TBI Injector Thought

[91GMCSuburban]

If I use my 454 TB on my 350 with the injectors from the 454 TB and a vacuum referenced fuel pressure regulator, would I be OK? I would think that with the dynamic fuel pressure changes, the 75# injectors would perform correctly at idle or low throttle.

Your thoughts.

 

[bigburban383]

Your computer should adjust to stochimetric. Get an Air/Fuel guage and adjust your fuel pressure.

 

[91GMCSuburban]

I do have a guage, and will adjust my range of fuel pressure, but I have heard that the 454 injectors (75#/hr) don't flow well at idle or low throttle, but I am thinking that the VRFPR would remedy this problem.

 

[91GMCSuburban]

I need some expert input here...

 

[loafer]

Maybe I'm missing something here...

If you are running TBI you do not need a vacuum referenced fuel pressure regulator, as the ijectors are always at atmospheric pressure, therefor you run at a constant fuel pressure.

If you are running the factory ECU you will need to program a new PROM chip to run injectors other than the stock ones.

The ECU can only make small adjusments to the AF ratio with the O2 sensor, and won't be able to compensatre for larger fuel injectors.

Dropping the fuel pressure to compensate for the large injectors is also not an option because the GM TBI systems already run at a low fuel pressure of 9-13psi.

 

[Thunder]

Why do you want to use 454 injectors? A 350 doesn't need them. The 350 ECM is not programed for that much fuel flow and wont work with them unless re chipped. Unless you have a heavly modded 350 your stock injectors should be fine.
Just use the stock injectors and put in a adjustable fuel pressure regulator, either manual or vacume. To compensate for the air increased air flow.
IMO If your 350 is stock or mild built 75 lb hr injectors are too much for it. You dont want to lower the fuel pressure to make it run right it will hurt performance. Higher FP atomizes the fuel better. That is the main reason for fuel injection.
If you want to run a FI system at lower pressures than it was designed for. You might as well just put on a carb.

 

[91GMCSuburban]

Here is where I am going with this:

I will be putting together a new engine with ported vortec heads, 454 TBI, headers, cam and new chip to boot. I did not want to spend $250 on 67# injectors if I could just use my existing 75# injectors. I figured with the use of the VRFPR and the possiblity of me stroking this engine as well, I would be OK.

 

[fortcollinsram]

IMHO, the 454 injectors are WAY too big for a 350, even if it is mildly built. I doubt that the computer will be able to get the pulse width of the 454 injectors low enough to provide a stoich condition at idle. The VRFPR does nothing for fuel delivery at idle; it provides the same pressure (~12psi) at idle as the factory non-adjustable regulator does. It simple is a remedy for built motors that need more fuel in loaded (read: pulling) conditions. I think your best bet would be the 454 thorttle body with some decent, flow-matched injectors. For instance, I think the TBI 350s that were in the Police-issue Caprices had flow ratings about 10#/hr higher than that of a stock injector.

I think 454 injectors would need a MINIMUM of a stoutly-built 383 that has some serious fuel needs.

 

[fortcollinsram]

Oh as a side note, when I swapped in my 454, I buttoned everything up but I had forgotten to swap the ECM for the 454 ECM. The damn truck didn't even want to start, it just cranked over and over then I realized I had the 350 ECM in there still; swapped ECMs and it fired up on the first crank.

That leads me to believe that the you will need a pretty radical chip to allow the ECM to control 454 injectors on a 350CI motor.

Chris

 

[91GMCSuburban]

Thanks for the info. I was hoping not to have to buy new injectors.

Besides turbo city, do you (or anybody) know where to find those police (67#) injectors?

 

[Thunder]

For the price of a custom chip to run those 454 injectors. You can buy a set of flow matched injectors and a adjustable FPR. If you dont go too wild with the cam you may still be able use the stock chip.

 

[Thunder]

[ QUOTE ]
Maybe I'm missing something here...

If you are running TBI you do not need a vacuum referenced fuel pressure regulator, as the ijectors are always at atmospheric pressure, therefor you run at a constant fuel pressure

[/ QUOTE ]

Loafer FYI. The reason for running an adjustable FPR is to fine tune your fuel flow to your engines needs. The stock setting can be anywhere between 9-12 lbs. That is too low for performance needs. The pump will give 15 or more lbs psi. The stock injectors can take up to 30 PSI. If you put on a bigger TB or add more flow to the engine IE headders, Cam, intake, heads, or TB mods You need to be able to get the FP higher. A 1/2 pound increase can make a lot of diference.
A vacume referenced regulator(GM Marine 454 apps) is nice because it gives a lower fuel PSI at cruise and low speeds(high Vacume). This gives better fuel economy. When you mash the throttle the drop in manifold vacume causes the regulator to add more fuel pressure. Giving better performance.
I have a manually adjusted reg in my TBI 350 with mild mods. At 14.5 psi I get the best blend of MPG and performance.