Upcoming RX-7 to be the next Mazda Diesel?

Mazda is developing a new generation flex-fuel rotary which can apparently run on just about any fuel including gasoline, diesel and castor oil confused: ).

Likely to debut in a new generation RX-7.

I suspect even when burning diesel it would still be spark ignition and wouldn't get very good mileage, but I'm all for a new RX-7.

http://www.motortrend.com/future/future_vehicles/1004_future_mazda_rx_7/index.html

yeah, it would be DI + spark.

The issue isn't if they can do it, but how will they meet emissions regulations as it gets tighter and tighter. Rotary is the antithesis to clean.

The main thing about using diesel is that they might be able to get away without the oil metering pump for seal lubrication. A rotary that doesn't burn oil? That's crazy stuff

The rotary has been touted as being able to handle assorted fuels for well, since it was invented. It's been produced, in limited (i.e. one at a time) quantities even with diesel combustion. It's been studied with even hydrogen, when that was being explored as a fuel.

I wonder how well the huge surface to volume cooling surface would mess up diesel combustion efficiency.

The keen observer would observe that there haven't been any alternative fuel rotary engines used in a vehicle.

That observer would also find a vertiable cornucupia of diesel wankel threads.

hydrogen is a joke. Unless of course I wanted a RX-8 that was slower than a Prius.

That surface area to displacement volume is a deal killer for rotaries. Too much heat gets sucked into that shiny metal. So efficiency will always suck compared to a good piston engine. But damn those things are fun to drive!!! Nothing can touch the smoothness, compactness and general zippiness.

mysql said:

The main thing about using diesel is that they might be able to get away without the oil metering pump for seal lubrication. A rotary that doesn't burn oil? That's crazy stuff

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Until it starts running on gasoline, ethanol, or anything non-diesel.

Sorry Mazda, but I'm pretty sure that your apex seals will always be such a critical failure point that diesel will be forever out of the question.

On the other hand, since the rotaries have two injectors per rotor, cleanliness shouldn't be such a big problem. Perhaps this is what allows them to claim multiple fuel use.. a little creativity with fuel injection and voila! Perhaps they start the ignition with gasoline and send diesel into the chamber through the second injector? (Pure speculation)

The problem I see is that Mazda is terrible at making things last. The cars are beautiful, the handling has been magnificent, but the bottom line has always been that turbocharged rotaries are not a good engine design. Under high boost, if an injector gets dirty or old, detonation occurs, destroying the apex seals. It happens fast.

Oh gawd... that concept picture is awful. The front end looks like a grinning baleen whale. No thanks!

Wankels are an elegant idea on paper but there's just too many drawbacks IRL.

The seals, the combustion chamber volume to surface ratio, limited maximum CR, the elongated shape of the combustion chamber, the uneven heating of the stator, low duration of combustion "stroke" in crank degrees, excessive overlapping intake and exhaust "strokes", lousy scavenging, etc.

There's a reason the 4 stroke ICI block & bottom end have remained largely unchanged since the sleeve valve engine went the way of the dodo. And a reason why scantly a manufacturer bothers with Wankels. And not even Wankels alone, at that.

Rotary beats pistons in applications where you need WOT for long periods of time.

That means racing and airplanes.

For sports cars, it's fine (though lacking in power if in NA form). But for the general consumer, I don't think Mazda will be able to do anything other than make a halo car out of it.

My RX-8 was turbocharged at 12 psi (310 whp/260 rwtq) for 2 years. I owned the car for 6 years total. The engine was great. It had a crack in the front iron housing from incorrect dwell on the ignition coils, but if it weren't for that, the engine would still be completely original with zero issues. It had 65,000 miles when I sold it.

mysql said:

My RX-8 was turbocharged at 12 psi (310 whp/260 rwtq) for 2 years. I owned the car for 6 years total. The engine was great. It had a crack in the front iron housing from incorrect dwell on the ignition coils, but if it weren't for that, the engine would still be completely original with zero issues. It had 65,000 miles when I sold it.

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A little JB Weld would have fixed that right up!

mysql said:

The engine was great. It had a crack in the front iron housing....
It had 65,000 miles when I sold it.

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65,000 miles and it had a cracked housing? That's what you consider great?

If you missed a 1 or 2 in front of the 65,000, then that's different, but 11k miles a year for 6 years is not something I'd consider to be worth the effort to type.

mysql said:

Rotary beats pistons in applications where you need WOT for long periods of time.

That means racing and airplanes.

For sports cars, it's fine (though lacking in power if in NA form). But for the general consumer, I don't think Mazda will be able to do anything other than make a halo car out of it.

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True. We're not likely to have a rotary powered Mazda 3 any time soon.

Ever hear one of those 4 rotor road racing cars at full wail? Mother of God were they loud! Glorious, but loud. They certainly weren't down on power even without forced induction, ~700bhp from 2.6 liters.

Flex fuel or not I'd still love to have a reincarnated first generation RX-7. Put a fixed roof on the Miata chassis and throw the rotary engine in it and they'd have a real winner. Hoperully the cost savings from deleting the folding roof would cancel out the more expensive engine.

I can dream, can't I? In the mean time a Honda S2000 or Subaru/Toyota FT86 will have to suffice.

Edit: Whoops, I forgot the prototype cars were 4 rotors, though Mazda did make a few 3 rotors for other forms of racing.

Lug_Nut said:

65,000 miles and it had a cracked housing? That's what you consider great?

If you missed a 1 or 2 in front of the 65,000, then that's different, but 11k miles a year for 6 years is not something I'd consider to be worth the effort to type.

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notice it wasn't exactly stock... in stock form, even the "high power" version was 230hp at the crank, and his was 310 at the wheels... big difference.. The "standard power" version was only 190hp at the crank, so if he started with that one, it's a dramatic power difference with only 1.3 Liters to work with..

^ Exactly

BTW it wasn't a cracked rotor housing, it was a front iron housing. A $300 part new.

Making 400 whp is pretty easy without engine modifications. Just spray a little meth to keep the charge temps down and increase boost to 16 psi.


PS: For the high power version of the engine, 190 whp on a stock car is quite good. Many dyno in the 180's. No one in their right mind buys the automatic (low power) cause the redline is below the peak powerband of the motor!

aah I see... That would just about explain why I can embarrass an automatic rx8 with my 99.5, and pull away from a "high power" one...

TDIJetta99 said:

aah I see... That would just about explain why I can embarrass an automatic rx8 with my 99.5, and pull away from a "high power" one...

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RX8 is a starved motor. You wouldn't be pulling away from a FD3S with your MKIV...

What's a FD3S?
So far I've run into a dozen or so assorted RX8's around here and they are all slow, LOL... There's one guy that turbocharged his and I can't touch that one with the TDI.. The camaro eats him alive, LOL....

TDIJetta99, most people who slap on a turbo kit go for the greddy turbo. If you install it as designed, it makes 6 psi and ~240 whp. Gaining 60 whp over stock is nice, but it really isn't fast until you get into 300+ range. Part of the issue is that the turbo is properly sized for 6 psi, but no more. Once you increase boost, it tops out quickly and the engine wants more air than it can supply. You can still make ~270 whp with that setup.

Long story short, they need to replace the turbo, add a boost controller, then they'll be halfway decent. But just saying "It's turbocharged" doesn't mean much since the amount of power variation is greater than what the car makes stock

TDIJetta99 said:

What's a FD3S?

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It's the '93-'95 RX-7 Twin turbo. (or single turbo) Mine does a 1/4 mile in less than 13 seconds. Well, that is... it did when it was running.

they called that the rats nest for a reason



the rx8 was supposed to be a reliable rotary vehicle... instead they programmed it with too little oil for the seals (OMP) which caused a ton of engine failures in the early 2004/2005.

mysql said:

they called that the rats nest for a reason

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I call mine a rats nest too, unfortunately that is because there have been so many rats' nests in the engine bay.

^^ that is completely ridiculous!

here's mine. Very few vacuum tubes.

2 thumbs up for that cold air intake. I'd like to see where the filters are...

I've had the car setup with MAF and MAP.... MAF with the stock car's ECU (using accessport) is far more advanced than any aftermarket stuff. Individual maps for each gear.

But the MAF setup is extremely important and it needs enough space before and after the sensor for the air flow to be smooth. It goes straight for a bit, then has a nice smooth elbow to the front of the bumper, then it goes down in front of the radiator. I've also had it just turn into the bumper and sit there, but your filter is limited in size.

Heat off the radiator isn't an issue since it blows away from the intake. AITs are low.

mysql said:

here's mine. Very few vacuum tubes.

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Better but it still looks like a nightmare to work on.

My neighbor has a 3rd gen with a turbo'd 3 rotor in it (20B?) and there no denying it - she wails!

it's very easy to work on... we pulled the engine out in my garage. The engine is amazing... amazing that it actually works. So few moving parts. Engine is held together by a few bolts. No valves, no timing belt. There is literally nothing to it.

mysql said:

Long story short, they need to replace the turbo, add a boost controller, then they'll be halfway decent. But just saying "It's turbocharged" doesn't mean much since the amount of power variation is greater than what the car makes stock

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I have no idea what they guy has in the car, I don't know him, nor have I ever spoke with him.. All I know is that it has a turbo (you can hear it) and it's significantly faster than my TDI.. That's why I only said "it's turbocharged" because that's all I know about it.. I've run into him on local roads 3 or 4 times, once with the Camaro (runs high 11's)..

mysql said:

it's very easy to work on... we pulled the engine out in my garage. The engine is amazing... amazing that it actually works. So few moving parts. Engine is held together by a few bolts. No valves, no timing belt. There is literally nothing to it.

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I remember putting together an older 13B with a holley 4bbl carb.. By the time it was all said and done, it looked like a 5 gallon bucket with some spark plugs sticking out of the side.. Fun stuff...