underdrive pulleys

[akcamaro02]

i was lookin at getting an alternator and water pump underdrive pulleys but i was wondering
A. if they are both even worth it and
B. if an electric water pump would be better for the money than just a UD pulley.

Any charging issues with alternator UD pulley??

[LETZRIDE]

Re: underdrive pulleys

Ive used both an electric water pump and the UD pulley for the pump. The electric pump is better, and keeps the car much cooler.

[nwilson44]

Re: underdrive pulleys

i was lookin at getting an alternator and water pump underdrive pulleys but i was wondering
A. if they are both even worth it and
B. if an electric water pump would be better for the money than just a UD pulley.

Any charging issues with alternator UD pulley??

Not too sure with specifics about these products with our particular cars man, but the whole idea of under drive pulleys is to help REDUCE Parasitic loss. An electric water pump would ELIMINATE Parasitic loss on that particular pulley. It seems like you would not want to under drive your alternator because of the voltage loss you may suffer due to that. In addition I am not sure where you live but the heat really gets to it as well, when the A/C, Electric fans, ect are pulling on it. I just replaced mine with an AC Delco, and when its upper 90's and I am running my A/C it'll drop to around 13 or less.

Up to you man but the eletric water pump gets my vote. I would consider under driving my power steering as well just because I dont like the typical overboosted american car power steering.

Just a last note, if you wanted to, I would recommend the ATI Racing harmonic balancer and an electric water pump. I think that pair would give you the most positive affects you are looking for.

Hope this helps. (even though its coming from someone who doesnt know these cars all that well) :twak:

[FIREBIRDV6RAGE]

Re: underdrive pulleys

ive seen that electric water pumps gives more horse power since its taken out of the equation from being a load on the engines accessories belt. id say thats a plus :)

[akcamaro02]

Re: underdrive pulleys

yeah i know a guy who owned an ls1 and put an alternator underdrive pulley and he always had problems starting it on the first try, that what i wanted to be sure didn't happen.

so if you're using an electric water pump, what's the purpose of having an underdrive pulley on it then? isn't it electronically driven and not mechanically driven?

[nwilson44]

Re: underdrive pulleys

yeah i know a guy who owned an ls1 and put an alternator underdrive pulley and he always had problems starting it on the first try, that what i wanted to be sure didn't happen.

so if you're using an electric water pump, what's the purpose of having an underdrive pulley on it then? isn't it electronically driven and not mechanically driven?

The electric pump eliminates the pulley all together. An electric motor turns the impeller as opposed to the pulley attached to the crank. Someone made a comment about it running cooler after the electric pump switch. I am guessing because when you under drive the factory unit, you slow down the flow of coolant throughout your block in exchange for less drag on your crankshaft.

[akcamaro02]

Re: underdrive pulleys

so wouldn't the flow on an underdrive be lower than a stock pulley? any negative side effects to that? overheating? etc..

i've heard goods and bads about the Electric WP, some say it's good, some say it goes bad too quick, some say it's only good if you do city driving and at higher speeds can't produce the coolant flow the engine needs..sounds like one of those things that is hit or miss.

just haven't heard any negatives about the underdrive but using logic, the flow must be lower if the pulley is turning at a slower speed.

[LETZRIDE]

Re: underdrive pulleys

underdrive pulley should technically spin the pump faster.

the EWP flows thousands times better than the belt driven pump. If you really want to see, pop the cap on the rad when it's cool, flip the pump on on and let it run for 10 seconds or so...then flip it off while the cap is still open, just don't have your face anywhere near the hole because it erupts like a volcano.

My car with an EWP and 160* thermostat runs stupidly cool...in fact I am running probably a good 15-20 degrees cooler from when I did have an underdrive pulley. My car barely sits between the first and second line of the temp gauge and doesn't move.

Actually, Last summer when we were diagnosing some issues I had with the car, the electric wire pulled off the battery (because we forgot to tighten the bolt down) and the car almost overheated on a a WOT blast down the street. The car was almost at redline, so much to the point that it was hissing as the overflow spilled out.

I hooked the pump back up and ran the pump/fans for about 3 minutes and had the car back down to ambient temps.

[nwilson44]

Re: underdrive pulleys

so wouldn't the flow on an underdrive be lower than a stock pulley? any negative side effects to that? overheating? etc..

i've heard goods and bads about the Electric WP, some say it's good, some say it goes bad too quick, some say it's only good if you do city driving and at higher speeds can't produce the coolant flow the engine needs..sounds like one of those things that is hit or miss.

just haven't heard any negatives about the underdrive but using logic, the flow must be lower if the pulley is turning at a slower speed.

http://www.vividracing.com/catalog/w...m5-pulley1.jpg

Under drive means that you are literally UNDER driving the pulley. This calls for a smaller pulley which means the angular velocity of the pulley is less because the pulley's radius is smaller and travels the same distance at a given engine speed. This allows the engine to work less on that given accessory because it doesn't have to spin the larger pulley in the same amount of time that it does the smaller one.

Logical example. If you are idling at around 600 RPM, and your stock Water pump pulley has a Diameter of 5 inches. (all theoretical here) This means that your 5 inch pulley has to rotate at 600 RPM along with the engine. So the distance your pulley travels is the circumference of the pulley or the distance around the outside of the pulley. (C=2piRadius).

So if you UNDER DRIVE It you use a smaller pulley to reduce the distance of rotation, therefore causing your engine to work less to turn a specific pulley because it does not have to rotate it as far.

If you under drive your water pump, you are actually flowing less coolant because the belt is still covering the same distance over a given amount of time and the pulley is smaller. In order to correct this you would have to increase the size of the crankshaft pulley.

So decreasing the size of your water pump pulley, slows down the circulation of your coolant. The electric water pump is good because it is not dependent upon an engine RPM. It can turn independently of the engine and keep the flow rate of coolant up when the engine is turning relatively slow (Idle for example). It will also eliminate the pulley all together, which frees up some power.

So basically if you want to reduce the work load on your engine, you can decrease the size of your pulley's. This will allow your engine to turn them slowly relative to the crank pulley's speed and free up some power. However, this comes with consequences. If you under drive your water pump you decrease the flow rate of coolant. If you under drive your alternator, you are spinning it slower and therefore producing less voltage at a given RPM. Power steering would be the one I would do because It would give you less assist and not allow the over boosted feeling you get.

All of those set backs with the alternator and water pump are greatly increased when its hot outside. 95+ degrees. Think about it. Hope this helps.

[nwilson44]

Re: underdrive pulleys

So if this is more clear then think about it this way. A smaller pulley travels less distance in the same amount of time as a bigger pulley. So at 600 RPMs a 5 inch pulley travels twice as far as a 2.5 inch pulley in the same amount of time. This means the 5 inch pulley HAS to travel faster to accomplish a rotation in the same amount of time as a 2.5 inch pulley.

I think this is easier to understand.

[bigbrian442]

Re: underdrive pulleys

Lots of bad information in this thread.

On anything but the crank.....The larger pulley spins the shaft slower. A smaller pulley spins the shaft faster.

On the crank.... a smaller pulley spins everything the belt drives slower. The ATI Super Damper is larger in diameter than the stock damper to spin super chargers faster.

[nwilson44]

Re: underdrive pulleys

Lots of bad information in this thread.

On anything but the crank.....The larger pulley spins the shaft slower. A smaller pulley spins the shaft faster.

On the crank.... a smaller pulley spins everything the belt drives slower. The ATI Super Damper is larger in diameter than the stock damper to spin super chargers faster.

I think you are right. The slower you can spin something on the engine the less power it robs.