Does the RPM reading we get measure the RPM's of the ouput shaft, or the rotor? If it's the output shaft, then the rotor is actually red-lining at 3000 rpms, and if it's the rotor that is measured, then the output shaft is turning 27000 RPMs at redline. Anybody know the answer to that one?

The dealer sales guy (they are all experts of course) told me that the rotary is capable of 13k-15k RPM, so the rev-limit on the stock machine was very conservative. Any truth to that statement ?

Thanks,
Tbone

 

good question. I would like to know this too.

 

The RPM on the tach is the speed of the output shaft. The rotors rotate at 1/3 that speed. 9000 rpm = 3000 rpm of the rotors.

 

RPM's measure the output shaft. At 6,000 RPM the rotors are loafing at 2,000 RPM.

Edit: Just saw and followed the link posted below by Tbone on how a rotary engine works. Very intersting, worth a visit.

 

Just for a comparison isn't it true that a piston engine with a crankshaft rpm of 6000, that the real rpm's of the pistons would be less than that, or am I wrong

 

For every revolution of the crankshaft, the piston makes one comlplete up-down "cycle" if you would. It takes 2 rpm for the intake, combustion, exhaust, intake cycle to happen.

 

If you can get your mind around the e-shaft spinning three times as fast as the actual rotor, is it too much to compare it to a V8 that has the camshaft as ITS output shaft? (i.e. twice crank speed)

Check out some drunken midnight musings (and subsequent 'flame' beatings!)
on this subject......

Renesis torque is 450 ft/lbs!

aah...the good old days!

S

 

The camshaft in a V8 engine runs at 1/2 the crankshaft speed, not twice. The crank rotates twice for every camshaft revolution.

 

If the camshaft runs at half the crankshaft speed and the crankshaft speed is 6000 rpm's does that mean the camshaft and or piston rpm's is 3000 rpm's

 

The up-down cycle of the piston is the SAME as the crankshaft (pistons don't have a rotation, hence they don't have an "RPM"). The camshaft controls the up-down motion of the intake and exhaust valves, which occurs at 1/2 that rate.

For every TWO rotations of the crankshaft:
- The piston goes up and down twice:
- down for the intake stroke
- up for the compression stroke (one crank rotation done)
- down for the power stroke
- up for the exhaust stroke (second crank rotation done)
- Intake valve opens and closes once, during intake stroke
- Exhaust valve opens and closes once, during exhaust stroke
- Both valves are closed for compression and power stroke

So, at 6000 rpm, each piston goes through an up-down cycle 6000 times per minute, resulting in 3000 power strokes per minute (every other cycle). The cam runs at 3000 rpm, resulting in each valve opening and closing 3000 times per minute.

(Unless you're talking about a 2-stroke or 2-cycle engine like your weedwacker or chainsaw, where the rpm to piston-cycle is still 1:1, but there is a power stroke for each crank rev because the intake and exhaust stroke is combined at the bottom of the power stroke.)

 

which i'll never let you live down, ray

 

I see that Stealth can't even remember that a camshaft goes half crank speed....

The dolt is probably drunk AGAIN!
.
.
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doc

 

I read somewhere in official literature that the engine is spin-rated to 14K. So the dealer is right on that account.

The limits are put on the engine because of either the torque converter or the clutch/flywheel assemblies (depending on model).

 

oh i know ray!! doesn't that guy just get soooooo annoying??

 

w2aew, Thanks for the Education.....

 

So this meansthat when we driveour automatic Rx8s to redline the rotors are only @ 2500 RPM? Wow. I wonder if automatic Rx8s will havea longer lifespan than manuals - since the average automatic Rx8 owner would generally keep the rotors going at lower RPMs than the average manual owner (and the 4 gears vs 6 gears factor as well).

 

high rpms are good for the engine

 

Yeah but your engine will be running longer because it takes you twice as long to get there! j/k

 

so the rotors can spin at 14k? or is that the shaft? Cause if the rotors can spin at 14k, and at 9k rpm at the shaft the rotors are only doin what? 3k or 4. THats 10k more that we can spin these rotors. Or am i wrong? Cause if thats the case i will get a chip and raise the rev limiter! : )

 

Tony - good idea but make sure toget back to us as soon as your tranny and parts start popping off. In the meantime well be placingbets.

 

:d

 

No - the rated RPM is for the output shaft, not the rotors. However, it is limitations in the rotor & gear that set the limit.

 

As has been stated earlier, the engine rpm is measured by the speed the eccentric shaft is rotating. The rotors turn at 1/3 the speed of the eccentric shaft. This is why it takes the engine 3 complete revolutions to fire all 6 chambers on 2 rotors.

Max rpm is limited by so many things. The intake manifold doesn't flow enough air for one thing. The porting isn't optimal although it could work wityh short runners. At very high speeds, the lack of a center bearing for support on the eccentric shaft can cause the shaft to warp. This leads to rotors crashing into housings. This is why many rotors are race clearanced. The clearances are increased to account for this. The most obvious solution is to add a center bearing. Guru Racing sells these eccentric shafts.

Another problem is bearings. Racing Beat had the problem on their old Bonneville 1st gen RX-7 that above 13000 rpm (sustained speed) the bearings would go sayonara. At these high speeds, seals also chatter worse and seal less. The flywheel and clutch will explode unless specifically designed for these speeds. A ballistic scatter blanket is a must for these rpm's. Stationary gears also start to lose teeth up high.

There's alot you have to think of when operating at higher max rpm's. The rotors themselves are almost never the problem.