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.

[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.

[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.