ok
so on a piston engine we have the speed that the valve can close at, or the short life of the parts required to increase the speed enough.
ie valve seats tappets and valve springs etc.
the mass of the componetns that change direction, piston and rods.
and ultimatley the ability to flow enough air to fill the combustion chamber,
but on a rotary what stops the revs increasing?
ie why cant i screem the thing to 20,000 rpm?
the ports can be opend to silly large amounts way more than you could hope to flow through a cylinder head (i assume)
we have no valves no springs no pistons. in fact nothing at all that changes direction, just rotates,
so again, WHY can i only rev to piston levels, in fact not even, v-tec anyone?
anybody know? i would imagine some of the pro builders on here would.
im just a monkey with a few tools compared to some people on here but im strugiling to see why theres not many silly rpm rotarys.
been pondering this all day after playing with a bike at 14,000 rpm
Some vtec motors the b16/b18 range have been known to rev to up to 11k rpm\'s, so good question fella i\'m interested to hear a good explanation for this too.
Also to add how safe is hitting the limiter on rotaries as i hit the limiter regularly on my dc2 which was near as makes no difference to 9k
Yeah its a strange one isn\'t it? A V4 bike can rev way up at 15,000RPM and like you say a B16B EK9 CTR will rev to 9,000RPM. Similar or beter figs must be possibul with the rotary and yet my Turbo II\'s tacho redlines at 8,000RPM.
There must be some reason! And it would be intreresting to find out how high the 787B Le Mann racers were able to rev to! :Giggle
Havn\'t a clue what the answer is but heat ??
I did read something the other day saying that once they figure out how to make the housings out of a certain type of metal (kryptonite I think :) ) then you\'d be able to rev to 20k.
Mazda took Renesis Engines to 13,000rpm on Dynos without problems. Apparently the Clutch components don\'t like more than 10,000rpm, they go pop.
Thinking about it carefully. If you could get enough air in, coupled with enough fuel that you could make it as high as you like! I think it is not the actual engine but the intake, fuel system and exhaust that restrict the engine. Certainly the 13B MSP in the RX8 spins quite happily beyond 9000rpm without problems. Far smoother than a vtec too!
2 main problems prevent high revving.
1) The rotor is quite heavy. At very high revs the centrifugal force of the Rotor is enough to flex the stationery gear. This causes apex seal failure, and or the Rotor comes into contact with the Rotor housing.
2) Harmonics. This can cause the through bolts to snap.
rotaies can easily rev over 10k if you have a 2 piece e shaft. obviously thats not all.
but the mainfactor of everything is money.
four pots can rev to 14k and as mentioned above and well beyond 14k. but they have been redesigned from the ground up. shortening rods, and crank throw, reducing piston height and increasing bore width, so the pistons dont have to travel far in the bore. also the valves have a direct physical connection to the rockers, and use superstrong springs. some use the rocker to push the valve down and lift it back up
Quote from: Martiny;5458532 main problems prevent high revving.
1) The rotor is quite heavy. At very high revs the centrifugal force of the Rotor is enough to flex the stationery gear. This causes apex seal failure, and or the Rotor comes into contact with the Rotor housing.
2) Harmonics. This can cause the through bolts to snap.
agreed also add if want to rev higher then clearanced rotors are needed as you will get chatter marks on the housings, and as been said 2 piece e-shaft as well, dowels to stop flex of the plates.
Also you need good porting to make it worthwhile to rev higher, standard ports on a REW peak power is produced just before 8k where the power tails off.
To rev higher ideally you want a PP port
so lighter rotars would be the obvious starting point for this?
and a 2 piece e- shaft?
anybody make them?
You can lighten the Rotors a little, but Blitzboy said "machined " . I think this means removing the material from the part of the Rotor that is likely to hit the housing under high revs.
I thought dowels were needed for big horsepower, not really to allow higher revving?
Flame spread period ie the amount of time it takes for the fuel to burn is a major factor.
On a piston engine anyway
Phil
the triangular rotor isn\'t rotating in a circular motion, it wobbles back and forth inside the housing... there must be large forces generated by it... I reckon there is a vibration limit in it.
i cant find anywhere that dose light weight rotors.
is there nowhere that makes them?
i would have thought you could get lighter ones now than mazda made 20 years ago?
alloy of some sort no?
Here\'s a link to some rather in depth conversations, just to prove there\'s a bit more to it all. My tiny brain hurts just reading it!
http://www.rx7club.com/showthread.php?t=334609
^^ thats for NA application, you wouldnt use rx8 rotors on a turbo rotary.
WeeJimmy if you want clearenced rotors on a turbo rotary speak to Ross at Dragon im sure he can he can sell you some, as his record holding drag car used to rev just past 10000rpm, I dont know what mods he done to the E-Shaft
Quote from: RedRummy;546101the triangular rotor isn\'t rotating in a circular motion, it wobbles back and forth inside the housing... there must be large forces generated by it... I reckon there is a vibration limit in it.
It\'s also \'wobbling\' at about 2.5 (I think) times slower than the main shaft - so at least it\'s not wobbling at the full engine revs.
I found that bearing/lubrication issues were the biggest killer, I kept incresing revs and got to a certain revs were the engine went in a big way, no det, just E shaft flex, and the resulting beakages.
what revs did it blow Ross, I know you used to rev the old beast at 10k on loads of runs
Quote from: weejimmy;546129i cant find anywhere that dose light weight rotors.
is there nowhere that makes them?
i would have thought you could get lighter ones now than mazda made 20 years ago?
alloy of some sort no?
try "Racing Beat" ?
http://www.rotorsportsracing.com/performancetuning/guru2pcshaft.htm
HTH adam