I am building a 383 stroker with a 847 cam and running a 12 vortech supercharger on it. I have a 58mm TB and I know my fuel pumps
will be able to deliver enough fuel. I am trying to figure out what size injectors to run. I am thinking of 42 lbs high resistance injectors but I am not sure. Any input would be appreciated.

 

i would ask around in the forced induction forum!! i couldnt tell ya since you have a blower and that changes EVERYTHING

 

It will depend on your HP output. 42Ib injectors will be enough for about 537 HP(Flywheel HP).

Start by HP for NA motor. Injector size= (HP*0.5)/(0.8*8). Assuming your 383 stroker will deliver 450 HP. You should run 35Ib injectors.


Your supercharger kit should have a supplemntal fuel system (FMU), that will take care of additional fuel requirement when under boost. You don't want to run very rich at idle (no boost) and flood your engine.

 

What type of fuel pump are you running? Are you running an S-trim?

 

Man! I would like to know how would you engine run at idle with those 83Ib injectors. I guess they are low impedence. Did u do any progrmming to trim the injection at idle.

 

Rich is running 93# injectors

I feel so insecure looking at my little 30# injectors

 

It idles like a stock car, lol. My injectors are low impedance injectors and I am able to run them via my FAST system. The cheapest way to run low impedance injectors is by running the Accelornics Low impedance box. I was running 55lb Sieman injectors and my car made a little over 500 rwhp on a Mustang dyno (10 lbs of boost D1SC). The injectors proved to be too small (95% duty cycle).

 

I know a guy running 160 lb injectors in his V6 Grand National and it idles better than some stock cars. He drives his car 100 miles a week. It all comes down to tuning.

 

A little off topic but, why that cam w/ a blower???

 

At the least, get 50lb injectors, which are the largest high-z injectors usually available. The 42lb injectors may be marginal or even plain too small. And the 50lb'ers will only be marginally more expensive.

The typical injector sizing formula is too small for a centrifugally SC LT1. I know this for a fact, have seen it many times. The formula using a BSFC of 0.5 seems to not take into enough account the hp needed to drive a centrifugal. And keep in mind that it refers to hp at the flywheel, not the rear wheels.

As far as idling, even very large low-z injectors seem to be fine. I believe it's because of the "peak and hold" characteristic of the low-z injector drivers. Even though the injectors are large, the large peak current resulting from the low-impedance design can open the injector quickly. I am using 93lb injectors with the Acceleronics box and it idles fine.

Going lean on a blower motor is very, very bad. Don't short change yourself on the injectors.

Rich Krause

 

I would stay away from MSD 50 lb injector. They like to stick at higher fuel pressure. I know Siemans just came out with a 55lb high impedance injector.