VAC Race underdrive pulleys - do they work ?
 

I am trying to get a bit of extra speed from the CSL without causing any issues and the underdrive pulley mod always seemed to make sense.

The idea is simple.
Underdrive the water pump and the power steering pump.
Less rpms on both water pump and power steering pump.
Engine cooling should not be affected as the water will have more time to cool down in the radiator and the tuners claim there is temperature decrease in the power steering circuit.

I ordered a set of VAC Ultralight pulleys from Martin (trackm3).
VAC (as other tuners) claim 8hp gain throughout the powerband.
They come with the longer belt.

Here are the photos ;)

The new VAC pulleys. Excellent build quality.
http://www.clubcsl.com/CSL/pulleys/I...20_1126229.jpg

The OEM pulleys. Also made from aluminium.
http://www.clubcsl.com/CSL/pulleys/I...20_1126335.jpg

VAC water pump pulley. 137mm diameter. Weight 214g
http://www.clubcsl.com/CSL/pulleys/I...20_1127209.jpg
http://www.clubcsl.com/CSL/pulleys/I...20_1128574.jpg

OEM water pump pulley. 116mm diameter. Weight 211g
http://www.clubcsl.com/CSL/pulleys/I...20_1127350.jpg
http://www.clubcsl.com/CSL/pulleys/I...20_1128431.jpg

VAC power steering pulley. 147mm diameter. Weight 304g.
http://www.clubcsl.com/CSL/pulleys/I...20_1127554.jpg

http://www.clubcsl.com/CSL/pulleys/I...20_1128261.jpg

OEM power steering pulley. 121mm diameter. Weight 153g.
http://www.clubcsl.com/CSL/pulleys/I...20_1128061.jpg

http://www.clubcsl.com/CSL/pulleys/I...20_1128347.jpg

The steering wheel now feels a bit stiffer, nothing too dramatic. I like it.

Now the performance results part.
I made the tests with the exact same conditions (temperature / wind), in the same performance track using my RaceChrono telemetry (10Hz GPS).
Weight of the car was exactly the same and I used only 3rd gear to eliminate differences from gear changes.

Speed from-to (km/h) -> Before (secs) / After (secs)

60-130 -> 5.7 / 5.6
60-150 -> 7.5 / 7.3
100-150 -> 4.3 / 4.1
130-150 -> 1.8 / 1.7

As you can see the car is up to 200ms faster in acceleration.
This is a significant change (same effect as reducing 32kgs from the CSL).
See this post here -> http://www.cslregister.com/forum/sho...3&postcount=84
Also note the difference in the times... this is the difference between 0 Celcius temperature and 25 Celcius :)

I am looking forward to test them on the track and see the difference in top speeds :beer:

The pulleys definitely improve the performance and in my opinion they cost very little considering the gains !
Highly recommended !

i have the 3 pulley kit and is a good mod. Nothing extraordinary, but...

Had for a while, took off while under warranty.

Wouldn't bother again

I fail to see how under-driving these by approximately 10% will make any significant difference. The steering will feel the same at 5000rpm as it used to at 4.5k rpm, I can't say I have noticed any engine speed dependance on steering feel, if it got gradually lighter at higher engine speeds it would be odd. Likewise for the 8hp change, seems a lot to me. That is 5kW of energy thaf was being soaked up, I assume it went to heat? Any independent dyno tests available, or better still tests of the power steering pump to see power required at different speeds?

MC

Difference in the reduction of the steering wheel pump is ~17%.
It makes difference as there is reduction of the losses.
The telemetry shows the results in my opinion and the gains are very clear at least to me.

My understanding was there is a pressue regulating valve in the PAS system to cap system pressure, given the requirement for low speed manoeuvring / parking etc I would guess it reaches max pressure at fairly low engine speeds so any perception of steering feel changing at high rpm on track is likely to be placebo?

I run them on my car (not sure which make), mainly just to give the various pumps an easier time when it is constantly at high RPM - for potential reliability alone I like them.

No idea on performance improvements but if the data (not telemetry unless you are braodcasting it :P) shows an improvement then fair enough - one thing I can say is I don't believe there is any way it can make it slower so why not :)

Fair point Nathan :thumbs: :hahaha:

Alex i'm a little bit confused. The VAC pulleys are heavier!?

They have to have a bigger diameter to under drive so it stands to reason.