fuel pressure setting question

[pettsir]

i have a 96 LT4. i am probably gonna replace my fuel injectors(to try and solve an existing problem). and wile i'm at it an adjustable fuel pressure regulator. i am thinking of going with the SVO #30 injectors. are these any good? i haven't heard anything bad about them like the accel injectors. what is a good brand for the adjustable regulator? and what is an optimum fuel pressure setting? the car has the cut-out air lid,K&N air filter, relocated IAT sensor, the T-body coolant bypass, an air foil, a granitelli MAF, a hypertech PPIII,and a set of SLP headders. any advice would be appreciated. thanx in advance.

 

[Mad-Mic]

why do you want to add larger injectors?

if your motor is stock, which it seems to be, there is no need to upgrade to a larger injector. it will only cause you problems down the road. alot of guys that think larger injectors will give you more hp is all wrong. they will only cause you to run really rich and trying to detune with fuel pressure only makes it worse with the spray pattern not being a fine mist as it should be.

i'm not sure about LT motor fuel pressure sorry i can't help you there. just put a fuel pressure gauge on what you got now to get a good base for the new injectors. if you go larger then you will need to use less fuel pressure but negates the fuel spray pattern that is essential to fine tuning for horsepower.

 

[UB2 SLOW]

I have the Accel 30# and I have no problems. I have my Fuel Pressure set at 47PSI and I have a 14.5-14.7 Air/Fuel ratio. I agree with Mad-Mic if your car is stock to mildly moded, you dont need the bigger injectors. You might actually suffer from them. If you have or are planning on a H/C change then yes, you would benefit. I would also advice you to get a better fuel pump. After I did all my mods, my car was getting fuel starvation with the bigger injectors, and increased fuel pressure. I got a walbro 340 fuel pump. No problems now.

 

[Moonunit 451]

The Holley AFPR is very nice and easy to work with, no tools required to adjust. I was looking for a link or a PN and can't find one right now. One thing I do know is on the Summit website it is listed for a 305 or third gen application.

 

[vettered91]

I'm with Mic and Bryan, you need much more mods before you go for the 30's. You can get more advantage now with stock's and high pressure! I don't have much mods and I'm running 47PSI with the OEM injectors and still very rich but the MSD Ignition helps a little to burn the fuel!

 

[pettsir]

i want to replace the injectors because i have an intermittent problem that i think is related to the injectors. it is my understanding that the stock 96 LT4 injectors are somewhere between #27-#28 anyway. is going to the #30 SVO or accel injectors really that big of a leap up? the LT1 and L98 injectors are well below #26 depending on the year, that would be a big jump. considering the size of the stock injectors do you still think the #30 are too big? and i have heard people swear that tuning there fuel pressure either a couple pounds up or down depending on the engine and year has made a dramatic improvment at idle and WOT. is there any truth to that? thanx again.

 

[RdRacerZ28]

LT4 injectors are 26#, 94-97 LT1 Injectors are 24# and 92-93 Injectors are 22#. THere is absoluley no reason to install a 30# injector. I would find a Bosch or Ford (made by Bosch) injector of your same size. You could even use a 24# injector with no problems. Accel injectors are horrible quality. The adjustable reulator will be a nice tuning tool. At WOT you want 13:1 A/F ratio. UB2SLO posted they have 14.5-14.7 A/F Ratio. I would hope this is at part throttle. It is too lean for WOT.

 

[UB2 SLOW]

At WOT you want 13:1 A/F ratio. UB2SLO posted they have 14.5-14.7 A/F Ratio. I would hope this is at part throttle. It is too lean for WOT.

Sorry that was a typo! It should have said 13:5-13:7. I hit the 4 button twice. Hey I never said I could type. Maybe I should preview my post huh!

 

[RdRacerZ28]

No problem!!!!!! I looks like I need to learn how to spell! lol

 

[WhalePirot]

Squirt size

I found a great deal on SVO injectors and have no problems with them ('cept the F--d thing). The Super Ram hides them well, tho.

In researching, I found a few tuners who liked smaller injectors with higher pressure and those that like the opposite. Proper spray, from proper pressure seems to make a lot more sense. You can feed more or less fuel through a given injector pulse by varying the fuel pressure, but the sequence seems out-of-whack to proper tuning. Bigger jets in a carb deliver more fuel, too, but is it optimally tuned?

I concur with the above comments on injector sizing and pressure. I run 30pph, but have a 406; highly modified, running stock fuel pressure (adustable).

My sequence: build engine; pick injectors w/ size based upon HP output; set stock fuel pressure; have chip cut to feed injectors proper-sized pulses to achieve optimum burn.

See: http://www.jimsperformance.com/tech.html

 

[UB2 SLOW]

Let me see if I remember this. Increasing the fuel pressure makes the engine run richer and decreasing causes it to run leaner, if you have a NON-stock ECM. If it is stock the ECM will lean or richen out the mixture to maintain correct levels, right?

 

[RdRacerZ28]

Let me see if I remember this. Increasing the fuel pressure makes the engine run richer and decreasing causes it to run leaner, if you have a NON-stock ECM. If it is stock the ECM will lean or richen out the mixture to maintain correct levels, right?

This is correct, but ONLY in closed loop,closed and part throttle. WOT doesn't use the Oxygen sensors and therefore has no idea what the mixture is. Changing fuel pressure directly effects WOT mixture and cold/open loop mixture because in both these situations the ECU doesn't use the Oxygen sensor voltage. The ECM can only correct a certian amount. The "correction" factor is the Block Learn parameter on your scanner. This tells you how much the ECU is richening or leaning out the pulse width to achieve the desired A/F ratio (14.7:1). This is why using too alrge of an injector on an engine cause rich idle mixtures and surging etc......the ECU can't correct the pulse-width enough to lean out the mixture. When the engine is under a lod and you're driving the car, it can often times work fine because the engine is able to use the fuel.