Underdrive Pulleys
 

Any underdrive pulleys out yet?

Been looking myself prolly just grab entire package when i buy the sc

i guess any car forum has to go thru the underdrive pulleys/light way pulleys threads.

Let's get the myths out of the way so people can make an educated choice.

i'll start (this does not necessarily applies to rotary engines)-

UD pulleys refers to pulley that are different size than the oem one, some car will have problem at idle, some will experience dimming head lights or stereo problem. it usually should state a percentage decrease. it 'underdrive' the alternator or pumps to free up powers to the crank(s). if a pulley is 15% UD, that means, at idling of 800 rpm, your alternator/pumps are only running at 680 rpm.

Lightweight pulleys refers to pulleys that are usually significanly lighter (about half) due to the lack of harmonic dampener use in oem pulley. Due to the reduced rotational mass, the crank spins up faster, again, providing better acceleration but not direct HP. Think lighten flywheel, which is on the other end of the crank. if lighten anything, gives you HP, then i'll start losing weight ;P
Draw back are on some engine which larger amount of crank vibrations, and the lack of dampening amplified the vibration causing crank bearings and other damages.

so, who has used pulleys on rotaries with success? Does the ecentric shaft (crank) causes any problems?

TerenceT thanks for the explanation, however, I already knew this.

I'm sure someone will make/design underdrive pulleys for the accessories... maybe not the crank pulley. There are many cars which can use underdrive pulleys with little or no powerloss issues, however the RX-8 might not be one of them. We'll have to see. I know that the Mustang underdrive pulleys do not visibly impact the A/C or the electrical systems (as long as you don't have a huge aftermarket stereo which is draining power like a mo-fo).

I'm not entirely sure about the lightweight pulleys.... my guess... probably not.

I had underdrive pulleys when I had my RX-7's, the rotary was perfectly fine with it; there was never a rougher idle or any other negative loss on accessories. Perhaps there was on A/C, but I never run the A/C, so I wouldn't have noticed that at all.

One more thing, the pulleys I had for both cars were from RX-7.com.

Thanks!

I'm sure they'll come out soon enough.

pulleys
 

shane racing has pulleys.

www.shaneracing.com

Yeah, I saw these and they look good and are a good idea as long as it's not under dirven. If it's just a lightened pully kit then it would be worth it. Still not sure about the fitment since I haven't seen these anywhare else.

Do lightened pulleys and flywheels really make that much of a difference? Pardon my ignorance, but that wasn't one of the mods back in the day I was into souping up cars....

i know they have made a difference with wrx's....but i have not heard anything about them on this car though......it hopefully should!



andrew

Of course you haven't heard anything about it on the 8, there's just not very much on the market yet. Underdrive pulleys are pretty popular on other cars. It's simple physics, lighter pulleys mean that the engine has to work less just to turn them, which means less power loss.

Vivid, what do you have against underdrive pulleys? Is it because you fear that you won't have enough power for your stereo? ;)

Isn't your air conditioning weak enough already? ;)

I am very leery of underdrive or lightweight pulleys - I know they're popular with many these days, but I don't trust that they're properly engineered. For example, it is pretty much guaranteed that a lightweight crank pulley on a turbo or supercharged Miata will cause an oil pump failure within a few thousand miles. The typical pulley, like Unorthodox Racing's, does not incorporate the harmonic damper that is built in to the factory crank pulley, and it turns out that it is critical at higher power output levels (like when FI) for the Mazda B6 and BP engines. I've also heard that the harmonic dampers are critical on BMW inline-6s and the Contour SVT V6s, but don't know a lot about those.

Especially on an already quick-revving engine like the Renesis, I can't imagine that the measly 1 or 2 hp that might be achieved is worth the potential risk.

Regards,
Gordon

I feel you can get power in other areas rather than squeesing the life out of it for such minimal gains.

hi guys just new here as you could probably tell as its my first post hi to all firstly , just a quick one on what i do know about lightened pulleys , they will make the car rev easier and quicker but the down side is that u will lose torque , they work similar to a lightened flywheel

I don't think there is a harmonic damper on the rx8 main pulley. The Rx8 pulley looks the same design as the one on the rx7 and the rx7 one does not have a harmonic damper.

The stock main pulley have two sections. One to drive the AC and the other to drive the alternator and the water pump. You can keep the AC one the same size so it does not under drive the AC but it can under drive the water pump pulley and alternator pulley. On a rx7, the normal underdrive percentage is 20-25%.

It's going to free some HP to the rear wheel but it's not going to be 15-20 rwhp like some companies claim.

Chuck Huang

not really sure how the rotarys work exactly basically havent pulled one apart yet but many other companys have harmonic dampeners at the front eg piston engines is because there is flex in the crank at the front and many have oil pumps eg which is the last piece from the crank hence if u dont have the dampener to stabilize the flex all stress goes to the oil pump which in all cases if replaced with a non dampener will crack the housing in the pump also it will make idle and rev more rougher and once it cracks there go ur oil supply but then again the rotor crank is a lot smaller , hope that clears things out

So we should just wait and see on these?

I've had great success with aftermarket pulleys on Fords and Minis but I'm waiting to see user feedback here before jumping in on this one...

http://www.mini2.com/gallery/persona...ront_thumb.jpg

Flywheels will make the biggest difference. Holy shit, flywheels make a huge difference. Pulleys on the other hand..

I put a lightweight underdrive unit on my Subaru. All it did was dim my lights at idle :(

Has anyone bought these yet?

I had underdrive pulleys on my FC and FD with no problems. I would expect it to be the same with the 8.

Maybe I'm being naive, but I can't see respectable tuners like Petit, Shane Racing, or RX7.com offering underdrive pulleys for rotary cars if they were largely detrimental.

Wut u guys think about Unorthodox aluminium flywheel??

(see bottom of page)
http://www.corksport.com/main.php3?p...3Fcat%3D260823

Might be better than MS one?

Even better... http://www.unorthodoxracing.com/select_mazda.html

You'd be better off buying a chromoly flywheel. Less resistant to heat warping.