Under Drive Pulley Kit?

gungfudan · Dec 2, 2018

I am changing out everything on the cooling system soon and adding an electric fan. I am wanting to go ahead and put an Under Drive Pulley Set on. I am having trouble finding a brand to go with anyone know which brand I should go with?

gungfudan · Dec 3, 2018

I keep seeing underdog pulleys being mentioned on old forum posts when I do a search but I guess they went out of business. I found the crank pulley but not a whole kit. I don’t want my alternator to not charge the battery.

adsm08 · Dec 3, 2018

Wouldn't changing the alternator pulley out to keep the ratio the same almost completely defeat the purpose?

The alternator has the heaviest rotating inertia in the FEAD, and the idea of an underdrive pulley is to change the ratios between the crank and the rest of the drive to make them "lighter" at the cost of their rotational speeds. It seems to me like going through all that trouble to install the under drive crank pulley would be almost completely defeated by keeping the drive ratio of the heaviest piece the same.

gungfudan · Dec 3, 2018

That makes sense when you explained it like that. I did not look at it that way I was going off the post I read. Basically the posts are saying that they were buying a kit. I also write a review on an under drive pulley made my jet performance that I found on SummitRacing.com That stated the person now had a voltage drop when running heater, ac, etc... so that is why I asked about a whole kit. But the way you explained it makes sense.

adsm08 · Dec 3, 2018

gungfudan said:
That makes sense when you explained it like that. I did not look at it that way I was going off the post I read. Basically the posts are saying that they were buying a kit. I also write a review on an under drive pulley made my jet performance that I found on SummitRacing.com That stated the person now had a voltage drop when running heater, ac, etc... so that is why I asked about a whole kit. But the way you explained it makes sense.

They aren't called under drive because they make the driving gear spin faster than the others, but because they cause the driven stuff to move slower than the original design.

This will cause the alternator to under charge, mostly at idle, and can be noticeable with a lot of electrical load. In extreme cases you can also get cooling issues at idle because the water pump is spinning slower too. Most of these problems aren't really there once the engine gets off idle.

pjtoledo · Dec 3, 2018

where is the proposed electric fan getting it's power from? a slower alternator isn't what you need.

if anything, a smaller crank pulley is all you need. that decreases all the accessories.
if you frequent heavy stop 'n go traffic a slower cooling & charging system is the last thing you need. if you're out in the country and at hi speeds all the time I can see real benefits from the under drive.

some guys that run under drives increase the idle speed to compensate.

McCormack 2 · Dec 3, 2018

Underdrive pulleys are not worth it in my opinion. Although I've never run them, I have a hard time believing that there is anything but the slightest bit of performance to be gained, and it doesn't make sense to slow down your alternator and water pump.

I do however have an electric fan, and I noticed a small but worthwhile performance gain, especially on throttle tip in. I also like that my engine is quieter.

gungfudan · Dec 3, 2018

McCormack 2 said:
Underdrive pulleys are not worth it in my opinion. Although I've never run them, I have a hard time believing that there is anything but the slightest bit of performance to be gained, and it doesn't make sense to slow down your alternator and water pump.

I do however have an electric fan, and I noticed a small but worthwhile performance gain, especially on throttle tip in. I also like that my engine is quieter.

And this is why I ask questions. I was running an electric fan either way. But I will not be installing an under drive pulley.

McCormack 2 · Dec 6, 2018

dancron · Dec 15, 2018

I've had my underdog performance pulley set in my truck for the last 8 years with no issues. No cooling issues even on the hottest summer days sitting in NJ traffic.

However, I believe the overall power gain is negligible from the under drive, its in the weight. The pulleys are significantly lighter then the factory set. Less rotational mass will allow the engine to rev faster, much like converting from a clutch fan to E-fan.

Unfortunately underdog performance is no more, so you'll have trouble finding the pulley set. IMO you should get an overdrive alternator pulley if you install the e-fan. You may run into charging issues without it. You wouldn't want to make your truck less reliable for a negligible amount of power.

gungfudan · Dec 17, 2018

dancron said:
I've had my underdog performance pulley set in my truck for the last 8 years with no issues. No cooling issues even on the hottest summer days sitting in NJ traffic.

However, I believe the overall power gain is negligible from the under drive, its in the weight. The pulleys are significantly lighter then the factory set. Less rotational mass will allow the engine to rev faster, much like converting from a clutch fan to E-fan.

Unfortunately underdog performance is no more, so you'll have trouble finding the pulley set. IMO you should get an overdrive alternator pulley if you install the e-fan. You may run into charging issues without it. You wouldn't want to make your truck less reliable for a negligible amount of power.

I actually ran into an issue when I was taking off old parts. I need to move the wires to the alternator. So I went to remove the main wire going to the battery and the nut was so corroded that it would not come off. It was actually make the stud come out of the alternator. So I figured since it was that bad I would get a new alternator so I upgraded to the 130 amp alternator. I have had no issues so far with charging. The truck actually runs better without the belt driven fan. I mean it runs way better.

Under Drive Pulley Kit?

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