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8/10/2026 7:01 AM  #1


Recommendation for a Hi Amp Alternator in 66 EFi 302

Please can anyone recommend an alternator for my 66 302 EFI which runs a serpentine belt. 
My old alternator just gave out and to be honest it seemed to be struggling at idle to produce power as the fuel pump could be heard to reduce in noise significantly. I think the old alternator was a 75A and im looking for a 130 or 150 but will be advised by your responses. Please also recommend where to purchase as I will be visiting my uncle in California soon and can get one delivered to his address and then bring it back to the UK.
Thanks for the usual excellent help.


Bullet Bob equipped car,
 

8/10/2026 10:06 AM  #2


Re: Recommendation for a Hi Amp Alternator in 66 EFi 302

I bought a Bosch 3G alternator for a 1995 Mustang with a 5 liter from Rock Auto in 2017. The part number at the time was AL7534N. It's still working good. You might want to think about fuses to protect the wiring. There are several illustrations on the internet to copy for the conversion, if necessary. 


John  -- 67 Mustang Coupe 390 5 speed
 

8/10/2026 11:27 AM  #3


Re: Recommendation for a Hi Amp Alternator in 66 EFi 302

I use and have good results with Powermaster alternators. 

 

8/10/2026 11:39 AM  #4


Re: Recommendation for a Hi Amp Alternator in 66 EFi 302

Thanks for the replies. The AL7534N looks good and is a replica of my current alternator but with a bigger output. That would fit the bill.


Bullet Bob equipped car,
     Thread Starter
 

8/10/2026 1:38 PM  #5


Re: Recommendation for a Hi Amp Alternator in 66 EFi 302

I got mine from Powermaster too.  I suppose any 3G would work, but you may have to clock the housing, etc.  

 

8/11/2026 5:04 AM  #6


Re: Recommendation for a Hi Amp Alternator in 66 EFi 302

As previously suggested, if you’re going to a high amp output alternator, be sure to fuse it correctly.  Without proper protection, if there is a short, these alternators can help make quite a fire.


65 Fastback, 351W, 5-speed, 4 wheel discs, 9" rear,  R&C Front End.
 

8/11/2026 8:37 AM  #7


Re: Recommendation for a Hi Amp Alternator in 66 EFi 302

I took a look at the Power Master Alternators and was surprised at the output. I'm going to order one of those and the fused connector. 145A at idle will keep the fuel pump etc running at a good rate. Thanks for all the info.


Bullet Bob equipped car,
     Thread Starter
 

8/11/2026 9:36 AM  #8


Re: Recommendation for a Hi Amp Alternator in 66 EFi 302

Some powermaster alternators do not provide good output at idle.   Notice I said some as I am sure some will take exception to this. This depends on the engine speed and pulley ratios, of course, and not all of them appear to have this problem.  I do a lot of support on the Holley EFI forums and I have seen enough low output at idle issues and noisy power to recommend staying away from the 1-wire alternatives.  Just my experience.  The Ford 3G alternator in the 90 or 130 amp ranges provides consistent clean power down to idle and works well with EFI as well as high current loads like fans or pumps.  A real benefit of the 3G over the one-wire alternatives is that they are available nationwide at parts stores where an aftermarket unit may be days away.  The last two installs I did use a Delco branded 3G from Summit and in my truck I am still running a pick and pull take-off after 10 years.

=13pxhttps://www.summitracing.com/parts/ADO-335-1113

 

8/11/2026 11:00 AM  #9


Re: Recommendation for a Hi Amp Alternator in 66 EFi 302

GPatrick wrote:

Some powermaster alternators do not provide good output at idle.   Notice I said some as I am sure some will take exception to this. This depends on the engine speed and pulley ratios, of course, and not all of them appear to have this problem.  I do a lot of support on the Holley EFI forums and I have seen enough low output at idle issues and noisy power to recommend staying away from the 1-wire alternatives.  Just my experience.  The Ford 3G alternator in the 90 or 130 amp ranges provides consistent clean power down to idle and works well with EFI as well as high current loads like fans or pumps.  A real benefit of the 3G over the one-wire alternatives is that they are available nationwide at parts stores where an aftermarket unit may be days away.  The last two installs I did use a Delco branded 3G from Summit and in my truck I am still running a pick and pull take-off after 10 years.

I agree 100.

=13pxhttps://www.summitracing.com/parts/ADO-335-1113

 


Bullet Bob equipped car!
 

8/11/2026 11:20 AM  #10


Re: Recommendation for a Hi Amp Alternator in 66 EFi 302

GPatrick wrote:

Some powermaster alternators do not provide good output at idle.   Notice I said some as I am sure some will take exception to this. This depends on the engine speed and pulley ratios, of course, and not all of them appear to have this problem.  I do a lot of support on the Holley EFI forums and I have seen enough low output at idle issues and noisy power to recommend staying away from the 1-wire alternatives.  Just my experience.  The Ford 3G alternator in the 90 or 130 amp ranges provides consistent clean power down to idle and works well with EFI as well as high current loads like fans or pumps.  A real benefit of the 3G over the one-wire alternatives is that they are available nationwide at parts stores where an aftermarket unit may be days away.  The last two installs I did use a Delco branded 3G from Summit and in my truck I am still running a pick and pull take-off after 10 years.

This is an interesting distinction. I do not have fuel injection and can't really hear my radio, so I wasn't concerned with clean power, nor can I comment on that application. I have used Powermaster in various high load applications for over 20 years and am satisfied with the quality and support. I use an AGM battery which likes a higher charging voltage and I have dual electric fans which pull a lot of amperage, so I called Powermaster and the tech advised that the alternator would put out 130 amps at idle and about 15. something volts. I can't find the test tag that came with the alternator, so I don't have a clear recollection of the output voltage. I am not pushing Powermaster, it just fits my needs at this time.

=13pxhttps://www.summitracing.com/parts/ADO-335-1113

 

 

8/12/2026 6:46 AM  #11


Re: Recommendation for a Hi Amp Alternator in 66 EFi 302

If you install the 145-amp alternator, make sure that you size the wiring and fuses for the circuits accordingly.  I doubt the original alternator cable was designed to current 145 amps.  And you don’t want the individual circuits exposed to that amount of amperage.  That is one reason modern vehicles have so many fuses installed.  


65 Fastback, 351W, 5-speed, 4 wheel discs, 9" rear,  R&C Front End.
 

8/13/2026 11:40 AM  #12


Re: Recommendation for a Hi Amp Alternator in 66 EFi 302

I'm running whatever came with my CVF setup.

 

8/18/2026 3:11 AM  #13


Re: Recommendation for a Hi Amp Alternator in 66 EFi 302

Thanks for all the replies which I have taken note of. I do intend to run two fans when I get my AC up and running. I did contact Powermaster with my requirements on two occasions via email but did not get any response. I will not be over to California until November so I have plenty of time to get one ordered to bring home. I am not set on a 145A but just need something that will give me high Amperage even at idle so your alternator "Boss347 Convertible" sound just ike what I am looking for. Even if I have to change the pulley size to get the current up will be fine but I have to remember to get the appropriate size Surpentine belt to go with it.


Bullet Bob equipped car,
     Thread Starter
 

8/18/2026 10:00 AM  #14


Re: Recommendation for a Hi Amp Alternator in 66 EFi 302

gkm24, Powermaster should be able to supply voltage/amperage figures at any given rpm. I would figure out your alternator pulley ratio, take into account your idle, cruising and power rpms, and ask Powermaster to install a pulley that meets your needs. I don't know if Powermaster will install or provide such a pulley, but it might be worth asking. Good luck.

 

8/19/2026 5:44 AM  #15


Re: Recommendation for a Hi Amp Alternator in 66 EFi 302

boss347convertible wrote:

gkm24, Powermaster should be able to supply voltage/amperage figures at any given rpm. I would figure out your alternator pulley ratio, take into account your idle, cruising and power rpms, and ask Powermaster to install a pulley that meets your needs. I don't know if Powermaster will install or provide such a pulley, but it might be worth asking. Good luck.

In addition, provide Powemaster your idle RPM.  Typically, the alternator's RPM is 2 to 3 times engine RPM. 


65 Fastback, 351W, 5-speed, 4 wheel discs, 9" rear,  R&C Front End.
 

8/19/2026 5:57 AM  #16


Re: Recommendation for a Hi Amp Alternator in 66 EFi 302

BobE wrote:

boss347convertible wrote:

gkm24, Powermaster should be able to supply voltage/amperage figures at any given rpm. I would figure out your alternator pulley ratio, take into account your idle, cruising and power rpms, and ask Powermaster to install a pulley that meets your needs. I don't know if Powermaster will install or provide such a pulley, but it might be worth asking. Good luck.

In addition, provide Powemaster your idle RPM.  Typically, the alternator's RPM is 2 to 3 times engine RPM.  And the alternator needs about 2000 RPM to provide power. 

 


65 Fastback, 351W, 5-speed, 4 wheel discs, 9" rear,  R&C Front End.
 

Board footera


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