Shit just got real, 39B yo!

[Fangin]

4 Rotors have been around for 20 years, don't know what's so new about them?

Keen to hear this thing at full noise!!

What sort of RPM do you guys expect it to pull?
Obviously won't be as rev happy as a 13b, but should still rev fairly high?

[racerdad1]

yeah i cant wait to hear it too! oh dont think i can give out that sort of info but depends on how high you mean, like mad mikes car while it sounds like its reving through the roof its limiter is at 8500.

[racerdad1]

Come to the 4 and rotor nationals today and check it out!

[RRM]

5 and 6 rotor engines are hard to build because of several reasons, but the main reason is the e-shaft length itself

The e-shaft length, because of the length of the shaft itself and the power that each rotor produces there is a very strong tendency for the shaft to twist. This causes the front rotors to run ahead of where they are supposed to be; true, this could be accounted through changing the ignition timing on the forward rotors, but the deflection changes with rpm and load, so you can only 'predict' how far ahead the forward rotors are, this would mean that you would have to be VERY conservative on the timing, which leads to far less power. Top fuel dragsters have a similar problem, in that you can get up to 20 degrees of twist in the crank at full power, they compensate by having the crank throws actually offset by a calculated amount to compensate for the twist at a VERY specific RPM.

Of course, if the car is a purpose built race car (like the mentioned Top Fuel dragsters), which would be in a certain rpm band and under load almost all the time, then you could tune it to run good there, but it would sound and run like ass everywhere else, and the conservative ignition timing at low RPM would probably eat apex seals (and exhaust manifold, turbo, etc) very quick because of the massively increased EGT's.

Of course, if you REALLY wanted to get fancy, then you could place an optical sensor at the intake port of each rotor housing to detect the position of the rotor, and run an ECU for each rotor, using the optical sensor in place of a trigger wheel. But even with this you still run the risk of the e-shaft itself failing due to stress/too much twist.

It sounds like a six-rotor would avoid all those nasties and be a lot happier if the torque was taken out of the eccentric shaft to the transmission at a point halfway along the shaft (via gearing onto a separate output shaft) rather than at the rear end of the shaft??

The front and rear end rotors would then each be only 3 rotors away from the point where the load is (the output to the transmission) and three-rotor engines presumably don't have problems with excessive torsion in the eccentric shafts...?

Note - I'm not offering to design or fund that project, mind...

[J15guy]

It sounds like a six-rotor would avoid all those nasties and be a lot happier if the torque was taken out of the eccentric shaft to the transmission at a point halfway along the shaft (via gearing onto a separate output shaft) rather than at the rear end of the shaft??

Yea, that's what I suggested further on, like what a few of the more powerful inline-8's did

Although I have been giving this some more thought, and I have come to the conclusion that it could also be that the shafts fail at a very specific RPM due to harmonics. As the long length of the shaft could make the shaft have a natural torsional frequency low enough that, at a certain RPM, the higher frequency of the 6 rotor design (frequency of the power pulses compared to 2, 3, and 4 rotor engines at any given RPM) could be the same as that natural frequency, destroying the shaft.

But we wont know for sure until they fire it up, because there is more info on the internet about big-foot then 6-rotor engines.

TBH though, I hope I am wrong on this one... as impractical as a 39B would be, I would love to hear and see it in person

[racerdad1]

But separating it in the middle would turn it into 2 20bs haha. Also it keeps being compared to huge powered drag car engines were the cranks do twist eg top fuels . Thing is they have close to 10,000hp so it's a bit different. I guess well find out when the crank goes to get ballenced.

[NVMY R]

Looking good mate

[cubic]

Can we get an estimate of when this will get a dyno run? Looking forward to ending the speculation!

[racerdad1]

I Think about 3 months . Just depends how every thing goes.

[Klasse]

This is a 12 rotor in the states:

Insane Engine: A 12-Rotor – Twin-Turbo – 5,000 Plus Horsepower Monster | | BangShift.comBangShift.com

Although hp seems to different depending on where you read.

[Coupe-R]

About the crank twist, i would assume much of this could be eliminated with crank design it self and material, or with the load in the middle as suggested, it will still sound like a 39B as all exhaust will collect into one or two or 3

About the optical sensor, you could do this with one decent ecu im sure with ignition tables/changes for 6 rotors. You can usually adjust fuel for individual cylinders so I don't see why ignition adjustments or offsets for each cylinder aren't possible with one ecu. However as said it won't be 10,000 hp so crank twist may not be a crazy concern as with harmonics, that should also be able to be engineered around or dampened.

[NVMY R]

Hey racerdad are you able to do updates for us if you are allowed and keep us in the loop.

[NVMY R]

Klasse - Cool, but not as cool as a straight 6.

[Fangin]

This definately isn't as cool as a straight six, it's infinitely cooler!!!

Firewall chop looks a little rough, but this is going to be a drag car so I'll let it slide

Also, is there a build thread on this car, maybe on (dare I say it) Rotahavik?

[jeff8827]

hi guys , just been reading this thread . Might be worth pointing out that ppre have nothing to do with the design of any of the 4 or 6 rotor shafts that I make.