What are you guys doing for injectors? I was originally going to go with 30lb SVO's but the online calculators say I need a 36lb.

What lb is your injector?
What is your duty cycle?
How much power are you making?

I figured I could judge best seeing what everyone else is doing.

Thanks

 

I just ordered the 30# SVO and a variable fuel pressure regulator. I too ran a calculator that said 32 to 34.3 depending on bsfc of .45 or .5 for 440 hp. I did not know if they are talking rwhp or at the crankshaft. I figure that I would rather be a little small and push up the fuel pressure then be too big and possibly lose drivability and mileage. This is for a new 383.

I know when I logged while driving from engine builder to storage I was seeing pulse widths of 18-20 ms. while going from 25 mph to 45 down a side street. I know I was slightly rich, too.

In a couple of weeks I will have results to report.

 

When running 30lb SVO's, my duty cycle was around 90%. So I went to 36lb's for the new motor.

 

I'm using 30# injectors but I should have got 36#.

 

Hmm ok...seems like 36's maybe a good choice than.

Anyone else?

 

I use 48# but according to the formula I need 50's but they are hard to find at a good price. Use the formula IFR = HP * BSFC(0.5) / 8 cyl * 0.8(suty cycle) So that is

Injector flow rate = (HP * 0.5) / 6.4

flow rate is in lbs per hour.

You could try this site too
http://www.smokemup.com/auto_math/fuel_injector.php

You have to know what your expected HP will be. That is crucial

good luck

 

Calculator says I need 36.4lb injectors...pretty close.

 

I run 30's in my 396 w/ no problem and I'm still rich. Fuel trims must be off but if Iever spray then 36lb's would be the choice for me.

 

See thats what I dont understand...people are running rich or have plent of room with 30's but the calculators say 36's which is it?

 

30 SVO on my 383. I dont know the duty cycle, but they arent close to being maxed.

Ford rates their injectors at a different PSI than chevy. I think the correction factor is x1.2, but no sure about that...

In other words a 30lb SVO injector is really like a 36lb chevy...

 

The online formulas for injector sizing are VERY conservative. They assume a brake specific fuel consumption (BSFC) of 0.50#/HR/HP. For an N/A application, that is probably too high. I have my actual engine dyno data, and I ran 0.45#/HR/HP or less on the final tune. I suspect that you might even find some well tuned engines are able to achieve even lower BSFC's... but I think that 0.45 for a weel tuned NA application is a good assumption.

For running a dry nitrous setup (300HP N2O on top of a 500HP N/A engine) I saw BSFC figures of 0.52#/HR/HP. Obviously, N2O only affects choice of injectors if you are running a dry system. Wet, you size the injectors for the N/A HP, and add the fuel for the N2O elsewhere.

Then you look at duty cycle... they recommend 80%. Each type of injector - ball (OEM RP), pintle (Bosch/SVO/Denso/etc.), disc (Lucas) - will have a slightly different duty cycle limit, and there will be a difference between high impedance and low impedance/peak & hold injectors. Maybe try 90% duty cycle.

Also... use flywheel HP to calculate fuel demand. RWHP means nothing to the calculation formulas... my losses were only 12% with an M6 and almost 20% with the A3, so you have to use flywheel HP.

Bosch/Ford/SVO/etc. injectors are GENERALLY rated at 2.7bar = 39.15psi. That compares to 3.0 bar = 43.5psi for the OEM RP's. The consequence of running the SVO's at 43.5psi is an increase in flow of 5.4%.... so the factor is 1.054X, not 1.2X.

As far as injector size, if you are on the border at 30psi, either up the fuel pressure, or go to 36's. There is really no downside with doing this. The stock PCM should be able to drive the 36's at the low, sub-1mS pulse widths required for idle.

If your injectors are too small, they obviously can cause lean out problems and loss of peak HP. I'm not convinced that these problems, caused by excessive duty cycle, will even show up in the 1 or 2 seconds that the engine actually runs at peak fuel consumption on a dyno pull. Run them for extended periods of time, and they will overheat, start to flutter, and start to wear out. Eventually, this is going to catch up with you. Why not bite the bullet and opt for "fat" sizing rather than "tight" sizing.

To actually answer your question, I run Bosch 64's at 4bar (58psi), making them 74's. And with the full shot of juice, duty cycle is about 67%. But that's with the MoTeC computer driving them. And the car idles like a kitten, at 800rpm, and will pass rolling emissions with cats.

 

Thanks you fred about fixing my adjustment factor for the SVO injectors. I said i wasnt sure, and i wasnt! 1.054 it is!

 

No question, go for the 36#. BTW: I think Bob Kennedy has a nice price on some Siemans 42lbers he picked up if you want to check that out.

Rich Krause

 

Thanks for the extensive clarification Fred. Covered everything I needed to know.

 

Thanks, Fred

I was worried that I made a bad decision to get 30# svo instead of 36. But if I use .45 bsfc and 90% duty cycle for 440 hp I get < 28# required. I was hoping that I might run the fuel pressure lower then 43.5 and this says I can.