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Axis Racing · 10-27-2011, 10:35 AM

Art,

I may be going out on a limb here, but I think you may be looking in the wrong area. Kind of like using a butterfly band-aid instead of having a cut sewn up...

You touched on what I believe is the answer. Your ECU may be able to run anywhere from 8 to 20 volts, but the tune definitely changes. Rather than have to run the alternator, you could tune the engine at each voltage via the battery adder function. The correct way to do it is to tune the engine while it's powered by a variable voltage inverter. Tune the car at a given voltage, like 13v, then adjust the inverter's output voltage to match another cell on your battery adder table in the ECU. Adjust the adder function on both the ignition and fuel (most likely it's a multiplier on the fuel) untill the engine is making the same power at the new voltage and then move on to a different voltage. Tuning the battery adder stuff is quick and painless, all you have to do is pick a single RPM point and adjust the battery adder function to get the engine running correctly...

Once you've done this, you will be able to run sans alternator with a decent battery and not loose ET. More than likely, you're loosing between 8 and 12 amps to the fuel pump, and a bit more than that to the water pump. Start the runs with the battery at roughly 12.5v or so, and end it in the 11's. No big deal if the battery voltage correction factors are set correctly!

10-27-2011, 10:35 AM	#16
Axis Racing Junior Member Join Date: Oct 2011 Posts: 14 Likes: 0 Liked 0 Times in 0 Posts	Re: Fuel pump amperage draw? Art, I may be going out on a limb here, but I think you may be looking in the wrong area. Kind of like using a butterfly band-aid instead of having a cut sewn up... You touched on what I believe is the answer. Your ECU may be able to run anywhere from 8 to 20 volts, but the tune definitely changes. Rather than have to run the alternator, you could tune the engine at each voltage via the battery adder function. The correct way to do it is to tune the engine while it's powered by a variable voltage inverter. Tune the car at a given voltage, like 13v, then adjust the inverter's output voltage to match another cell on your battery adder table in the ECU. Adjust the adder function on both the ignition and fuel (most likely it's a multiplier on the fuel) untill the engine is making the same power at the new voltage and then move on to a different voltage. Tuning the battery adder stuff is quick and painless, all you have to do is pick a single RPM point and adjust the battery adder function to get the engine running correctly... Once you've done this, you will be able to run sans alternator with a decent battery and not loose ET. More than likely, you're loosing between 8 and 12 amps to the fuel pump, and a bit more than that to the water pump. Start the runs with the battery at roughly 12.5v or so, and end it in the 11's. No big deal if the battery voltage correction factors are set correctly!