR injector would appear to be the minimum size you consider.

Thanks, ordered some BLUE Lucas 42.5# injectors @ 43 psi.

If you're approacing 600HP, you might want to check the flow capacity of the 255 LPH Walbro at 43.5psi.