What is the difference between a LW flywheel and LW underdrive pulley ? <flame suit on>
04-07-2003, 08:10 AM
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What is the difference between a LW flywheel and LW underdrive pulley ? <flame suit on>
Please help me on this one.
It's OK to use a LW flywheel (attached to crank), but it's not OK to use a LW flywheel pulley (attached to crank)?
It's OK to use a LW flywheel (attached to crank), but it's not OK to use a LW flywheel pulley (attached to crank)?
04-07-2003, 08:15 AM
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there's a harmonic balancer on the stock s4 crank pulley...the dual mass flywheel is also damped
for crank vibrations...any aftermarket part for either of those loses the damping put in from audi.
i believe people with lightweight flywheels do notice some little chatters or vibes at certain rpms, but to no ill-effect
i believe people with lightweight flywheels do notice some little chatters or vibes at certain rpms, but to no ill-effect
04-07-2003, 08:18 AM
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People tend to think that the lightweight pulley's will hurt the car...
especially accessory pulley's. The truth is an underdriven accessory pulley is not going to lower the voltage to an unsafe operating condition for the ecu's. the alternator is rated to run 14.? volts. The under drive pulley won't reduce it to anything under 13. Unless you are running some crazy *** stereo, in which case, why bother trying to make the car faster.
Pulleys for these cars are more concentrated on lighter weight versus underdriving. the lighter sprung weight is where you will see a lot more power versus underdriving. The only thing to be concerned about is if the pulley is harmonically balanced which unfortunately most underdrive pulleys are not. So you can tend to get vibration at higher speeds.
Pulleys for these cars are more concentrated on lighter weight versus underdriving. the lighter sprung weight is where you will see a lot more power versus underdriving. The only thing to be concerned about is if the pulley is harmonically balanced which unfortunately most underdrive pulleys are not. So you can tend to get vibration at higher speeds.
04-07-2003, 08:42 AM
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unh...a pully is sprung weight, not unsprung weight.
Unsprung weight is ONLY those components not actually supported by the shocks like the wheels/tires/brakes/suspension components.
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04-07-2003, 08:47 AM
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Oh I reread what you said...
you are saying reducing unsprung weight is more beneficial than sprung weight not that the pulley IS unsprung weight.
The point of an underdrive pulley is not weight but to reduce the amount of engine power used turning the alternator. Every device driven by the engine (water pump too) consumes HP (takes energy to produce work) so by reducing the amount of "load" the alternator puts on the engine, HP is increased.
Risk is you are screwing with a system that may have some damping/harmonic properties built in to it which MIGHT create some real long-term problems in the engine.
IMHO, utterly worthless thing to do on a street car unless you are racing for money every week.
The point of an underdrive pulley is not weight but to reduce the amount of engine power used turning the alternator. Every device driven by the engine (water pump too) consumes HP (takes energy to produce work) so by reducing the amount of "load" the alternator puts on the engine, HP is increased.
Risk is you are screwing with a system that may have some damping/harmonic properties built in to it which MIGHT create some real long-term problems in the engine.
IMHO, utterly worthless thing to do on a street car unless you are racing for money every week.