Underdrive Pulleys

Joe Dirt

Active member
Joined
Aug 29, 2008
Messages
35
Location
Kootenay
Will be getting underdrive pulleys for my 85 vette. They claim .1-.2 seconds off the 1/4 mile times. Sounds like a good idea.
 
Yeh, for a track only car, good idea.....problem is on the street, the alts don't put out enough at idle, and the water pumps don't circulate enough and cause overheating problems, and too boot sometimes the steering gives problems too....

I thought of that too, but after listening up for a while to all the complaints, I decided to leave well enough alone on that one....

YMMV....
 
Yeh, for a track only car, good idea.....problem is on the street, the alts don't put out enough at idle, and the water pumps don't circulate enough and cause overheating problems, and too boot sometimes the steering gives problems too....

I thought of that too, but after listening up for a while to all the complaints, I decided to leave well enough alone on that one....

YMMV....

I have to agree here. We put them on the "57, and now it is too hard to steer at idle.
 
I had them on my 70 when I had the stock motor in the car. The problem I finally ran into was at the Grand Run in Pigeon Forge Tn. Bumper to bumper traffic and I was idling along with the fan running as hard as it could go. We were listening to the radio and charging a cell phone at the same time. This was the first time I had ever ran into trouble with my car on the road. All the draw ran the battery down far enough that the car died right in the middle of all that traffic. I managed to get some help pushing the car to the shoulder of the road. Got it jumped off and held the RPM's up while I took the car to a parking lot to work on it. Removed the battery and alternator and took them to Autozone and had them checked. Both checked good. The only thing I could attribute the car stalling was the dead battery. That and my idle was around 650 RPM, definitely not enough speed to keep a charge on the battery with that load.
 
Yup had them on my 82, to get the alternator to charge above 12 on the dash I have to rev the engine up once. Other than that no problems, didn't overheat or kill the battery.
 
I see underdrive crank pulleys sold with a smaller alternator pulley to compensate. However, I hear about too many people taking underdrive pulleys off of street cars.
 
So here is what I am thinking:

A 30% underdrive pulley would be fine if you planned accordingly.

My truck idles at 600rpm or so, so if you had a good water pump and idled at say 900-1000rpm you'd be straight.

My firebird also drove down the street on the highway at 2000rpm or so, my corvette with the muncie and a 3.55 rearend cruising at around 3000rpm would also be fine.

A low RPM motor would not like an underdrive system.
 
I have them on my 84. To be honest I really bought them because they look nice and dress up the engine compartment :rolleyes:
I found that there were NO problems with cooling as some claim. The kit was from March #4445 http://www.marchperf.com/pg10.htmlIt included an undersized alternator pulley which promptly TOASTED the alternator the first time out!
I replaced the smaller pulley #112 with the almost stock size #208 sold in their peformance series kit (#4130)http://store.summitracing.com/partdetail.asp?autofilter=1&part=MCH-208&N=700+115&autoview=sku

The alternator runs PERFECTLY. It is only average .5 amps lower than it ran with stock pulley. There is NO major loss of Amperage at Idle with ALL accessories, lights etc!!! :hi:
 
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