Originally Posted by flemdeazy

Thanks Justin, those are all really good ideas. I will get on putting my car on a diet tonight. I have an automatic, so could I still get the pulley you mentioned? Thanks again. Very good advice.

Originally Posted by flemdeazy

Thanks Justin, those are all really good ideas. I will get on putting my car on a diet tonight. I have an automatic, so could I still get the pulley you mentioned? Thanks again. Very good advice.

Originally Posted by Inaccurate

The pulley is not about HP gain. Thus, the dyno might not reflect a gain.

The pulley is about dynamic weight loss. The dynamic weight loss is equivalent to removing 100 lbs from the car. And, a 100-lb reduction in weight is good for 1/10 reduction (one car length) in your 1/4 mile ET. It is equivalent to adding 10 HP to the car in terms of the performance improvement.

Don't worry much about stock size or undersize. The gains come from the lightweight, not from the diameter.

The pulley is about dynamic weight loss. There is a weird, inexplicable phenomenon that happens when gaining performance via weight reduction. I can not explain how or why this phenomenon occurs! But from my experiences with removing weight from my car (from small chunks to big chunks), the phenomenon is real. When gaining performance improvements derived from weight reduction, you will feel *less* g-force after the weight reduction mod. Therefore, do not use the sensation of increased g-force (aka, Butt Dyno) to evaluate the performance improvements from the UR Pulley... it won't be there.

This inexplicable phenomenon is "at play" when people say "It revs-out quicker but doesn't feel quicker". I read this comment often in regards to the pulley. I agree that it does rev quicker. However, I do not agree with the attitude in which it is stated. It is implied that "yes, it revs quicker but the car is not quicker." Now, think about this for a second. How can the engine rev quicker without the car gaining the respective MPH too ??? The transmission gearing did Not change. It is quicker.

Do Not use the Butt Dynometer to measure the performance improvements from your TL Diet (click here)

Originally Posted by csmeance

Also to add in my on it, the pulley works by reducing spinning mass. More torque is required to spin a heavier object, simple physics. The UR Stock Diameter Pulley does just this. It's lighter thus allowing the motor to use less power to spin the crank pulley.

Now the question is how this will affect the car, it does in many ways. First and foremost is the reduction in parasitic loss from spinning unnecessary weight. Second comes the benefit of time; the UR pulley, both stock diameter and under-drive, allow the motor to rev up slightly faster to a given point. The reason for this is the same as the first, less load on the motor.

Some simple calculus could show this, your dy/dx or a(t) of the equation of power required to spin the pulley over time would should you the slope at any given point in the RPM range. This equation would use the relationship (Related Rates) of the weight of the pulley in regards to how much power is required to spin it during a given time period. The overall graph of the UR pulley would be steeper due to the decrease in time that it takes the motor to rev.

To experience this, rev your car in neutral, it jumps up pretty quickly. Now do the same thing in drive, it'll take a bit longer as now the motor has quite a load to move. (not recommended to try this for extended periods nor bang off the rev limiter, don't break your car and blame me...)

As far as the under-drive pulley, it works by helping further remove parasitic loss from other components of the car such as Power Steering. The car is using power to spin the other components at a given RPM, lets say 1000. With the stock pulley being 7 inches in diameter, that means the belt is moving at 7pie/revolution = 21.98 inches every time the pulley spins. This times 1000 RPM means that it's moving 2198 inches a minutes at 1000RPM.

The UR pulley with it's reduced diameter (I believe it's 6.5 inches) using the same equation will come out to 20.41 inches/revolution or (13pie/2)/revolution meaning it'll be moving 2041inches per minute at 1000RPM.

In stupid terms, the belt is moving less, thus giving less power to the other components.

The question is will you feel this power using a butt dyno or see it on a dyno at a shop? The answer is yes and no. You will see, hear and feel the motor rev up faster, thus allowing you to get into the power band faster. However will you feel that surge of power you get when you go from a low HP car to a high one, no. At the dyno shop, will you see it, yes and no. Dyno's can easily have an error of 2%, so with a 200 WHP car it can be + or - 4 HP. The UR Stock diameter pulley will barely add any measurable power, may be 3-4 WHP the UR one, maybe 5-7 WHP. The real benefit is having less load to spin thus allowing you to unlock the power band faster and thus acclerate faster.

Remember, a dyno does not measure how fast your car is, it measures how much horsepower and torque you have. It can give a general idea of track times, however the only way to find them out is go to the track and try it yourself.

In my honest opinion, to spend 200+ dollars for 5 WHP isn't worth it, I'd rather spend the money elsewhere such as on an ipod or something.