Does anyone have any experience with lightweight crank pulleys ?
Do they work ?

 

They wheel is simply to small a diameter for lightening it to make any measurable difference.

Take 4-5kg off your flywheel instead.

 

I'm concerned that I would have too much trouble of getting used to the rpm's dropping too quickly with a lightened flywheel though.

 

Eh? You'll just get used to it.

Incidentally, if you're worried about a lightened flywheel causing you problems, lightened pulleys will cause exactly the same effect, albeit less pronounced.

 

I've got a 4 Kg flywheel and it makes gearchanging easier. Just have to get used to it to avoid stalling the engine when starting off.

Les

 

I fitted light weight pulleys. They look good and the ones I fitted are smaller diameter and under drive the alternator and power steering but by a small enough amount not to be noticable. From memory the total weight saving was 3kg. On its own I cannot say I noticed any difference.
I also run a 5.2 kg flywheel from Roger Clark Motorsport. It took a little getting used to, to avoid stalling occassionally. The only down side I have found is that drag 1/4 mile starts are more difficult but then how often will you do these.

 

Yes they work, but they cause you charging system to underrun because most of them are smaller in diameter. So lights inside the car and headlights can be more yellow.

 

This won't be the case if all three pulleys and belt are bought as a kit.

If all three wheels are reduced in diameter by the same percentage, with the belt shrunk to suit, the rotation speed of the alternator and PAS pump will be the same as with the standard setup.

Of course, with smaller pulleys, the belt tension needs to be higher to generate enough friction to prevent slip, so question would be whether the increase in power loss through the belt would outweigh any gains from the reduction in rotating mass...

 

Perrin make a nice light crank pulley - stock size, but does lose the harmonic balancer. Can't comment whether this will have an effect or not....haven't fitted it yet.

Richard

 

Above a certain RPM, in my case 1400/1600rpm, the alternator output is adequate to exceed demand on the battery. Also remember I am running a small motor bike battery in place of the O/E and even with that I have experienced no problems or yellow lights etc. although I am careful to limit demand on the battery when the engine is not running.

 

am a little confused here.

You arent changing the input drive pulley on the crank shaft, so the belt size is irrelavent, its linear speed is the same.

in one turn of the crank the belt will move about 6 (2pi) times the radius (r) of the crank drive pulley, this means that the smaller pulleys you have just fitted will need to turn faster in order to displace the same 6r of belt.

linear velocity is constant as it is determined by the crank pulley, this is the belt speed, linear velocity V = Wr where W is angular velocity ie. the rpm of the alternator etc.

if r of the alternator or powersteering pulley goes down, then W its angular velocity, must go up to maintain the same belt speed.

This will make the engine harder to drive as it has a greater load on it.

The only thing is, these things are an established product, so i can only assume I have made a mistake somewhere.

Can someone please point it out to me?

 

Anyway I'm going for just a lightweight pulley (MrJosh@nasioc), don't want the hassle of finding a new smaller belt. According to general information on the Net, the 'gains' are mostly due to reduced weight. Will post my results later.

 

Lightweight and underdrive are two different properties pulleywise.

Lightweight simply means lighter construction, therefore less mass to rotate.

Underdrive will increase the diameter of the driven pulley relative to the drive pulley, thus lowering the speed at which the accessory is driven relative to the engine speed.

If you keep the standard crank pulley, along with it's integral harmonic balancer, then you would need to increase the diameter of the acessory drive pulleys in order to "underdrive" them. These larger diameter pulleys would tend to be constructed from lighter materials/designs than the smaller diameter OE units they were replacing.

 

would a lightend flywheel make a car faster down the 1/4 mile strip?

any figures for reduced times with just a lightend flywheel?
i would be instrested in this, when its time to change the clutch

 

I am not sure any gain would be quantifiable in terms of 1/4ml times. My own experience of going from a 9.2kg flywheel to a 5.2kg was that getting a good start is more difficult and requires a different technique. Cannot say there were direct performance gains, tick-over was marginally lumpier and it is far easier to stall when setting off. Going from the standard flywheel of around 12kg to the 9.2kg I could find no detectable change in performance, tick over or driving characteristics.