12abridgeport

Can someone please tell me if there are any advantages to a rotary motor versus a piston motor at this moment?

1. They can rev higher...formular cars can go up to 18000k, winston cup cars can go up to 9000, and my parents Mazda 626 V6 can go up to 7000k in stock form.

2. They are smoother than pistons...i used to think so until i took for a ride a '98 corolla and it was much smoother than both of my rx7's used to be. You would be surprised.

3. They can make more horsepower...all i have to say here is that 4 cylinders have been running 6's in the 1/4 for a few years now, i think v6's and v8's are out of question. I believe rotaries haven't broken the 6 second barrier yet and even if i'm wrong 4 cylinders have been there for a while now.

4. They get better gas mileage than pistons...not really.

5. They are more reliable...maybe in a stock form, without turbos, and even still not as reliable as some honda motors or some v8's.

6. They are cheaper to build than pisstons...far from being so.

7. They get better emissions...hell no!

8. They are easier to build...Obsolutely!!!

9. They are lighter than piston motors...Yes.

10. Rotaries have rotors...no rotor for pistons..damn!


I guess it's 3 to 7 and the pissons are leading. Please someone see if i might have left something out.

projekt

the problem with trying to improve the rotary is that no one has the urge or money to think new. when pistons engines were new, they had detachable cylinders. that's where that term comes from. the block only contained the crank and rods (half the time). Think of a rotary without having to bolt the center housing to the two rotor housings? make that all one piece with a front cover (rotor shaped) so you can install the rotor.
how about if you totally changed the standard =O layout? would things be different if the intake started at the top of the engine to make it like this:
*|
-O
that could help out with the 'swirl' of the intake mixture since it's still fresh.
do i have the money to test these ideas? no. does mazda? maybe, but they have to sell normal rotary cars before they'll ever get funding to experiment.

peejay

If revving higher is what you are concerned about. The rotary that we know (Mazda) starts getting iffy as far as internal loads go over 8000rpm.

If you can make an engine that makes the same power at a lower RPM, the lower RPM motor generally will accelerate you faster since it wastes less energy accelerating itself due to higher rotational inertia at higher engine speeds.



I think a lot of that is exhaust noise. Remember noise is vibration, and a rotary makes a lot of exhaust noise, so you get a lot of sound vibration.

A lot of the boingers nowadays are damned smooth, though! First time I drove a Zetec powered car (a Contour) I was shocked by how smooth a four banger could be. Then I drove its Duratec-powered version (2.5l V6) and was *amazed*.



Rotaries have never been about fuel economy... the main push was better NOx emissions in the 70's, back when meeting upcoming NOx standards meant drastically reduced engine life for boingers.

Then the catalytic converter was invented, and that problem melted away, and the only use was for a small Japanese company's "identity". Which brings us here...



Rotaries are VASTLY more reliable than piston engines in racing! They are more overrev tolerant (revs just wear things out faster instead of making things blow up), and they are dead simple which means fewer things to go wrong. Only four bearings, no camshaft drive, no camshafts, no valve springs, no valves...

For street engines, it's a tossup. Most newer engines can do 200k-300k with no problems, just like ye olde N/A rotary.



Well... "it depends".

If you're building an engine from the ground up, for street use, then yes that could be true. If you're building a racing engine, the rotary is much cheaper, especially if you start with a core engine in good condition.



See above. EMISSIONS was the main reason why there was a big push to rotaries in the pre-catalyst 70's. Rotaries are high in HC and CO but that can be solved fairly expediently. NOx is trickier to deal with but rotaries are naturally low in that.

[/b]

Not really. Not the way we're given them. You could do much better with any assortment of four-bangers.

But then you have the reliability issues involved if you're racing...

12abridgeport

That is exactly my point, they don't really have any real advantages over piston engines, so why would anyone try to put a lot of R&D into them and spend a lot of money just to come somewhat close to a conventional engine?

Peejay, most of your responses made sence and some could be argued both ways, like the reliability issues in racing. However, even when building a race engine rotaries are much more expensive. Let me give you an example: look on e-bay and you can find a completely rebuild 302 block that has been bored out, has higher compression pistons, cam, ported heads, etc...all the good stuff for only $900 plus shipping. 900 dollars is what you would spend on a full seal, spring, and gasket set for a 12a, left alone something like a 13brew.

Oh yeah, look at gears for mustangs, they go for like $190 price range compared to like $400 price range for rx7's.

Kenku

Rotaries are still lighter than I4s of around the same power output. And more compact.

And this 302 you mention... does it have forged internals? Will it withstand several seasons of road-racing without needing to be rebuilt? I kind of doubt it, seeing as how $900 is less than the cost of one good head.

Reliability in racing... talk to people who do road-race piston engined cars, top people in the Production or GT classes. Ask them how much money they spend keeping the engine together. It might be surprising.

12abridgeport

A lot of them come with forged internals stock...if you look for the right one.

Kenku, you are right, i did a quick search and the motor comes as a short block meaning without the head but still with everything else and a completely rebuild block compared to just some seals and springs that you would get for a rotary in that same price. I'm not even going to bother to calculate the horsepower and tourque per dollar spent.

peejay

But that eBay engine isn't a *race* engine. It'd be a street engine that can handle a little racing because it'd be inherently unstressed for the given HP.

A *race* engine would have expensive pistons, expensive rods, zero-balanced crank, enormously expensive valvetrain parts, real heads, a better block... while a *race* rotary still uses mainly stock parts because they're good enough, so there isn't *that* much difference in price between a stock and a race engine.

Put things into perspective, and part of the reason I went rotary. I wanted to throw a cam into my 429. Well, to do that, I'd have to pull the heads and send them out to have the pedestals machined for adjustable rockers and guideplates. I'd have to *buy* the adjustable rockers and guideplates. And hardened pushrods. While the heads would be off, the valve guides would have to get milled down for higher lift, since you can't *find* any decent 429/460 cams anymore that aren't humongoid lift. Humongoid lift that might have required milling the piston tops for clearance, but fortunately that doesn't require engine teardown. (It Can Be Done!) As well as a gasket set, timing chain, and of course the cam and lifters.

Basically, nearly four figures.

With the rotary, I just pulled the engine apart, ported it, threw it back together with a Mazda gasket set ($92 at the time, I think). And even *that* wasn't necessary since most of the gaskets and O-rings can be made or sourced cheaply elsewhere.

If I wanted to go over 8500 for some reason, I could've sprung for carbon apex seals ($240) and hardened stationary gears (forget, I think $160ish each?) and readjusted my pressure regulator up a bit higher. And then my engine would be most of the way there to being a *race* engine, too.

- Pete (And then I blew the rods out on the 429 anyway...)

12abridgeport

I don't know about 429 or what not but have a few friends that are into small blocks. Basically without having to rebuild the motor, in just the main parts alone you would have to spend in the $400-500 range to get close to 400 fwhp. Not sure about durability issues though.

Again this is possible to be argued back and forth. But my point being is that if you took a v8 (ex. a mustang that is being hated on this forum so much) and an rx7, basically you would get more horsepower per dollar spent with a mustang.

12abridgeport

Peejay, i think i see the point you are trying to make. I guess rotaries could be made somewhat more durable for a little bit cheaper, but i would say that can vary a lot also.

peejay

A couple years ago, SCCA ClubRally's Group 5 champion had a $500 homebuilt peripheral port engine.

12abridgeport

Ok, now unless he had like 90% of it manufactured somehow himself i would say put the down.

I've built the bridgeport myself twice, with my own porting and spending about 800 dollars on seals and gaskets with out replacing oil seals, even with bumping oil pressure without spending any money to 95 psi. That wasn't enough money spent on a properly functioning brigeport, left alone a PP engine. Just the balancing alone for it is like $500. Carbons $250. Intake manifold $250. Machined rotor housings $?? Clearanced rotors..Lighter flywheel..Hardened gears..

Basically it goes like this, it's very possible of building a rotary motor and spending almost 0 dollars. Just so it would run. Hec, i even know someone that did that. But if you want it to perform and last, have a good compression all the time, you would have to get out some major cash.

peejay

Here's what he said on specialstage.com... you'll find that most of what you suggested is unnecessary.

IRON apex seals are used because the carbons apparently don't last very long with not-quite-clean air. So if you're keeping the revs below 8000 anyway, you don't *need* all the badass internal modification.

12abridgeport

Well i guess he did manufactured like 90% of it. Definetly giving the guy props for that. However this is not a typical motor build up. Also building a PP motor just to have a powerband from 7k to 8k just seems to be a little bit unreasonable but i guess he did manage to win. The dude definetly got my respect for that. I love all the ghetto made things some real skilled people do without having to spend a lot of money.

peejay

A PP won't have a powerband from 7k to 8k.

NSU P-ports had torque peak 4500, power peak 5500...

Kenku

Yeah, really. From various sources, pport powerbands seem to beat side ports from around 4k RPM onwards, given large race-style ports. It's just part throttle that they start sucking.

12abridgeport

Actually i believe it's the pp motors that have smaller intake ports that might start making more power in the lower end. There were some people in this section providing dyno numbers with smaller and larger runners and the smaller ones start at around 4500k.

Kenku

Right, the smaller ports make more low-end than the bigger ones. However, even the big ones make more power than the side ports starting at surprisingly low RPMs. Everyone always thinks of pp motors as having powerbands that are unusably high, but it's not the case.

peejay

"Someone" was telling me about how his friend with a huge bridgeport would pull away from his -SE starting at a 2000rpm roll.

And a P-port should have nicer low end than a bridge...

andrew lohaus

well, the 26b in the lemans car had a very usable powerband and a redlineof 9k IIRC. it did have those nifty variable intake runners tho.

projekt

how did this turn into a pissing contest? i post a phenomenal idea about how to improve the rotary and it becomes a pushrod discussion! WTF!

12abridgeport

Actually we have been discussing peripheral ports for the last 8 or 9 posts if you notice.

12abridgeport

And this is how it turned into a pissing contest...i quote myself on this one.

Kenku

Well, okay. First, making the engine one piece with detachable front and rear covers. Problem is how exactly to do that. The rotor housings are aluminum cast around a heavily chromed steel strip. The side plates you *can* make out of aluminum, but if you cast them as one piece with the rotor housings, how exactly are you going to machine them flat? You can't really, as if you cast it as one piece and then machine the side plate flat, you're going to have a lip of aluminum where the steel wear strip isn't... *PLUS* non-uniform rotor housing widths. It's pretty much non-equivalent to making a one-piece cylinder block, because the geometry of the rubbing surfaces is more complicated.

Secondly, changing where the ports are. Well, there's a reason why the ports are where they are. The exhaust port is located so that it's open after combustion when the chamber volume is getting smaller, and the intake ports is located so it's there when the chamber is getting larger. If you put the intake port on the top, it will be open when the chamber is getting smaller... and what *that* means, is that it's trying to pump air *out* of the engine. Now, there's some engine concepts that do that, but it only works with supercharging... Miller cycle engines keep the intake valve open for a while after the piston starts moving upwards, because the supercharger makes up for th compression lost.

Swirl is a specific kind of turbulence in the combustion chamber; the problem is that the intake charge moving past the rotor housing pretty much negates all of that.

There really *HAS* been a lot of research done on rotary engines. And Mazda continues to do more... and believe it or not, other companies do too. It's sometimes a pain to find the fruits of their research, but the data is out there if you know where to look.

projekt

about the one piece unit, i don't think it would be tough to adapt modern tools to deburr the inside of a rotor housing. the epitroid could be 'bored' as two very large circles, right?

here lemme show you a BAD redition of my idea...

projekt

i know this isn't an epitroid but it's the best i can do with such little time.