Alternator Underdrive Pulley

[blykins]

Anyone ever had issues with their alternator pulleys being too big in diameter? If my engine is idling, the alternator will not charge the battery....If it's over say 2000 revs, it will charge. All of this being verified with a battery charger with an alternator checker on it.

It's a pain in the butt....especially recently...the car has been idling a lot while tuning on the carb....it hasn't been charging the battery enough...which didn't give my MSD enough juice to really give me a good spark....sooted the plugs up and it had a little miss to it....

I'm running March pulleys.....guess I'm gonna have to look for a smaller one....any ideas?

[HighPlainsDrifter]

Hi,
I ran a 5 liter mustang with underdrive pulleys, same thing happened,low charging so I just put the stock small pulley back on the alternator, works good after that. The stang picked up 1 tenth in the 1/4, .010 isn't worth the hastle.
Perry.

[blykins]

That's what I thought...when the battery is getting low, I can tell it.....I can rev the engine over 2 grand and hear the fuel pump get louder and see my key switch ignition light get brighter....

I have March pulleys....wonder if they offer a single alternator pulley by itself?

[djseed]

I had the same problem with my BB and underdrive pulley set. At Idle or just off idle it couldn't keep up with the 2 fans, lights, blinkers and MSD. I was using the standard 1 wire Ford 70 amp chrome alternator. Another SPF fellow had the same problem and recommended the PowerMaster alternator - 8-37140. It produces about 80 amps at idle without the underdrive pulleys. With the underdrive set it worked perfectly and I have not had a low battery since the change. It came as a kit with the larger charging wire for the starter.

http://www.powermastermotorsports.co...le_chrome.html

[oldmachdriver]

Im wondering if this what im facing...i just had my battery tested and the alt. both were fine but the the alt was a 61 amp...and when i run the external electric fans the amp meter nose dives....im thinking i may need a larger alt.

[392cobra]

"I have March pulleys....wonder if they offer a single alternator pulley by itself?" - blykins

Well,it is a good news/bad news type of deal.

You can buy individual pullys from March.But in all their many different sets the alternator pulley size remains the same.
2 11/16" dia..

Yesterday I ordered a 5 1/4" water pump pulley to replaced my 6 1/4" directly from March.
Performance pulley to high water flow pulley.

The crank pulley in the two sets are the same too, 5 1/2".

http://www.marchperf.com/pg33.html

[vettestr]

Hello All,
I am a Kit manufacturer and see a couple of issues that haunt cars on a regular basis. One of them is underdrive pulleys regardless of manufacturer so not picking on March, they have good quality products for sure.
I will not install underdrive pulleys in our shop because of the compounded problems they cause like overheating = low voltage that has hurt on board computers etc.... I have researched replacements and go the other direction in most cases or driving the waterpump at a higher RPM for low speed driving and heat problems. We install a simple toggle switch on the alt. to affectively turn charging off for short timed runs but then allow full charging when the stop watch is clicked off. We do install deeper grooved pulleys to keep from loosing belts at high RPM with great results. We also have our rebuilder/supplier of starters and alt. (HOT ROD) the parts to increase performance at low RPM and have solved hidden problems by doing so.
Our alternators. will have 90% output potential at 1500 rpm so no voltage sags in stop and go traffic or parades are a thing of the past. Our cooling systems or waterpump will maintain a minimum of 12PSI at 1500 RPM because this is the magic minimum pressure to ensure coolant absorbs the maximum amount of heat from engine to let the radiator do its job and run at least a 18 PSI cap always. (this was a trick Ron Davis of Davis Rad taught me) A toggle switch on the alternator plug wire allows driver to turn off charging system for timed runs but then charge at high rate when flipped back on because of other mods by our builder. Unless you have special need for the only way your car is driven stay away from underdrive pulleys. The tiny % of improvement offered for a very narrow area affects all the other parameters of your cars usage in general.

[DAVID GAGNARD]

After expirementing with under drive pulleys for about a year on three different vehicles (street car,p/u truck,race car) and talking to 2 different manufacters of pulleys,I have found out you DO NOT need under drive pulleys and SHOULD NOT use under drive pulleys on anything but a race car NOT used on the street...........

On a street driven vehicle I have found the crank pulley should NOT be anymore than 1 inch diameter smaller than the water pump pulley..........By going to under drive pulleys,you MAY save 5 to 10 hp tops,not worth it for the overheating/charging problems...........I used under drive pulleys on my street 65 Fastback for a year and was always watching the water temp gauge in traffic,not worth the headache!!!!!!!!!!!!!! Now,my crank pulley is exactly one inch diameter smaller than my water pump pulley and I can drive the Forth of July parade with my daughter in 100 degree heat for 45 to 60 minutes,the first 45 minutes the temp stays on 180 (180 thermostat),after 45 minutes of idling it slowly climbs and after another 15 minutes or so it is all the way up to 190,which I can live with,can't remember the last time it was past 195...............

Under drive pulleys are NOT WORTH the few hp you save for a street driven vehicle,even the March people will recommend only use them on full blown race cars!!!!!!!!!!!!!!!!

David

[Frank Messina]

After doing some inquiring, March directed me to their "Power and Amp" series of pulleys which I used on my motor. I'm really happy with them. I have 14V at idle from my 3G and no issues with cooling. Got lucky for once.
Frank

[wizard]

I have visited this issue as well, and the problem with going to a smaller pulley is that you don't get enough bite on the smaller pulley and the belt will slip (As explained by March tech). The correct solution is to go to a larger crank pulley. This will also increase your water flow and the "parasitic" load on the engine. But as stated very well previously above, the hp gains aren't worth it staying "underdrive".
(edited for typos and grammer - mwj)

[Jack21]

March has at least two (and possibly more) pulley ratios to choose from. The popular underdrive ratio (which causes charging, and cooling problems), and a "Street Rod ratio" which is more suitable for street driving. I'm using the street rod pulleys, and have no issues with charging, or cooling.

Using an Edelbrock water pump, 180* thermostat year round, and a standard Delco alternator.