vette40th

Good Luck. I had a friend running 36#'s with a 396, 496 RWHP/automatic 4500 rpm stall, 670 lift solid roller, 12.5 to 1 compression. This was an 10 sec street car with no NOS or Boost. He ran 46 psi.
I think that formulas are guidleines, not absolute. If the 30#'s werent good enough, why do som many HiPo manufacturers use them, IE LPE, More, MTI, TPIS. They are the ones that do R&D for most of our products.

JustNO

That's also my question..! Man I'm with you.. I totally agree with you.. My friend's camaro has 600hp at flywheel and he use 30lb injectors @ 60psi.. According to formula its impossible ,but he hasn't a problem.. Ohh I'm so confused ..Maybe I can go with 37lb injectors @ 43.5 (stock psi)..

vette40th

I would personnaly call someone like LPE etc, as they and the other companies, know how these cars run. Racetronix, are a good comapny , dont get me wrong, but when it comes to motors that actually run, LPE, MorePerformance, MT!, TPIS these are the guys that have a proven history.

JustNO

Please let me know when you ask them okay?

Racetronix

Unless someone has built a certain combo before it is hard to say what the motor's BSFC is going to be so it is always best to side with caution when choosing an injector. A little larger never hurt anyone but not enough will. Why V8 owners have this obsession with choosing the smallest possible injector they can get away with under ideal circumstances is beyond me.

Many tuners jack the fuel pressure way up to compensate for undersized injectors. Some tuners fail to see the problem with running certain types of injectors over 80% DC and allowing for hot soak protection trims etc which can raise WOT fuel demands by 10% or more under less than ideal conditions. Just enough on a dyno does not cut it on the street.

FYI vette40th I have tuned many cars ranging from 15 second stockers to 1400+HP 7s SuperStreet dragsters for over 10 years. I work with factory and aftermarket ECM/PCM's. Racetronix is also a FAST AND an Accel EMIC dealer which requires quite a bit of know how. My background is in electronics engineering technology so I have an advantage when it comes to understanding the programming and vehicle electronics. Racetronix also manufactures vehicle control systems and harnesses for race cars. I also have a very good understanding of what an injector can and can not do and why thanks to our in-house R&D. Most tuners do not have the technical background and experience that Racetronix has to offer and that is why I spend many hours helping tuner shops with their problems. Please do a bit more homework before you go off passing judgment. There might be a bit more lurking behind my recommendations than you might expect.

After all things considered if JustNO wants to buy a small injector that is fine. We will provide him with whatever he settles on.

Jack
Racetronix

JustNO

If you had a look at 5th page,you could see that I'm completely trust your experince..

RobbyRob

Sorry guy's , but Jack (racetronix) is right.

JustNO

yes it should be right!

1-bad-z28

just because something works don't mean it is the best. vette40th, what could you get out of that motor if you did run some bigger injectors? Worse thing that could happen is it don't run good and you go back to the 30#ers. I think you are just so set on having 30# injectors that it don't matter what anybody tells you which is fine if you never want full potential out of what you have. I always try to keep an open mind about things and realize that what I have may not be the best I could have.

vette40th

Relax guys, My motor is running 30#'s because it was recommended by the engine builders, MorePerformance. These injectors were also recommended for the cam , GMs847 which they sell as the Crane. This was a few years ago.
There are not people obsessed with smaller injectors, why do you state that. I didnt pass judgement, I only told what MY COMBO is doing, and that 30#'s are fine for alot of HP. There are so many variables in a motor, and BSFC is a portion of the formula that is not always .50, right. Being a engineer, you should know, unless it is law, it is not absolute.
Whats the big deal here. If a injector is rated at 43psi, and you put it in and run it at 58 psi, doesnt that defeat the purpose, likewise, if you get a big injector, and have to turn the pressure down, because the tune cant get that much fuel to burn effectively, doesnt that defeat the purpose. Kinda like turning the water pressure down when washing the car cause the hose is too big, and it just rolls out. That being said, be objective here.
Like I said, my motor works, why change it. On my spped Density, if I purchase the injectors, and retuen it, that costs some money, an dthat money can be spent somewhere else, unless someone can prove to me it makes more power. Right now, the people that built the motor, and others I have sked with the same combo , use 30#'s.
So dont execute me.
you guys are pretty quick to hammer someone just becaue they dont go with your flow sometimes.
ps, do a pole of injector size. Bet most people are running 30# -24# with motors putting down 380hp-420hp to the wheels (NA)

KOSletten

I'm still using the stock injectors. Using the pulse width data from an AutoXray
scanner, during a WOT run in 4th gear, the injectors are at 60% duty cycle at
4000rpm, 81% at 5325rpm and up to 87% at 6000rpm.

My engine is making about 415-430 fwhp. The calculations show that I should be using somewhere around a 34# injector.
What would you recommend, Jack?

fastcamz28

Racetronix,

I've done a search and still have a question. Mods are in sig regarding the engine. Plan to run 100 hp nitrous shot initially and move up to 150 hp shot(motor has 217,000 on it so 150 may have to wait!). Also plan to install the Walbro 255 fuel pump. Question: should I move up to the 32# injectors (have original stock ones now)?

Thanks!
Mike

KOSletten

Here is a GRAPH showing injector pulse width and rpm. The black vertical line
is marking injector pulse width of 18.20ms at 5325 rpm resulting in a injector
duty cycle of 81%. At 6000 rpm the pulse width is 17.30ms or 87% duty cycle.

Here is a DYNO GRAPH with air/fuel ratio.

So.......will the 32# injectors be the best selection or should I go all the way
up to the 37# injectors? The car is only street driven and no more HP producing
mods are planned.
Kevin

Racetronix

81% DC is on the edge. 87% DC is too high.

If you are happy where you are at now perhaps a slight increase in FP will get your injector DC down at your desired A/F & max RPM.

If you think you need a larger injector select one which will meet your long-term goals. There is no need to buy twice. The 37's and the 42's are the same price. Both can be tuned for factory quality idle and A/F.