How much amperage can an alternator support? no really...

cody at cody at
Tue Feb 5 16:25:15 PST 2008

You might consider either changing the pulley on the alternator to  
spin it slower or even if you can afford it buy a racing alternator.

The OE setup is designed to be able to keep everything running when  
the engine is at idle, while your engine really only needs it to start  
really having good output over something like 2500rpm. Changing the  
pulley ratio to spin the alternator slower will move it most efficient  
RPM range up to more like where your engine is usually running at, and  
the improved drive ratio will help pull less torque draw on the engine.

Likewise a racing alternator will be designed to run at much higher  
revs. We've got one on the V8 944 we are campainging in NASA and it's  
pretty killer. It charges about 12.5v at idle, but comes up to 14v  
arround 3,000rpm. We dyno'd the car with and without the alternator  
and came up with a dead wash - no power loss, actually a slight  
improvement. The torque required to spin the alternator is made up for  
by the stronger ignition and quicker injector opening times with the  
extra voltage. Our car has no lights except brakes though, so in our  
case we used a 50amp Denso unit (see below link - they go up to  
120amp). Not very expensive, right around the same cost as a stock  
replacement really, but it will require some fairly basic fabrication  
to mount.

-Cody Forbes

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