msd overdrive alternator pulley?

moneypit94

Active Member

May 23, 2003

1,723

2

39

Macomb, IL

Jul 14, 2010

#1

• Jul 14, 2010

• #1

I have been watching my dumby voltage guage and noticed it moving coming off idle. Well i Just remembered that I have underdrive pulleys and never replaced the alternator pulley.

I found just an overdrive alternator pulley on ebay that should put the rpms of the alternator back to about stock. But then I found one from MSD that "should" fit that would actually put the rpms little higher.

Stock i think is 57mm, this overdrive pulley is 48mm, and this msd one comes out to be about 42mm.

ebay listing said:

Ford alternator overdrive pulley. Has an outside diameter of 1 7/8" (48mm). 6 grooves

Will increase idle output by 20amps, over the standard 3G 57mm pulley, used on 94-95 GT Mustangs. For use on 87-93 Mustangs with 3G upgrades and underdrive crank pulley.... or use on 94-95 with underdrive crank pulley, to get the alternator speed back to stock RPM.

6 groove 48mm pulley

Click to expand...

So to help out at idle i was thinking maybe it would be benificial to have some more amps then stock? I need to replace the one i have but which route would be best? Plus with the monster fuel pump, tranny cooler fan and anything else i have added it might not be a bad idea?

 

HISSIN50

"How long does it take to get help in here?

15 Year Member

Nov 29, 1999

31,179

33

129

Jul 14, 2010

#2

• Jul 14, 2010

• #2

Just make sure you don't overdrive the alternator. 3G's dont like to spin over 15K RPM.

 

4Jenna

Founding Member

Sep 12, 2001

4,326

6

69

AZ

Jul 14, 2010

#3

• Jul 14, 2010

• #3

I took mine in and had a 200a stator installed for 60$ at the local starter/alt place.

Helped my car out alot. I had similar issues, with the stock pulley.

-Chris

 

4Jenna

Founding Member

Sep 12, 2001

4,326

6

69

AZ

Jul 14, 2010

#4

• Jul 14, 2010

• #4

Also I may have a stock pulley collecting dust in my tool box, you can have it if you want it.

-Chris

 

moneypit94

Active Member

May 23, 2003

1,723

2

39

Macomb, IL

Jul 14, 2010

#5

• Jul 14, 2010

• #5

It has a stock pulley on it now. I bought a used alluminum underdrive kit from a guy without alternator pulley. My chrome alternator has a chrome pulley and all i was thinking at the time was it goes nicely with the other pulleys. Its supposed to be a 200 amp alternator but at idle its spinning slower then it should be now.

I haven't done the math to see what rpms it will be running. Does anybody know what size a normal crank underdrive pulley runs?

 

toyman

10 Year Member

Jul 19, 2007

1,944

54

79

Vernon BC

Jul 15, 2010

#6

• Jul 15, 2010

• #6

moneypit94 said:

I haven't done the math to see what rpms it will be running. Does anybody know what size a normal crank underdrive pulley runs?

Click to expand...

About 127mm (5"). 127/42 x 6000 rpm = 18000 rpm. That will over spin the alternator. The 48 mm one will spin it at 15800 @ 6000 rpm. Some underdrive cranks are a little bigger so the numbers will increase as the crank pulley gets larger.

 

moneypit94

Active Member

May 23, 2003

1,723

2

39

Macomb, IL

Jul 15, 2010

#7

• Jul 15, 2010

• #7

thanks for the info. I ordered the 48mm. Was like 18 dollars after shipping. Im not sure with it being an aftermarket alternator if it would have overspun it at 15,000 rpms but its best to be safe anyway.

 

revhead347

Apparently my ex-husband made that mistake.

20+ Year Stangneter

Jun 14, 2004

9,296

1,640

214

Acworth, GA

Jul 15, 2010

#8

• Jul 15, 2010

• #8

The voltage dropping at idle a little bit isn't that big of a deal. As long as it doesn't drop below the battery voltage I wouldn't even worry about it.

Kurt

 

4Jenna

Founding Member

Sep 12, 2001

4,326

6

69

AZ

Jul 15, 2010

#9

• Jul 15, 2010

• #9

So if you rev to 7200rpm the what

hehe