What size injectors?

[bullitstang1313]

What size injectors do you think I should use?
Here is my setup
Intake: I currently have a Trick Flow Street Heat but was thinking of upgrading to GT40
Cam: I currently have an F303 but might upgrade to custom
Heads: Currently I have ported stock with 1.6 FMS roller rockers but will be upgrading to AFR 185's
Shortblock is a freshly rebuilt 5.0 with new pistons, bearings, and rings.
I have bbk equal length shorties, off-road h-pipe, flowmaster dumped, underdrive pulleys, and a MSD 6AL with blaster coil. Should I go with 24lb injectors or step it up to 30lb injectors?

 

[TomCat]

I think you'd be fine with 24s.

 

[Grn92LX]

Going from a tfs street to a gt40 isn't an upgrade, thats a slight down grade.

Afr 185's, custom cam, and at least an rpm intake (i'd do an rpm II or a holley personally and make some good power) on a 306 will do anywhere from 325hp-400hp depending on the cam and how high you rev. You want 30's. What pistons are you running? Don't forget to add in a mandatory valve spring swap.

 

[bullitstang1313]

I'm running hypereutectic pistons and I have already upgraded the valve springs on the stock e7's in order to be able to handle the higher lift cam, but I was just wondering if 30's would be too much for my combo. Eventually, I'm going to start building a 331 stroker with forged internals and put a kenne bell on top, but that is going to be awhile so i'm just trying to upgrade what I have now.

 

[Grn92LX]

30's aren't too much. And you aren't using the 'upgraded' valve springs from your E7's on the afr 185's Your valve springs WILL be picked by the cam grinder after the cam is designed. Budget in an extra $150 or so for that, no way around it.

I told you, done right and you can see 400rwhp. How can a 30lb be too much? You may have some idle problems but wyat do you expect when you rely on a "calibrated" maf only to do the job?

EDIT- the kenne bell blower you can only use a stock or gt40 style intake. Obviously for a blown 331 you'd want a ported gt40 lower. I'd do a better intake and run a centrifugal blower but its too far ahead to plan for you yet. You WILL be upgrading injectors for the blown 331 as well.

 

[just4bob50]

if your going to have someone tune it with a chip go with the 42lb injectors. that way you wont ever have to buy them again. A good tuner will have the ability to reduce the duty cycle of the injectors to fit your application. If your going to tune it yourself id go with a 255 pump and an adjustable pressure regulator and 24psi injectors. oh buy the way i havent seen one test yet where the street heat intake out performed the GT-40. All the ford mags consider the GT-40 the intake to beat for street level intakes.

 

[5spd GT]

If you have a tuner for the combo your currently making you would be fine with 30's. If you don't have someone to tune then get the 24's. Much more forgiving and they will give you enough fuel.

Get the AFR 165's. 185's are a bit much...plus you will likely have to flycut your pistons to let the 2.02 valves clear the reliefs.

Your intake is fine for now as far as flow is concerned.

Get 24's right now...

I have 30's...they are to much. I'm around these cars quite a bit...I'm pretty familar with rich/lean conditions, that's for sure

If only I had the money that my injectors had (runs "rich")

 

[9 Deuce GT]

I have to disagree that 30's are too much right now. I have had 24's and 30's, and with a properly set up mass air system, my car runs perfect with out a tune. Plus, if you are planning on a 331 soon, get the 30's now.

 

[5spd GT]

9 Deuce GT - I thought you were experiencing hot start problems/rich idle. My car runs just fine with 30's but that is the limit on injectors (without a tune) that should be put on a h/c/i. I was simply saying for now the 24's is what he needs. If he is getting a 331 soon (it will have to stay N/A though) the 30's are obviously the wiser choice.

I get good gas mileage and it runs fine but I have a rich idle and to much cranking fuel.

 

[txstang84]

what kind of pistons are in your block now? you mentioned new ones...in which case the 202's in the AFR 185's would not be too much. the 165's will give great low end and mid range, but the 185's will provide any top end you may be seeking. but, 5spd GT does have a point, if your pistons are not cut for the big valves, better just go with the 165's.

and 30's would be more than enough for you, but if you can get it tuned, you should be fine. a friend of mine battled with his 30lber's on his motor, but after alot of farting around with the fuel pressure, timing, base idle setting, etc, it finally got alot better...admittedly, he still should get a dyno tune though.

edit: just thought about something else, if you still have the FRPP 1.6 pedestal mount rockers, you might as well stay with a pedestal style head (Y, X, or Z GT-40's, Edelbrock performer 5.0, AFR 165) unless you want to upgrade your rockers too...the 185's if memory serves are only available in stud mount versions...

 

[9 Deuce GT]

Maybe it's due to the fact that the Pro-M 80mm I bought has their elbow system, but my car now runs and idles perfect, just like it did when I switched backed to the 19's and stock MAF to test it. When I had the ****ty C&L MAF, it would not start. The Pro-M seemed to cure all of my problems.

 

[Grn92LX]

Afr 185's are available in pedistal, though stud is the right way to go. If you have an aftermarket piston with deeper reliefs, use the 185's. What brand hyper pistons are you using?? Go with 30's now and you can use them on your n/a 331 until you get the supercharger for it, then its time to step up to a big injector.

 

[just4bob50]

Again buy more than what you need now and you wont have to spend the money over again. I know that i have enough fuel for 500rwhp , and im no where close to that now, but when i put my heads and cam on the motor along with 3 more pounds of boost i know that all i need is the money for the retune. Plus ( more than enough ) usually only costs a little more than ( just enough )

 

[vristang]

Using the 400hp estimate by Grn92LX, I ran some numbers.

At a duty cycle of 75% and pressure of 39psi you will need 29lb injectors.

At a duty cycle of 95% and same pressure you will need 23lb inj.

Running the lower duty cycles will prvide longer injector life. However, if you get too low, the metering will become erratic as the valve will be unable to fully open, before it needs to close again.

 

[just4bob50]

Almost all the tuners i talked to reccomend not going above 80% duty cycle to avoid injector failer and as a result motor damage.

 

[5spd GT]

He is not going to get 400rwhp with that 302. That is what I was talking about. A 331 if done streetably (with accessories) isn't going to see 400rwhp. The 30's are better for the 331 for sure.

 

[vristang]

Almost all the tuners i talked to reccomend not going above 80% duty cycle to avoid injector failer and as a result motor damage.

At 39psi and 80% duty cycle...

27.4lb injectors.


Definitely go with the 30lb.

36lb injectors will put you at nearly 60% duty cycle.

That is making the assumption that this combo will make 400hp.

 

[vristang]

I mis-read an earlier post. My excel calculator is set up for flywheel hp, not rwhp.

If anyone can provide an hp estimate for this combo, or any other, I will run it again.

I could provide the formulas as well.

 

[just4bob50]

heres something to consider, both the SVT cobra's and lightnings are OEM 42lb. injectors. I cant tell you how many times Ive seen my friends buy and rebuy parts because they didnt keep in mind what they wanted the end result of their motors to be.

 

[5spd GT]

just4bob50 - Yeah but from the factory (OEM) those cars are tuned to those injectors. So they give them enough fuel for sure. There not going to borderline it and the whole computer/maf/etc is all tuned to work together. It is different than even a dyno tune IMO but a little.