What is a good baseline to know what size injectors to run?

You can see the mods to my motor in my sig.

Right now I have a set of 24lb/hr and 30lb/hr injectors.

Some people are telling me to run the 24's and some say at WOT the 24's will fall flat on their face.

Any thoughts on this?

The multiplier I found for injector size stated the 30's would be used for up around 500hp. That seems to be a bit much hp for a 30lb injector, although, I could be totally wrong.

 

i dont think u will see enough rpm's with that tpi to warrant 30#'ers

24 should be fine.

 

www.geocities.com/scwizzo/graph.jpg

There's a graph I made to show how much horsepower injectrs can take. 24lbs can handle around 350 hp at 85% duty cycle before they get above that. 24lbs should be good for you.

The equation you use to find out is http://www.geocities.com/scwizzo/equations.html

 

That is great information. How about throttle body size? Would you recommend stepping up to a 52mm or staying 48mm?

 

I don't think you'll see an increase going bigger. The 48mm can handle around 635 cfm pretty easily.

Your engine is maybe seeing 520-550 cfm. Usually people don't step up to bigger throttle bodies until they hit the 400 hp mark, or if they have a blower. A 52mm can handle about 770 cfm, in my opinion it'd be overkill.

 

I'll let you know more after today's dyno session. I'm putting down 322RWHP with 24# injectors and currently at 75% duty cycle and running rich. So when the final tune is in I will post the RWHP and injector duty cycle. How efficient your engine is and the BSFC has a part with the injector size.

 

That would be awesome. I will wait to see your results!

 

When I built my 406 I used a stock TPI with ported stuff and I programmed the 90 F-body computer for 24lb injectors.. it ran with a serious bog so I tried increasing the fuel pressure this helped but it still had a bog.
I then installed 30 lb ACCEL injectors and this cleared the problem right up.. I know I could use more in the way of TPI tubes, manifold, etc but the injectors made all the difference in the world.

 

I am going to take a guess and say that your 406 is putting out a ton more horsepower than I am with my 350.

With my motor combo I think I am going to be in the window of 350chp. I have had one engine builder tell me to run 24# injectors and another told me to run 30# injectors.

The one that told me to run 30# said I should run those because at WOT as I pull into the higher rpm ranges the injectors will pretty much be saturated and it would hurt my performance.

The one that told me to run the 24# injectors said that I will only exceed the limitation of the injector if I build the motor more or run NOS or a super charger. I have no plans of doing either so I am really leaning towards staying with the 24's. Regardless, I do have a set of 24's and a set of 30's.

 

I can tell you I'm up to 330RWHP with #24 pound injectors on my 350. I know the duty cycle was under 80% but will get the details later.

 

At 85% duty cycle I made 230fwhp in my V6 with 22lb. injectors. (and thats spinning up to 6200) So with two more injectors, and all the injectors 2lb/hr. bigger, I'd say 24lb should be plenty, especially since you have TPI so you shouldn't be spinning it nearly that high.

Shawn

 

I am still running my 24#/hr FMS injectors in my 395 cu.in motor, but at 52 psi fuel pressure.

With your current mods, 24s is all you need, and you should not require a Eprom change.

If you install an AFPR and run the 24s at 56 psi (where they will flow about 28#/hr), you should be able to make 400 Hp at the flywheel.

 

This all some great information. I did forget to list in my sig that I do have an afpr. I suppose I will be putting the old 30#'ers up for sale

 

what brand are they.

 

My 30's are FMS injectors.

 

how much u want for them?

i need a second pair.

 

I sent you a PM

 

Further update. As stated above I'm putting down 330RWHP. That is with the 24# injectors at 43.5 pounds, and 80% duty cycle at 5700 rpm. So I still have some wiggle room as I can crank the pressure up to 50#. However with the next go around I will be putting in the #30 pound injectors. Looking for a big horsepower increase and I'm at the edge of the 24 pounders now.