What is the difference between S4/S5 13B and Renesis?
 

I've done some searching, and I've seen a few threads concerning swapping the Renesis into a FC N/A, and while that's intriguing, I'm wondering what the difference is between the motors themselves that ends up with such a big HP difference.

Obviously exhaust ports were changed, and higher compression ratio...but what else?

I was thinking about this because my motor is prolly going to have to be rebuilt this summer (coolant seal is possibly busted). On my to-do list of mods is my desire to swap out the ECU with MegaSquirt, so ECU issues wouldn't be an issue, assuming I can look to the MS forums for help when I need it.

Other than possibly having to have some mounts fabbed, does it seem like a worthwhile idea? I know it'll prolly cost more money than a rebuild, but it seems possibly worth it to me, assuming I might be able to find a wrecked RX-8 with good motor and tranny? :)

in terms of power levels stock - stock. the renesis is makes more power beause of the exhaust being moved to the side, this allowed a much more agressive port timing w/ out all the overlap caused by peripheral exhaust ports(imagine how a RX-8 idles,a nice 750 rpm hum, then imagine how any other 240 bhp rotary idles, brap-braping away at 1500). as far as internals go the e-shaft is lighter, stationary gears are better(mazdatrix recommends them for upgrading earlier 13b's), apex seals are shorter(height) and in turn lighter...w/ the renesis, mazda had 10 years to address many of the problems inhearent in rotaries, and advancing technologies in metalergy and casting helped make this motor possable.

It's pretty simple. The reason behind the big power increase is just like any other engine. The idea is to increase volumetric efficiency at a higher RPM. How do you increase volumetric efficiency? Give it enough flow or time to fill the chambers. In a piston engine, if you're trying to make big power at higher rpms, you'll need to increase your flow(ported heads, bigger valves, more lift, ported manifold, etc..) and change your valve timing events(increasing duration, increasing overlap.) Same thing with the renesis. Not only did Mazda increase port size by going to the side ports, they also changed the timing events when chambers open and close. In fact this variable port design is just the rotary version of variable valve timing and lift, just like VTEC. I'm not sure if the Renesis never has overlap throughout all of it's rpm ranges, but if it does have zero overlap, then there will be lots of pumping losses and it isn't taking advantage of scavenging in the higher rpms. Back in the day when they started making engines, engineers realized that it was better to open the valve during the power stroke because it was easier to let the gas escape with high chamber pressure than to pump it all out on the exhaust stroke. By not having overlap, you're not allowing the chambers to fill up to as much as 125% or even more through scavenging. That is why the S2000 motor makes such good power, all through valve control. It is indeed an interesting subject. I recommend you check out the QUASITURBINE website, if you are really interested in alternative engine designs. They really point out the drawbacks of the Wankel design. Oh yea, another thing, check out Mechadyne. These Brits are going to REVOLUTIONIZE Pushrod technology. The 2008 Viper are already using their concentric camshaft patent with vvt in an OHV V10. It's amazing! Z06 are revving to 7000rpm stock. GM using cam phasing on OHV. Chrysler with Displacement on Demand. I wonder what they'll come out with next.

By the way, I posted earlier on here about port timing events of the Renesis, but nobody wants to respond. Does anybody know where to find this information?