i have a 88 n/a with underdrive pullys among other things. i am having trouble charging the battery with more than 3 acceries running. the altenator just cant keep up. i know that a fd altenator can be adapted to a fc. is there anybody out there that makes a 80-100 amp altenator for the fc that is a bolt on?

 

This issue has been covered a few times already, but I'll save you the trouble of searching for it.

The 89-91 FC's alternator puts out 80 amps, compared to the 86-88's 70 amp unit. My 87 n/a is also facing the same problem, but has killed my battery at least 4 times already. Since the difference between the S5 FC alternator and the FD alternator is maybe $20, I just got a FD alternator and either get the pulley swapped or get one from banzaitoyota, made to fit the proper application.

The other option available is to go to an alternator shop and get it rebuilt to put out more power, but that would depend on the shop's reputation, skills and so on.

One thing I should tell you: The pulley is going to be a b*tch to get off there. I still haven't gotten mine to budge, and I've had my FD alternator for over a week. The process to swap it voer is covered here, but you can search for that in the FC archives

 

Put the stock pulleys back on. The underdrive pulleys are not helping the situation and for minimal power increase (if you can even measure it at all) are not worth the hassle.

 

agreed!

 

i think my 6 port is doing well with it being on stock ports. right now im at 153hp 105ft/lb of toqure. the pullys made 7hp and 4ft/lbs. i have more to do to it before i switch to a 4 port na. i should be at 170-180 by june (still on stock ports).

 

Dito What Aaron Cake said about the pulleys. You may get some power gains (although I REALLY doubt 7 hp) but you still need to keep your battery charged.

I have the stock s4 alternator and the stock s4 pulleys and I have no charging issues except with headlights, front and rear wipers, heater, and rear defog all running. Under those circumstances I have to drive in 4th gear to provide enough current for all the accessories.

I am not trying to poke fun, but 153 Hp and 105 lb-ft of torque????

I believe the 153 whp, but the torque is quite low.

(Bone stock except for advanced timing and aftermarket mufflers mine made 138 hp @ 6300 rpm and 136 lb-ft. @ 2500 rpm at the wheels.)

I find it difficult to believe that you are making that much horsepower with that little torque.

The numbers mean that you must be making 105 lb-ft of torque at 7650 rpm (which I seriously doubt on a stock-port, OEM fuel injected s4 NA) to make 153 horsepower.

You might want to check your numbers.

 

7HP (which is within the margin of error on most dynos) is not worth continuing charging problems if you plan to drive the car on the street.

 

If you stick w/ the underdrive pullies, only thing I can think of is turn the idle speed up a bit. Unless you're having problems charging going down the road, in which case the alternator is probably weak. Does it undercharge at all rpms, or just in the lower ranges?

 

This may be a newb question, but my car has alternator issues as well. At idle (750rpm), my voltage gauge is reading 12 volts even and doesn't improve untill I have the engine going at least 2000rpm.

Is this normal?

 

If you add the FD alt to make up for the lack of alternator output and upgrade the water pump to make up for the lack of coolant flow, then both will eat up more horsepower and you'll be right back to where you were before you bought the underdrive pulleys. Either increase your redline or go back to stock pulleys.

Akagis: Unless all of your accessories are on and cranked to full, this is not normal. Your alternator is failing. You can replace it now or wait until it dies. But you might get stranded with a dead battery, so carry some jumper cables. The voltage should be 12V when your car is off or your battery may be dying. Find a reference to a good local alternator shop and/or save your warranty info, because replacement alternators are a gamble in regards to how long they last. Don't buy online. That way returns will be easier if the need arises.

 

^^^^ Agreed, I bought an alternator off a guy on here, and it's starting to go out too. Only had it for three months. Thank god they aren't all that expensive!

 

Thanks for the answer, EricGrau, that was what I was thinking as well. A couple weeks ago, I bought an FD alternator at Advance Auto Parts with a lifetime warranty and just need to get the pulley for it.

 

Good, just make sure you save your warranty info, just in case. The lifetime warranty doesn't mean the alternator is any better. I should know...