what size injectors would i need on a 383 that is 10.5:1 with AFR 203's, a ported lt1 intake and a gm847? i was thinking of 36# or 38# but using the calcualtor on iroczone.com said i would need like 42#. anyone? i don't know if i was using it right. switching over from carbs, in the efi learning phase.

 

Actually you could run 24s or the LT4 28s. Either size would give you good resolution for fine idle control. I ran the LT4 injectors for some time. You won't have any problems with either size.

 

24s would be way too small IMO, you'd run out of fuel way early at WOT. Nothing like injectors locking up to blow up your brand new motor.

36's would be my guess just based on the airflow you're looking to have with the extra displacement and AFRs.

 

any other opinions or is chris on target. i know that 28's would be entirely too small for my engine. i see that racetronix sells 38's. it is alomst a happy medium between the what we were thinking and what the calculator says?

 

I have never seen TJ Wong give bad advise.

 

well i don't have any injectors right now, so i need to buy new ones anyway and i would like to buy the right ones the first time and be done with it. i think it would be pushing 28's kinda hard? i see what you are saying. its like using a 600 cfm carb on a 350 instead of a 750cfm. both will work. yet i heard that 24-28# were only good for like 400hp. i think that i will be well over that number? i could be crazy cause i don't really know great as much as i would like to about efi, but from what i have heard the 28's wouldn't be the right choice.

 

Just some good links here for Injector comparisons etc.

http://www.gnttype.org/techarea/fuel.../fuelpage.html

Enjoy

 

24s Are Good Through 600 Chp Ask Me How I Know Thats What I Run

 

I have a set of FMS 24# in the for sale area. They actually are like 26# at 43lbs pressure.

 

I have 24# in my 406. Had the same 24# in my 383. They were too big for the 383.

 

Why do a lot people think they need big injectors with more cubes?
I would think what really matters is how its tuned.

 

I agree.

 

i am not doubting anyones opinion on here. its not cubes that i am worried about it was horsepower. i see that in looking for injecotors some say up to X amount of hp. that is why i was thinking you needed a larger injector. i know enough to know that the more hp you have the more fuel and air you will need to power it hence a larger injector. i don't know everything about efi or injectors nor have i claimed to. i just want to understand how you can make the 24# work with that much hp and not be running a extremely high duty rate and/or psi on them. i am sure alomst anything is possible. please explain it to me.

 

also i want to get my car back out on the road asap so i know what the hell to buy for it

 

what year is your car

 

For the price you just can't beat the LS1 injectors from SLP, 25lb/hr @ 43psi or 28 lb/hr @ 58psi. They are true Bosch injectors, which seem to last forever.

 

TJWong and Corkvett both have extensive experience with high performance vette engines. To ignore their recomendations would foolish in my opinion. They as well as others say 24# are what you need, then just get 24# and be done with it.

 

First of all how are you calculating injector size? Are you using the standard calculation that for every one Hp at WOT that one Hp requires 1/2 pound of fuel per hours? Or otherwise known as the BSFC constant? Or otherwise known as BRAKE SPECIFIC FUEL CONSUMPTION.

If you run the calculation for injector size which is what a lot of people do using a BSFC constant of .50 and a maximum duty cycle of 80 % or .80 it would look like this:

Horsepower x BSFC / Number of injectors x Max duty cyle

For example for a 500hp engine where a BSFC = .50

500 x .50 / 8 x .80 = 250 / 6.4 = 39.09 lbs/hr

One also has to remember that this is all theoretical. In reality for a normally aspirated street engine a BSFC is more likely .40 or even as low as .30. Using those numbers for the same 500hp engine you can come up with either 31 or 27 lb/hr injectors. And at the same time if you change the maximum duty cycle to .90 you can come up with 24 lb/hr. In our F stock eliminator car which has a 355 LT1 which dyno'd on a SuperFlow engine dyno at 535Hp, we run 19 lb/hr injectors. This car runs 10.70's, depending on conditions we can "tweak" the fueling by adjusting the rail pressure up or down.

The other issue on 99% of all street engines is how long are you actually running at peak power? This is the time that you will be requiring the peak fuel capacity. It is here that is where its very important that your complete fuel system is up to snuff. I can't begin to tell you how important that is. I have had to tune several Corvettes that has had inadequate delivery. In these cases it doesn't matter what size the injectors are is you can't get the fuel to them.

The first thing I do before making full power passes on the dyno is to make moderate passes below the redline to check for proper fuel pressure or tell tale signs of fuel starvation. Once I determine that fuel delivery is adequate, full power testing can begin. We run stock 24lb injectors on Vortech or prochraged blown F and Y bodies. Granted their kits do come with FMUs, but they work. It is better in case of a blower to install larger injectors and get the PCM recalibrated. But for 99% of all NA 383 engines that I see, we run 24's on them. The smaller injectors give better tunability in the low end as compared to their large capacity cousins.

 

fwiw we just has a 460 rear wheel hp ls1 dyno tuned. It was run to(and made power to) 7100 rpm. We used 30 # ford motorsports injectors and the tuner had fits tuning them down. Also I built my 383 and 406 for power. Most guys in the know on this forum disagree with the "bigger is better" theory that most forums seem to promote. This is because many have proven it on the street and strip. If your car was my car, I would be looking for a cheap, used, set of lt4 28# injectors.

 

Go with 24#.