what fuel injectors are best for my set up?? please help

Casino

New Member
Nov 11, 2007
13
0
0
i have 94 mustang 5.0. it has a racing cam, headers, h pipe right now. and my injectors are shot. but i plan on doing the whole msd setup, k&n air intake, basically mild modifications. im looking to get some good injectors but i need to put them now. which ones would be good for my setup?? please help
 
  • Sponsors (?)


By racing cam, what do you mean? What are your cam specs?

Do you have stock or aftermarket heads?

More info would be helpful, but if you have a mild to moderate performance cam with stock heads and intake manifold, and plan on keeping it that way, than I would stay with the stock 19lb/hr size injectors.
 
If you put an outrageous cam in with stock heads, keep the stock 19 lb. injectors. You'll almost certainly never pass their useful range with stock heads, unless you have some sort of power adder. Take a look at the mods in my signature. I still have 19 lb. injectors with that, and although I'm certainly leaning out a bit, it shows that you can use smaller injectors.
 
Injector HP ratings: divide flow rating by.5 and multiply the result by the number of injectors. This uses a 100% duty cycle. These ratings are for naturally aspirated engines.

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

The preferred duty cycle is about 85% maximum, so for a safety factor multiply the final figure times .85.

304 HP x .85 = 258 HP
385 HP x .85 = 326 HP
480 HP x .85 = 408 HP

Remember that the above ratings are at 39 PSI. Increasing the pressure will effectively increase the flow rating. Example: a 19 lb injector will flow 24 lbs at 63 PSI, and a 24 lb injector will flow 30 lbs at 63 PSI.

See http://users.erols.com/srweiss/ to get the calculators used in these examples.

Here's the duty cycle explanation. Duty cycle is how much of the time the intake is open the injectors are turned on. The 85% figure means that for 85% of the time the intake valve is open, the injectors are spraying. The idea is that you want some percentage of the duty cycle left over so that you have some room to grow the process.

If you are at 100% and you need more fuel, all you can do is turn up the fuel pressure. That means the whole fuel curve from idle to WOT is affected. Maybe you are already too rich at idle, and turning up the fuel pressure makes it worse. If you had some injector duty cycle left to play with, a custom tune could use that where it is needed. That would not over richen the whole range from idle to WOT.