Increasing Fuel Pressure
Thread Starter
Three Wheelin'
Joined: Nov 2001
Posts: 1,446
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From: Northern Kentucky
Increasing Fuel Pressure
I have decided to go back with the stock injectors in my 1981 Callaway trubocharged 928. This is because I am now running 30lb injectors with a stock fuel map, resulting in a very rich mixture across the whole map. I have a microfueler to richen up the mixture on the top side, it is equipped with two 30 lb injectors.
My goal is to replace the 8 injectors on the engine with stock units, then ramp the pressure up to suit. (I tried coming down with the 30 lb units, but I am not atomizing the fuel below 2 bar) My pressure regulator is adjustable and will increase the fuel pressure under boost as well. Right now I have one of the two injectors from the microfueler unplugged, since I don't need it. I bet I could run it on just the 8 that I have in the engine and be fine. My hydrocarbons are very high right now.
Does anybody have experience with ramping up the pressure on an early system?
If so, how high did you go and for what reason. I am thinking I will come in around 50 psig on the rail and then start coming down until I can get it back into closed loop without too much trouble. Callaway informed me they run stock injectors on the twin turbo Vettes with two high flows off of the microfueler. They also claim to be running stock fuel pressure at the rail?????????
Anybody out ther adjusted their pressure up on an early car?
My goal is to replace the 8 injectors on the engine with stock units, then ramp the pressure up to suit. (I tried coming down with the 30 lb units, but I am not atomizing the fuel below 2 bar) My pressure regulator is adjustable and will increase the fuel pressure under boost as well. Right now I have one of the two injectors from the microfueler unplugged, since I don't need it. I bet I could run it on just the 8 that I have in the engine and be fine. My hydrocarbons are very high right now.
Does anybody have experience with ramping up the pressure on an early system?
If so, how high did you go and for what reason. I am thinking I will come in around 50 psig on the rail and then start coming down until I can get it back into closed loop without too much trouble. Callaway informed me they run stock injectors on the twin turbo Vettes with two high flows off of the microfueler. They also claim to be running stock fuel pressure at the rail?????????
Anybody out ther adjusted their pressure up on an early car?
Chronic Tool Dropper
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Just another reminder--
If your HC measures high, chase down the poor combustion quality problem. This is typically an ignition problem.
To measure the performance of the injection system, watch the CO reading, sampled ahead of the cats. CO quantity in the raw exhaust correlates directly to fuel mixture, which is what you are adjusting with fuel pressure and injector size.
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Several folks on the list have complained of problems after changing to higher-flow injectors, especially a problem with relatively stock engines. The turbo engines qualify as 'stock' as far as injection is concerned, all the way up until the engine is under boost. So use caution when adding more fuel pressure and/or larger injectors. At manifold pressures lower than atmospheric, these changes will probably cause more problems than they cure.
My two sense.
<img src="graemlins/yltype.gif" border="0" alt="[typing]" />
If your HC measures high, chase down the poor combustion quality problem. This is typically an ignition problem.
To measure the performance of the injection system, watch the CO reading, sampled ahead of the cats. CO quantity in the raw exhaust correlates directly to fuel mixture, which is what you are adjusting with fuel pressure and injector size.
-----------
Several folks on the list have complained of problems after changing to higher-flow injectors, especially a problem with relatively stock engines. The turbo engines qualify as 'stock' as far as injection is concerned, all the way up until the engine is under boost. So use caution when adding more fuel pressure and/or larger injectors. At manifold pressures lower than atmospheric, these changes will probably cause more problems than they cure.
My two sense.
<img src="graemlins/yltype.gif" border="0" alt="[typing]" />
Thread Starter
Three Wheelin'
Joined: Nov 2001
Posts: 1,446
Likes: 0
From: Northern Kentucky
Bob,
I agree with you totally......because under N.A. conditions, the engine doesn't need all that extra fuel. For the guys who bore or stroke an engine, a larger injector makes more sense, since it is more of a linear relationship. I only need the extra fuel under boost. I have also learned the microfueler is adjustable.....giving me even more resolution!!!
I am hoping the stock injectors under about 50 psig does the trick. Then I'll be "back in the loop", and hopefully getting much better mileage as well as putting down another 20 or 30 HP!!!
I agree with you totally......because under N.A. conditions, the engine doesn't need all that extra fuel. For the guys who bore or stroke an engine, a larger injector makes more sense, since it is more of a linear relationship. I only need the extra fuel under boost. I have also learned the microfueler is adjustable.....giving me even more resolution!!!
I am hoping the stock injectors under about 50 psig does the trick. Then I'll be "back in the loop", and hopefully getting much better mileage as well as putting down another 20 or 30 HP!!!