Can someone explain an Underdrive pulley?

[camarohead]

Originally Posted by Jon@Texas-Speed

I have never seen an issue caused by an underdrive pulley other than a charge issue. If you did need it, you could run the overdrive alternator pulley and I don't see how it could hurt anything at all.

Jon

thx for the info jon.....underdrive pulley it is. might as well get all the hp i can get when i do the cam change.

[ITGuy11]

If you plan on a supercharger in the future, do not install an underdrive pully!

[Spartan01]

They can be a good idea.
Here is why:
Less parasitic loss of the accessories. So, imagine you had to run a mile with a 40Lb backback on. Now imagine just before you start you take 10Lbs out of the pack. This is a quick and dirty version of the same concept.

Also, most high quality underdrive pulleys are lighter than the stock pulley. Cutting weight is important, cutting rotational mass and weight is even more important. This is a part that is literally moving right at the crank, so any kind of weight reduction will be beneficial.

In response to SaltyFlats: i had a 96 mitsubishi eclipse that would always throw the belt after the underdrive pulley was installed. After a while I was able to figure out that this particular model was very easy to accidentaly install beckwards. The difference of belt placement was less than 1/2 of an inch. This was enough to cause the belt to jump. Just something to check, make sure the pulley is on correctly.

[LSX Camaro]

Originally Posted by cab2g

The under drive pulley never sounded that exciting to me for that reason. All your belt driven accessories will run more poorly. The mod may be cheap, but it has too many negatives for me to really want to use it. But, I'm not knocking anybody who uses one. A strong AC just happens to be a priority of mine!

Fluidampr makes a 25% underdrive pulley that keeps the A/C pulley at the stock size.

[dekan513]

with a cam its a good ideal . ur cam will idle higher which will make up the diff from the pulley so should turn about the same from idle. which is were it will count. i didnt do one with my cam but i think im gonna go back and do one. on a max effort n/a stock cubes bulid.

[LS3 SS]

Originally Posted by Spartan01

They can be a good idea.
Here is why:
Less parasitic loss of the accessories. So, imagine you had to run a mile with a 40Lb backback on. Now imagine just before you start you take 10Lbs out of the pack. This is a quick and dirty version of the same concept.

Also, most high quality underdrive pulleys are lighter than the stock pulley. Cutting weight is important, cutting rotational mass and weight is even more important. This is a part that is literally moving right at the crank, so any kind of weight reduction will be beneficial.

In response to SaltyFlats: i had a 96 mitsubishi eclipse that would always throw the belt after the underdrive pulley was installed. After a while I was able to figure out that this particular model was very easy to accidentaly install beckwards. The difference of belt placement was less than 1/2 of an inch. This was enough to cause the belt to jump. Just something to check, make sure the pulley is on correctly.

Bringing back a 2 year old thread?

[the_fast_one]

My ac still blows ice cold and hard and my volts are still above 12 volts with everything running. Yesterday was 109* and there was no problem listening to the radio, charging my phone, and max ac. Also seems the motor revs a little easier aka faster.