Alright. I would like some advice from experience from you guys. According to a calculator, and engine with 500 crank HP requires 40lb injectors. I dont think though that a 383 with fully ported LT1 heads and a reasonably mild cam (low 230s intake / low 240s exhaust) and LTs and all other bolt ons, would require 40lb injectors.

Correct me if Im wrong here, but shouldnt a setup like that be good on 30#ers and a stock pump, or would I be robbing myself of some serious HP/TQ by going with that fuel setup. I think there are plenty of other people out there wanting to know the real answer to this question, so lets make a good discussion out of it.

Base the answers on this setup.

383 6" stroke 11.2ish/1 compression
LE heads 260s/190s 2.0/1.56 valves 1.6 rockers
Cam specs mentioned above (will be a custom grind in that area)
jethot LTs
matched intake/ 58mm TB

thats pretty much the basics, so what do you think?

 

I was using 30# Ford SVO injectors with my 383 setup and they worked fine. I was dynoing 400RWHP. Now I am running 50s because of the supercharger.

 

I'm running 30#'s on mine.

 

There's athread on the first couple pages where a guy w/ a 383, AI heads etc. got dyno'd, picked up quite a bit by going from 24 to 30, and thinks there's even more in it if he goes to 36's. (I believe that's what he meant)...

 

If you are really making 500fwhp then 36lb injectors would be the minimum size I would use, where 40's would be a nice cushion. It really depends on the fuel pressure you intend to use. I personally would probably run a 36lb injector and around 50psi fuel pressure, and verify my duty cycles were OK. Also for prolonged periods of WOT the stock fuel pump would probably not get the job done. I would definately want to upgrade the pump anwhere over 400fwhp. Of course this is JMO

 

The online "size your injector" formulas tend to be very conservative. They typically assume a brake specific fuel consumption of 0.50 Lb/Hr/HP. That is typical of a "stock" or sloppy performance tune, but a well tuned performance setup will generally be closer to 0.45 Lb/Hr/HP. Just making that change, and assuming you are still limiting duty cycle to 80% brings the calculated injector size for 500 flywheel HP down to 35.2 Lb/Hr. A 36# injector should be fine.

You will probably find people running 30's and making 500HP, but that will mean they are running a 94% duty cycle, and if its not actually costing some significant loss of HP, its definitely shortening the life of the injectors.

There is no downside to going a little "fat" on the injector size, as long as they don't get so big that the PCM can't turn them down to the ~1 millisecond pulse widths required for the engine to idle.

I run 78's.... actually Bosch 64's @ 58psi.

 

my stock pump couldnt keep up with my little 364rwhp, the racetronix walbro 255lph is a great kit $150
jesse

 

The Vortec T-Rex pump works well, but it's loud!!!

 

Alright, so say I end up making in the 420rwhp/tq range with this setup. I have accell 30#ers right now. If I were to dynotune it to where the A/F is just right, and the injectors are running at a 90 something % duty cycle. Its fine to run them for a little while then switch over right? And will it need to be tuned again, or will the injectors just run at less of a duty cycle?

 

Good info here...those are some big injectors

So for a 383 making ~425-445 rwhp w/ a madwolf/pcmforless tune, What's the reccomended size? Looks like by those numbers, the 36# injectors are barely enough, is 42# what would be necessary? What is it with SVO injectors, you can run a smaller injector with more FP?

Just tell me what I need LOL.

 

Im running the Accel injectors in my 383, basically the same h/c setup also, and the injectors are fine...plenty of fuel...My duty cycle is only like, the 80's%...and my FP is around 45psi on the regulator....

 

Which are what size?!

 

D'oh!!! Im sorry, I have the 30#'s....

 

If you make in the 420HP range the 30's will be fine. I run stock injectors on my Heads, Cam, Header car at 50psi, My rwhp on motor is around 358 and my duty cycles are around 88%. I also run a wet N20 system setup for 150shot. I originally had a 5176 NOS kit that came with the supplemental fuel pump which I continue to run. I would recommend you upgrade the fuel system asap. If your duty cycles do go higher than 90% just turn up the fuel pressure a little. You should be fine up to around 55-60 psi if you have to go above that to get under 90% then I would go bigger on the injector. Good Luck!

 

88% DC?
Adjust the FP and then have to rescale the ECM/PCM fuel tables and take a guess at the injector constant and PE tables.

Better idea... Get a properly sized injector so you can run normal pressures (injector will be more linear), have a known injector constant and keep your DC UNDER 80%.