do underdrive pulleys really help? Options

[nate95]

Just curious if any body had put an underdrive pulley on there car, and how much of a difference it made, or how much HP you gained,, thanks.

[celicaST]

Just curious if any body had put an underdrive pulley on there car, and how much of a difference it made, or how much HP you gained,, thanks.

first off, you are NOT going to gain any horsepower. only way to gain more power is to burn more fuel, end of story. what you will gain though is engine response as there is less rotational mass for your engine to turn as it revs up. this is just like installing a lighter flywheel or reducing the weight of your car. your engines power puts energy into both accelerating your car forward and acceleraing the rotating components in your car. so technically it will make your car quicker, but think about it... a few lbs of weight off of the underdrive pulley is very minimal percentage wise (add up the mass of all rotating comonents: gears, axels, wheels, crankshaft, etc). i dont have one, but im willing to bet you wont notice a difference at all. dont be a fool for marketing, in my opinion that money can be better spent at making your car faster.

This post has been edited by celicaST: Aug 5, 2006 - 3:53 PM

[Bitter]

most aftermarket underdrive crank pulleys...
1. dont have a dampener so they are much more likely to throw random misfire codes
2. will spin the alternator, PS pump, ect much faster and that can cause accelerated wear, damage to the alternator/voltage regulator/electrical system, difficulty turning due to less torque drivingt the PS pump, and a host of other undesirable issues.

[Kwanza26]

most aftermarket underdrive crank pulleys...
1. dont have a dampener so they are much more likely to throw random misfire codes

Actually most stock toyota crank pulleys don't have dampners... unless of course you consider the rubber glue that holds the two piece, twin row pulleys together 'dampners'... What about the single row ones than?

2. will spin the alternator, PS pump, ect much faster and that can cause accelerated wear, damage to the alternator/voltage regulator/electrical system, difficulty turning due to less torque drivingt the PS pump, and a host of other undesirable issues.

Quite opposite actually... think bike chain. smaller pedal pulley (crank pulley)= less force needed to drive rear wheels (accessories)... but consider the engine doesn't actually spin faster (rpms when driven) and is also dictated by the tranny... the accessories actually spin slower because of the reduced crank pulley size. Make sense? Take for example... an overdrive pulley for superchargers. These are typically larger... as opposed to underdrive pulleys which are smaller.

IMO... an underdrive pulley along with weight reduction is actually the better mod to do compared with exhausts and such (on an n/a motor). Its closest equivalent is something like direct weight loss to the crank... which is similar to a light flywheel.

[pure_dx]

in some cars, it works better, and in some it wont do anything, for the 5s and 7a, i'd stick to stock pulleys

[m0dd3d1]

in some cars, it works better, and in some it wont do anything, for the 5s and 7a, i'd stick to stock pulleys

i'd second that! i bought an Unorthodox Racing underdrive pulley, and you really can't notice a difference, it's supposed to add a bit of torque, but it was an impulse buy, and totally not worth it!

[Kwanza26]

The difference also depends on the engine. On the 5S... an UD pulley isn't gonna be as helpful as it would to a 7A. This has a lot to do with how the underdrive works, where in the powerband it benefits, and the type of engine. The 5S being the big stroker... will feel much less gains from mods that reduce crank load (UD pulley, light flywheel)... because it has a big stroke versus a short rod. The 7A too has a fairly big stroke for its rod length, but not quite to the degree of the 5S.

[Bitter]

most aftermarket underdrive crank pulleys...
1. dont have a dampener so they are much more likely to throw random misfire codes

Actually most stock toyota crank pulleys don't have dampners... unless of course you consider the rubber glue that holds the two piece, twin row pulleys together 'dampners'... What about the single row ones than?

2. will spin the alternator, PS pump, ect much faster and that can cause accelerated wear, damage to the alternator/voltage regulator/electrical system, difficulty turning due to less torque drivingt the PS pump, and a host of other undesirable issues.

Quite opposite actually... think bike chain. smaller pedal pulley (crank pulley)= less force needed to drive rear wheels (accessories)... but consider the engine doesn't actually spin faster (rpms when driven) and is also dictated by the tranny... the accessories actually spin slower because of the reduced crank pulley size. Make sense? Take for example... an overdrive pulley for superchargers. These are typically larger... as opposed to underdrive pulleys which are smaller.

IMO... an underdrive pulley along with weight reduction is actually the better mod to do compared with exhausts and such (on an n/a motor). Its closest equivalent is something like direct weight loss to the crank... which is similar to a light flywheel.

yea, i goofed up on the 2nd point i was thinking of smaller acessory pulleys.


my crank pulley has a thin rubber peice between the crank peice and the belt peice, i doubt that my 7afe and the ST's 7afe have different crank pulleys. its not as robust a peice of rubber as other pulleys ive seen but its there.

[K-ESD]

Thanks Kwanza26 for your knowlege and solid answers
I learned something new today

[Bigmeanbulldog55]

Kwanza always bashes on the 5sfe motor, especially in NA trim. I have wanted an underdrive pulley, but I'm worried about the rpms needed to run accessories. Everyone knows the 5s is a happy at lower rpms. That is the rod/stroke thing Kwanza was talking about. You would regularly have to run the motor faster to make accessories work propperly. I have a light weight flywheel, and it picked up a little, but not much. Every little bit helps though. If anyone has an underdrive pulley for the 5s that they are willing to sell because they didn't like it, I'll buy it, as long as the price is right.

[puretone]

underdrive pulleys, not balanced, is all i gotta say....just like the balancers on your driveshafts, i wouldnt mess with those, there was ALOT of engineering put into them for a reason!

This post has been edited by puretone: Aug 10, 2006 - 10:55 PM

[Bigmeanbulldog55]

underdrive pulleys, not balanced, is all i gotta say....just like the balancers on your driveshafts, i wouldnt mess with those, there was ALOT of engineering put into them for a reason!

The crank is what is balanced. The pulley is semetrical, I don't see how it's used to balance.

[Bitter]

pulleys need to be balanced as well, not to mention that most crank pulleys have a rubber dampener that helps to absorb vibrations so you dont get erroneous misfire codes.

its about DSM's but can be applied to most any other motor http://www.machv.com/tip11cranpul.html

This post has been edited by Bitter: Aug 11, 2006 - 1:16 AM

[Kwanza26]

pulleys need to be balanced as well, not to mention that most crank pulleys have a rubber dampener that helps to absorb vibrations so you dont get erroneous misfire codes.

its about DSM's but can be applied to most any other motor http://www.machv.com/tip11cranpul.html

All gospel... at least when it comes to toyota engines. Those "rubber damners" do absorb vibrations... but it's nothing more than glue for the most part. If it were such a big deal, little things like over tightened drive belts, slightly overtorqued/undertorqued pressure plate bolts, grease build up... would all upset the crank balance. I've run underdrive pulleys on damn near every performance engine we've built at my shop... and never had a problem for 8 some odd years. Myth. There's a lot more needed to upset the crank balance than a crank pulley weighing a few pounds less. Hell... driving the car hard upsets the crank balance more than an underdrive pulley...

[ExSane]

I've also learned some new stuff. Thanks Kwanza26.

[puretone]

pulleys need to be balanced as well, not to mention that most crank pulleys have a rubber dampener that helps to absorb vibrations so you dont get erroneous misfire codes.

its about DSM's but can be applied to most any other motor http://www.machv.com/tip11cranpul.html

i was in 'duh' mood yesterday, i was thinking harmonic balancer. regardless those underdrive pulleys are made with specific weight for a reason tho right?

[Fastbird]

first off, you are NOT going to gain any horsepower. only way to gain more power is to burn more fuel, end of story.

I didn't see it posted, so I thought I'd clear up a point here. The above statement is isn't ecactly right (don't get me going on the burn more fuel part). Yes, you can "gain" power by putting an underdrive pulley on a car. However, I quoted gain because it's not a overall gain in the normal terms, but rather the reconstitution of parasitic power losses by the motor not having to work as hard turning all the accessories.

[pandakid]

where can you get pulleys?

[AllTrac96]

kwanza i don't see you come around very often but when you do your knowledge is generally right on the spot and very well explained. thanks for the info!

[DeW_H0e_GT]

where can you get pulleys?

first site i can think of is nopi.com