light weight pulleys
- Thread starter mike1981
- Start date
Lightweight pulleys can upset the engine harmonics, lead to slight vibration on crank cycle, which could eventually cause you problems.. It's all engine specific though and I don't have any experience with them on 1.8T. Shouldn't put stress on other components, but some of the kits come with an underdrive pulley for the power steering.. Might not be worth it for minimal gains, especially on a road car.
In-line-four engines like our 1.8Ts need the dampening of crankshaft vibration to prevent the breakup at high engine rpms. This is not singular; flat-plane V8s can disintegrate themselves as well if undamped. For this reason, modern straight-four engines use a damped metal-rubber crank pulley - or a Fluidampr pulley, for whomever is ready to take the cost.
Alternator pulley is also a one-way clutched pulley. This makes it heavy, nearly 1 kg, compared to 0.13 kgs for an aluminum pulley. Lightweight pulleys on alternators do not bring great benefits, since most effort taken by the alternator is to overcome the magnetic eddy currents during electricity generation.
Power steering pump pulley may bring some gain if they are also underdriven - release some small amount of engine hp otherwise needed to run the pump, at the expense of increased steering effort.
BTW: original spring-driven belt tensioner can take one underdriven pulley, either power steering or alternator, but not both, one needs shorter belt for it.
Alternator pulley is also a one-way clutched pulley. This makes it heavy, nearly 1 kg, compared to 0.13 kgs for an aluminum pulley. Lightweight pulleys on alternators do not bring great benefits, since most effort taken by the alternator is to overcome the magnetic eddy currents during electricity generation.
Power steering pump pulley may bring some gain if they are also underdriven - release some small amount of engine hp otherwise needed to run the pump, at the expense of increased steering effort.
BTW: original spring-driven belt tensioner can take one underdriven pulley, either power steering or alternator, but not both, one needs shorter belt for it.
I would suggest under driven pulleys on alternators and power steering may have a small benefit on high revving units... 8krpm+ perhaps
leaving the crank damper in place or replacing it with a Fluidampr
leaving the crank damper in place or replacing it with a Fluidampr
However, if the power steering pump is the only one under-driven (slightly larger lightened pulley, as the Integrated Engineering model), this should result in a bit heavier steering, and therefore better stability / control over the steering at highway speeds?
Or it's an illusion and stability is just as before, while parking and slow speed steering gets annoying?
Or it's an illusion and stability is just as before, while parking and slow speed steering gets annoying?
I think in the rev ranges on racing, the change in speed would be impossible to perceive behind the wheel
I have never noticed a change, and I race, rev to 8600rpm in badgerwagen
I have never noticed a change, and I race, rev to 8600rpm in badgerwagen
Thank You
There was some formula floating around the net, showing how to calculate joules/second needed to spin a disc of given weight from zero to 6000rpm. It fell somewhere around 616 J/lbs. Then it could be converted from J/s to hp.
Example: by changing a standard-driven pulley from 2.11 lbs steel to 0.66lbs aluminum, gain is only a miserable 0.84 hp at 6000 rpm.
Fluidamprs are about 2 lbs heavier than stock rubber-steel pulley, yet they recover a couple of hp as proven on the dyno, due to dampening effect. It takes energy to vibrate a 30 lbs forged steel crank, and it has nowhere to come from, except from engine itself.
PS One more question: are aluminum underdrive pulleys less sturdy than stock steel pulley? Does the belt wear down the ridges on them over time?
There was some formula floating around the net, showing how to calculate joules/second needed to spin a disc of given weight from zero to 6000rpm. It fell somewhere around 616 J/lbs. Then it could be converted from J/s to hp.
Example: by changing a standard-driven pulley from 2.11 lbs steel to 0.66lbs aluminum, gain is only a miserable 0.84 hp at 6000 rpm.
Fluidamprs are about 2 lbs heavier than stock rubber-steel pulley, yet they recover a couple of hp as proven on the dyno, due to dampening effect. It takes energy to vibrate a 30 lbs forged steel crank, and it has nowhere to come from, except from engine itself.
PS One more question: are aluminum underdrive pulleys less sturdy than stock steel pulley? Does the belt wear down the ridges on them over time?
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