Lynn E. Hanover

At te very top of the HP race are the drag racers, Cooling is not a problem for a 9 second run, so I am surprised that they are not epoxy filling the rotor housings to help prevent flex.



X amount of HP at any specific RPM requires a specific amount of torque. Whatever amount that is at any point means that the crank is turning one way with a very large amount of force. And that means that the very same amount of force will appear inside the engine and be carried out through the motor mounts.



So there are two effects to deal with that dowels or oversized studs can help with. The engine twists in the opposite direction of the crankshaft rotation. Equal and opposite as in Newton. So, 300 Foot pounds out the crank means that 300 foot pounds will appear in the motor mounts. Same every time, every engine, every car, english or metric.



The other is as a result of extreme cylinder pressures causing the sparkplug side of the rotor housings to move away from the rotor face. (flex) You can see this on a teardown as the black areas on the aluminum housings where they scrub on the iron housings. This action is powerful enough that dowel pins can move the hole in the irons by cracking them out, and in some cases by breaking off the dowel pin ends.



So what do those real fast guys do to eliminate the broken engines? They use either extra dowel pins and or oversized studs to clamp the stack together. The over sized studs require that the engine pieces be assembled and the normal stud holes through all of the pieces be precision reamed to the size of the stud

plus (guessing here) about .0015".



So as with the extra dowel pin, if the rotor housing starts to move it gets support from the dowels and or the studs. In the stock situation, the stud is so much smaller than the holes that the housing is free to flex quite a bit without touching the stock bolts.



Please notice that the early engines had the motor mounts bolted to the front cover. So when you pump up a 12A it starts cracking the front cover through the stud holes. Why is that? When engine power went up, the motor mounts were moved to the center iron. Now to the rear iron are they not? And why was this done do you think?



And over the years, case bolt thickness and torque numbers went up with HP and torque.



So that the torsional load on the engine will be apposed where it is the worst. Right at the rear iron.



And increased case bolt diameters and torque adds clamping load and makes housing movement less likely.



Notice the top dowel hole in the rear iron usually gives up during an overboost or detonation cycle.



So (Oversized) studs and additional dowels do work. Without those fixes and some others we have yet to discover, there would be few successful drag racing rotaries.





Lynn (Studs) Hanover

Heath

So in a fairly high hp engine that retains the stock tension bolts is it wise to increase the torque value of said bolts?

How about the larger aftermarket studs? Do you torque them to factory specs or a bit above?

Maxt

I've been present for the tear down of a fair share of motors that were north of 700hp in 2 rotor configuration, that ran for multiple seasons in drag cars, and engines of the 500 hp range used for circuit and time attack. All these engines used nothing but stock tension bolts, and there was no sign of any kind of weakness in that area. These engines burn seals down past the hardening level from high combustion pressures before they break anything related to holding the block together.

Mazda themselves says the greatest shocks to the rear iron is full engine misfire,not detonation at full engine power. Detonation will dent the rotor and break other parts, before the rear iron falls apart.but when the rear iron is allowed to go from full engine torque to almost nothing during misfire and back to full in a split second, regardless of what is done, the rear iron will probably still crack somewhere, sometimes part of the bell housing flange breaks off, other I have seen spit the frost plugs out.

Again its all avoidable by setup and tuning, if some of the more well known rotary competition engines from Japan were torn down and photographed people would be amazed at how bone stock they were...

Lynn E. Hanover

Racing Beat says to torque high output turbo engines to 32 pounds vice 24 pounds for normal street engines.



They also say to use antisieze compound on the threads, and this alone means that for example, that the case bolts are being tensioned much higher than the stock engines with clean dry threads.



You need to ask Guru about stud torques.



500 HP (250 HP per housing) is not a high output rotary. Racing Beats 900 HP three rotor (300 HP per housing) was derated for long term aircraft use. This means that you can cool it at this power rating, and expect it to run for a thousand hours at this output, not just 7, 8, or 9 seconds. That is high output.



A 700 HP or more, two rotor is a high output rotary engine.



My 245 HP 12As (122 HP per housing) scrub the aluminum on the irons. I reduce the edges of the chrome so they don't make flakes. The aluminum shows you where it is moving. It gets dark where it moves. I torque to 28 pounds with antisieze on the threads and under the bolt heads.



If my aluminum moves around, I know damn well a 500 HP 13B is moving the aluminum around. Imagine the compressive load on the hot side of the engine when you torque the hell out of the case bolts and then heat the engine up during operation so that the housings try to get wider. And still the aluminum scrubs.



You don't need to do anything until housing flex starts to cause you problems, like seals dying early and blowing all of the water out, or blowing the end caps off of your radiator. Nope, no need for studs or dowels at all.



Lynn E. Hanover



Want some aluminum end plates?

j9fd3s

Maxt

The housings will always move around, since they dont all have the same rate of expansion , rate of heating or totally the same construction, in fact thats why the stock tension bolts are a floating design to begin with and is pinned diagonally and in only spots, with out some minor movement, thermal cycling alone would would crack the pinned points.. There is no point in fighting the laws of physics that you cant control, materials grow with heat and there has to be mechanical provision for that, the motor is constructed in that way to allow for that, and stopping the design expansion just moves deformation to other places, which in turn has an internal effect on combustion sealing which most people are unaware of, but because they simply done something extra, they think they have made the motor somehow stronger.. Putting added crush on parts doesnt really do anything either, the o-rings arent going to seal any better, that flatness of the surfaces has more relevance on seal than torque values, but torque values will affect flatness, especially if it starts to lift the material around the threaded bosses.

Maxt

When a motor is put together to the "T" with a good tune and properly measured and matched parts, most would be suprised to what it will live through.. That famous little yellow car in Japan with a 3 rotor in it, runs some pretty stock components..

j9fd3s

well the misfire thing makes a lot of sense! lol the only engine trouble i have is paul, he can break anything i can build. other than that i have had no engine trouble, ever.

GMON

Max,



Devils advocat here, so 700hp on an s4 ?? Doable with stock configuration?



Im guessing most of the engines that get to that point are FD engines.



Your thoughts??





Great comments by the way. Its what I want to hear, and thats what worries me, seems too easy

j9fd3s

i would think mazda beefing up the s5+ is basically catering to the high hp tuner people....