New Mazda RX-7 on the way

[sportyaccordy]

Opposed piston engines are very, very different from a traditional piston engine like what is in a car.  Each cylinder pair is balanced from an NVH point of view.  And the setup of those Ecomotors is akin to stringing multiple independent engines together in series with a clutch between them so you could shut them on and off, which you certainly could do with any engine type.

Wouldn't rotaries daisy chained together be the same thing?

Also would it be possible to either let the unused rotors vent to atmosphere (so you are not needlessly pressurizing), or pressurize the intake charge of the existing one (through valving of the exhaust back into the intake)? There are different things they could do.

[MX793]

Wouldn't rotaries daisy chained together be the same thing?

Also would it be possible to either let the unused rotors vent to atmosphere (so you are not needlessly pressurizing), or pressurize the intake charge of the existing one (through valving of the exhaust back into the intake)? There are different things they could do.

Stringing multiple independent rotaries together in series is different from putting a clutch between two rotors in a single motor.  You'd have to have dedicated ignition systems and likely dedicated exhaust tracts (so that you aren't blowing exhaust from the running rotor into the deactivated one).  At which point, you've basically built two independent rotaries.

And the Wankel will still be compressing air even if you vent the exhaust to atmosphere.  They are still Otto cycle engines that process air in finite clumps.  They aren't continuous flow engines like a Rankine cycle turbine.  Venting to atmosphere would be no different than cutting the fuel supply to one piston on a piston engine but letting it continue to pump air.

If you had the appropriate plumbing and valving in place, you might be able to divert exhaust from the "dead" rotor back into the intake and use it as something of a supercharger for the live rotor, but if you do that, will you really be saving any fuel by deactivating it?  The dead rotor is now doing work as a compressor (which consumes fuel), and the live rotor is now getting forced induction, which will prompt greater fuel consumption by that rotor to compensate for the increased airflow.

[2o6]

MX, your thoughts on shutting off ports, similar to what they do with cylinder deactivation now?

I think the real use of rotaries in the future is in a Chevy volt like application as a generator.

No joke, I heard a Chinese company (Chery, I think) was experimenting with a Rotary range extender.

[sportyaccordy]

Stringing multiple independent rotaries together in series is different from putting a clutch between two rotors in a single motor.  You'd have to have dedicated ignition systems and likely dedicated exhaust tracts (so that you aren't blowing exhaust from the running rotor into the deactivated one).  At which point, you've basically built two independent rotaries.

And the Wankel will still be compressing air even if you vent the exhaust to atmosphere.  They are still Otto cycle engines that process air in finite clumps.  They aren't continuous flow engines like a Rankine cycle turbine.  Venting to atmosphere would be no different than cutting the fuel supply to one piston on a piston engine but letting it continue to pump air.

If you had the appropriate plumbing and valving in place, you might be able to divert exhaust from the "dead" rotor back into the intake and use it as something of a supercharger for the live rotor, but if you do that, will you really be saving any fuel by deactivating it?  The dead rotor is now doing work as a compressor (which consumes fuel), and the live rotor is now getting forced induction, which will prompt greater fuel consumption by that rotor to compensate for the increased airflow.

Well my thinking is, a DoD system has waste in it by spinning dead parts and compressing air that won't be used for combustion. The decoupling system would eliminate all those losses at the expense of complexity (back flow problem could be solved with valves). The blow through system would minimize some of the losses by removing what would essentially be an air spring in the dead rotors' combustion chambers. The "supercharging" system makes the most sense. Yes the dead pistons would consume fuel by compressing the air. But thats the case with any DoD system. By pushing that compressed air back into the intake tract you increase efficiency by using waste energy to replace the energy you would have spent to create intake manifold vacuum and pull combustion air through. It wouldn't be 100%, and its possible driving multiple rotors to supercharge 1 or 2 would consume more power than the engine generates. But its still worth looking into. Only impediment is cost

[MX793]

Well my thinking is, a DoD system has waste in it by spinning dead parts and compressing air that won't be used for combustion. The decoupling system would eliminate all those losses at the expense of complexity (back flow problem could be solved with valves). The blow through system would minimize some of the losses by removing what would essentially be an air spring in the dead rotors' combustion chambers. The "supercharging" system makes the most sense. Yes the dead pistons would consume fuel by compressing the air. But thats the case with any DoD system. By pushing that compressed air back into the intake tract you increase efficiency by using waste energy to replace the energy you would have spent to create intake manifold vacuum and pull combustion air through. It wouldn't be 100%, and its possible driving multiple rotors to supercharge 1 or 2 would consume more power than the engine generates. But its still worth looking into. Only impediment is cost

You're better off with an air spring than compressing and then dumping air.  Yes, it takes work to compress the "spring", but that work will get released back into the motor again for a net loss that is near zero (basically, you just have whatever entropy is in the system to contend with as far as losses go).  That's how it's done in piston engines.  But with the way a Wankel moves, I'm not sure the air spring will be as effective.  I do think that, due to port overlap, the only effective way to manage DoD is to use a reed valve in the intake port with some kind of controlled valve (probably a poppet) on the exhaust port.  That should prevent, or minimize, any back feed into the intake manifold when you re-enable a dead rotor without needing to juggle valve timing controls on both the intake and exhaust sides to transition between running states.

And the more I think about it, the more I think that shutting down a rotor but trying to pump the air from that rotor into the live one won't work.  First, what's to stop pressurized air being dumped into the intake manifold from simply blowing back out of the air filter?  Forced induction systems don't have parallel intake tracts (one pressurized, one not).  Second, the rotors in a Wankel are identical and run at the same speed.  They therefore will have the same volumetric efficiency.  What you really need for an effective supercharger is for the compressor rotor to be spinning faster, or otherwise pumping more air, than the combusting rotor.  Otherwise you may as well just dump the air right into the exhaust, you're not getting any gain.  The compressor rotor won't be compressing a large enough volume of air to pressurize the intake tract for the runner, but you're still performing work of pumping air through the dead rotor.  Using 2 rotors to feed a third might get you enough flow volume for effective supercharging, but the plumbing required would be rather complex (both intake and exhaust) and I'm not sure the efficiency gain would be worth the added complexity.

[sportyaccordy]

Ah yea I forgot about that glaring leak point in the system haha. Scratch that completely. In any case DoD or decoupling is probably the way to go.

[Onslaught]

You're able to get Pontiac parts still because they shared all their parts with every other GM car that was just a rebadged version of the Pontiac.

Engine parts and stuff like that are easy to get on those cars. But body parts or things made just for that car and no others are another story. And you made a good call for passing on the Pontiac. Not that it's a bad car but it could turn into a pain in the ass down the road.

[Laconian]

How cool would it be if rotors could be smooshed together like Lego blocks? Upgrade your Wankels like you would add sticks of RAM to your computer.

[r0tor]

How cool would it be if rotors could be smooshed together like Lego blocks? Upgrade your Wankels like you would add sticks of RAM to your computer.

Would you like an...

R12 http://rotarynews.com/node/view/1150

Or

Inline 6 http://www.7tune.com/tag/6-rotor-engine/

[nickdrinkwater]

Are Mazda trying to go bust intentionally?  This is possibly the worst use of resources and development budget for them, in my opinion.  Good for the enthusiast but bad for the health of the company.

[MrH]

Again, it's only a handful of engineers...that's not going to make or break them by any means.

[Onslaught]

Are Mazda trying to go bust intentionally?  This is possibly the worst use of resources and development budget for them, in my opinion.  Good for the enthusiast but bad for the health of the company.

I doubt they have everyone working on this. It's probably not even close to a priority right now. I'd think the new Miata is probably the car that has a good amout of their work going into. They have a new CX-5 and 6 out or coming out. So that's just leaves them with the 3 and MX-5.
And if the RX-7 is based off the new MX-5 then it wouldn't cost them all that much anyway. Hell, perhaps Alpha will want one of these new RX cars just like the MX-5 they will make a version off.

[S204STi]

On a side note, can either of you Wankel guys point me to some good info on tuning up an FC RX7?  I don't think it's turbo'd.

[Onslaught]

When you say "tuning" up are you talking about an actual tune up or making it go Zoom Zoom more?

[S204STi]

When you say "tuning" up are you talking about an actual tune up or making it go Zoom Zoom more?

Sorry, tune up.

Looks like plugs, possibly wires, possibly that pulse dampener thingy.  Anything else I should be looking at?

[MrH]

Italian tune up afterwards.  Get everything nice and fresh, let it warm up for awhile, and let er rip to burn out any carbon deposits.

[hotrodalex]

Italian tune up afterwards.  Get everything nice and fresh, let it warm up for awhile, and let er rip to burn out any carbon deposits.

[S204STi]

Heh... I imagine I will, but other than that... lol

[Onslaught]

http://www.autonews.com/article/20131118/OEM06/311189930/new-mazda-boss:-rotary-is-a-no-go#axzz2l2NMTq1Z

I figured this would happen. Looks like I'll have to just keep the one I've got and build a few more.

[r0tor]

Within 3 years with that loser at the helm, Mazda will be transformed from a passionate and fun car producer - to trying to out bore Toyota.

[Onslaught]

Just because of emissions I'm not shocked if we never see one again. With that said, I'll never buy a 4 banger sports car again and if that's all Mazda makes then I'll never buy another new Mazda again.

[MrH]

You hate 4 cylinders more than you like Mazda?  I'm legitimately shocked...

[Onslaught]

You hate 4 cylinders more than you like Mazda?  I'm legitimately shocked...

Hate is a strong word. I like your car just fine. But I'm old, and I like motors that are quiet when I'm just tooling around and then sound like the devil's having his nuts twisted off when you get on them. I like for them to be smooth as silk too. And most 4 bangers just don't have that.
And let's be honest, Mazda isn't known for making world class piston engines. They don't suck ass or anything but when you make a list of some of the greatest piston engines of all time Mazda isn't on that list.

If it turns out that the rotary is dead and gone then any new sports car I buy will have to be from a more expensive brand now. Something like a Cayman S or something.

[12,000 RPM]

Thats just exhaust tuning. Slap a Helmholtz 1/4 wave resonator in the exhaust tract tuned to drone and you can have a quiet straight pipe system if you want. 4 bangers sound boring though.

[Payman]

Hate is a strong word. I like your car just fine. But I'm old, and I like motors that are quiet when I'm just tooling around and then sound like the devil's having his nuts twisted off when you get on them. I like for them to be smooth as silk too. And most 4 bangers just don't have that.
And let's be honest, Mazda isn't known for making world class piston engines. They don't suck ass or anything but when you make a list of some of the greatest piston engines of all time Mazda isn't on that list.

If it turns out that the rotary is dead and gone then any new sports car I buy will have to be from a more expensive brand now. Something like a Cayman S or something.

You don't hear much about Mazda engines, but they've quietly been the most reliable engines out there.

[Onslaught]

You don't hear much about Mazda engines, but they've quietly been the most reliable engines out there.

Yes but if they came out with a sports car it's have some turbo 4 in it. And my understanding is the ones in the MS6, MS3 and CX-7 had some problems with them. I'd much rather have a V6.

[r0tor]

Hate is a strong word. I like your car just fine. But I'm old, and I like motors that are quiet when I'm just tooling around and then sound like the devil's having his nuts twisted off when you get on them. I like for them to be smooth as silk too. And most 4 bangers just don't have that.
And let's be honest, Mazda isn't known for making world class piston engines. They don't suck ass or anything but when you make a list of some of the greatest piston engines of all time Mazda isn't on that list.

If it turns out that the rotary is dead and gone then any new sports car I buy will have to be from a more expensive brand now. Something like a Cayman S or something.

Completely agree

[Onslaught]

I'm not sure what I think about this new Mazda boss. I understand they they must make money and last year was the first year they actually turned a profit in a a long time. So I get wanting to make cars like the 3, 6 and CX-7 and selling the shit out of them. But he basically said that a new RX car would need to sell 100K cars a year. No RX-7 at anytime has ever sold that many cars! Hell, if this is his thinking then the Miata could be on the chopping block too one day!!!

[MX793]

The MX-5, which would be at a substantially lower price point, struggles to hit 25K units per year globally.  Even at it's prime in the early 90s it never even hit 75K units annually.  I don't think the Mustang even sells 100K units a year anymore.

The expectation that any niche vehicle is going to consistently have a take rate of 6 figures per year is nuts.

[Payman]

The MX-5, which would be at a substantially lower price point, struggles to hit 25K units per year globally.  Even at it's prime in the early 90s it never even hit 75K units annually.  I don't think the Mustang even sells 100K units a year anymore.

The expectation that any niche vehicle is going to consistently have a take rate of 6 figures per year is nuts.

Agree. The only future these cars have is through sharing development/manufacturing costs, like the BRZ-FRS and the new Miata-Alfa Spider.