If you have a gigantic alternator, like a 225 amp propower or something, would there be any harm in running an underdrive main pulley? Would the size of the alternator compensate for the drop caused by the pulley? This would be under stop and go conditions, obviously.

 

225 amp is rediculous for an RX-7 IMHO. But yes.. I think what you are asking is possible. I think the main problem is that at idle, the lowest speed of the alternator would be even less.. so, whether it would be making 14.4 volts at that speed is debatable. Even with the higher amps.

But I know little to nothing about alternators..

 

gotta have the mAd TyTe SuBz aNd AMpS y0!

all joking aside, I'm trying to find a way of having the benefits of underdrive, while keeping the car streetable in the city.

 

Werd... Well, there's nothing wrong with 225amps.. just overkill. I suppose there's nothing wrong with overkill.

 

I am running an underdrive pulley on the alt, and e-shaft; no issue at all.

 

You must be planning on some serriously bangin system.. 225.. damn

 

Are you actually considering running an alternator that big? If you're installing equipment that truly needs 3kW of electrical power I’d suggest you bought the wrong type of car.

Upgrading the alternator and then underdriving is a completely pointless exercise. It should be pretty obvious that if you underdrive it you not only reduce its load on the engine but you also reduce its output. Using a more sensible example, if you replace an 80A S5 alternator a 100A FD one, and then underdrive it by 20%, you end up with an 80A alternator. So for the price of an alternator and a pulley you've achieving exactly zero improvement.

Underdriven alternators are completely unnecessary on street cars anyway. The downsides far outweigh the minimal benefits.

 

Those are opinions, not facts. Help him out, if he gets a 225amp alt, and underdrives it by a 20%, he will still have 180amp...

Plenty for a SERIOUS sound systems

 

and if its not, thats why God made capasitors. They are life savers!

 

Well, capacitors are band-aids on a serious sound system, but they still work in the right places.

NZ, I'm not talking about an underdriven alt pulley, I'm talking about an underdriven main pulley. I understand that underdriving a bigger alt is pointless. It's simple math really. I'm asking because of the warning that Racing Beat has on their underdriven main pulley page about it being a danger of producing enough power for the accessories.