First off, here is my combo:

'95 LT1, bored .030" with Speed Pro Powerforged pistons, 11:1
stock LT4 heads/intake
Combination Motorsports TN-236XL, 236/242 duration, .555"/.576", 112lsa
BBK 58mm TB
SVO 30# injectors
Walbro 255 lph in-tank

I ran an '04 Lightning last night and made a datalog of all 3 runs. I'm hitting high 90% injector duty cycle near the top of 4th gear. I have a slight lean situation at all times during part throttle, and its running very lean during WOT. If he doesn't see this I'm e-mailing Ion as he did my tune and get him to richen up the mixture some, but I'm wondering if I'm running out of injector as well?

Thanks for any help.

 

to be honest with you i think you need a little more injector than the 30# the factory Lt4 had 28s (97 ss,97 bird and 96 GS vette)so i would lean towards the racetronix 32.2 or possibly the 36s but nothing more..is your fuel pump running the correct psi,get a guage on it and make a pass watching the psi

 

I'm pretty sure 30#'s are good for at least 420 RWHP and I wouldn't think you'd be there with stock LT4 heads and that cam.

 

well ok, thats kinda what I was hoping to hear. I put a guage on it just after I put the new pump in but I don't remember what the pressure was. I know it was a good 10 psi higher than the factory pump I had in before.


also, instead of replacing the injectors if it comes down to it, could I not just get an AFPR and bump the pressure up with a corresponding adjustment in the program?

 

Assuming 450 flywheel HP, a BSFC of 0.48 #/HR/HP, you would be running 90% DC with a 30# injector. To get in the ballpark on injector size, multiply flywheel HP by .07 . That will give you an 85% DC, assuming the 0.48 BSFC. A "good" tune will run lower than that on BSFC, so the .07 multiplier has a bit of fat in it.

You can't size injectors based on "rear wheel" HP.... the injector has no way of knowing if you are losing 12% on a stingy M6 drivetrain, or 22% on a loose TH400 conversion.

Your fuel system should be providing 43.5psi at max load. If its running 10psii higher than the stock system after a fuel pump replacement, either you put in a huge pump that the stock FPR can't handle, or you have a restriction in the return line on your fuel system. Replacing the stock pump with a larger one should not cause a 10psi increase in system pressure.

If you really are running at 53.5psi, your PCM should have been tuned for a 35.09 #/HR injector constant. In which case, you shouldn't be maxing them out.

And, what program are you using to measure Duty Cycle? TTS DataMaster seems to produce screwy results for injector pulse width and the resulting DC.

 

ahh, I am infact using Datamaster.

as far as the fuel pump, I forgot to mention this was after I also replaced the fuel filter, which was clogged. I think my previous readings were off, hence the higher pressure afterwards.