Injector size ???????

jc91sc

Registered User
I'm upgrading my 91 SC AOD FINALLY and am tryin to see which size injectors I NEED to go to. I have 36# injectors from a 95SC I'm putting in, but I don't know if they'll be enough. Here's my list of mods so far.

CAI
73mm C&L
70mm BBK (thinkin of going 75mm real soon)
ported IC tubes
ported inlet plenum (91 Blower)
10% OD
(raised SC top coming soon)
IC fan
Trans-Go shift kit
2.5in Tru-Dual exhaust (ported manifolds coming soon)
Magnecor 8.8mm wires


Future "Want-To(s)"
Ported and Polished Heads w/roller rockers
94-95 Blower w/S porting
aluminum driveshaft
Ryan's U/D Aluminum pullet set (FULL SET)
3.73 Rear



Thanks for the help fellas (and ladies if it applies):D
 
They are fine, I have those in my car and it is in low 13's. You will need to step up to 42's at least if you do internals and look for real power. I am kind of pushing it.
 
I wouldn't quite go that far. 30's will make 300hp at 100% duty cycle but I wouldn't want to do that. Now if we could crank up pressure and keep it that way without the computer messing with it then you're all good. I would much rather have 60psi or even more pushing through my injectors but this computer keeps cranking it back a little at a time.
 
injectors

Yup,that's 300 FWHP.And yup that's at 100% duty cycle.But how often and for how long are you actually turning the rpm's to produce that much hp?My peak is at about 4,700 rpm's.By the way my a/f ratio is at 12.3:1 at max hp output.I think we get too anal about injectors and WAY oversized xhaust systems.That's my .02.
 
Ya, I would just err on the conservative side for the duty cycle because it also heats up the fuel and that causes loss of horsepower. Now cranking up the pressure I like, Mustangs do that with there 19# injectors and make them work for supercharged apps. I would like to be able to crank my pressure up to like 80lbs. That would make the ijectors work like 50# injectors but not have the driveability probs like big injectors cause. Can a chip or the EEC tuner adjust for fuel pressure mods too?
 
If you change the pressure, you would just need to adjust the injector size. The computer does not measure fuel pressure and the injectors react linearly with pressure.

Aaron
 
Anytime you run injectors above the 80% duty cycle you stand the chance of the sticking open thats why manufacturers rate the injectors at 80% that is the max safe duty cycle.
30 lb. injectors are capable of supporting 275 HP safely and thats about it.

Yup,that's 300 FWHP.And yup that's at 100% duty cycle.Front wheel HP? Surely you meant crankshaft HP. :confused:
 
No, haven't dyno'ed it yet. Based on 1/4 times and mph and where it is now I would guess about 360 hp. But may be a little more if I can get the upper end of the rpm range working right.
 
I may be a little high on that hp number. I just looked at David and Chris's numbers and I don't think I am quite there yet. Seeing their numbers makes me think 330hp, which would probably be 410 or so at the flywheel.
 
I think my biggest prob right now is that my power drops off (or flattens) once it gets above 5000 rpm and doesn't use the cam's full potential. I really think the MS Inlet plenum would help that out a lot. Mine is ported pretty good right now but I can only do so much. Problem is, that's a lot of money for me right now.
 
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MIKE 38sc said:
Anytime you run injectors above the 80% duty cycle you stand the chance of the sticking open thats why manufacturers rate the injectors at 80% that is the max safe duty cycle.
30 lb. injectors are capable of supporting 275 HP safely and thats about it.

Yup,that's 300 FWHP.And yup that's at 100% duty cycle.Front wheel HP? Surely you meant crankshaft HP. :confused:

FWHP= FlyWheel Horse Power
 
If you follow up with your "want to"s...

Something like a Dr. Fred 520 cam would make a lot of sense. Then I would recommend the 42's with a tuner or custom programed chip. That head work won't do as much without those.

Lee
 
Aaron, hate to tell ya put you're probably around 280rwhp. That's where I was stuck for almost 2 years with stock based plenums. That's why you're goes flat up top (mine died around 4800 now it pulls to 5500 easy... I get scared going much above that since it's at 17 PSI with the 23% OD).

And the stock 30# injectors will make 260RWHP and that's it. There's quite a few people that have run them and that's all they'll make. Usually, it blows apart before bigger injectors are installed to see what it could really do. The stock 94-95 injectors are really 34.3# and good to about 280-285 RWHP. I'd seriously recommend 38's before installing ported heads and a better blower.

And actually the head work will do more than a cam. The stock exhaust ports blow so bad they're a major limiting factor. The stock cam isn't all that bad compared some other stock cams. I made 260 RWHP and 350 RWT with just ported stock valve heads, a stock 94 blower, 190 lph fuel pump, 70 mm TB and a catback exhaust. Probably a little more if I'd put bigger injectors in.

And remember, Muskrats have 8 injectors to our 6. So they're 8 - 19#ers deliver 152# of fuel total and our 6 - 30#ers deliver 180#. Many V8's can run 8+ PSI boost on just 24# (192# total) and incredible boost on 30's (240#) or 36's (288#).
 
Blackbird SC,Ive seen the 34.3 # number floated around for a while(didnt you flow test the 36# rated injector?).Have you flow tested 38 or 42 lb injectors to see what they really flow?
 
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