rx7 pulleys on an rx8 ?
12-11-2011 | 03:29 PM
#1
rx7 pulleys on an rx8 ?
Sorry if this has been answered I did search but I have been offered some custom underdrive pulleys from an RX7 there alternator and water pump will they fit and work ok im not looking for any performance gain but there seriously sweet looking but I dont want to screw anything up.
07-15-2012 | 04:42 PM
#6
https://www.rx8club.com/rx-8-discuss...rx-8-a-233937/
Pulleys
(can cause warranty hassle, and justly void warranty if the issue is electronics related)
Don't. You might ask "why?", so here is an explanation:
There are 2 "benefit" points to changing to aftermarket pulleys.
The 1st "benefit" is a reduction in the weight of the pulley. This is a similar concept to going with a lightweight flywheel to assist with a more responsive engine. The problem is, the weight you are saving is very very very small, and it's close to the center of rotation, so there is very little gain by reducing it. It takes roughly 10lbs of weight saved at inch from the center of rotation to equal the interia savings of 1lb of weight saved at 10 inches from the center of rotation. Lightweight flywheels are still rather large in diameter (almost larger than the core engine block), and much of the weight stripped is near the outside of the flywheel. Pulleys have only a few inches and at most maybe a pound, and most of the weight to remove is near the center.
The 2nd "benefit" is to underdrive one or more accessories. The problem with this is that under driving your alternator is bad for your electronics and battery, and underdriving your water pump can have significant penalties to your ability to keep the engine cool. And all it takes is 1 overheating, or even undetected localized hot spotting, and your housings can warp and your engine is done. Underdriving your A/C is without penalty, but removing the AC system completely would accomplish the same AC effectiveness as underdriving it, and leave your car lighter and without the AC compressor drag at all, so it's the better choice (and cheaper).
Even the large main pulley should be left alone, as it needs to act like a stabilizing influence on the e-shaft, like the flywheel does to the other end. You can lighten the flywheel without adverse affect on the e-shaft, because it is still the heavier end. A greater difference between the two ends increases instability and flex. Adding weight with a pulley that is also a proper harmonic damper is common for high power piston engines, though a rotary is compact enough with lower lateral stresses (lateral in relation to the e-shaft rotational axis), that this hasn't been seen as necessary.
(can cause warranty hassle, and justly void warranty if the issue is electronics related)
Don't. You might ask "why?", so here is an explanation:
There are 2 "benefit" points to changing to aftermarket pulleys.
The 1st "benefit" is a reduction in the weight of the pulley. This is a similar concept to going with a lightweight flywheel to assist with a more responsive engine. The problem is, the weight you are saving is very very very small, and it's close to the center of rotation, so there is very little gain by reducing it. It takes roughly 10lbs of weight saved at inch from the center of rotation to equal the interia savings of 1lb of weight saved at 10 inches from the center of rotation. Lightweight flywheels are still rather large in diameter (almost larger than the core engine block), and much of the weight stripped is near the outside of the flywheel. Pulleys have only a few inches and at most maybe a pound, and most of the weight to remove is near the center.
The 2nd "benefit" is to underdrive one or more accessories. The problem with this is that under driving your alternator is bad for your electronics and battery, and underdriving your water pump can have significant penalties to your ability to keep the engine cool. And all it takes is 1 overheating, or even undetected localized hot spotting, and your housings can warp and your engine is done. Underdriving your A/C is without penalty, but removing the AC system completely would accomplish the same AC effectiveness as underdriving it, and leave your car lighter and without the AC compressor drag at all, so it's the better choice (and cheaper).
Even the large main pulley should be left alone, as it needs to act like a stabilizing influence on the e-shaft, like the flywheel does to the other end. You can lighten the flywheel without adverse affect on the e-shaft, because it is still the heavier end. A greater difference between the two ends increases instability and flex. Adding weight with a pulley that is also a proper harmonic damper is common for high power piston engines, though a rotary is compact enough with lower lateral stresses (lateral in relation to the e-shaft rotational axis), that this hasn't been seen as necessary.
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