I was reading in <a href="https://www.thirdgen.org/techbb2/showthread.php?s=&threadid=119061">this</a> post about disconnecting the ground on the alt when at the track so that It does't drag on the engine. How would you go about doing that and why would it help? The alt would still spin wouldn't it?

 

doesn't make sense. never heard of that. If I think correctly, the alternator is still grounded by the mounting hardware. Not to mention with the ground taken off, the computer is going to run off the battery. which is not good. not enought juice.

 

I thought the alt got its' ground from the case.
Don't see any easy way to break that connection.

You could break the alternators' pos wire connection to the battery.
You would need a relay capable of handling the output of the alternator which can be >100 amps and be rated for continous use. That might be a little hard to find.
You could simply disconnect the big red wire from the rear of the alt. when racing. Just be careful.
The other end of that wire is conencted straight to the batt. and if it touches metal, there's gonna be big trouble.
You could install an INSULATED dummy terminal near the alt so the wire could be temporaily connected to it and not be flopping around. Of course, you would want to disconnect the battery while messing with the alt hot wire.

The drag an alternator produces when working is substantial.
The drag an alterntor produces when it's just spinning is next to nothing.

I made a battery charger from a brand new Briggs 5HP eng connected to a 75 amp alternator via belt and pulleys. When I energize the field sufficiently to make the alternator produce its' rated output, it will almost kill the eng. It's pretty dramatic.

 

Would it be possible to install some sort of variable resister to reduce the drag from the ALT but not remove it completely? Would the ignition system suffer from not having the alt connected? I don't want to risk misfires from not enough juice.

Thanks for the information ZZ28zz

 

Don't know how you could install a variable resistor with an internal regulator.
If you had an external adjustable regulator, you could lower the voltage output and save a little maybe, but they're dinosoars, and not worth converting too.

I would think that you could get a few mins of run time before low voltage becomes a factor, assuming your batt is in good shape.
You would want to eliminate everything you could that draws elec.
and re-charge batt between runs.

The only way you'll know for sure is to try it.