Confused with Injectors and Fuel Pressure

It is a good question

My first question is, are you running the Ford Racing 302 engine with the GT-40 heads?

If so, that horsepower rating is done with no accessories or drivetrain (for sure) losses factored in. So in reality, you could be seeing 20-25% bhp loss.

So if that is the case, you are just fine.

Now, on to fuel pressure calculations. Joe (jrichker) typically post:

A 19 lb injector will flow 24 lbs at 63 PSI, and a 24 lb injector will flow 30 lbs at 63 PSI.

Take your brake specific fuel consumption number (.4-.6)and multiply it times the injector rating in pounds per hour. Then multiply that by the number of cylinders.

19/.5 = 38, 38 x 8 = 304 HP
24/.5 = 48, 48 x 8 = 384 HP
30/.5 = 60, 60 x 8 = 480 HP

So we can work this backwards.

If 63 psi on a 19 lb injector can support the same horsepower of a normal pressured 24 lb injector, that is a 61% increase in fuel pressure for 24% more horsepower support.

So anyways, 63-39 (assuming 39 psi is the baseline pressure), is 24 psi.

There is an 80 horsepower difference between what 19 lb and 24 lb injectors can support.

80/24 = 3.3

So for every 3.3 added horsepower support, one needs an extra 1 psi.

Joe will help make corrections and this is not a set formula that I know of, but it is just working with what is already stated.

Good Luck.

From what i came up with you need them to be 26.9lbs.

I got this off of another web site. Its the formula for finding the injector size.

345/8=43.125
43.125*.50=21.5625
21.5625/.80=26.953125

Here is the web site to. http://www.flowtechinduction.com/technical.htm

That formula is quite accurate as well

However, I am assuming that the 345 HP rating he is referring to is without drivetrain and accessory losses.

He would need to be in the 300-310 rwhp range for 345 bhp with accessories factored in.

5spd GT said:

That formula is quite accurate as well

However, I am assuming that the 345 HP rating he is referring to is without drivetrain and accessory losses.

He would need to be in the 300-310 rwhp range for 345 bhp with accessories factored in.

Click to expand...

That is true. I just done it based off the known hp.

Now that we know your engine set-up...

You are just fine

It is a very close set-up to the '93 Cobra engine. They had GT-40 heads, Cobra intake, larger maf, etc. They come with 24 lb injectors from the factory, and they have it set-up with some good slack.