There ARE limits of how much you can boost any engine.

This is assuming the fuel mixture is correct (this alone can cost a few engines to find out), the octane is high enough, nothing else has changed, etc. etc.

What we are talking about here is the physical / design / metallurgy limits of engines. This is normally an incremental process (and very expensive) — as more boost is added, the next limit is found. THAT one is then “corrected”, and you move up to the next limit. On piston engines, we mean cylinder heads lifting, bending, head bolts stretching and/or breaking, piston tops collapsing, rods bending, cranks breaking, main caps breaking, etc. etc.

On rotary engines, the first limits normally found are breaking apex seals. This is most often incorrect fuel mixture. However, the seals can actually take a large amount of boost, as shown by the front running Import Drag cars, if everything else is “right”. The limits are then moved up to the rotor housings and rotors.

If you visualize a side view of a rotary engine, as boost is increased to large numbers, the rotor housing can be actually pushed out away from the rotor. This normally quickly results in a lost water seal. If the seal happens to still hold, then the housing material around the tension bolts can hit the bolts, and/or the dowel pins (usually the one at the rear) can literally break the rear side housing below the oil filter. Mazda has added more metal, and bracing ribs across this area as the years have gone by. dowel pinning the rotor housings to the side housings can help – but it will just move you to the next level of breaking the newly doweled area of the rotor housing, and/or the rotors.

A new limit we now have seen (which prompted writing this FAQ), is collapsing the rotor face.

Images below show some of these results.

As you probably have noticed by now, this is not a “fix-it” FAQ. We are not selling solutions here, just attempting to make our customers, and all rotary enthusiasts, aware of the limits of rotary engines. We still consider them , far-and-away, the best “bang for the buck”, and are SO glad that we never have to deal with: cams, heads, valves, valve springs, lash caps, valve train geometry, head bolts/studs, cam spockets, pistons, rods, main caps, cc’ing cylinder heads, 5-angle valve jobs, unobtainium valves, line boring, unobtainium rod bolts, harmonic dampeners, cam followers, etc. etc.

Click on image for larger view
Side Housing Rotor housing showing horizontal lines where it is moving against side housing
Rotor Housing This shows where the water seal let go — the dark area on the left
Rotor Housing Another shot
Side Housing Image of side housing showing where rotor housing was moving against it
Side Housing Another shot of side housing
Rotor This shows where the face of the rotor actually collapsed in the area between the pocket and the apex seal groove
Rotor This area is where the rotor casting is the thinnest
Rotor Another image
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