MolaKule
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Is the rotor and the case aluminum or steel. The reason I ask is adding more light-weight
rotors should increase the torque at little additional weight.
rotors should increase the torque at little additional weight.
synth bad for rotary engines?
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All of that was true... 30 years ago! A lot has changed since then. The rotaries made from the 13B (early 80s) on up have been solid and reliable. I had a '95 RX-7 twin turbo that I hammered mercilessly for years in SCCA solo II autocross and it held up with no problems. They'll happily run at 8000 RPM all day long as long as you're going fast enough to dissipate the heat. They were underrated too. Mazda rated them at 255 BHP so one would expect 215 at the rear wheels on the dyno but they actually put down around 235.
Going through the gears on that rotary was a truly exhilirating experience. It is so smooth and just keeps on pulling harder and harder as revs climb. It felt a lot like a high performance motorcycle engine.
They DID burn oil though, not because the seals leaked (they didn't) but because they had oil injection which kicked in based on throttle and RPM. If you drove it like a grandma it would not burn any oil at all but when you open it up and let it rip it would go through 1 quart every 500 miles or so.
Anyway I've always wondered why Mazda disrecommended synthetic oil for these engines. I thought it was because of the oil injection, maybe synthetics didn't burn as clean in the combustion chamber. But that was just a guess on my part and it looks like Mazda had different reasons.
It would seem to be a moot point using synth oil on a rotary anyway, since they like to get oil changes every 2500 miles.
I'm glad to see Mazda reintroducing the rotary. Their latest rotaries have been reliable power plants putting down prodigious amounts of power from a small, light engine. It is the ideal engine for high performance cars, making the entire car lighter, better balanced, with a lower center of gravity.
Hot-Rodding the ringdings (Aussie term for Mazda rotary), as similar to other engines. Port (read valve) sizes and timing (read cam timing) are all adjusted at the same time with a grinder.
There's a variety of available porting techniques, that like the piston engined equivalents shift the torque peak up and down the rev range.
A mate had a J ported 12A in an RX2 for a while, and it went considerably harder than just about any of our traditionally worked piston engines.
The engines are light, so adding more rotors isn't that major a problem (the 20B is a three rotor set-up, and they raced a 4 rotor at LeMans).
It's odd conmustion chamber shape gives a low octane requirement, making it one of the few engine designs that can run hydrogen with minimal modification.
Felix Wankel himself was concerned with the seal length on the engines (He was into designing sealing systems for all sorts of applications when he came up with his rotary engine - although his original design was really a rotary engine, with all of the components rotating around their centres of mass, rather than nutating like they do in the stationary outer case engiens that we use). A lot of the apex seal issues can be attributed to carbon build-up due to people "lugging" them. The seal jumps the carbon, then starts a chatter ,ark on the casing.
the problem with synthetics i believe is that synthetic oils typically have a higher flash point and are more resistant to burning. this isnt good for a rotary as a rotary uses oil similar to a 2stroke, it injects it into the engine to be burned up. these engine are quite literally "oil burners" but it is decigned into the engine, just like a 2stroke outboard motor also "burns oil".
so, a nice synthetic with a high flash point may not fully burn off, so it creates carbon and fouling and such on the rotors and ports. this makes the apex seals chatter, and everything else go wrong. lets face it guys, synthetic 4stroke piston type oil is NOT meant to be used as 2stroke oil. it doesnt work very good in this application.
imagine running your outboard motor on a mix of gas and 10w30 and you will understand what i am talking about.
the ultimate solution for this is to disable oil injection alltogether and run with a pre-mix of gas and oil. you use common 2stroke oil for this, at a rate of 200:1 for casual driving, and 100:1 for spirited driving. this way you still get oil lubrication, but you also get the clean burning of 2stroke oil.
this is the main problem with the rotary in my opinion. and also the solution
[ July 11, 2003, 08:04 PM: Message edited by: cryptokid ]
so, a nice synthetic with a high flash point may not fully burn off, so it creates carbon and fouling and such on the rotors and ports. this makes the apex seals chatter, and everything else go wrong. lets face it guys, synthetic 4stroke piston type oil is NOT meant to be used as 2stroke oil. it doesnt work very good in this application.
imagine running your outboard motor on a mix of gas and 10w30 and you will understand what i am talking about.
the ultimate solution for this is to disable oil injection alltogether and run with a pre-mix of gas and oil. you use common 2stroke oil for this, at a rate of 200:1 for casual driving, and 100:1 for spirited driving. this way you still get oil lubrication, but you also get the clean burning of 2stroke oil.
this is the main problem with the rotary in my opinion. and also the solution
[ July 11, 2003, 08:04 PM: Message edited by: cryptokid ]
The rotor is aluminum, but the block is iron.
The main problem with the Wankel that can never be solved is that it has a high "wetted-area" for it's displacement because of it's combustion chamber shape. A piston engine exposes far less area to the flame front and hence is more efficient.
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Hmmm ...are you sure? The first I heard of the rotary was the Mercedes-Benz C111 ..a four rotor Wankel. This was a race car prototype and predated any production cars.
The first rotary powered car was the NSU Prinz. I have a copy of the original July 1960 Sports Car magazine in which it was reviewed. It was a single rotor, 250cc normally aspirated wankel putting out about 44 HP at 9000 RPM.
This car was followed by the NSU Ro80, and then after that came the Mercedes & GM cars, and finally the Mazdas.
Mazda won the Les Mans with a rotary engine, the only japanese car company i believe to accomplish that. Don't underestimate the ability of the Japanese to improve existing inventions
A friends Dad (he was a mechanic) had Artic Cat snowmobile back around 1970 that had a Wankel rotary engine. I recall him saying how the engine seemed to want to keep winding up and made a weird sound compared to the other 2-stroke engines. I do recall him having many problems with it but I don't recall what those were. I think those problems led to Artic Cat dropping that engine.
I bet his son still has that sno-cat, they never sell or throw anything away.
btw-He was not using any synthetic in the Wankel, if anything he was using Artic Cat oil or Standard Oil (Amoco now BP) which was was he was selling in the gas station.
[ July 12, 2003, 01:14 PM: Message edited by: Mike ]
I bet his son still has that sno-cat, they never sell or throw anything away.
btw-He was not using any synthetic in the Wankel, if anything he was using Artic Cat oil or Standard Oil (Amoco now BP) which was was he was selling in the gas station.
[ July 12, 2003, 01:14 PM: Message edited by: Mike ]
I run synth in my rotary. No problems. The biggest problem was the lack of regular maintenance and incompetent owners. When a car is oil injected and cooled, it would be a good idea to check and top off the oil regularly.
Gotta love all the rumours concerning why Mazda does not recommend synthetics-- I heard that it was a lack of big money sponsorship from a certain synthetic oil company. There aren't too many oils that will not burn completely during hot rotary combustion.
2 spark plugs were mainly for better emissions.
Mazda could've knocked 100lbs from the rotary if it switched to aluminum on the rotors and iron housings. The rotor housings are already aluminum. Aftermarket aluminum housings and lightened iron rotors are available and expensive. It is a sandwich engine and not a block.
Profit, and not emissions, is why the rotary almost died.
Oil on the rotary is pretty beat up by 3k miles. I personally wouldn't run ANY oil over 2k miles myself. Oil injecting wear metals, gasoline, blowby contaminants, baked oil...... for seal/rotor/housing lubrication can't be good. Also, poor oil quality causes injectors to clog and the oil metering pump to fail which guarantees engine death.
Gotta love all the rumours concerning why Mazda does not recommend synthetics-- I heard that it was a lack of big money sponsorship from a certain synthetic oil company. There aren't too many oils that will not burn completely during hot rotary combustion.
2 spark plugs were mainly for better emissions.
Mazda could've knocked 100lbs from the rotary if it switched to aluminum on the rotors and iron housings. The rotor housings are already aluminum. Aftermarket aluminum housings and lightened iron rotors are available and expensive. It is a sandwich engine and not a block.
Profit, and not emissions, is why the rotary almost died.
Oil on the rotary is pretty beat up by 3k miles. I personally wouldn't run ANY oil over 2k miles myself. Oil injecting wear metals, gasoline, blowby contaminants, baked oil...... for seal/rotor/housing lubrication can't be good. Also, poor oil quality causes injectors to clog and the oil metering pump to fail which guarantees engine death.
Using Synthetic Oils in Rotary Engines
This has got to be one of the most frequently asked questions ever!
Here is our answer:
The Rotary engine has an oil injection system that injects small amounts of oil into either the intake tract, carb, or rotor housing (depending on year/model). This is needed to lubricate the various internal seals and surfaces.
The injected oil MUST BURN, and must burn clean. The root answer to the question is that not ALL synthetic oils burn, and not ALLof them burn clean.
The ones that do not burn accumulate until they foul the spark plugs.
The ones that do not burn clean can leave residues of various substances (like ash? plastic? non-organic sand?) that accumulate until the spark plugs foul, or a seal sticks -- could be apex seal, side seal, corner seal, or oil control ring. The normal consequence of a stuck seal is an engine tear down.
In the many years we have been involved in rotary engines, we have NEVER had a problem with GOOD petroleum based oils. They work fine! They are less expensive than synthetics. (We use Castrol 20-50 GTX). They burn clean, etc. etc.
The problem with answering the original question is that it is NOT a simple yes or no. We DO simplify it to a "NO", but that is because we do NOT know whether the specific brand of synthetic the customer has in mind will work. AND, if it does not work, how long will it be before the damage shows up, and how bad will the damage be? Maybe it will take 10,000 miles, maybe 50,000 miles?? Maybe the engine will fail due to something unrelated to the oil, and there won't be enough left to determine why the failure happened.
WE are not willing to take that gamble, are you ?
Then, take a minute to think of WHY you want to use a synthetic. If a rotary engine (properly maintained, oil changes at 3K intervals, etc.) can still be running fine at over 200,000 miles, the engine does not need any more cooling, the gas milage will not be any better, etc. etc. WHY do you want to spend more $$ and gamble on engine and/or spark plug damage? (If you are into the fossil fuel thing, pollution, depleting our resources, etc. then you should not be driving ANY car!)
We are not chemists, and we do not have the time, $$'s, nor inclination to do 100K mile tests of various synthetics in rotary engines.
We DO use synthetics in the transmissions and rear ends - it works fine.
http://www.mazdatrix.com/faq/synthetc.htm
This has got to be one of the most frequently asked questions ever!
Here is our answer:
The Rotary engine has an oil injection system that injects small amounts of oil into either the intake tract, carb, or rotor housing (depending on year/model). This is needed to lubricate the various internal seals and surfaces.
The injected oil MUST BURN, and must burn clean. The root answer to the question is that not ALL synthetic oils burn, and not ALLof them burn clean.
The ones that do not burn accumulate until they foul the spark plugs.
The ones that do not burn clean can leave residues of various substances (like ash? plastic? non-organic sand?) that accumulate until the spark plugs foul, or a seal sticks -- could be apex seal, side seal, corner seal, or oil control ring. The normal consequence of a stuck seal is an engine tear down.
In the many years we have been involved in rotary engines, we have NEVER had a problem with GOOD petroleum based oils. They work fine! They are less expensive than synthetics. (We use Castrol 20-50 GTX). They burn clean, etc. etc.
The problem with answering the original question is that it is NOT a simple yes or no. We DO simplify it to a "NO", but that is because we do NOT know whether the specific brand of synthetic the customer has in mind will work. AND, if it does not work, how long will it be before the damage shows up, and how bad will the damage be? Maybe it will take 10,000 miles, maybe 50,000 miles?? Maybe the engine will fail due to something unrelated to the oil, and there won't be enough left to determine why the failure happened.
WE are not willing to take that gamble, are you ?
Then, take a minute to think of WHY you want to use a synthetic. If a rotary engine (properly maintained, oil changes at 3K intervals, etc.) can still be running fine at over 200,000 miles, the engine does not need any more cooling, the gas milage will not be any better, etc. etc. WHY do you want to spend more $$ and gamble on engine and/or spark plug damage? (If you are into the fossil fuel thing, pollution, depleting our resources, etc. then you should not be driving ANY car!)
We are not chemists, and we do not have the time, $$'s, nor inclination to do 100K mile tests of various synthetics in rotary engines.
We DO use synthetics in the transmissions and rear ends - it works fine.
http://www.mazdatrix.com/faq/synthetc.htm
A friend of mine had a ratty little red Mazda pickup with the Rotary engine when I was in high school (early 80s). I don't recall the year of the truck but it had a ROTARY badge on the tailgate.
That little truck was a blast to drive, it could outaccelerate lots of cars you'd swear would beat it. Like others have said, the engine seemed to spool power as the revs climbed. It didn't handle very well so it was a point and shoot deal on the twisty back roads. Dirt roads were where we tended to let it rip anyways. MEGA oversteer! Unfortunately a BIG bull moose got in its way and the truck was totaled.
I still think that was the coolest 2 wheel drive truck I've driven, and I don't like 2wd very much.
That little truck was a blast to drive, it could outaccelerate lots of cars you'd swear would beat it. Like others have said, the engine seemed to spool power as the revs climbed. It didn't handle very well so it was a point and shoot deal on the twisty back roads. Dirt roads were where we tended to let it rip anyways. MEGA oversteer! Unfortunately a BIG bull moose got in its way and the truck was totaled.
I still think that was the coolest 2 wheel drive truck I've driven, and I don't like 2wd very much.
How true. Japanese engineering solved the problem that the Germans and Americans could not solve: sealing the rotary engine and making it reliable.
A German invented it and built a running prototype, but couldn't improve the idea enough to make it viable. The Japanese didn't invent it, but they improved it enough to make it reliable.
But let's not disparage the value of improving existing inventions. That's what real engineering is all about, and if it didn't require a different kind of creative thinking, the Japanese wouldn't be so much better at it than everyone else.
[ July 12, 2003, 12:32 PM: Message edited by: MRC01 ]
My dad has been into rotary engines as long as I have been alive. My dad owned a whole slew of RX-2s, and 3s when I was growing up. He used to buy them, fix them up and sell them. He had one RX-5. He bought a '79 RX-7 in '79. He had an '81 and an '85 later on. He had the first '87 Turbo RX-7 in the US. Later on his company tested the first RX-7 twin turbo ('93) in the US. For those of you that know the original preproduction test cars it was the silver one. They did the durability testing on the car for the US. They had it after all of the magazine shots were done but before it went on sale.
Anyway, as many have said rotary engines are designed to burn oil. There are no oil control rings in them to lubricate the "cylinder walls" in this case rotor housings or "rings" in this case apex seals. Oil gets pumped in by a metering pump to lubricate everything. Most racing rotary engines use premix added to the gas just like 2 cycle engines.
Some have said that rotary engines have problems with emissions due to this. Well Mazda has addressed that as well with the new Renesis rotary in the RX-8. The intake and exhaust ports have been moved from the sides of the trochoid housings to the back of the side housings. Due to the longer intake and exhaust runners, torque is up. The old 13B-REW twin turbo made 255 hp in turbo form. The new 13B Renesis makes 255 hp in naturally aspirated form and more torque down low. My local dealer is on notice to call me the minute they have an RX-8. I may buy one when I finish graduate school next summer.
So when you have an engine that is designed to consume oil, you know contaminates the oil more than a piston engine (boinger in rotary speak), why would you bother with synthetic anyway? Even if the new oils will work, you sure aren't going to use extended drain intervals on a rotary.
Anyway, as many have said rotary engines are designed to burn oil. There are no oil control rings in them to lubricate the "cylinder walls" in this case rotor housings or "rings" in this case apex seals. Oil gets pumped in by a metering pump to lubricate everything. Most racing rotary engines use premix added to the gas just like 2 cycle engines.
Some have said that rotary engines have problems with emissions due to this. Well Mazda has addressed that as well with the new Renesis rotary in the RX-8. The intake and exhaust ports have been moved from the sides of the trochoid housings to the back of the side housings. Due to the longer intake and exhaust runners, torque is up. The old 13B-REW twin turbo made 255 hp in turbo form. The new 13B Renesis makes 255 hp in naturally aspirated form and more torque down low. My local dealer is on notice to call me the minute they have an RX-8. I may buy one when I finish graduate school next summer.
So when you have an engine that is designed to consume oil, you know contaminates the oil more than a piston engine (boinger in rotary speak), why would you bother with synthetic anyway? Even if the new oils will work, you sure aren't going to use extended drain intervals on a rotary.
I have been living and breathing rotaries for 25 years and hope to write a new book on the rotary eventually.
I have an owner's manual for the 1994 RX-7, which explicitly states more than once not to use synthetic. The issue seems to be that certain synthetics--I suspect "brand M"--leave too much ash after burning, partly because of the basic chemistry of the oil and partly because of the detergent and additive package. Ash leads to hot spots, which leads to detonation, which will kill a rotary even more quickly than it will a piston engine.
Mazdaspeed, Mazda's performance shop, offers a street version of the special synthetic oil that was used in the Mazda 787B racer that won Le Mans in 1991. This stuff runs about $34 a liter (about a quart), and if memory serves, it uses polyolefin chemistry. Others have successfully used Red Line, which is polyol ester based. Clearly some synthetics can be used without problems, but Mazda wants to play it safe.
59 Vetteman, your '74 RX-4 did not use a catalytic converter. No Mazda did until after 1979. Your car and other US-spec Mazdas of the '70s used a device called a thermal reactor, which took the place of a conventional exhaust manifold. Yes, it would get hot. Its purpose was to provide the burning fuel and air mixture leaving the engine a place to finish burning. Contrary to popular belief, the Mazda rotaries sold here were among the cleanest engines available on cars in the US. Mazda didn't have to use catalysts until years after everyone else. (I believe that BMW was one of the few others to use thermal reactors on US-spec cars.)
The sealing issues were licked by the early 1970s. If they hadn't been, there would have been no way to make the Wankel meet the pollution standards of the '80s and '90s. Mazda restricted the rotary to the RX-7 in most markets because of what it told a British car magazine was "lazy maintenance" in the US, and this decision was wise. RX-7 owners regularly report getting well over 150,000 miles before overhauls, in part because sports car owners maintain their vehicles. GM's problems were allegedly with cracking around the spark plug holes. I and other observers suspect that the real problem was the "not-invented-here" syndrome, as Mazda is a much smaller company than GM but was able to make the rotary work.
The issue about the rotary having a disadvantageous surface area to volume ratio is true, but this can be worked around. And for related reasons of geometry, the rotary is ideal for stratified charge applications, as Rotary Power International has been demonstrating with prototypes for some years, and for hydrogen fuel, as Mazda has repeatedly shown.
But in a nutshell, Mazda says not to use synthetics because of ash and detonation issues with certain brands.
I have an owner's manual for the 1994 RX-7, which explicitly states more than once not to use synthetic. The issue seems to be that certain synthetics--I suspect "brand M"--leave too much ash after burning, partly because of the basic chemistry of the oil and partly because of the detergent and additive package. Ash leads to hot spots, which leads to detonation, which will kill a rotary even more quickly than it will a piston engine.
Mazdaspeed, Mazda's performance shop, offers a street version of the special synthetic oil that was used in the Mazda 787B racer that won Le Mans in 1991. This stuff runs about $34 a liter (about a quart), and if memory serves, it uses polyolefin chemistry. Others have successfully used Red Line, which is polyol ester based. Clearly some synthetics can be used without problems, but Mazda wants to play it safe.
59 Vetteman, your '74 RX-4 did not use a catalytic converter. No Mazda did until after 1979. Your car and other US-spec Mazdas of the '70s used a device called a thermal reactor, which took the place of a conventional exhaust manifold. Yes, it would get hot. Its purpose was to provide the burning fuel and air mixture leaving the engine a place to finish burning. Contrary to popular belief, the Mazda rotaries sold here were among the cleanest engines available on cars in the US. Mazda didn't have to use catalysts until years after everyone else. (I believe that BMW was one of the few others to use thermal reactors on US-spec cars.)
The sealing issues were licked by the early 1970s. If they hadn't been, there would have been no way to make the Wankel meet the pollution standards of the '80s and '90s. Mazda restricted the rotary to the RX-7 in most markets because of what it told a British car magazine was "lazy maintenance" in the US, and this decision was wise. RX-7 owners regularly report getting well over 150,000 miles before overhauls, in part because sports car owners maintain their vehicles. GM's problems were allegedly with cracking around the spark plug holes. I and other observers suspect that the real problem was the "not-invented-here" syndrome, as Mazda is a much smaller company than GM but was able to make the rotary work.
The issue about the rotary having a disadvantageous surface area to volume ratio is true, but this can be worked around. And for related reasons of geometry, the rotary is ideal for stratified charge applications, as Rotary Power International has been demonstrating with prototypes for some years, and for hydrogen fuel, as Mazda has repeatedly shown.
But in a nutshell, Mazda says not to use synthetics because of ash and detonation issues with certain brands.
The documents from Mazda of Australia below state that syn and syn blend oils are NOT to be used in older rotaries, while for the new RX-8 engine, syn is OK, although conventional is still preferred (copied from an earlier post of mine, link below):
"Although Mazda suggests otherwise, evidently synthetic oil is OK for the new rotaries (page 1 and 2 below, and their oil weight discrepancy, when compared to U.S. owner's manuals, reflects the fact that these are Australian documents):
http://www.rx8club.com/attachment.php?attachmentid=24688
http://www.rx8club.com/attachment.php?attachmentid=24687
http://theoildrop.server101.com/ubb/ultimatebb.php?ubb=get_topic;f=1;t=007884#000000
[ February 01, 2005, 07:17 PM: Message edited by: TC ]
"Although Mazda suggests otherwise, evidently synthetic oil is OK for the new rotaries (page 1 and 2 below, and their oil weight discrepancy, when compared to U.S. owner's manuals, reflects the fact that these are Australian documents):
http://www.rx8club.com/attachment.php?attachmentid=24688
http://www.rx8club.com/attachment.php?attachmentid=24687
http://theoildrop.server101.com/ubb/ultimatebb.php?ubb=get_topic;f=1;t=007884#000000
[ February 01, 2005, 07:17 PM: Message edited by: TC ]
Nope.
Mobil okays use in rotaries, but warns that Mazda has an issue up until recently.
The problem arose with certain esters which have a very high combustion temperature.
The design of the rotary requires a certain amount of oil in the combustion chamber at the apertures and seals, and eventually these lubes left a residue that destroyed both.
And yet some people swear Red Line works great in rotaries, so go figure.
.
I owned an RX2, RX3, RX4, and an RX5 during the 80's and loved them all. What a blast to drive up to redline and shift. They did have their problems, one being gas mileage and the other coolant seepage past the rotor seals. This was primarily caused by running the slightest bit low on coolant resulted in hot spots and cooked o rings. Two of mine were lost this way because of teenage drivers. They remain my favorite car though.
The older Mazda rotary engine used to INJECT ANTIFREEZE into the engine at certain very cold conditions.
I believe this was the core reason for the ban on synthetics. Something didn't react/mix well.
Mazda seals are now different, synthetics are much better, and they don't inject antifreeze into the engine anymore.
Many have great results with M1.
I believe this was the core reason for the ban on synthetics. Something didn't react/mix well.
Mazda seals are now different, synthetics are much better, and they don't inject antifreeze into the engine anymore.
Many have great results with M1.
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