I am looking to add a little alternator rpm by way of running a larger crank pulley on my 360.

My Powermaster alternator wants about another 75-100rpm to put out what I need to keep 14v. My current setup is:

Alt Pulley: 2.7"
Crank Pulley: 6.7"
Ratio: 2.5:1

Powermaster recommends a 3.5:1 ratio for low rpm/automatic configurations. My crank pulley is as shown with a 6.7" "base" pulley and the secondary single belt pulley bolts in as well.


What options are out there to run a larger "base" pulley?

iirc on my SB I had a 7&1/4 dia crank pulley & it was very close to the dampener dia. EDIT I've seen (2) different dia OE alt pulleys. EDIT the one I had was 3 or 4 grooves & it needed a smaller pump pulley to clear

I'm not sure those LA crank and water pump pulleys came in different diameters? Getting a different diameter alt pulley would be another way to get there, but again I think they are all the same size. If you had a friend with a lathe you could always have one made out of aluminum.

Beat me to it. I would throw the alternator pulley in the lathe and recut the V to reduce the diameter slightly. Measure over pins to keep track of progress. Should be less than a hour labor, maybe twenty minutes for someone that has cut a few and has a stub arbor and tooling ready to go. These little jobs like this have paid for my lathes over and over through the years.

mancini racing offers two or three different diameter alternator pulleys (single grove). i believe their powermaster as well .

So far, not much of an update unfortunately.

The truck now has EFI with a pretty stable 750rpm idle, small electric fan and it will flirt with 13.0v when idling in gear. Which is "okay", but I am not content with that.

I have a call setup today, hopefully, with Powermaster to discuss options.

I may just have to make an alternator pulley myself, but I prefer not to disassemble the new alternator to do so, but it seems like a necessary evil. The largest factory crank pulley I have seen is 7.125", a 6% improvement. I may try to find one of those first before tearing into my new alternator.

Goody,

I've been experimenting with pulleys on my 340 Cuda this summer and have found the following which may be of help:
(1) The OEM 3 groove A/C crank pulley for a 340 has the following diameters. 2 innermost grooves are 7 1/2 inches, outermost groove is 7 5/16 inch. So if you use the inner grooves, your pulley ratio would be around 2.8:1.
(2) Do you use the post-70 solid state voltage regulator? If so, there is one available with an adjustable output voltage from www.alternatorparts.com. I use one on my Cuda and the voltage is set at 14.6V which works well for me.

Hope this helps

Thanks, do you happen to have the part number for the 340 pulley? That seems like it would certainly help.

For question two, this is an internally regulated alternator, no Factory Mopar wiring a all.

Probably not what you want to hear. But ditch the oem style for a modern alternator. My go to for EFI swaps is the 90's Toyota 4-runner alternator. Small, cheap at junkyards and internally regulated. AndyF makes brackets, But you can easily make your own.

The Denso alternator I had ~10 years ago on my 'Cuda didn't seem to do much better at idle. It discharged with the HHR fan running and no a/c. Perhaps others ended up with better idle performance than I did, but I am hesitant to jump to that one just yet.

Next step is a bigger crank pulley unless Powermaster has a bright idea.

Hi Goody,
The pulley is currently on my car, so I can't get look for the part number. But here's an ebay auction with a pulley that looks like it. It shows the P/N to be 3614377. Judging by the pics, the diameters look right, but you'd better confirm with the seller.
Good luck!

How old is that Powermaster alt ? firts versions of them were the regular 78-80 amps units already existant from stock on mid 80s. These are able to source around 45-48 amps at iddle ( and this is actually talking about 2000 alt rpms ) which having cooling fans could be not enough. Newer 90-100 amps version could be more adequate able to give around 55-60 amps iddling

From the distance, the alt already have the smaller pulley available for these alts.

I'll take a gander, thanks!



The alternator is brand new and ordered recently. As my truck sits right now, I am getting about 1,800 alt rpm while the engine is at 750 rpm. I got off of the phone with Powermaster today and there's really no good ideas coming from them other than a smaller pulley [which doesn't exist] or a new larger crank pulley [which seems to exist].

A buddy of mine has a lathe, so I will provide him my stock alternator pulley to turn it down. If he can get it from 2.7" OD to 2.3" OD, we'll be in business. At the same time, I am going to try to source a larger crank pulley.

is there enough meat in the "v" section to turn those pulleys down without making the side wall section super thin ?

I found this cross-section online for a dual pulley, seems like it.

looks good.

just for curiosity, what are the specs for it ? rated output ?

A larger crank pulley will spin everything faster (a/c, water pump, power steering) which will cost power.
The smaller alternator pulley will solve the problem you're having without that loss, which will also cost fuel economy.
Every bit helps.

Per the handwritten card included with the alternator.