I was thinking on the drive home today (in a piston powered, turbo'ed car) that while higher compression adds torque, mechanical advantage can to. That is, an eccentric shaft has a relatively small offset from axis whereas crank shafts have a greater offset...

It would be theoretically possible to add a planetary gearset to the inside of a rotor that would allow for a greater e-shaft 'throw' and at the same time use gearing to give it more oomph.

Of course, this would add complexity, but so do variable length intakes

i have an idea what you are talking about... but what would that do to your RPM range ?

depends how it's geared. If the planetary gearset makes it so the greater-offset e-shaft (lets just call this one the crankshaft) rotates slower than the stock e-shaft per rotor rotation, you'd have higher rotor RPMs for a given speed but greater torque.

So why don't you just build a bigger rotary? Change the geometry so the E shaft has more offset and the larger rotor moves around larger stationary gears. This would make the engine tall and wider, but it would do for more torque. Otherwise you should just change the trans or rear axle ratios to spin the enigne faster since that's all puting a reduction gearset inside the engine would do.

*edit*

So how's that catalytically ignitied diesel rotary coming along?

slowly - if something like that could be developed overnight on a modest budget it'd have been on the road long ago. Probably a few years before a reliable plug-and-play system is viable. But even Felix Wankel needed more than a few months to go from idea to running prototype.

And a bigger rotary would get into diminishing returns, including greater fuel and air requirements. By using gearing to allow 13B displacement rotors, but a greater cranking throw, would keep current breathing, sealing, and packaging technology viable while addressing a weakness in the current design. The main drawback I can see is the planetary gears would be whirring around at very high RPM.

You really missed the point. All you are proposing is to spin the rotor faster than the E shaft. That's why the car has a transmission. It's to match the engine torque to the road speed and load requirements.

not at all. I'm proposing using a planetary gear to crank a greater offset with greater mechanical advantage thereby increasing the engine torque. With proper gearing there'd be little change in rotor or shaft speed.

get a heavier flywheel? ;)

edit - I tried illustrating it, but realised that enlarging the e-shaft lobe would do something similar with fewer headaches

why dont more cars built today usea a rotary engine?

partly due to a rotary's low torque and thermal efficiency, and because most car company's engineers understand piston engines - to get them thinking rotary would require a change in corporate culture.

so they are good they're just not well understood ?

You could just supercharge it...

Both piston engines and rotary engines have their strengths and weaknesses, just as diesel piston and gasoline piston engines do.

I like the fewer parts and smaller size of rotaries, but I like the torque and inexpensive parts of piston engines. You can rebuild Chevy 350s for peanuts, simply because there are so many of them so there's more aftermarket support. Same with my Chrysler 2.2 litre 4 cylinder.

When it comes to piston engines, I like turbodiesels. Others may prefer V8 supercharged gas engines. Because each different approach have unique strengths, they each have their fans.

turbos make more torque...

pro to supercharger -vs- turbo: usually cheaper, possibly simpler installation
cons: everything else

Supercharger = time spent changing pulleys

Turbo = time turning boost up

Could add a D-valve to a single turbo for faster spooling.

Variable nozzle turbos are cool but the Garrets I've seen tend to suffer from sticking vanes.

MBC or EBC... time turning up boost?

I'm proposing using a planetary gear to crank a greater offset with greater mechanical advantage thereby increasing the engine torque.Torque is a function of displacement, not stroke.

Example 1: Two 427s, one with a 4.25" bore and 3.76" stroke and the other with a 4.125" bore and 4.00" stroke will produce almost identical power and torque curves, given the same valve timing and intake setup. The "big bore" 427 may have a small advantage in unshrouding the valves further, but it's negligible and probably offset by slightly reduced friction in the stroked engine with less piston ring surface area.

Contrary to popular belief, the "stroked" 427 will not produce any more torque than the 427 with the shorter stroke, and this has been proven both with engine simulation software as well as real-world engines. The only real advantage is piston speed. All things being equal, the shorter stroke engine will potentially have a higher rpm potential due to lower piston speed, assuming it had an induction setup allowing it to breathe well at higher rpm.

Example 2: The new 427 LS7 (4.00" stroke) produces 470 lb-ft. of torque, but my 396 LT1 (3.875" stroke) produced 560 lb-ft. despite having less "mechanical advantage". The difference was mostly due to increased cam duration and intake and exhaust efficiency, since my 23-degree heads didn't flow as much as the LS7 12-degree heads (~330 cfm vs. ~360 cfm intake). Power output is simply a function of how much air and fuel you can get into the engine and burn at any given rpm.

The same goes for rotaries. A smaller rotary engine can't equal the airflow of a larger rotary engine until higher rpm and/or with more boost. Bottom line, the only way to increase torque with a rotary engine is to add more displacement, and the easiest way to do that is to add more rotors.

So why don't you just build a bigger rotary? Change the geometry so the E shaft has more offset and the larger rotor moves around larger stationary gears. This would make the engine tall and wider, but it would do for more torque.While this is true, Mazda experimented with this and the stillborn 15A and 21A were the result. The problem with larger rotors and housings, besides weight, is less efficient combusion because of the increase in length and surface area of the combustion chamber. The rotary is already terribly inefficient from a fuel consumption standpoint. Increasing the size of the combustion chamber just increases the problem.

MBC or EBC... time turning up boost?


2-3 seconds.

Torque is a function of displacement, not stroke.

True. And as I said in an earlier post, when I sat down and sketched it out it didn't make much more sense then a larger e shaft lobe anyhow. Ah, well, just one of those drive-home musings that went nowhere...

True. And as I said in an earlier post, when I sat down and sketched it out it didn't make much more sense then a larger e shaft lobe anyhow. Ah, well, just one of those drive-home musings that went nowhere...

Ding, ding, ding! We have a winner!

always the optomist, aren't ya Josh? Glad you weren't on my development team when we made the C-6 machine gun vehicle mount everyone said was impossible...

Hey, it's possible to draw things that can't exist, but you couldn't even get your idea onto paper. There were folks that have tried all kinds of ways to convert the reciprocating psiton motion to rotary motion including using gears very similar to planetaries, but only one the connecting rod and offset crank pin are with us today. You're just repeating history.

Mazda, with all their R&D money has managed to make a rotary that still gets worse economy and makes equivalent torque and horsepower of a highly developed 2.2L boinger. Sure, the parts count is lower, but we know how cheap that makes them to build. Micro-porous-channel chrome plated sheet steel inside an aluminum housing anyone? No wonder rotor housings cost $700 each.

Hey, it's possible to draw things that can't exist, but you couldn't even get your idea onto paper.

actually I did get it on paper. But when I did I realised that, like your idea of going with larger rotors, the benefits were outweighed by the disadvantages. It could exist, and could function, but just like GMs 8-6-4 engines of the early 80s or Chrysler's Ultradrive of the early 90's, sometimes solving one problem creates another.


There were folks that have tried all kinds of ways to convert the reciprocating psiton motion to rotary motion including using gears very similar to planetaries, but only one the connecting rod and offset crank pin are with us today. You're just repeating history.

actually no. I was posting a musing of a way to add torque, not reinvent the principles of turning explosive force into rotational motion.

And if the world really worked on 'one thing works, and one thing only' you wouldn't see diesels alongside gas engines; direct-injection alongside conventional injection alongside carb'd engines. But you do. And even in your con-rod example, there are heavy, forged con rods like GM uses and small, delicate con rods like Honda uses. There are different systems for lubricating the wristpin you mentioned. There are OHC valve systems, and pushrod systems. Why? Because people postulate a new way of doing things, weigh the advantages of the new system against the disadvantages, and go from there.

You, however, jump in at the postulation phase with 'if it worked' someone would have thought of it already'. If you were hanging out with Felix back in the day you'd have probably tried to talk him out of pursuing his adaption of a pump to a combustion engine. What next? Gonna tell Jimlab 'If V8s were so great, Mazda would've put 'em in RX-7s from the start'?

If reading posts about new concepts bothers you so much, quit reading them.

Reading about new concepts doesn't bother me at all, but what I expect you came up with isn't new, revolutionary or practical. Care to share your drawing with the class? Can you show us how it would add torque without increasing displacement or engine speed?

The Cadillac 4-8-6 engine was an early and unfortunate adaptation of cylinder deactivation. Technology has now progressed where cylinder deactivation is now viable. Chrysler's Ultradrive is similar in that it wasn't a mature technology, but just about every automatic now in production is electronically controlled. So what!?

Again you're missing the point. You've come up with nothing new. That's it!

I didn't claim to be reinventing the wheel, I posed the question as to whether it was a viable way to enhance the torque within the engine. Jimlab posted an intelligent answer. You posted your usual negativity and reinterpretations of what was being postulated so you could argue against what you wanted to.

Example: Just because I mention using a planetary gear, you presumed I meant gear reduction in the engine - even though I was clearly taking about using gears to allow greater crank throws. Then you go on your own tangent about how transmissions provide gear reduction, yada yada yada... You presume an arguement that doesn't exist, then go on about how nothing new could possibly work. It's a stale routine, Josh.

There is no way to gain mechanical advantage (torque) without moving the rotor farther. It's just like a lever and fulcrum. You are proposing to move the fulcrum. That means that the rotor spins faster or the e-shaft spins slower. It's that simple. Really. I'm sorry if you haven't kept up. If you can show me your perpetual motion machine then go ahead.

Jim complicated the matter by bringing up a comparison between short stroke big bore engines and long stroke smaller bore piston engines. Did you notice how I went straight to an e-shaft with a greater offset which would, all else being equal, make for a larger engine that would make more torque? There was nothing wrong with the info Jim provided, but it isn't relavent to your idea.

There is no way to gain mechanical advantage (torque) without moving the rotor farther. It's just like a lever and fulcrum. You are proposing to move the fulcrum. That means that the rotor spins faster or the e-shaft spins slower.

no, it's not. What I proposed was using a planetary gear to offset the throw of the crank. Gears allow for changing the geometry of a path, as anyone who's played with a spirograph knows. Sorry you haven't kept up.

And no, a greater offset wouldn't neccessarily mean a larger rotor, all else being equal. It can be done with a larger lobe on the e-shaft and a larger hole in the rotor to accomodate it.

no, it's not. What I proposed was using a planetary gear to offset the throw of the crank. Gears allow for changing the geometry of a path, as anyone who's played with a spirograph knows. Sorry you haven't kept up.

And no, a greater offset wouldn't neccessarily mean a larger rotor, all else being equal. It can be done with a larger lobe on the e-shaft and a larger hole in the rotor to accomodate it.

The geometry of a rotary, the epitrochoid, is fixed in regards to the center of the offset of the eccentric shaft. You can make the eccentric larger and run it inside a larger bearing, but you cannot move the center of the eccentric without the rotor moving through a different path.