fuel injector recommendation needed

[Veight7]

I'm finally at the stage of needing to buy my injectors for my project. I'm thinking I need at least 36lb/hr maybe 42lb. I will be running this car off megasquirt

I don't think it makes a difference but just to give a much info as possible, this car is going to spend most of its time doing autox and road tracks.

Specs:
306 with girdle
AFR 185s
Fti cam (lost the spec sheet)
Victor jr. efi intake
1 5/8 long tubes

[sspstang]

Street or track car? Street 36s track 42s.

[HOOCBB]

So much more info is required before a ballpark estimate can be made.

What is the projected HP? Boosted? N2O?

Fuel pressure makes a huge impact on the injectors as well.

If you will be running at ~43 PSI and pushing 300 HP at the crank, you only need 24 lb injectors.

If you are projecting to push 500 HP (at the crank) at ~43 PSI of rail pressure, then you would need 42 lb injectors. You could use 38 lb injectors if you increased the rail pressure to ~46 PSI (theoretically).

[Veight7]

It will see some limited street driving possibly on the way to some event around DFW but 99% track use car.

And I'm going for around 400 hp at the wheels and I have no clue on fuel pressure but I was planning to start at about 43psi

[HOOCBB]

It will see some limited street driving possibly on the way to some event around DFW but 99% track use car.

And I'm going for around 400 hp at the wheels and I have no clue on fuel pressure but I was planning to start at about 43psi

Assuming upper 400 HP range to achieve 400 at the tire...at 43.5 PSI and 80% duty cycle, 36 lb injectors would fall a little short. I would run with the 42s and back the duty cycle down in the tune. Better to have more capability than not enough.

Also, run an adjustable fuel pressure regulator so you can fine tune the fuel system a little more.

I am concerned that a 306 may not achieve that HP level with the setup you have listed. I may be wrong though, as I don't have a lot of experience with pushrod 5.0 performance.

BTW, my numbers are based on the info at this site.

http://www.rceng.com/technical.aspx

In addition to the info above, Holley claims higher HP capabilities with lower flow rates. It looks like they use either 90% or 100% duty cycle to achieve the higher numbers.

http://www.holley.com/data/TechService/Technical/Selecting%20A%20Fuel%20Injector.pdf

[sickpony]

32's ?

[FoxBodyNick]

That build would perform fine with 30# injectors. I dont see why you would need 36# or 42# unless you were spraying it and in that case your BSFC will raise around .6. There are plenty of 331 NA combos running fine with 30#.

Injector Rating x # of injectors x Injector Duty Cycle / (.5 for N/A) Brake Specific Fuel Consumption = Maximum Horsepower

30 x 8 x .9 / .5 = 432 HP (naturally aspirated) at the crank

His build is going to probably make a little less or right at 400 at the crank but this is without knowing his Compression Ratio and Fuel he is using and the injectors at 90% duty cycle which is still a safe maximum tune. Back it down a tad to 80% and he will still have enough injector for this combo..

[Veight7]

Assuming upper 400 HP range to achieve 400 at the tire...at 43.5 PSI and 80% duty cycle, 36 lb injectors would fall a little short. I would run with the 42s and back the duty cycle down in the tune. Better to have more capability than not enough.

Also, run an adjustable fuel pressure regulator so you can fine tune the fuel system a little more.

I am concerned that a 306 may not achieve that HP level with the setup you have listed. I may be wrong though, as I don't have a lot of experience with pushrod 5.0 performance.

BTW, my numbers are based on the info at this site.

http://www.rceng.com/technical.aspx

In addition to the info above, Holley claims higher HP capabilities with lower flow rates. It looks like they use either 90% or 100% duty cycle to achieve the higher numbers.

http://www.holley.com/data/TechServi...20Injector.pdf

I've already got an Aeromotive A1000 FPR for the fine tuning.

I don't know if I will hit 400 either. I'm guesstimating from others dyno sheets I've seen on other forums. They are claiming to be running 302s with AFR 165s and smaller intakes claiming 350RWHP but it IS the internet so can't take it for 100% truth.

Thanks for the links. I'm new to EFI stuff so I'm learning as I go.

[Veight7]

Also I know this is lacking some build info. Unfortunately this is all the info I currently have as I had all the work done almost 4 years ago and its just been sitting in the garage as a short block and parts with a lack of funding I kinda forgot a lot of it . I'm going to get it all put together this weekend or the next and I'll be able to check compression and stuff but I do plan to run it on 93 Octane if I can get it to tune out

[FoxBodyNick]

your typical 302/306 AFR/cam combo will make 310-330 rwhp at stock compression. Some of the ones you might see making more power are 10.5:1 motors and such. Thats all I can assume.

[Veight7]

your typical 302/306 AFR/cam combo will make 310-330 rwhp at stock compression. Some of the ones you might see making more power are 10.5:1 motors and such. Thats all I can assume.

Yep that's all I can do too is assume. Going off these work sheets there is no reason I would need 42# for sure and you're right 36# might be pushing it too, but I think I might get some 36s for the initial tune cause I can drop the duty cycle and if it's still too much I can swap them out for some 30s. I would rather it be running too rich than lean. If the numbers don't turn out like I want I'm going to be converting to 331.

[FoxBodyNick]

347*

[Veight7]

347*

lol yes, I've been up since 4AM

[OsoSlow]

24lb or even 30lbs inj. Will be plenty.... hell I'm running 30lb inj on my 347 on. 150shot

[FoxBodyNick]

30# on a 347 with NO2?? you should need more injector than that! lol you might be leaving quite a bit on the table.