Underdrive Pulleys?

[rubicon_in_ga]

I've heard of drag racers and hot rodders using underdrive pulleys to eek the last little bit of horsepower out of a motor. Just wondering if this idea has ever been applied to the multifuel engines since these beasts are already a bit anemic in the horsepower department? Honestly I don't know much about underdrive pulleys except that they're supposed to reduce drag and resistance from belt driven accessories on the engine like the alternator.

For the record, I do plead ignorance because I don't own a Deuce yet, so I'm not even sure how many belts these engines have or if it'd even be a practical modification.

 

[rattlecan6104]

some guys here have flat out replaced their fan with an electric unit. Not under driving the system, but definately freeing up a little extra power along the lines of what you are thinking. I am thinking however it is a moog point with these engines, I dont notice an rpm change when the air compressor kicks in like one would when their A/C unit kicks in on their car.

 

[eric_banks32]

They work by slowing down the alternator and water pump and such which puts less drag on the motor freeing up power. Most people in the hot rod world don't use them anymore because your losing accessorie efficiency to pick up a marginal power gain. It was a short lived fad. The only real gain is in a high reving motor. I'm talking 7-8000+. At that RPM alternators don't like to last so slowing them down a bit helps. There is more to be gained by getting the fan off the front of the motor but finding an electric one that can flow enough air would be the problem then. My . Look elsewhere for more power.....

 

[rlwm211]

I would guess that the only power you could possibly reap from unloading a fan belt driven device on a deuce would be to get rid of the fan. The fan is NOISY. If a fan is NOISY it is moving a ton of air, probably more than necessary and in many cases where none needs to be moved at all. I have heard of someone putting an electric fan on a deuce to cool the radiator and coolant on an as needed basis. whether this is reliable in the south in the heat you have is unknown.
As far as the Alternator and air compressor go, you have such little electrical load on a deuce to make the alternator work at all once the batteries are charged. The air compressor runs on demand and I would say making it turn slower would lonly make the compressor cycles longer.

So, the only potential horsepower robber is the fan and how many it sucks up is yet to be determined.

RL

 

[rubicon_in_ga]

Thanks for the responses guys! I figured the fan would be a major horsepower robber (mechanical fans usually are) but I didn't know what other belt driven accessories a Deuce might have since I don't have one to look at in person yet. I'm pretty handy with automotive electrical so the electric fan idea may be something to look into when the time comes. Thanks again!

 

[m16ty]

I really don't even think an electric fan would make enough difference to matter. On big heavy diesel engines, your're just not going to notice anything. On hotrods, a fraction of a hp could mean the difference in winning and loosing going down the strip (where times are measured in fractions of a second). The deuce is a whole different animal.

IMO, the only practical way to get very much more hp out of the deuce is to either pump more (cooler) air into the engine or swap engines.

 

[doghead]

If you want a drastic increase in power and speed, drive with both windshields fully opened!

You won't actually gain any speed (or power) but, with all that wind in your face it feels like you did!

 

[Josh]

 

[Kohburn]

underdrive pulleys are really intended for engines that are pushing high rpm. the high rpm puts a much more excessive load on the components like the alternator and water pump.

in the case of the water pump it can even cause cavitation which stops the coolant from flowing when it is most needed.

on a low revving engine like the deuce there will be almost no change in power however the systems will likely not be able to get enough rpm to function.

imo to free up power you need to get rid of the unclutched mechanical fan.

 

[Ridgerunner]

When I bought one of my Mustang GT's it already had the underdrive pullys on it. When the car is at idle, it will not charge the battery. There just isn't enough RPMs at the alternator, at a stop light or in stop and go traffic.

For something you drive on the street, it's a complete waste of money. For something that sees lots of track time, where tenths or hundredths of a second count, sure.

 

[Jake0147]

I look at it like this-

The belt system drives the fan, the water pump, the alternator, and the air compressor.

The alternator is not placed under a high demand anyhow, and it's demand (engine load) will NOT change with engine RPM. No gain.
The water pump is very small relatively speaking, (as are most all in a full flow cooling system design) and even when the thermostat is closed, the full flow of coolant is required to redistribute heat within the engine from a few crazy hot areas to the entire rest of the engine. I wouldn't want that underdriven.
The air compressor, like the alternator is a fixed demand, but it's a little different. While it's pumping you could free up a couple of ponies (literally, a couple) by pumping slower, but then your air does not build as quickly as it should. While the compressor is more than adequate, I wouldn't call it overkill, and surely not something I'd want to compromise on since I don't believe it's something that you'll feel from the driver's seat.

It really comes down to the fan. There may be a mathematical formula (I'm sure there is...) that could approximate the actual horsepower it costs at any given RPM, but I don't know it. Based on other published facts and some extrapolation (read-my best estimate), I think you're looking at fifteen plus, maybe eighteen ponies at the rated speed. That's something right there, but underdriving that alone (if it could be done...) is going to net you three or five of that back, and still compromise the cooling on the few times that you need it.

I'd look into the electric fans. They still place their full load on the engine (via the alternator) but only when they're needed, and realistically I don't think the actual "on-time" will be all that much. Finding one large enough however may prove a challenge. A member here, SasquatchSanta played with this some on a bobber if you want to search through his posts. He's a little north of you and he still felt the need to put his original fan back in place during the summer months. He had an LDS installed, but it was turned back so far that I don't think it was making the horsepower (and thereby the heat) that an LDT in original trim would make.