calculated to be <1HP but only in the lower gears where the rate of change of RPM is greatest. In the higher gears where rate of change of RPM is much much slower no significant benefit at all.

I can provide calcs to prove the point - however consider this thought experiment.

How can a 1/4HP electric motor on a grind wheel accelerate from 0 to 6000RPM in <1seconds with its heavy grind wheel attached ?

Thus removing a few lb's of weight from a crank pulley when compared to all the other rotating masses is going to have a miniscule effect.

Removing weight from a crank pulley is much more significant on light weight high revving vehicles.

 

Timf so your point is that it is worth installing on our cars? From what I deduct the car might rev a tad faster? or not at all? We are not going to get more HP but get there faster....?

 

We saw an increase at the wheels of around 8-10hp. That was not calculated on paper, it was recorded on a dyno. The increase in power is due to the smaller diameter (underdrive) of the pulley as well as the decreased weight. Once again though, the original reason for doing the pulley was to eliminate the "backing off" issue that we were dealing with on our high HP builds. The added power that we found was just a pleasant surprise.

 

Are there any other benifits as allowing the engine to rev more freely?

 

Yes it revs quicker. Nothing too huge but better is better. (I hope that answeres the question)

 

Sent an e mail to Rodd please ask him to reply please

 

A couple of points

#1
A typical shop dyno has a measurement uncertainty much greater run to run greater than the calculated gain available from just a lightened pulley - see below.

The formula is I=(.5)(m)(r)^2, where "m" is mass in Kg and "r" is pulley radius in meters.

Now add this, a formula for horsepower required to accelerate a rotating mass:

P=(1/746)(1/s)(.5)(I)(omega^2),

where "746" is a unit conversion constant for watts to horsepower, "s" is seconds of time, "I" is inertia, and omega is engine speed in radians/second.

Combine the two equations and you get

Horsepower=(.25)(1/746)(m)(r^2)(omega^2)(1/s).

Plug-in some numbers for say 0-40 MPH. I choose 40 MPH to simplify the calculation by not considering gear changes.

Starting in 1st gear, it is running wide-open throttle, and it needs say 2 seconds to accelerate to 40. The radius of the crankshaft pulley is say 7.5cm. A weight of 4 pounds equates to a mass of 1.8 Kg. At 40 MPH the engine is turning about 6000 RPM, and this gives an omega of 628 rads/sec.

Crunching the numbers gives a result of just .7 HP. Insignificant. This is in 1st gear, in higher gears the gain is even less.

#2

Under drive accessory pulleys do reduce parasitic drag, but I doubt they consume 7.5kW or there abouts - more likely 4-5 HP but again within the measurement uncertainty of a typical shop dyno.

Bottom line - dyno runs are not proof of anything, just a marketing tool

Dyno's are good for tuning on the fly but not for making absolute measurements.

FYI I used to work in Formula 1 with air conditioned engine test cells and we could never manage better than 5% repeatability (no transmission in place which cause variable losses)

 

It does indeed, Thanks.

 

anyone with LWFW's run these? Feedback?

 

You are correct about gaining hp due to the under drive. We are figuring about 3 hp gain with a better response. What we are really looking for is the response. We lightened, pistons, rods, crank, pulley and clutch/flywheel. The complete rotating mass.

The members need to be aware that underdrive means exactly what it says. You will be underdriving everything the belt/pulley operates.

 

I run the RS pulley with my Aaco lwfw
Its smaller/lighter then stock

 

We just installed the EVOMS Lightweight UnderDrive Crank Pulley today for a customer of ours.. If I wasnt so tied up today I would have been able to take more detailed pics.. Ill be doing the same install on my GT3 and will take some more detailed photos..

I can tell you this.. The crank pulley fitment is SPOT ON.. The larger dowel is definitely a better design and the replacement bolt it comes with is very smart as well.. Its smaller and comes with the proper belt so its an underdrive pulley which means MORE HP.. How significant in a car that makes 600 or 700 Hp?? Thats hard to answer but any more HP without more boost along with being a stronger setup is a BONUS to me.. Below are some pictures of what i am referring to as far as the dowel, size of pulley etc..

 

Good stuff, thanks guys.

 

so for a stock 996tt tiptronic this will be any good ?!

 

I would also like to know...