I'd like to switch from 22lb to 24lb injectors. Is a prom change needed or do you compensate with fuel pressure changes?

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92Z28
89GTA

 

Why do you want to change?



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GTA -89:383, 4-bolt,Free flow muffler,dual 3" HF cats, Edelbrock headers, Canfield heads, 1.52 RR 7/16, ZZ-9 cam, Big Mouth, AS&M LTR, !plenum, 52 TB, MSD 6AL, TPIS level V prom, Superior shift-kit and all the minor mods,looking for a SR ...
http://www.itv.se/tacs/members_cars/m279/m279.html (Swedish Trans Am Club)

 

I am going to need them.

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92Z28
89GTA

 

Ideally you like to keep the rated pressure for a good spray pattern, and adjust the PW in the EPROM...but I'd see how it'll run with just adjusting the FP first.

Depending the fuel requirements for the engine, you might be fine.

 

Fuel pressure does not behave in a linear fashion. It has it's greatest effect at high load (like WOT) and least effect at low loadm (like deceleration and idle).

22 to 24# may not sound like much, but it is a 10% increase. If you are planning more mods, then it will compensate. If they are SVO injectors, they will behave more like 26-26.5 depending on your fuel pressure. Now you are talking about 20% more fuel.

The biggest problem is, that the stock eprom is designed to be overly rich my GM, but about 15-25% (depending on engine and type - list two cars). Combine those two things and you are looking up to 40-50% more fuel (remember you have to multiply them together ... not just simply add as they effect each other). I predict it will burn more gas, possibly cause issues if you have emission testing and hurt performance if these engines are basically stock.

 

For gods sake, here is what I have......

355
10.8:1 compression (not just a guess)
SuperRam base/plenum/runners
SLP 1 3/4 headers
HEAVILY ported Edelbrock RPM's
LPE "219" cam
Crane AFPR
CompCams Pro Mag 1.6's
Prom by Fastchip (crap)
Vigilante 2600
Transgo
yadda, yadda

I expect my 22lb'ers will be near max duty cycle. The injectors I am looking at are LT1 24lb'ers. They are cheap. I appreciate the help guys, but some of you should stop trying to express your vast amounts of knowledge with words. It simply does not do the information justice.


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92Z28
89GTA

[This message has been edited by Acceld Z (edited August 31, 2001).]

 

Whoa, let's not turn this into a flame war. From your original post it was understood by Glenn and myself as well, that you had a stock or near-stock setup, in which case his answer was well explained. The original question had such a lack of detail that a general answer was required. Now that you have listed your mods it is a much more easily answered question.

So to answer your updated question, I think 24# LT1's will suit your combo well. 24# SVOs with some PROM work (since you don't like your current one) would be nice also. Hope this helps.

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1990 IROC 350
Mods: Too busy trying to make it run right to mod it.
Airfoil, Dynomax cat-back, MSD coil, 180 t-stat, Bald Eagle tires,
Hypertech fan switch, Accel 23# injectors, Holley AFPR, ported plenum,
Ported Daytona Yellow stock base, Moroso valve covers, other stuff,
Ruger P95DC, hot wife, new oil filter, thick rubber floormats, no cats.
18.0 @ 85MPH since I'm one big-a$$ MF
"It's better to have and not need than to need and not have."

 

I did not intend to offend anyone. I simply wanted to know if a prom change is needed / prefered with an injector upgrade. Again I was not trying to flame anyone. I occasionally type before I think. So would the 24lb LT1 injectors be a worthwhile upgrade? The SuperRam is allready out of the car.

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92Z28
89GTA

 

I hate to ask a stupid question... O.K. - no I don't.

Doesn't Ed Wright offer a free "reburn" or two with the PROMs he provides? I seem to recall reading that somewhere. If that's the case, why would you hesitate? Try the setup with the current PROM, and if it doesn't behave, get a reburn.

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Later,
Vader
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"Get UP - Drop the bombshell!"
Adobe Acrobat Reader

 

Just run the stock ones until you have a problem with one or more and then replace with the 24's. You shouldn't need a prom change.

 

Unfortuanately "Ed" doesn't offer the free reburn. I wish that where the case. My combo has changed slightly anyways. I am going to educate myself in the ways of the force..err..PROM burning this winter.

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92Z28
89GTA

 

I'd like to swap them now while the SR is off. It just makes more sense.


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92Z28
89GTA

 

A prom change would be ideal, but for the time being you might be able to get away with lowering the fuel pressure down. I can understand why with a SR you dont want to tear in there again, so maybe you should swap them in and see how it runs, maybe lower the fp if necessary. It will more than likely run rich, so make sure the plugs arent totally soaked in fuel after you get it running.

 

Cool, that's what I was fishing for. Thanks guys

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92Z28
89GTA