I was considering ls1 injectors for my lt1 m6 car which wont have more than 380rwhp or 450 flywheel, but I woul like the duty cycle to staybelow 85%. If this were a problem with the 60 psi the ls1 injectors were rated at, do they respond well to increased pressure and would this be a good way to do it?

 

They are flow rated at 58psi (4 bar). You would probably have to push them close to 80psi to get the flow you need to keep it under 85% DC. Will your fuel pump flow the required amount at 80psi? That's more likely to suffer from reduced capacity at high pressure.

 

Maybe a 30 lb/hr svo set would work a little better/easier. Is there some rule of thumb you are going off of to come up with the approximate duty cycle for my power output? I know of a way to do it based on afr and ve but not by power output.

 

I've tuned lots of LS1s with the 28.8 injectors in the 390~400 rwhp range with inj duty cycles around 90% at those levels. You take that 28.8 4 bar injector and put it in a 3 bar fuel system and they are going to be around 25.1 lb/hr.
Duty cycle = inj pulse width X rpm/1200
This site has a decent calculator.
http://www.rceng.com/technical.htm

 

To estimate duty cycle, I have to assume a brake specific fuel consumption (BSFC). A conservative way to do that is to start with 0.50 #/HR/HP.

(FWHP x BSFC) / 8 = estimated fuel consumption per injector:

(450 x .50) / 8 = 28.125 #/HR

required flow / target duty cycle = Injector size:

28.125 / 0.85 = 33.09 #/HR

To get a 28 #/HR (@4 bar) injector to flow 33.09 #/HR, you would have to increase the pressure by:

(operating pressure / rating pressure )^0.50 x 28 = new flow capacity

(81 / 58)^0.50 x 28

(1.3966)^0.50 x 28

1.1818 x 28 = 33.08 #/HR

....hence I said "close to 80psi".

If the LS1 injector is rated a 28.4 #/HR, it would take a bit less pressure.

All of this is dependant on the true BSFC of the engine. A stock production engine might have a BSFC of 0.50 #/HR/HP. A very efficient tune on a street and strip setup might get you as low as 0.45 #/HR/HP. An engine tuned for max performance at a specific RPM (e.g. NASCAR engine) probably can do better than 0.40 BSFC. After we got done with my stroker on the engine dyno, it was running at 0.44 to 0.45 BSFC.

A rough way to get to your correct injector size it to multiply flywheel HP X 0.07 That assume an 0.476 BSFC and an 85% DC. Should get you in the ballpark.