Was told NO Fuel Press. Reg. w/ bigger injector? Why does everyone waste their money?

[Blk91stang]

I talked to LaRocca's Performance about what fuel system I should run on my car. I will have ported stock heads, typhoon intake, and a 6lb sc-trim supercharger. He recommended me throwing out my 73mm C&L for a 80mm Pro-M, 42# injectors, and tossing the FMU. He told me that I dont need a chip burned or a fuel pressure reg (slim chances). The reason he said this is because the mass air meter will read the air coming into the motor which will let the injectors give the right amount of fuel. If this is the case than why do we need a fuel pressure regulator if the mass air meter will regulate the right amount of fuel? He said if we need it he will throw one on. What's the theory behind this? I'm tending to believe a guy who drives a 7 second car and works on mustangs 24/7. Can anyone shed some light on this topic?

 

[90mustangGT]

He is correct in that your computer uses the MAF to add the right amount of fuel, and will add enough as long as the injectors can handle it. With undersized injectors this can help give them a boost, which is a crutch, but with 42's, I doubt this is a problem. The only thing is that the computer tends to run too rich. I put a AFPR on my setup, I don't know actual numbers but by backing off the pressure a couple lbs, it made a noticable difference. By running less fuel pressure you can lean it out a bit.

IOW: A AFPR is more for tuning purposes.

 

[Blk91stang]

Yea these 42's can handle over 500rwhp, im only shooting for 340-350rwhp. Yea im going to get my car dyno tuned by him and he didnt think it was necessary at all to have one. Sounds good to me!! Fuel Injection can get confusing!

 

[redterror302]

I agree with 90mustangGT. It is usually for an engine that has undersized injectors that need a little bit more fuel. The stock fuel pressure regulator keeps the fuel around 38 psi I thought I heard. Stock 19 lb injectors max out at 60 psi, and are capable of around 300hp. So if you have around 270 or so, and would rather not change injectors, then upping the fuel pressure a few pounds would be beneficial.

When you have more injector capability then what is needed, I imagine it would not be as important. It seems as if you would be able to dial it in exactly if you have an adjustable regulator though. I would just go with what Larocca says, especially since it wouldn't be hard to swap out the stock one for another one anyway if needed.

 

[SmockDoiley]

Bull crap!! My friend was running a Mass Air car with Trickflow heads and intake with a 17 lb Procharger and that bitch ran stupid rich with the 42's. 42's are not needed for NA street duty 302's. Those are reserved for blown strokers. We had to lean the crap out of it with the FPR. JBA dynoed the car and said to step down to smaller injectors, but they also dont know anything Mustangs IMO.

 

[mustangdaren]

I have heard but a few out of the bunch running 42's that haven't had problems with the car being to rich at low speeds. That is why my 42's are still setting here in the box until I can save for a custom chip if needed. I think a FPR is good to have. When I changed my fuel pump from a FMS 110lph to the Walbro 255/340lph my fuel pressure at idle with vacuum plugged jumped from 38psi to 45 psi. Good thing I had the adjustable regulator cause I could adjust it back to around 40psi where I wanted it. I am not doubting LaRocca Performance but the way I look at it if you got the money to put a supercharger on a car then $60-$100 is a small price to pay for some tunability, especially on a blown engine where the correct air fuel ratio is critical to prevent turning your engine into a bucket of broken parts.

 

[highhorseb]

Heres some good reading on the subject.

http://www.corral.net/forums/showthread.php?s=&threadid=432558&highlight=AFPR
http://www.corral.net/forums/showthread.php?s=&threadid=139053
http://www.corral.net/forums/showthread.php?s=&threadid=433468&highlight=AFPR

 

[Blk91stang]

I know, my intentions were to buy 30# injectors and a regulator. He said why go to 30's when you can just throw on 42's which will support more power and now u can rip off that FMU and the car will drive perfect! He also said I would have to sign a waver if I want to use my 73mm C&L becuase hes not responsible if my motor blows up! lol so much for these C&L's i guess? He had about 10 used ones laying on the shelves