Hmm Skyactive-R you say? Rotory you say? Hmmm..

The car looks decent but not great. The sides of the car are the worst part. At first impression it has boring slab sides, they seem to be near-featureless curtains of metal. But when you look closer there's a little hint of...Bangle sides I'm not sure about having no fenders at all either. It's almost like they started with a "hovercar" and put wheel wells in as an afterthought with a giant hole saw.

Anyway there are signs that this new vehicle will be a very high end 6-figure sports car to compete with the R35 GTR. It has carbon brakes. Those would bankrupt any working Joe very easily. Next that hood that goes on forever suggests that the engine will have many rotors, which suggests high power at the very least, and unless Mazda has made some major breakthroughs, hellacious fuel and maintenance costs.

If I were working for Mazda, and in charge of the rotary, with absolutely no information on things which they undoubtedly have built reams of...

I would start with small rotors, and lots of them. I think swept volume is the issue. Imagine the fuel economy if you had a 3 liter reciprocating engine with one cylinder. Or two. Maybe the right answer is six rotors, or eight, or twelve.

They probably know the answer to this already, but the ideal size of each combustion chamber should be knowable.

In reply to tuna55:

plus, 4 rotor engines induce ear-gasms.

Fueled by Caffeine wrote: Ohh a concept.. Awesome. They totally happen.

Mazda has a history of concept vehicles entering production.

Reading between the lines, MSRP will be around $60k. Also it looks too much like the Ambiguously Gay Duo's car.

tuna55 wrote: If I were working for Mazda, and in charge of the rotary, with absolutely no information on things which they undoubtedly have built reams of... I would start with small rotors, and lots of them. I think swept volume is the issue. Imagine the fuel economy if you had a 3 liter reciprocating engine with one cylinder. Or two. Maybe the right answer is six rotors, or eight, or twelve. They probably know the answer to this already, but the ideal size of each combustion chamber should be knowable.

Hi Tuna55,

I think you start with the compression ratio which dictates the velocity of the flame propagation wave which sets the maximum RPM. Once you’ve got the compression ratio and RPM defined, you can work through displacement and bore to stroke ratio to get the desired Hp and torque values.

You actually want the fewest number of chambers (rotor or cylinder) possible as that gives you the highest volume to surface area ratio…volume gives you useful work – surface area gives you efficiency loss due to heat convection and frictional. So, the fewer rotors or cylinders the better in terms of BSFC (best specific fuel consumption) as measured by pounds of fuel burnt per hour per Hp but designers are constrained by compression ratio limitations.

Additionally, there are considerations regarding symmetry to reduce counterbalancing requirements, power pulse intensity which dictates how strong components need to be made and how smoothly the engine runs and some other stuff.

Added later…

I’ve given thought to the optimal rotary engine configuration over the years and I’ve come up with the idea of a three rotor design where the center rotor is both wider and taller than the two outer rotors….think Football shape. This design would provide better rotational mass balancing than previous designs (the two ends would offset the center), superior volume to surface area ratio (the closer you get to a sphere the better) and would still allow for side porting as the center rotor would “peek” out around the two smaller rotors on both sides.

Thoughts???

GameboyRMH wrote: Anyway there are signs that this new vehicle will be a very high end 6-figure sports car to compete with the R35 GTR. It has carbon brakes. Those would bankrupt any working Joe very easily.

I don't think 100k+ when the target is the Cayman. But I also don't think Miata + 10% either.

tuna55 wrote: If I were working for Mazda, and in charge of the rotary, with absolutely no information on things which they undoubtedly have built reams of... I would start with small rotors, and lots of them. I think swept volume is the issue. Imagine the fuel economy if you had a 3 liter reciprocating engine with one cylinder. Or two. Maybe the right answer is six rotors, or eight, or twelve. They probably know the answer to this already, but the ideal size of each combustion chamber should be knowable.

Larger and fewer is better for thermal efficiency. The only issue with that becomes combustion speed limits - the bore gets to be too large for efficient combustion because parts of the chamber are too far away from the plug. I believe it's beyond 84mm where you start to see diminishing gains from increased bore vs. increasing detonation.

With Mazda rotaries, torque would go out out of proportion with displacement every time they widened the rotors. Volume was going up faster than surface area was, so better thermal efficiency.

Knurled wrote:

tuna55 wrote: If I were working for Mazda, and in charge of the rotary, with absolutely no information on things which they undoubtedly have built reams of... I would start with small rotors, and lots of them. I think swept volume is the issue. Imagine the fuel economy if you had a 3 liter reciprocating engine with one cylinder. Or two. Maybe the right answer is six rotors, or eight, or twelve. They probably know the answer to this already, but the ideal size of each combustion chamber should be knowable.

Larger and fewer is better for thermal efficiency. The only issue with that becomes combustion speed limits - the bore gets to be too large for efficient combustion because parts of the chamber are too far away from the plug. I believe it's beyond 84mm where you start to see diminishing gains from increased bore vs. increasing detonation. With Mazda rotaries, torque would go out out of proportion with displacement every time they widened the rotors. Volume was going up faster than surface area was, so better thermal efficiency.

I understand most of what you said here. The issue that I see offhand is that the rotary triangle is shaped such that the compression space becomes really oblong as displacement increases. Rotors are really thin. A sphere is the best surface area/volume that you can make, so you'd want the chamber as spherical as possible to maximize this (one variable which I cannot confirm, nor have any data to back up as being important to maximize fuel efficiency), so that, to me, looks like a smaller diameter rotor. Perhaps a wider rotor with the same perimeter. I am not sure, but it would be super-neat to play with variables with 3D printed models.

RX Reven' wrote:

tuna55 wrote: If I were working for Mazda, and in charge of the rotary, with absolutely no information on things which they undoubtedly have built reams of... I would start with small rotors, and lots of them. I think swept volume is the issue. Imagine the fuel economy if you had a 3 liter reciprocating engine with one cylinder. Or two. Maybe the right answer is six rotors, or eight, or twelve. They probably know the answer to this already, but the ideal size of each combustion chamber should be knowable.

Hi Tuna55, I think you start with the compression ratio which dictates the velocity of the flame propagation wave which sets the maximum RPM. Once you’ve got the compression ratio and RPM defined, you can work through displacement and bore to stroke ratio to get the desired Hp and torque values. You actually want the fewest number of chambers (rotor or cylinder) possible as that gives you the highest volume to surface area ratio…volume gives you useful work – surface area gives you efficiency loss due to heat convection and frictional. So, the fewer rotors or cylinders the better in terms of BSFC (best specific fuel consumption) as measured by pounds of fuel burnt per hour per Hp but designers are constrained by compression ratio limitations. Additionally, there are considerations regarding symmetry to reduce counterbalancing requirements, power pulse intensity which dictates how strong components need to be made and how smoothly the engine runs and some other stuff.

See what I wrote above. Assuming that the chamber shape, and surface/volume raio is important, it seems a wider rotor, or several smaller rotors of the same perimeter, would work.

tuna55 wrote:

RX Reven' wrote:

tuna55 wrote: If I were working for Mazda, and in charge of the rotary, with absolutely no information on things which they undoubtedly have built reams of... I would start with small rotors, and lots of them. I think swept volume is the issue. Imagine the fuel economy if you had a 3 liter reciprocating engine with one cylinder. Or two. Maybe the right answer is six rotors, or eight, or twelve. They probably know the answer to this already, but the ideal size of each combustion chamber should be knowable.

Hi Tuna55, I think you start with the compression ratio which dictates the velocity of the flame propagation wave which sets the maximum RPM. Once you’ve got the compression ratio and RPM defined, you can work through displacement and bore to stroke ratio to get the desired Hp and torque values. You actually want the fewest number of chambers (rotor or cylinder) possible as that gives you the highest volume to surface area ratio…volume gives you useful work – surface area gives you efficiency loss due to heat convection and frictional. So, the fewer rotors or cylinders the better in terms of BSFC (best specific fuel consumption) as measured by pounds of fuel burnt per hour per Hp but designers are constrained by compression ratio limitations. Additionally, there are considerations regarding symmetry to reduce counterbalancing requirements, power pulse intensity which dictates how strong components need to be made and how smoothly the engine runs and some other stuff.

See what I wrote above. Assuming that the chamber shape, and surface/volume raio is important, it seems a wider rotor, or several smaller rotors of the same perimeter, would work.

I added something to my original reply while you were posting this...check it out and let me know what you think please.

In reply to RX Reven':

I need a picture. Can you draw one in paint or something?

Knurled wrote:

tuna55 wrote: If I were working for Mazda, and in charge of the rotary, with absolutely no information on things which they undoubtedly have built reams of... I would start with small rotors, and lots of them. I think swept volume is the issue. Imagine the fuel economy if you had a 3 liter reciprocating engine with one cylinder. Or two. Maybe the right answer is six rotors, or eight, or twelve. They probably know the answer to this already, but the ideal size of each combustion chamber should be knowable.

Larger and fewer is better for thermal efficiency. The only issue with that becomes combustion speed limits - the bore gets to be too large for efficient combustion because parts of the chamber are too far away from the plug. I believe it's beyond 84mm where you start to see diminishing gains from increased bore vs. increasing detonation. With Mazda rotaries, torque would go out out of proportion with displacement every time they widened the rotors. Volume was going up faster than surface area was, so better thermal efficiency.

84mm bore, you mean the nearly the same size as a 1.8 Miata engine?

That makes no sense given how many engines have much larger bores than that, or am I missing something?

z31maniac wrote: That makes no sense given how many engines have much larger bores than that, or am I missing something?

Anything engineered is engineered to different criteria.

tuna55 wrote: The issue that I see offhand is that the rotary triangle is shaped such that the compression space becomes really oblong as displacement increases. Rotors are really thin. A sphere is the best surface area/volume that you can make, so you'd want the chamber as spherical as possible to maximize this (one variable which I cannot confirm, nor have any data to back up as being important to maximize fuel efficiency), so that, to me, looks like a smaller diameter rotor. Perhaps a wider rotor with the same perimeter. I am not sure, but it would be super-neat to play with variables with 3D printed models.

Well, by changing that you would be changing some other significant dimensions, and IIRC if you go in that direction you will be significantly reducing available compression. Mazda's geometry has a theoretical maximum of 12:1 but the practical limit is much lower because of in-chamber airflow concerns. People experimented with replacing the old 9.4/9.7 rotors with RX-8 10:1 rotors (required milling the apex slots deeper, since RX-8 seals are much shallower) and the end result was no power gain and in some cases power loss.

The biggest problem, as I see it, with the RX-8's engine is that Mazda insisted on using the old tooling. In short, the tension bolts were positioned in the 60s and as they refined spark plug placement, they got more and more shortchanged for coolant flow because of the placement of those tension bolts. Poor coolant flow makes the housings warp around the spark plug, this warping harms compression. If they'd move the tension bolt location, they could solve that issue easily. But then they'd need new tooling. The RX-8's engine shares a remarkable amount of hard dimensions with the '67 Cosmo, and even some parts.

I'm not a fan of how they go thinner and thinner on the side seals, either. The .7mm seals are really pushing it for durability IMO, even before they stared forcing them to go over an exhaust port.

So more FD than Cosmo. I dig it, but it doesn't seem to have the same presence as a FD in its current form. I'll be interested to see what the production version looks like.

Knurled wrote: The biggest problem, as I see it, with the RX-8's engine is that Mazda insisted on using the old tooling. In short, the tension bolts were positioned in the 60s and as they refined spark plug placement, they got more and more shortchanged for coolant flow because of the placement of those tension bolts. Poor coolant flow makes the housings warp around the spark plug, this warping harms compression. If they'd move the tension bolt location, they could solve that issue easily. But then they'd need new tooling. The RX-8's engine shares a remarkable amount of hard dimensions with the '67 Cosmo, and even some parts. I'm not a fan of how they go thinner and thinner on the side seals, either. The .7mm seals are really pushing it for durability IMO, even before they stared forcing them to go over an exhaust port.

Now that's fascinating. What with advances in modern technology, the development process on a motor is so much more streamlined, it's hard to imagine banking on old molds. If what you imply is true, they've got an engineering team with far fewer resources than Mazda would have us think.

The series 1 RX-8's rotor housings had depressions in them where the exhaust ports used to be. Mazda has a history of this, the FD engines were the first ones that couldn't accomodate a top mount starter from a '73 RX-3. That's what that big opening on top near the oil filter pad was for. And it's awesome in a way because some things, like the RX-8's metal front cover gasket, are a vast improvement over the old AND are backwards compatible. My engine made externally entirely of pre-86 bits uses an RX-8 front cover/water pump housing gasket, solving the old oil pressure O-ring blowout issue. (And internally, it uses '88 rotating assembly, except for the non thermal pellet eccentric shaft...)

This actually is nothing unique to Mazda... lots of companies re-use tooling to an incredible degree. Small-block Chevies had the fuel pump boss all the way up until the end. Ford used one bore center across many different engine families, and when they raised the deck height of the Cleveland, they raised it to the same as the 460 probably also so they could use the same tooling. All Pontiac V8 heads had the provision for reverse-flow cooling that they stopped doing sometime in the late 50s.

Usually, a change of tooling snowballs into a complete change in other areas. Ford fixed the legacy problems with the Windsor by throwing everything out. Chevy fixed the legacy problems with the SBC and BBC by throwing everything out.

I think that Mazda may be stuck in the past a little too much with the rotary engine. I think they should go with a 4-banger hybrid or a v6 hybrid powerplant. If they don't want to call it a RX-? without a rotary, give the car an actual name.

I hope they build it, regardless of what they put under the hood.

In reply to Mr_Clutch42:

A car with an actual name? Blasphemy you say.

In reply to chiodos:

Introducing the 2018 Mazda Blasphemy ....

I like it!

Tralfaz wrote: In reply to chiodos: Introducing the 2018 Mazda Blasphemy .... I like it especially if I can see it spitting fireballs out of the exhaust!

FTFW

I am way more interested in the rotary range-extended EV mazda2 that mazda built, than i am in this thing (assuming it is not a hybrid). I feel like a rotary engine by itself will pretty much always be a letdown as an overall package in a car that isn't under 2500 lbs. Mazda themselves have pretty much killed my interest in a rotary vehicle as something i would spend 10s of thousands of dollars on.

Rufledt wrote:

NOHOME wrote: I will be honest, I never figured out what exactly "Sky-active" meant in the first place, so adding an R just fails to make me do a happy dance.

If i remember correctly, and i usually don't, Sky-active is just their marketing nonsense for similar tech in all new engines. Direct injection, higher compression, reduced friction, etc...

It's that and the entire philosophy of making things lighter so that the engine doesn't have to work as hard to produce more effective power (better lbs per hp ratio) and economy.

Also, Mazda has a history of concepts making it to production relatively unscathed. Add normal mirrors and door handles to this and a slightly less austere interior and this thing is production ready, much like the concepts that became the new Demio, MX-5, 3, and 6.