Max HP for stock injectors.......

85 Coupe 5.0 · May 25, 2007

I was doing a little research, and came across an interesting question. I found that stock 4.6 GT's have 19lb/hr injectors, i beleive from '96 till '04. Using a BSFC of .52 and calculating total HP, it came up to around 247HP. That may be o.k. for the '96-'98's, but what about when they went to 260HP on the PI's? By the calculations I come up with that would be too small of an injector right?

The only reason i'm really questioning it is because I just wanted to make sure i'm not going to need an injector upgrade anytime soon. With my current mod's i'm coming up with something like 295FHP. I am installing a set of comp 262's soon, and was just worried that I might be pushing the stock limit.

Stan Weiss · May 25, 2007

I get 248.46 Hp with .52 BSFC and 85% Duty Cycle. You can can run 90% duty cycle which gives 263 HP. The other thing is most modern engine have a BSFC of under .5 BSFC. So using .47 BSFC and 90% duty cycle I get 291 HP.

85 Coupe 5.0 · May 25, 2007

thanks Stan, wasn't sure on how all that worked and you definately cleared it up for me. So, i'm probably going to need an injector upgrade soon it looks like, as i'm really close to that HP figure. Probably some 21's I would assume?

four six · May 25, 2007

85 Coupe 5.0 said:
thanks Stan, wasn't sure on how all that worked and you definately cleared it up for me. So, i'm probably going to need an injector upgrade soon it looks like, as i'm really close to that HP figure. Probably some 21's I would assume?

Im not sure they make 21lb injectors, they do make 24lb though

40th GT · May 25, 2007

So wait, the stock injectors can only handle not much more than 30hp over stock?

85 Coupe 5.0 · May 25, 2007

40th GT said:
So wait, the stock injectors can only handle not much more than 30hp over stock?

It would seem so. I was curious, as the 4.6 uses the same # injectors as the 'ole 5.0's, but the 4.6 makes more power factory. So it looks as if the stockers can only handle around 290HP before needing upgraded.

My bad, i meant 24#.

Stan Weiss · May 25, 2007

40th GT said:
So wait, the stock injectors can only handle not much more than 30hp over stock?

The question is what is the BSFC of the engine and then we can calculate max. HP. Also that was at 90% duty cycle, some people will be brave and run 95% duty cycle. I have fuel injector table on my web site which will let you see the max. HP for different BSFC and duty cycles. http://users.erols.com/srweiss/tableifc.htm
I also have a calculator on my web site which lets you "Calculate Change in Fuel Injector Flow from change in Fuel Pressure" http://users.erols.com/srweiss/index.html#jcalc

XtorT'r · May 25, 2007

Bah I ran for a long time at 262rwhp on 19lbs'ers. My tuner kept telling me I could run them up to 300rwhp before they can't supply enough, so I'm on 24's now. I think 285-290rwhp is where you want to start thinking about upgrading them.

85 Coupe 5.0 · May 25, 2007

So I probably won't need injectors with the 262AH's i'm about to install then? Right now, with my 1/4 time a 3640lb race weight, i calculate around 295 Fly HP, so i'm going to be damn close with the cams.

jstreet0204 · May 25, 2007

Forget trying to calculate the injectors you need off of your calculated horsepower. It is a waste of time. You have an XCAL listed in your sig. Just datalog the injector duty cycle. If you are above 90% upgrade.

Kilgore Trout · May 25, 2007

There is some great tech in this thread

85 Coupe 5.0 · May 25, 2007

jstreet0204 said:
Forget trying to calculate the injectors you need off of your calculated horsepower. It is a waste of time. You have an XCAL listed in your sig. Just datalog the injector duty cycle. If you are above 90% upgrade.

I tried that, i'm not real familair with it though. The values listed are differnet than what i'm used to. Instead of listing actual duty cycle, it's in some other numeric form. It's the only thing I hate about XCAL2, why the hell can't the use actual percents and ms denominations. I'm going to go datalog real quick and try to find a conversion on their website. Thanks jstreet!

Mustang5L5 · May 25, 2007

four six said:
Im not sure they make 21lb injectors, they do make 24lb though

Actually, stock 2003-2004 GT injectors are 21.5#

85 Coupe 5.0 · May 26, 2007

Mustang5L5 said:
Actually, stock 2003-2004 GT injectors are 21.5#

So obviously there was an issue with the 19's being on the smaller side for the PI setup, even though that would mean that '99 to '02s had the 19's.

Max HP for stock injectors.......

85 Coupe 5.0

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