Is there a formula I can use in order to calculate the approx injector equivelant at higher pressures than normal? IE if I take an injector that is 24lb and I increase the pressure by X number of lbs how can I calculate what that injector is then equivelant to at a normal pressure?
Thanks,
Roy

 

well. You have to take into account manifold pressure too..

A injector running at 50psi at 100kpa, will be 40psi at 10psi boost. (relitive to the manifolds internal pressure). Basicly, your not rasing the pressure, your just keeping the fuel pressure to manifold pressure ratio the same.

Thats why you should have a 1:1 fpr. A lot of people think

So, you have to calculate any excess pressure after the 1:1 raise.

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

-- Joe

 

Thanks, that is exactly what I needed. I know you are a proponent of my ditching the fmu, converting to speed density and controlling everything through the computer. I am certain that is a much more accurate way to control the fuel. One of the reasons I went with a supercharger on this project rather than building a new bigger motor though is the ability to recoup my investment. Someday when I sell or change this car again (which I always seem to be doing) I want to be able to easily remove the system, return it to NA and resell it rather than having to give it away with the car. This is not a daily driver for me, I could car less about driveability, I just want it to go like hell when I hit the pedal. So I am trying to set it up with a reasonable tune using the FMU and spark retard that comes with the unit. I can burn new chips for the stock MAF setup thats not a problem. All the research I have done seems to indicate that you are correct my 24 lb injectors are not going to feed this stout 355 even at 6 lbs of boost. My current direction is toward a set of Bosch 30s at around 45 psi stock boosting them up to 85 or so at full boost. So operating under my less than ideal parameters (geesh I know I am going to get a lecture here ) does this sound about right for a motor that is going to be in the 4-450 hp range?
Thanks
Roy

 

If you look at a post I made a few days ago regarding fuel pumps, check out the issues with raising the pressure above 65psi. I know the "boost pump helps", but as you raise the pressure the volume goes way down.

My iron headed setup was prolly around 460-480hp. I used 36# injectors and they went static around 5500rpm at 65psi.

30#'s might work with the FMU though. Really gotta experiment. Every engine has a different BSFC.


-- Joe

 

Yes, there is, and I use it very often in my tuning efforts.

New inj flow rate = SQRT(new fuel pressure/old fuel pressure) x old inj flow rate.....

Example:

You have a 24#/hr Ford Racing injector and you want to know what it will flow at 52 psi fuel pressure.

First of all, you need to know that the rating of 24#/hr is gotten at 40 psi fuel pressure. Now we can solve this equation:

new flow rate = SQRT(52/40) * 24

new flow rate = SQRT(1.3) * 24

new flow rate = 1.14 * 24

new flow rate = 27.36 #/hr

done deal!!!!!!!!!!!!!!

 

K , I went to this site and did all the calc's . Maybe I am just nieve but . After this I have some important Q's

I did the calcs ......

Horsepower x BSFC / 650 x .60/
# of RC injectors x.80 ( duty cycle ) = 6.4 = 60.9375 lbs /hr



Convert cc/ min : 60.9375 x 10.5 = 639.844 cc/min



INJ size (lbs/ hr ) , 60.9375 x ( 80 % duty cycle) / .60 BSFC

= 80.25 hp x 8 injectors = 650 h



Fine ....it says I will need 60 lb injectors to hit these numbers. But I bought a BBS turbo kit . They claimed 650 hp with a stock L-98 ..... either this math is off ....or I am missing something. Becasue there are guys here running around them numbers ....with a lot less injectors. I used a 80 % duty cycle and the .60 BSFC fuel constant , instead of the ,50 ( for N/A motors )


any input .... I figured I'd tag it onto this thread to leave the link and the above relivant conversation

 

I haven’t looked at their advertising, but “with a stock L98” probably was intended as “with a stock engine with additional fuel added and timing taken away as appropriate.”

If I remember right, on the test car he actually added fuel by using a hobbs switch to activate what basically amounts to the fuel side of an N2O wet setup to add the additional fuel.

Secondly, 650hp is a bit ambitious for a stock L98, it would take about 20psi and some serious race gas or better to pull that off and I’m not sure what would let go first under those conditions. I’m would suspect that the 650hp refers to the maximum amount of air that the turbo supplied with the kit can move under ideal conditions.