Hey, how do u figure out what size of injectors u need?

I have a 412 small block (0.30" over, 3.8 stroke) 9.3:1 comp with je forged pistons and AFR 195cc heads, eagle 4340 6"rods, 4340 stroker eagle crank, comp cams 276HR-14, splayed billet main caps, arp hardware, Pro Magnum 1.6 RR's, hardened pushrods.

Thinking on Mini ram if I dont stay a LTR setup.

Gunna run a ATI Procharger at around 15psi. Cars my daily driver.

Any help would be apreatiated, thanx

 

it really has alot to do with the kind of engine management you intend to run.

 

U mean computer set up right?? This is my first forced air induction project. So I am still learning as I am going.

http://www.speedtoys.com/~bort62/7749/Main.htm

this is the one I was planning to use.

 

More then anything it depends on the HP that you make at the crank… any estimates?

 

In all honesty, I really dont have a clue what it will be putting out. Anyone got DD to run it through and find out?

I was hoping to find someone with a simular setup so I would be able to see what they're running.

 

If I recall the right numbers. injector flow X 2.04 = hp so 24# inj. be good too 48.96 HP each x 8 = 391.68 for a v8. there are alot of other things to concider as well like max rpm

 

I just was flipping through my camaro performance book because I was looking at injector sizes for forced induction. They gave a formula of injector size x 16 =total supported hp, so 88 tpi's formula sounds dead on as well.

 

The Syclones ran 15 PSI, and used 30 PPH injectors. They were setup for torque and shifted at around 4,500 RPM. If you want to run your engine up higher RPM wise then you need to run a large injector yet since you'll have less time for the injector events to occur in. Just to make the numbers easier, say they use 30s and shift at 4K rpm, 6K is 50% higher so you'd need to run 45s.

While a N/A engine might run .5 BSFC a turbo motor is going to be closer to .55 or possibly .6. As you crank the boost up you have to waste a certain about of fuel for in cylinder cooling to keep the motor out of detonation.

 

That would approximate a BSFC of .5 at 100% duty cycle.

You probably won't see a BSFC of .5 on a blown engine and you don't want to run it at 100% duty cycle. I would plan on about .6 and 80-85%.

Making some guesses, if well built and well matched parts that 412 and those heads could be capable of making around 535hp at about 6000rpm. With 15psi that works out to be about 800hp without an intercooler and 960hp with one (assuming 65% efficiency for both the compressor and intercooler). I'd assume that you're choosing a supercharger actually capable of moving that volume of air at 15psi.

No idea what any of this has to do with which fuel managment you run.
Assuming that all this comes together like that, at a BSFC of .6 and 80% duty cycle that adds up to 75lb/hr w/o an intercooler and 90lb/hr with. If you're not building the thing that serious (ex, most LTR intakes top out in the 4-500hp range NA, which would adjust your total downward 10-25%, aren't going to run an exhaust that will be free flowing enough for that…), then adjust those numbers downward accordingly. Since I'm not building the engine or putting it together in the car I can only guess what you'll actually end up with.

 

And here I was thinking only 42# like the Lightnings

Maybe I will stay LTR setup now, I was wondering how I was gunna get by Emision inspection anyways without the EGR.

 

attach the egr to the back of the intake manifold and they'll be none the wiser. A cam with more overlap then the stock cam will have more egr action anyway.

 

Will that large of an Injector work ok with the comprter?

 

I doubt it. Most injectors above 50lb/hr are low Z which would require a different injector driver. I can make up to a 77lb/hr high Z (saturated) injector, but I haven't seen anything even close to that big work with a factory ECM

 

So how big of an Injector can I go with the GM 1227749 ECM?

This news is totaly putting a damper on my excitement

 

I'm sure Bruce (Grumpy) will jump in here if he sees this but… Stock you can only use high Z injectors which have only been made up to 50lb/hr. Like I said before, some can be modified to flow up to about 77lb/hr. I personally have never seen a stock (obviously with custom chip) 749, 730, 165… run well on a V8 with larger then 30lb/hr but I've never tried to run larger myself either. I have seen 36's run but never with a good idle, but I don't know if it is an issue with the tuning or injector driver speed or what (36's top out at under 500hp at the crank). Most people blame this on larger high Z injectors being slow but I've seen 36's, 42's, 50's and 77's run perfectly with aftermarket ecms and mustang guys run 36's and 42's with their stock EEC IV ecm's all the time.

I have seen those ECMs work on smaller 4 and 6 cylinder engines with larger injectors, and there are people that have them working with larger low Z injectors after replacing the injector drivers.

I Grumpy has one modified like that that he's using to control 6 55lb/hr low Z injectors plus some assortment of additional 36lb/hr injectors mounted in the intake plumbing (I haven't been keeping track of the details lately)

 

Stay tuned, there is news pending on some new injectors coming out in the not too distant future.

I've been running 55 PPH injectors, with a modified 749, modified meaning the injector drivers have been changed. I've also been running a 7th injector full time, which puts me at a 60 PPH injector size, with my little 231 CID engine.

ATR makes and addition injector set-up. It normally running only part time and is boost tunable. I've found used ones for a little over $100, and depending on plenum design can mean adding alot of fuel if you want it.

While some poopoo the 7th injectors, I use mine for cooling the intake charge. And have eliminated the Intercooler since going with this set up. While I do suffer slightly intially I wind up ahead of the game with long term boost, since I don't heat saturate an intercooler.

 

My understanding when purchasing my 30lber's was that they would support up to 480hp. You may be able to swap up to 24lber's from 19 on an MAF setup without bothering the ecm but not on a SD system. That is my understanding of it all. I am not an injector expert yet. I used the above formula for determing my injedctor size...i.e: injector x16 = total hp.