Question about fuel injection from a newbie

[pbp1]

Originally Posted by Darrel Goheen

I am irritated! I believe what your are saying. It makes sense. But Holley and Fast and some others say it's best to run fuel pressure at what the injector is rated at. On most injectors they are rated at 44.5 so I've got mine right at 45. I will raise the pressure next weekend.

You can run any fuel pressure you want to within reason. Obviously, there are limitations on the low and high ends where the injectors will no longer function.

The only thing that is important is that you know what the injector flows at your new pressure. There are a couple of ways to do this, either using a mathematical formula to figure what it SHOULD flow, or, have one of your injectors flow tested at the new pressure.

[Darrel Goheen]

Originally Posted by pbp1

You can run any fuel pressure you want to within reason. Obviously, there are limitations on the low and high ends where the injectors will no longer function.

The only thing that is important is that you know what the injector flows at your new pressure. There are a couple of ways to do this, either using a mathematical formula to figure what it SHOULD flow, or, have one of your injectors flow tested at the new pressure.

Are you in agreement that 60 lbs of pressure will offer better performance/fuel burning than 45 lbs.? My plan is to run 4 back to back runs Fri night. Two at current 45 lbs. pressure then change to 60, change fuel pressure in software and make two passes to see if it makes any noticeable change in performance. Thanks.

[Ed Wright]

I used the math, which showed my 36 lb (FAST) injectors would be 42 lbs at 60psi. I changed that, raised the fuel pressure, hardly had to touch anything else.

Darrel, you have to make the appropriate change to your ECU tuning. Just turn up the fuel pressure will make your car run very rich.

I'm not sure I will be at Topeka. I may be done.

[Darrel Goheen]

Originally Posted by Ed Wright

Darrel, you have to make the appropriate change to your ECU tuning. Just turn up the fuel pressure will make your car run very rich.

I do know that I have to change the pressure in the software as well as regulator pressure. Now as to whether I'll remember to do either one or both is another question. My brain fails me frequently it seems. Thanks again!

[Dan Fahey]

Originally Posted by Ed Wright

No reason at all you could not alter tuning by altering the fuel pressure with the factory LT1 injectors. I know NHRA Stock Eliminator racers that do it all the time. Turn the fuel pressure up on an LT1 injector, they have a finer mist as well. That is the point. Higher fuel pressure atomizes the fuel better. That is the reason for higher fuel pressures being used. Better emissions is the main reason. Very small power increase are simply a bonus.

I use injectors from FAST in mine.

Was Testing LS1 and LT1 Injectors
The LS1 Injectors misted better than the LT1 using same fuel pressure.
Couple LT1s Injectors clogged up causing fuel delivery issues.
So went with LS1 Injectors...direct replacement for the LT1's.

If you increase the Fuel Pressure and not Change the MAP.
They Injectors will only supply the fuel in the MAP.
May get a finer mist but the PCM would eventually relearn and provide the fuel the computer was programmed.

D

[Darrel Goheen]

Originally Posted by Ed Wright

I use injectors from FAST in mine.

That's actually where my 60 lb injectors came from that I put in my LT1.

[cmracing]

Originally Posted by Darrel Goheen

Yip your right. 43.5 not 44.5. Like I said I believe you and it makes sense. I'll be raising my pressure to 60 this coming weekend. Will you be at Topeka Nationals? Thanks.

You are wasting your time and money unless you fix your power issues to your fuel pump. Raising the pressure will make things worse!

You should have a 10 gauge wire feeding the fuel pump. All the EFI cars I wire have a relay in the back, close to the battery, 20 amp fuse between the battery and relay. All wiring from battery to relay to fuel pump is 10 gauge. I also use a 4 pole battery disconnect switch. The smaller terminals on the switch are used to remove the power from the relay coil so when you hit the disconnect switch the engine stops immediately even if you have a working alternator (which I highly recommend you do).

I had a friend with a BS/A swap between 42lb/hr injectors and 60lb/hr injectors within 10 minutes for back to back passes. With keeping the A/F the same, the car ran identical. Don't listen to people telling you that large injectors are a problem.

Been doing this since 1986 and I'm not on here trying to solicit business. Several here know me. I don't have time or the inclination to take on any new projects anyway, just trying to steer you straight.

If you can't get and maintain 12.5 volts at the fuel pump park the car! Get a working alternator and that pump will be MUCH happier at 13.5 to 14.0 volts. So will the injectors.

[Ed Wright]

Originally Posted by Dan Fahey

Was Testing LS1 and LT1 Injectors
The LS1 Injectors misted better than the LT1 using same fuel pressure.
Couple LT1s Injectors clogged up causing fuel delivery issues.
So went with LS1 Injectors...direct replacement for the LT1's.

If you increase the Fuel Pressure and not Change the MAP.
They Injectors will only supply the fuel in the MAP.
May get a finer mist but the PCM would eventually relearn and provide the fuel the computer was programmed.

D

Wow! You have no clue. For one thing, MAP is Manifold Absolute Pressure.

[Ed Wright]

Originally Posted by cmracing

You are wasting your time and money unless you fix your power issues to your fuel pump. Raising the pressure will make things worse!

You should have a 10 gauge wire feeding the fuel pump. All the EFI cars I wire have a relay in the back, close to the battery, 20 amp fuse between the battery and relay. All wiring from battery to relay to fuel pump is 10 gauge. I also use a 4 pole battery disconnect switch. The smaller terminals on the switch are used to remove the power from the relay coil so when you hit the disconnect switch the engine stops immediately even if you have a working alternator (which I highly recommend you do).

I had a friend with a BS/A swap between 42lb/hr injectors and 60lb/hr injectors within 10 minutes for back to back passes. With keeping the A/F the same, the car ran identical. Don't listen to people telling you that large injectors are a problem.

Been doing this since 1986 and I'm not on here trying to solicit business. Several here know me. I don't have time or the inclination to take on any new projects anyway, just trying to steer you straight.

If you can't get and maintain 12.5 volts at the fuel pump park the car! Get a working alternator and that pump will be MUCH happier at 13.5 to 14.0 volts. So will the injectors.

Why in the world would anybody think a B/SA car needed 60 lb injectors? That is forced induction stuff.

[Darrel Goheen]

Originally Posted by Ed Wright

Why in the world would anybody think a B/SA car needed 60 lb injectors? That is forced induction stuff.

I didn't think I needed 60 lb. 36 lb would be plenty. I only bought the 60 lb because I had a friend with a set that had very little time on them that he sold to me cheap. I think my LS1 has 42's in it.