Alternator pulley size????

Jtmoney714

Jtmoney714

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I’m replacing my stock gm alternator with a 240amp Mechman unit. It comes with a 1.75”pulley. I believe stock is in the 2.5” range. Should I leave the 1.75 on or swap with old alternator? Or do the 3” pulley other places sell?
 

Old alternator seemed to work fine but when I had all my lights on the voltage would drop from 13.8 to 12.8 at anything above 3k rpm. Roll off the throttle and voltage jumped back up. Could be belt slippage or maybe it was undersized. But either way I’m starting fresh. 

 
A small pulley is going to slip easier, but it’s also going to spin the alternator faster.  Some alternators quit charging when they’re spun to fast.  Max recommend alternator rpm seems to be around 18000, so you’re probably above that when the engine is over 4500.  I’m not saying that’s what your problem is, but it’s worth looking into.

 
Do the 3'' we just had some made with the 1/4 high side rib,  Went rounds and rounds with these guys, Mechman thinks we are cruzing around at idle needing 200 amps under 1000 rpms,  and then when you rev it up and burn it up they make you almost pay for a new one, 

you dont need 200 amps at idle, so i would go with the 3'' pulley, 

Running a 3'' pulley my altenator is around 10 years old, it has never gone out,  

 
J Alper said:
Do the 3'' we just had some made with the 1/4 high side rib,  Went rounds and rounds with these guys, Mechman thinks we are cruzing around at idle needing 200 amps under 1000 rpms,  and then when you rev it up and burn it up they make you almost pay for a new one, 

you dont need 200 amps at idle, so i would go with the 3'' pulley, 

Running a 3'' pulley my altenator is around 10 years old, it has never gone out,  
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Thanks. Stopped by redline and grabbed 3” pulley. For those who swap out this pulley… I needed an inch longer belt. 

 
 
 
Are all of the alternators from  Fullthrottleguy ebay source good or just that GM model?

 
Bumping this old thread as I am texting JTmoney as we speak.

This past weekend I was dropping voltage real bad and having starting issues with the car. I do need to get my car re-wired also. 

Is everyone having goodluck with the mechman and 3" pulley?

 
Banshee380 said:
Bumping this old thread as I am texting JTmoney as we speak.

This past weekend I was dropping voltage real bad and having starting issues with the car. I do need to get my car re-wired also. 

Is everyone having goodluck with the mechman and 3" pulley?
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Have burned up a couple of Mechman also with the small pulley, Yes everything needs a 3'' pulley with the stock balancer 

I would try to keep the RPM on the alternator around 13,000 RPM,  

18,000 RPM for a continuous time will burn up any alternator 

Not sure your balancer size, stock balancer is 7.4''  

We Make 3.2'' High Rip Alternator Pulleys if you need one,  

 
I just picked up one of those 250 amp alternators from that eBay link. It replace my previous alternator that looks to have the same 4 pin plug with only a single wire landed on the L terminal. It seems like that L terminal is supposed to sense switched voltage through around an inline 500 ohm resistor. I put my volt meter on that L terminal and I am reading around 9V when my actual battery voltage is at around 12V. I am assuming the resistor is reducing the voltage this amount. Is there something I am missing?

 
3" for sure.

Both CBM and Redline sell their high output with the 3" pulley.

 
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