upgraded pulleys??

[worknprog.99]

my buddy has a 3400 grand am and he said he installed all new pulleys and a slightly shorter belt ,, he says it has faster response and slight HP gain..? he caled it an underdrive pulley kit?? idk i wasn paying to muh attention but my question is does this exist?

[KenshinZero]

There are light waight pullys, I donno if there is a kit, but I know RSM and a few other companys make under drive pullys.

[worknprog.99]

yeah he mentioned rsm... does it really make any difference to add lighter pulleys?

[KenshinZero]

Any reduction in rotating mass will yield better acceleration, so I would imagine there would be a difference, the question is, would it be noticeable. I don’t think it would be if you just sat in the car and hit the gas, maybe on a dyno where you could see the numbers.

[worknprog.99]

do you have any links to the rsm website im not seeing the right one..

[KenshinZero]

Yeah, its linked under the Z-Spec, dont know if that will make a diffrence, you could always google it, lol


http://www.z-spec.com/catalog

[worknprog.99]

thanks... what exactly does underddrive mean? like what is the difference between that and stock ?

[CactusWill]

Smaller pulley, less drag. Might give you a couple hp but nothing spectacular.

[KenshinZero]

both stock and aftermarket pullys are the same, as far as there function.
This is the info I have:

http://en.wikipedia.org/wiki/Underdrive_pulleys

An Underdrive pulley refers to an aftermarket crankshaft or accessory pulley (such as an alternator pulley) that is designed to drive a vehicle's accessories at a slower rate than stock. Underdrive in general means the input rate of rotation in a system is greater than the output rate of rotation. However, an underdrive pulley is considered to be an accessory pulley that is larger than the stock pulley or a crankshaft pulley that is smaller than the stock crankshaft pulley, even though the accessory may not necessarily be underdriven with respect to the crankshaft pulley.

The original purpose of underdrive pulleys was to extend the life of the belt-drive accessories on race cars in the 1950s and 60s which were not meant to rotate at such high speeds. Such belt-drive accessories include water pumps, alternators, and power steering pumps. Underdrive pulleys did not become mainstream until the mid to late 1980s, with their introduction from March Performance for fuel injected 5.0L Mustangs, Camaros & Trans Ams. They also appeared for small displacement engines in the mid-nineties with the entry into the market of Unorthodox Racing.

Underdrive pulleys usually are marketed as a performance enhancing item that increases the torque and horsepower output of an engine by reducing parasitic drag caused by belt-driven accessories, but more importantly by reducing the moment of inertia. Horsepower gains from underdrive pulleys alone are usually minimal, 1-3 wheel horsepower depending on the engine. HP gains from being lighter can be significant, from 4-14 HP for normally aspirated engines and 12-25 HP for forced induction engines. These are some of the best HP improvements enthusiasts can find for their money.

[Psyfox]

Really only works on older car engines. I know a guy with an IROC-Z and he had one installed and it made a HUGE difference. That and I bet rear-wheel drive as something to do with it since it directly affects the torque produced at launch.

[AbHeLlRaZoR]

if they were for older engines why is there such a wide selection of them for different applications? but then again they could be like a throttle body spacer.

[Psyfox]

if they were for older engines why is there such a wide selection of them for different applications? but then again they could be like a throttle body spacer.

There was a seperate pulley for the drive shaft...I thought at least. I don't know for sure or even if that would have anything to do with anything. I just saw it.

[KenshinZero]

if they were for older engines why is there such a wide selection of them for different applications? but then again they could be like a throttle body spacer.

I think for the most part they are, realy only ment for a race only sort of car, where even a few hp can cut secconds off lap times and such.

[AbHeLlRaZoR]

it's not race only lol too small of a mod, I'm pretty certain they are for the drive shaft, there is also altenator pulleys... I would like to know more about this mod to see if it's worth spending the money or am I better off saving my money and get head work, cams, and a custom tune?

[KenshinZero]

it's not race only lol too small of a mod, I'm pretty certain they are for the drive shaft, there is also altenator pulleys... I would like to know more about this mod to see if it's worth spending the money or am I better off saving my money and get head work, cams, and a custom tune?

You would be much better off getting head work and a good tune, the power gains from that would heavly out weaigh pullys. The under drive pullys have nothing to do with the drive shafts, only the alt. A/C condensor, ext...

[WhiteV6]

No. RSM is not underdrive. FWD and RWD have nothing to do with this and an UD pulley will benefit both the same way. You want to keep the stock pulley for now until we get a real pulley with damper. These non damper pullies are not a good idea, as the pulses from combustion will be absorbed by the timing chain and the cam, to the lifters, and pushrods, and valve springs instead of dampened but the dampener at the crank pulley. Powerbond is looking at making us an UD pulley (3400) with the damper and since they make our stocker, its pretty much the way to go if they can make it. The 24x portion is their only concern at the moment, with fitting the damper portion in the pulley still.

Lighter weight helps, but its not going to make a huge difference in HP. Acceleration and deceleration, sure.

[alerored04]

Ben makes good points. I have a fast forward performance underdrive pulley and I am pretty sure it was directly responsible for the keyway on the crankshaft shearing which resulted in piston/valve contact. It did go 90,000 miles before that happened though. After installing I did not notice what you could call a large hp gain but the throttle response was quite a bit crisper. Was that worth the initial expense of the part? possibly. Was that worth the blown motor and headache to pull it and rebuild? The only reason I would say yes is that it resulted in the purchase of a cam and a more aggressive build on the car. Other than that, definitely not. I would not purchase one again.

[-Alero-]

Ben makes good points. I have a fast forward performance underdrive pulley and I am pretty sure it was directly responsible for the keyway on the crankshaft shearing which resulted in piston/valve contact. It did go 90,000 miles before that happened though. After installing I did not notice what you could call a large hp gain but the throttle response was quite a bit crisper. Was that worth the initial expense of the part? possibly. Was that worth the blown motor and headache to pull it and rebuild? The only reason I would say yes is that it resulted in the purchase of a cam and a more aggressive build on the car. Other than that, definitely not. I would not purchase one again.



yeah i have the FFP one as well, and i too think its responsible for my valvetrain problem....i believe i installed that pulley at 33k miles or so, got 92k, and runs like garbage