I hope you guys understand what those crank pullies do . . . .

the crank pulley removes the harmonic balancer. Your driveshaft is now vibrating like a lunatic and just waiting to get all messed up. I've seen more cars than I care to mention blow from an underdrive pulley.

 

Well... a lot of garages like them.

 

Thread title edited.

cretinx - How about, if you're trying to say something helpful, that you do it without insulting people in the title of your thread? If you sound like you're trying to incite a flame war, people are less apt to listen to you. And people don't generally like to be called "morons" regardless of your point.

 

cretinx - you sure have a funny nick... did you mean "cretin-x"? :D

 

Since I'm not a moron I realize that a rotary doesn't have a harmonic balancer. There isn't much worry about. We have 2 rotors and 2 counterweights. That's it. The front counterweight is underneath the front cover where you can't get to it. I've run underdrive pulleys on my RX-7's for years. No problems.

 

oh wait.... who is a moron?

Thanks RG

 

Well, his avatar is an eclipse... Can't expect him to know everything about a rotary engine.

 

you've been PUNK'D! Now go back to the Eclipse forum...

 

Also have ran underdrive pullies in the past, they worked perfectly fine.

 

what I wanna know is how many cars do you have to see blown before you don't care to mention it anymore?

 

i haven't seen any 8s with blown engines, come to think of it, i haven't seen any 8 with a blown engine. Nor heard of one.

 

I have had my SR underdrive pulleys for months now and there are no problems. Quieter operation and better appearance. As far as measureable gains, who knows? Physics tells me there are some gains but that deoesn't mean my meager human senses can detect them.

Charles

 

physics...she can be a tricky mistress...

 

Hey RG,

Are there any worries about underdriving the water pump on a rotary? I could see UD on the alternator being no problem (assuming you're not also trying to run a monster bass box or other excessive electronics), but it seems like you'd still want all the cooling you can get, depending on your local climate.

 

I'm not RG, but...

I've always heard that underdriving the water pump can actually improve performance by reducing cavitation during high-rpm driving. My assumption is that the stock drive is optimized for street driving, and a different drive might be ideal for track driving. Now, how much difference it makes REALLY, or any possible negative impact on a street-driven car that has this modification...that I don't know.

jds

 

True. On the older RX-7's, the water pump started to cavitate at about 6500 rpm. THe RX-7 may not rev as high as the Renesis engines but I get higher than that. With an underdrive pulley, the cavitation point was taken up to about 8000 rpm or so. Unfortunately I don't know where the Renesis water pump starts to cavitate at. I do know that I never had any adverse affects using them on a street car though so you should probably be just fine using one.

 

Also, it's not a harmonic balancer, it's a harmonic damper. There is no balancing of the crank pully on the stock system. The damper's job is to minimize the amount of engine knock noise and that's it. I've seen separate tests done with and with out the harmonic damper. The tests were done with one of those fancy gizmo's that translates audible noise into a visual wave on a screen. In stock configuration the harmonic damper disapates the amount of noise from combution almost imediatly. W/O the damper unit the noise wave lasts for just a bit longer than a half second. My point is that the harmonic damper isn't a nessessary item and can be removed for performance.

Now under driven pullies in general are usually a hot topic for discussion and everyone will give you a different story about how it blew up someones engine or that it worked just fine. Personally, I prefer a lightened pully as instead of an under driven pully but hey, that's why we are all mature adults able to make our own desisions and purchaces. Do your research and get what you think is best for you and your project.