Question 1: Broadly speaking, look for a supercharger that's used on a a piston engine making a bit more power than you're aiming for with the rotary. Basically horsepower comes from air flow, a rate of something like 1.5 hp per CFM of air. Rotaries are a bit less thermodynamically efficient (that's why the exhaust is so hot), so that number will be a bit lower than it would be for a piston engine.
Question 2: Packaging-wise, the centrifugal blower almost always wins over any roots or twin screw blower. Alas, the boost rises with the square of the RPM, so it's going to make a peaky, high-strung engine even more so.
Generally speaking, I think the best supercharger to use is a turbo, but from what I hear the RENESIS engine really doesn't like those...
The bar napkin math is air volume per rev (combusted) engine X pressure ratio = supercharger volume per rev
So 1.3L X 1.7PR = 2.21L/rev. The M90 (90 cubic inces) displaces 1.48L/rev so you need to get the pulley ratio up to spin it faster. 2.21/1.48=1.49:1 pulley ratio. That also means you'll be spinning the SC up to 13,400 at 9,000rpm, pretty well matched.
In reality the supercharger less than 100% efficient and the engien VE varies so you may need to play with the pulleys.
Does the 5 rib belt work? If you need a custom crank pulley let me know. I've made them before and have an RX8 pulley hub sitting here.
84FSP
SuperDork
12/31/18 9:02 a.m.
I don't remember the cause but forced induction kits on the RX8 were wildly unsuccessful when they first came out. I'm not sure if it exacerbated issues already there (lubrication/fuel) or caused new ones.
Wiki reminds me that Depsey Racing went to the 20B-REW. The triple rotor 20B had 2 litres (1962 cc) of displacement, for their racers.
On the bright side make it work on the cheap and if it pops move on.
1. You need to know how much air the Moter pumps per revolution of the crank. With a piston engine it is half the engine diplacement due to there being 4strokes a rotary I think is 1/1 where as a piston motor is technically .5/1 so knowing this I think you would double the displacement of the wankal motor when using a supercharger calculator. Most calculators factor in looses in efficiency but you should check that as well.
2. If you really want a 9,000 rpm red line you are going to have t be carful with overspeeding the supercharger. Memory said that many of the older Eaton unit are limited to about 14,000 rpm and then bad thinks happen. So if you want that rpm you are going to have to use a larger supercharger and spin it slower because the roots type superchargers efficiency drops off at higher rpm.
3. You may also have to keep in mind your piping sizes as the air speeds in the piping is going to get quite high if you undersize the pipes.
Lastly something to consider. Rotary don’t play well with knock. No engine does but rotarys in particular due to the design of the apex seals. Supperchargers are best at adding power across the rpm range. Especially at the bottom end and this is where you can more easily get knock. Turbos are the opposite and play much nicer at higher rpms at the expense of some bottom end power. Turbos can also easily keep up with a rotarys rpms as a turbo is only working based on air movement and the energy in the exhaust. A turbo really does not know or care what the rpm is. This is why you don’t see supercharged rotarys. They are a poor match for each other. This is also why Mazda turbo is rotary’s from the factory.
