Injector Sizing, yet another question

Hello again. Man, I know this gets old me asking a lot of dumb questions.

I did search the forums, and it looks like most people recommend 36 or 40 lb injectors for a 383 LT1 engine.

My engine builder (Golen) says 30 lb/hr is what I need for mine. It is rated at 400 flywheel HP as delivered.

I guess my question is that a good starting point, 30 lb/hr?

I'm not too keen on buying 30 lb/hr injectors and then having to eat that cost (I know I can sell them, but that is a pain too) and buy bigger ones.

Also, do most (all?) injectors have the same electrical connector? Sometimes I see the same part number for my Mustang as I do for the F-Body.

Dazed and Confused, but intent on building this car!

The rule-of-thumb that I recommend is to multiply the flywheel HP x 0.07

400 flywheel HP X 0.07 = 28 #/HR

That is the minimum size injector you should consider. It assumes a decent tune (0.476 #/HR/HP BSFC) and a maximum 85% duty cycle. You'll have maybe 25HP headroom with the 30's in your Golen engine.

There is no down side to going larger on the injectors than the size you arrive at using the rule-of-thumb. If you bump the engine to 500 flywheel HP in the future, you would be looking at 36's.

Thanks so much for the information. I'll get the 30 pound injectors for now.

As for injector brands, I read tons of posts that said run away from Accel.

Thanks again, and nice ride! I peeked at your links in your sig...

Also, do most (all?) injectors have the same electrical connector? Sometimes I see the same part number for my Mustang as I do for the F-Body.

Dazed and Confused, but intent on building this car!


i have ford SVO injectors in my car, so yes

and i would go a step bigger than 30, i wish i did

I will probably start with the 30 pounders, as I have a set out of my Mustang before I upgraded.

Thanks

I have some 30# injectors that have less than 150 miles on them. I have a supercharged lt1 and it wasnt enough injector for the boost. So needless to say I need a bigger injector and will be selling these if your interested.

Thanks,
Waylon

The rule-of-thumb that I recommend is to multiply the flywheel HP x 0.07

400 flywheel HP X 0.07 = 28 #/HR

That is the minimum size injector you should consider. It assumes a decent tune (0.476 #/HR/HP BSFC) and a maximum 85% duty cycle. You'll have maybe 25HP headroom with the 30's in your Golen engine.

There is no down side to going larger on the injectors than the size you arrive at using the rule-of-thumb. If you bump the engine to 500 flywheel HP in the future, you would be looking at 36's.

How does this work for LS1 cars with 58 psi of fuel pressure rather than the 43 psi that LT1 injectors have?

The injector sizing formula, whether you use the ones on the popular online calculators, or my rule-of-thumb, is independant of the fuel pressure.

Example:

500 flywheel HP X 0.07 = 35 #/HR

It tells you what the injectors need to flow = 35 #/HR. If you have an LT1 operating at 3 bar (43.5psi), you get an injector of the calculated size (35 #/HR) that has been rated to flow 35 #/HR at 43.5psi. If you have a 4 bar (58psi) fuel system, you need an injector that has been rated to flow 35 #/HR at 58psi.

If you know the pressure at which the injector was rated, you can correct its flow rate by multiplying the rated size of the injector times the square root of (system pressure / rated pressure).

Example.... your LS1 with a 58psi fuel system, left the factory with injectors that were flow rated at 28 #/HR. If I use those same injectors in my LT1 with 43.5psi fuel system, they will only flow 24.3 #/HR.

Pressure factor = (43.5 / 58) ^0.5 = (.75) ^.5 = 0.866

0.866 X 28 #/HR = 24.3 #/HR

I run a set of 64 #/HR Bosch injectors that were flow rated at 2.7 bar (39.15psi). My fuel system operates at 58 psi.

Pressure factor = (58 / 39.15) ^.5 = (1.48) ^.5 = 1.217

1.217 x 64 #/HR = 77.9 #/HR

i have 90k on my accel injectors. talk about luck

Fred made a point that is worth re-iterating. In the context of high impedance injectors, there is essentially no down side to bigger injectors. From a decent source, large injectors are about the same price as smaller. So, go bigger and avoid having to upsize them in future.

Rich

Thanks Fred, my dilema is that when I bought my used #36lb injectors I didn't ask whether they were 36lb/hr at LS1 pressures or 36lb/hr at LT1 pressures. It's been fine for NA but I'm thinking about a small dry shot and don't want it to go lean. So I guess that my first test and tunes this year will be with the Autotap hooked up to monitor injector pulse width. If the PW is too high then I'll have to upgrade injectors before spraying.

Do you have a part # for the injectors? There are some online sites with flow and pressure data for a lot of injectors.

Do you have a part # for the injectors? There are some online sites with flow and pressure data for a lot of injectors.

No, I'll check and see if I can see it without pulling the fuel rail.