So the wonderful thread of "reliable JDM engine suppliers" has got me thinking about some interesting swaps. I saw the 20B engine for sale, but from what I have read, they were only offered as twin turbo setups. The question is how exactly does boost affect rotaries? In the sense of detonation with increased boost or removing boost all together?
Maybe it's a stupid question but to me rotaries are a bit like voodoo.
It's pretty much like a piston engine. If you get detonation, you get pressure spikes in the combustion chamber. In a piston engine you'll blow out the piston ring-lands or the piston itself. In a rotary you'll blow out the apex seals typically (could also kill corner seals or side-seals, and it's also possible to damage the rotor itself).
Factory boosted rotaries will have lower compression ratios, just like pistons engines. This is accomplished by using a rotor with a larger recessed area (like a dished piston). If you get a boosted rotary and run it NA, you'll have poor response and make less power than a comparable factory NA engine, since the compression ratio is so low.
One other thing to consider is that rotaries run really hot since they make a lot of power per physical size. An FI setup only exacerbates the problem by raising combustion chamber temps and pressures, so make sure the cooling system is in very good shape.
The 20B turbo has been very reliable on boost. Off boost the 20B of old, while not a slug, wasn't all that much more powerful than a non boosted 13B.
The conventional wisdom is that rotarties are more sensitive to detonation than a piston engine.
That said, with a good tune, you can run stupid boost in them. Mazdatrix started to cave in the faces of the rotors on their drag car.
http://www.mazdatrix.com/faq/boost.htm
Rotaries love boost! Keep it cool, keep oil in it, don't let it go lean, and it will make you happy! Wheeee!
Not that it matters to me. Do what you want. 
can you put N/A-higher compression- rotors from a 13b in a 20b?
Yes you can. A 13B rotor is the same as a 20B rotor, only there is three of them instead of two on the 13B.
In reply to belteshazzar:
You might not want to though. I've rebuilt 2 rotors with a friend of mine and it's probably the most difficult automotive job I've done. I can't imagine how crappy it would be to do a 3 rotor. Certainly not impossible, but certainly not any fun.
JohnyHachi6 wrote: In reply to belteshazzar: You might not want to though. I've rebuilt 2 rotors with a friend of mine and it's probably the most difficult automotive job I've done. I can't imagine how crappy it would be to do a 3 rotor. Certainly not impossible, but certainly not any fun.
I respectfully disagree, rotaries are extremely easy to rebuild. The hardest part is getting the flywheel nut off! Rebuild video<
In reply to Osterkraut:
You really think so? Fitting the rotors on over the e-shaft and keeping all the seals in place as you put it into the side housings? I thought that was a huge PITA. Sure there's a lot less parts than a piston engine, but it's really tricky to making sure everything stays in place.
May be I have a poor memory of it since it was 4-5 years ago and I was more of a n00b back then...
JohnyHachi6 wrote: In reply to Osterkraut: You really think so? Fitting the rotors on over the e-shaft and keeping all the seals in place as you put it into the side housings? I thought that was a huge PITA. Sure there's a lot less parts than a piston engine, but it's really tricky to making sure everything stays in place. May be I have a poor memory of it since it was 4-5 years ago and I was more of a n00b back then...
The rotor-e-shaft dance can be...interesting, but keeping the seals in place only requires petroleum jelly or a similar high-tack petroleum product.
Just a FYI for anyone running into detonation on a rotary, it does not sound like detonation on a piston engine. more of a knockknockknock (it is hard to explain) than the marbles in the exhaust sound. Found that out the hard way with to big of jets on my nitrous setup.
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