Recommended amperage for an alternator
 

Hello,

Looking to replace an alternator and was wondering what amperage should I look at to
support a mopar p4876728 or MSD6AL with a magnafuel pump and cooling fans.

Thanks in advance

Re: Recommended amperage for an alternator
 

I just changed a east coast electric to a 100 amp gm. the east coast was 75-80 amp but did not charge well at idle. the gm 100amp 1 wire charged well at idle but was constant 11.5-12.4 during run. today I ordered an msd 160 dynoforce to see if it will run about 12.8 13v during the run. I am not concerned about any horsepower loss as you might be. with that being said I will have the east coast setup listed for sale on here shortly.
My draws were from grid ign. data recorder, dual fans, electric water pump (csr), Weldon fuel pump, driver fan , light at night and stereo

Re: Recommended amperage for an alternator
 

Duster,

It is completely acceptable to have more alternator output than your system requires. An alternator only puts out the amperage required by the load.

It is common to see 85 amp - 100 amp rated alternators on drag race cars.

Personally, I chose pulley sizes that spin the alternator about 20% - 25% faster than the engine.

Example - 7200 engine RPM x 125% overdrive = 9000 alternator RPM.

Another example - 1200 engine idle RPM x 125% overdrive = 1500 alternator RPM. That is enough alternator speed at idle and does not over speed the alternator at high engine RPM

Re: Recommended amperage for an alternator
 

Make a list of the amp rating of everything your electrical system might be driving and total that up to find a starting range.

The problem with alternators on dedicated drag cars is that they don't usually put out a full charge at idle rpm and that's where your engine tends to spend most of it's time at the track.

If you pick a one wire alternator be sure to set it up correctly with the jumper to the right terminal. Use the remaining wire for a warning light of some sort. It comes in handy when you lose your adjuster hardware and drive belt at the track like I did Sunday. The light popped on so I took a look and everything was just gone.

The short version: 85 amps for the strip. 120-140 if it's a street car with lots of electrical stuff.

Dale