matts85vet

my new afr 180 elim heads should be arriving soon

the 1204 miniram flows 265cfm

the afr heads flow 260 cfm

the current unported 113 heads flow 190cfm

my current injectors are accel 24lb

thinking of going to 30lb because of the extra air flow and hp from the new heads

also is the 52mm throttlebody big enough?

what do you think?

FICINJECTORS

according to the sizing calculater at 80% duty cycle 24lb will support 310CHP.. However, many guys push to 90% which will support close to 350. I think you will be right a those numbers so wait till its running and see. IF you think you are over 350hp go to the bigger injector. What cam are you running?

John A. Marker

I am still running the 24 pound injectors without problems, although my AFR 180 heads are older and flow about 20 less. If you have an ADPR, up the pressure a little.

RRT vette

I agree with sticking with the 24lb injectors until you have it running.

matts85vet

thankyou for the responses!

my current whp is 287 on mustang dyno -- 360-380 chp? with a very rich (a/f=11) tune

the cam is lunati voodoo 60103 227/233@.05 110lsa

how will i know if i need bigger injectors if i wait until engine is assembled?

FICINJECTORS

any dyno scan will display duty cycle. If you are at 90% or higher DS I would suggest more fuel pressure or bigger injectors. Be carefull with the accels, I would not run fuel pressure above 4 bar

CORKVETTE1

matt this is right up my alley i also own a 85 vette probally one of the fastest street vettes on this forum. I had a 406 super ram vette ran 10,90s with 24lb injectors. I then ran a 434 down to 10.27 running the same 24lb injectors. And now i have them in my 355, that went as fast as 10.79. The 406 and 355 made well over 500 hp and the 434 made well over 600hp as you can tell from my ets. So my recomendation is stick with the 24lb injectors. In addition there are at least a 1/2 dozen other forum members on here that went in to the 10s with 24 lb injectors. Oh by the way i am still useing the stock computer and maf

Demonic85

I dont think you need new injectors unless you have the originals still in there. If that were the case I would upgrade to a newer style 24lb injector. I upgraded mine and with my mods I still have to tune the pressure way down to keep from running pig rich

GREGGPENN

Makes me wonder if formulas presented here are conservative, if you left power on the table, and/or if you're running lean. (With that much power, the attachment says you need more).

Should I assume you've dyno'd and proven otherwise?

Nathan Plemons

FWIW I'm running 24's and make 380RWHP, that would be well over 400 crank. It's probably not optimal but since I'm not wide open throttle 100% of the time I've never had a problem. I've been running this way for many years and many thousands of miles.

As others have said, get it running with the 24's. If you see it running lean at WOT and you can't tune it out, then see about an upgrade.

JimiHendrix

"scratching my head" some folks here swear that you need bigger injectors with more air flow. I am buidling a 383 with a 230ish cam Lt1 and 3.07 gears. Will stock Lt1 injectors be sufficient?

Nathan Plemons

I think the difference is between "sufficient" and optimal. On one of my data logs I go WOT for a second. At one instant I show 6100RPM and a duty cyle of 103.5 left and 97.8 right. Now if you consider that some folks say you shouldn't go above 80%, then I'm way less than optimal, but I'm sufficient because I've made hundreds of track passes and dyno pulls never with the slightest hiccup. Since I bought the car in 2001 I've had several 4 sets of injectors. When I first did my mods I bought a set of SVO 24's because they're supposed to flow a little more at GM fuel pressure than stock. I later replaced them with a set of 42's just because I got a killer deal on them and sold the 24's. I began having some problems with the car seemingly running way too rich, which I thought was caused by the injectors so I swapped out for a set of 24's which came off of some LT1 that just happened to be sitting around TEA. I have no idea what the story is with that engine, miles, etc. Now my problem ended up being that I needed heated O2 sensors. I could have gone back to the 42's but realized it was probably a bit of overkill so I just left in the 24's and sold the 42's.

So currently I'm running 24's, it has been in this configuration for 40,000 miles, with no problems at all.

From my experiences I can tell you, the car runs better with the smaller injectors. I might could eventually have tuned the bigger injectors to work, but I didn't make a bit more power with them, so why bother? My advice, if you upgrade, do so within reason unless you're looking for a track only car. If 24's won't cut it, see if 30's will, then 36's, etc. Reason being that really large injectors have a hard time operating and running smoothly at really short pulse rates. They do fine at WOT but are not optimal all the rest of the time. Consider what you use the car for mostly. Mine was always a driver that I took to the track every now and then.

CORKVETTE1

I told guys about this years ago, the difference is your lt1 car is sequential which means it fires the injectors once per engine revolution. The 85-89 cars are batch fired injectors which means they fire twice as often, those 24s will be like haveing 48s in there.

GREGGPENN

I know L98's are batch fire, but never heard they fire twice/revolution. This sounds wrong. OTOH, if allowed to fire twice, it would seem more possible to get that much HP out of a smaller injector.

FICINJECTORS

This is an article written about this
"Most early EFI systems were batch-fire systems where the ECM fired all eight injectors simultaneously. Usually batch-fire systems fire the injectors once per engine revolution. This way, the injectors could be sized small enough to be more easily controlled at idle. Later, sequential EFI systems were refined to fire an injector a few degrees before the intake valve opened. Generally, sequential injection offers more precise fuel control at the price of increased complexity. But on production engines, the benefits are more in the area of emissions and driveability than in performance"

STL94LT1

Nathan's car and mine are very close in horsepower and mods. We are both running the stock 24 lb injectors. Nathan's is batch fire, mine is sequential. We are both seeing nearly the same duty cycles at WOT. So, the sequential firing only once per revolution making the injector twice as big theory is not working in this situation.

Redeasysport

I am not getting this Nathan how can a duty cycle of 103.5 work? Here is what I have found to be good info

" Injectors will go static at about a 92% duty cycle and should be sized for an 80% duty cycle to leave some "wiggle" room.

Beyond the 85% figure horsepower can actually drop as the pintles or discs in the injectors are essentially "floating", trying to open and close before they can complete each event. At this point the injectors actually put out less fuel until they are fully pulsed static and then the final output goes to 90% of their rated capacity. Injectors should not be pulsed beyond an 85% duty cycle.

Injectors are rated when shorted open @ 43.5 psi (3 Bar). The injectors will, when pulsed, only achieve 90% of this figure. Also calculated is the expected injector ccm flow at the selected rpm and load (KPa)."

Your the second one (Cork 3rd) today to say smaller injectors work well so now I am confused.

I also believe I read that our batch fires work on 1/2 the injectors at a time I do not remember where I read that but has anyone else seen it?

GREGGPENN

O.K... I've thought about this a bit more and re-read the link provided in my first post above. Besides duty cycle, the efficiency of the motor is part of the calculation for determining the correct injector size. So, let's assume stellar efficiency, elevated fuel pressure, and the use of a 24SVO to see what we get...

Raising fuel pressure can also get more out of a smaller injector. 55psi is listed as the max recommended (though I'm sure higher is possible). Let's try plugging in 55psi.

If you conclude that a lower BSFC were required, and use the lowest BSFC value suggested @ 55psi (.45) here's what a 24SVO could do....

24SVO X (sq. rt (55/39))= 28.5lb/hr

(28.5 X 8)/.45 = 506HP (Assuming 100% DC is allowed).

If a race motor were even more efficient, maybe a lower BSFC should/could be used (e.g., .40?). Plus there could be some 24lb SVO's that put out a bit more??? If you stretch all the numbers going into the formula, it does seem possible that a 24lb injector could feed a 500-600hp motor.

And, Jon... Thanks for confirming injectors don't fire twice/revolution on an L98. I didn't think so.

gp

Redeasysport

Here is a nice little calculator
http://www.rbracing-rsr.com/calcinjpulse.html

MR NICE

is this true?never knew this, I have 24lb lt1 injectors in my 85 with lt1 intake swap, seems ok too me.If this is true would'nt it be pig rich?

















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