I used the calculator and even being generous, using 550FWHP and 80% duty cycle I come up with right around 30lb, I think it came out to like 33.0.

I'm currently running SVO 30lb injectors on my stock bottom end motor, I'm going to a 389 motor with AFR heads, should I be O.K., or do I need to look at getting larger injectors.

Thx.

Mark.

 

[QUOTE=93ZM6Tally]I used the calculator and even being generous, using 550FWHP and 80% duty cycle I come up with right around 30lb, I think it came out to like 33.0.

I'm currently running SVO 30lb injectors on my stock bottom end motor, I'm going to a 389 motor with AFR heads, should I be O.K., or do I need to look at getting larger injectors.

Thx.

Depending on your HP. 42#er's will make 700FWHP@52psi. Going easy on the pump and dropping the pressure will be much less HP. It takes a hell of a pump to do 52PSI at the volume needed
At 45psi and a 90% duty cycle a 45# will make 600FWHP

 

[QUOTE=1racerdude]Hate to seem dense but you lost me. But I think the general gist is to go with a much larger injector running at a lower, (normal), 45psi, ie a 45# or even larger injector so that I can support higher HP with less pressure.

And just to throw another little curve what effect would Nitrous have on my injector requirements. After I've got the motor broken in, tuned etc, I'm planning on adding a 200Shot wet system, maybe even dual stage.

Thanks for the reply.

 

I just went with 42# SVO's..Depending on H/C, and if you'll spray the motor, I think those would be fine. You could always turn them down a bit.

 

[QUOTE=93ZM6Tally]Yes a 42#@52lbs is rated at almost 48lbs.
Wet system will have no effect.

Yes bigger at less pressure,'cause ya are going to need a bigger than a 255 pump anywayIMO and it will take the strain off of the pump.

 

What calculator did you use? To get an answer of 33.0 #/HR at 550 flywheelHP, with an 80% duty cycle, you had to input less than 0.390 #/HR/HP BSFC. That seems very low. The standard calculators start with 0.500 BSFC. I have data from my engine dyno tuning as low as 0.430.... but anything under 0.400 would appear to be doubtful for a "street" application (the NASCAR guys can do it, but they run at almost constant RPM).

An 0.450 BSFC at 80% DC would give you 38.7 #/HR. That would seem to suggest 42#/HR injectors, at least running at rated fuel pressure.

 

Another question. Injuneer I found a calculator and you are as usual correct, but should I use projected HP numbers with or without juice. I hope to be somewhere in the range of 425-450 NA with a 389 and Ported AFR 210's. Add 200 to that, (I don't want to go buy another set of injectors after I get my juice kit installed), and your in the 625-650 RWHP range. Add back the loss of the valve train (~20 percent) so now I'm looking at 750 - 780 area. That puts me at about 61lb Injectors, (using .50 BSFC and 43.5PSI).

And then I start doing some conversions, (even without the nitrous), and unless I'm doing this wrong I'm going to be stressing a Walbro HP 255 (255lPH). I was under the impression that a Walbro would be more than enough for the levels of HP that I'm talking about. I know I'm over estimating HP, but I believe in a certain amount of overkill - to a point.

 

Your 389 should make 550-600FWHP with no problem @1.4-1.5HP per CI.Ya need to figure right in that neighborhood,unless ya are going for a NASTY mech roller and max heads and a Holley SR(more HP) for a trailer queen,and not street duty.IMO the 255 will be marginal but Racetronics makes a duel intank set up for high HP cars,Call them and see about it.

Ya may not need to add 200 to get where ya want to be.