Another Injector Size Question ?
Thread Starter
Racer
Joined: Sep 2001
Posts: 396
Likes: 0
From: simi valley ca
Another Injector Size Question ?
My brother and I want to replace his stock injectors on his 86 vette. We are leaning towards the accell inj, (cause i have them and have had no problems) the question is this: can we use a 30# and program the computer for the bigger injector so that when he decides to upgrade to a 406, we wouldn't have to buy another set, or are we stuck with the 24# injs ? Do you guys think that it may run bad with thte 30#s.
thanks,
joel
(we just recently reprogrammed his chip with lower temp settings :) ; this
chip burning is really addicting; i'm making a cable so that i can connect his car to WinBIn and get some readings)
thanks,
joel
(we just recently reprogrammed his chip with lower temp settings :) ; this
chip burning is really addicting; i'm making a cable so that i can connect his car to WinBIn and get some readings)
Drifting
Joined: Jul 2001
Posts: 1,897
Likes: 0
From: La Fontaine Indiana
Re: Another Injector Size Question ? (qkvette)
The bigger injectors will work fine but only if you totally reprogram the ecm for them I run much larger than that.
[Modified by black bart, 2:31 PM 4/2/2002]
[Modified by black bart, 2:31 PM 4/2/2002]
Team Owner
Joined: Sep 2001
Posts: 62,142
Likes: 1,729
From: Athens AL
C7 of the Year - Unmodified Finalist 2021
C4 of Year Finalist (performance mods) 2019
Re: Another Injector Size Question ? (qkvette)
30s are kinda big for a stock 86, but with a fuel pressure regulator you could fix it. Although i do think that the computer can adjust, i'm not sure. And im sure you could program for that injector size.
Racer
Joined: Sep 2000
Posts: 294
Likes: 0
From: Princeton Texas
Re: Another Injector Size Question ? (vader86)
It's my understanding that the intake manifold is the largest restriction on the stock engines. Until you get the engine to breathe better by increasing the porting on the intake manifold, adding more fuel will not help. This is the way I understand the injection system. The injectors are pulse width modulated, the longer the pulse, the more time the fuel is sprayed. The ECM by way of the O2 sensor will determine the proper pulse width for a given air to fuel mixture. I don't know what it takes to get to the maximum flow of the injectors but I doubt very seriously if a stock engine will reach this point. So Larger injectors may be under-utilized if installed on a stock engine and given the pulse width set by the ECM, your engine may actually to run too rich.
Thread Starter
Racer
Joined: Sep 2001
Posts: 396
Likes: 0
From: simi valley ca
Re: Another Injector Size Question ? (fiddleplayer)
thanks guys. i looked at his ecm setting, and it is currently set to 23#. i'm guessing setting this to 30 is all i need to make it work ? i would really hate to have to muck with the other tables, w/o a working scanner. thanks again
joel
joel
Drifting
Joined: Feb 2002
Posts: 1,952
Likes: 2
From: Little Rock Arkansas
Re: Another Injector Size Question ? (qkvette)
Don't put 30# injectors in a stock TPI... You'll have a pig!! Truth is you *can't* pull enough pulsewidth out of the base fuel map to make a 30 run well in a stock application. If you go any less than about 1.8-1.9 milliseconds you'll start having fuel distribution problems because the injector simply isn't designed to work with that little pulsewidth. The car will be very fat and extremely lazy because of this, not to mention getting really Sh&%ty gas mileage... Here's an equation to help size injectors correctly: HPxBSFC/# of cylinders x duty cycle
More specifically: Let's say you have a 400 horsepower engine and you want to know what injectors you should run. You take your horsepower (400) and multiply it by the Brake Specific Fuel Consumption (BSFC) which on a EFI motor is usually around .45 naturally aspirated. So: 400 x .45 = 180. Then you multiply the number of cylinders by the duty cycle of the injectors (you really don't want to run them at over 85% or you risk some static issues). So: 8 x .85 = 6.8 Now, divide your 180 by the 6.8 and you get your recommended injector size: 180/6.8 = 26 lb/hr. You need 26# injectors to run the motor.
-Jeb Burnett
More specifically: Let's say you have a 400 horsepower engine and you want to know what injectors you should run. You take your horsepower (400) and multiply it by the Brake Specific Fuel Consumption (BSFC) which on a EFI motor is usually around .45 naturally aspirated. So: 400 x .45 = 180. Then you multiply the number of cylinders by the duty cycle of the injectors (you really don't want to run them at over 85% or you risk some static issues). So: 8 x .85 = 6.8 Now, divide your 180 by the 6.8 and you get your recommended injector size: 180/6.8 = 26 lb/hr. You need 26# injectors to run the motor.
-Jeb Burnett
Safety Car
Joined: Mar 2002
Posts: 4,157
Likes: 0
From: Orange County TX
Re: Another Injector Size Question ? (qkvette)
That thing they call the O2 sensor, well it will adjust the pulse width down to where the mixture will be correct during closed loop. Could pose a problem with too short a pulse at idle speeds. Lowering the pressure will result in a bad spray pattern. You may get lucky, but there are going to be some problems.
Drifting
Joined: Feb 2002
Posts: 1,952
Likes: 2
From: Little Rock Arkansas
Re: Another Injector Size Question ? (Dryseals)
That thing called the O2 sensor will only pull out so much pulsewidth...It will not pull out enough to make 30# injectors run well in a 250 hp stock L98... And like I said, you can only pull out so much pulsewidth before you get into a very poor fuel distribution problem. Sorry...
-Jeb Burnett
PS- You're also taking into account that the O2 only controls feedback to the ECM at part throttle... What about WOT when the injectors are running off a preprogrammed fuel map?
[Modified by jburnett, 11:01 PM 4/2/2002]
-Jeb Burnett
PS- You're also taking into account that the O2 only controls feedback to the ECM at part throttle... What about WOT when the injectors are running off a preprogrammed fuel map?
[Modified by jburnett, 11:01 PM 4/2/2002]
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
Top 10 Most Explosive Corvettes Ever Made: Power-to-Weight Ratio Ranked!
Joe Kucinski
150 hp to 1,250 hp: Every Corvette Generation Compared by the Specs That Matter
Joe Kucinski
8 Coolest Corvette Pace Cars (and Replicas) of All Time
Verdad Gallardo
Top 10 Corvette Engines RANKED by Peak Torque (70+ Years of Muscle!)
Joe Kucinski
Corvette ZR1X Will Be Pacing the Indy 500, And Could Probably Race, Too!
Verdad Gallardo
Top 10 Corvettes Coming to Mecum Indy 2026!
Brett Foote
Top 10 C9 Corvette MUST-HAVES to Fix These C8 Generation Flaws!
Michael S. Palmer
10 Revolutionary 'Corvette Firsts' Most People Don't Know
Joe Kucinski
5 Reasons to Upgrade to an LS6-Powered Corvette; 5 Reasons to Stay LT2
Michael S. Palmer
Safety Car
Joined: Mar 2002
Posts: 4,157
Likes: 0
From: Orange County TX
Re: Another Injector Size Question ? (jburnett)
You are correct the O2 maynot be able to correct the reading, what is the percentage of correction that it can make? Oh and if you read you'll see I mentioned closed loop. At WOT you are no longer in closed loop.
Drifting
Joined: Feb 2002
Posts: 1,952
Likes: 2
From: Little Rock Arkansas
Re: Another Injector Size Question ? (Dryseals)
I can't remember what the exact number is an O2 will pull out, but it's only something like 14% which isn't that much. I know Accel recommends (as does FAST, Electromotive, and MoTec) getting the base fuel map within 3-5% (when programming) of stoichiometric before starting closed loop operation so the O2 doesn't have to "hunt" for too much correction... And yes, you're right, I missed the closed loop part...Sorry.
-Jeb Burnett
-Jeb Burnett
Thread Starter
Racer
Joined: Sep 2001
Posts: 396
Likes: 0
From: simi valley ca
Re: Another Injector Size Question ? (jburnett)
my brother's engine is actually the gm 300Hp crate motor (now the 330HP) with 52mm tb and 1.6RR. do you guys still think it would be too big for this application ?
thanks again,
joel
thanks again,
joel
Thread Starter
Racer
Joined: Sep 2001
Posts: 396
Likes: 0
From: simi valley ca
Re: Another Injector Size Question ? (Dryseals)
i meant that it is the equivalent to the new gm 330HP crate motor.
the mods that he has is just a custom burnt chip, 52mm tb, 1.6 rr(from 1.5), and 3.73 gears. we are actually going to order a set of the ford (yeah i know ford) injectors (19#). It's at a great price for <140$ for a new set. should be better than the original 17 year old injectors.
thanks ypu all for your input.
joel (i'll let you know how it runs after)
the mods that he has is just a custom burnt chip, 52mm tb, 1.6 rr(from 1.5), and 3.73 gears. we are actually going to order a set of the ford (yeah i know ford) injectors (19#). It's at a great price for <140$ for a new set. should be better than the original 17 year old injectors.
thanks ypu all for your input.
joel (i'll let you know how it runs after)