7 ms·

The benefit and trouble with rotary engines is their reliability -- fewer moving parts means they'll generally fail less during their life cycle, and running th

The benefit and trouble with rotary engines is their reliability -- fewer moving parts means they'll generally fail less during their life cycle, and running them under higher loads / higher output, within their specifications, will generally not reduce the life expectancy (as in, run a 100HP rotary continually at 30 or 100, nearly the same running life). But they will have a shorter overall lifespan. That large moving inner chamber and the outer chamber walls around it will wear down, and when they fail you replace a significant amount of that combustion chamber (or just junk the entire motor). It's a neat application of the technology, and particularly in contexts where either the motor is going to run for long periods at a specific speed or not be used all the time, it could make a great option for power generation.

busterarm 12y ago
2nd Generation Turbo RX7 owner here. Rebuilt 13B engines before. The reliability of the engine itself is way misunderstood. They aren't more or less reliable than any other engine (okay, they're way more reliable than Subaru engines...). The problems are with heat and lubrication. The early RX8s had a flawed design. 2nd and 3rd Gen RX7s had problems with their OMPs and terrible electrical problems. 2nd gens have really weak alternators stock. Turbos usually fail before engines do. Honestly the engine itself is awesome. Yes, if you lose a seal it will screw your engine (but usually the housings & rotors are salvageable). Piston engines throw rods and screw your whole car. If you bypass the OMP and run premix and actually do proper maintenance on your car, they will last. My 10AE has over 110k miles on it and has not blown up yet -- probably has another another 40k on it before it'll be ready for a rebuild. I still am on the stock OMP (it's an S4).
- caboteria 12y ago
  Glad to see their longevity is improved. I had a '74 RX-4 and the conventional wisdom at the time was that you'd get 70-80k miles before you'd lose compression on one of your tip seals. My dad got 80k on the first motor so we weren't too bummed. We changed the motor for a new one and it was still going strong when the body rusted away so badly it wasn't worth fixing. Fun car, though.
- mattlutze 12y ago
  This book[1] on the Wankel history considered 150k miles the life expectancy for the 13B, less than for previous motors. They're really cool motors, I'm in that boat with you. How they work means forced-induction doesn't necessarily impact engine life the same way FI on piston/crankshaft motors. That the piston motor is just going to last longer not needing or before it needs major restoration. A mildly interesting point is that heat isn't an easily mitigated factor, unless we're talking the exact use cases in the OP article -- generators, which run in a very controlled RPM band. Same when we talk about UAV engines or other electricity-generation applications. So, you can engineer the motor to be efficient at those rotation speeds WRT heat management and fuel efficiency. 1: https://books.google.de/books?id=IB2lMFqTTl8C&pg=PA117&lpg=PA117&dq=wankel+life+expectancy&source=bl&ots=_3t9jAEzs5&sig=Ymz3dkAEy-ibxmTPrVJmLh_CKYs&hl=en&sa=X&ei=yDc6VfnFCsuwsQGVxoGoBg&ved=0CDsQ6AEwAw#v=onepage&q=wankel%20life%20expectancy&f=false https://books.google.de/books?id=IB2lMFqTTl8C&pg=PA117&lpg=P...
- yason 12y ago
  My 10AE has over 110k miles on it and has not blown up yet -- probably has another another 40k on it before it'll be ready for a rebuild. That's really low. I don't think I've ever bought a car with only 110k miles on it...
  - snowwindwaves 12y ago
    in canada it is unusual to see cars with more than 300,000 km on them, so a vehicle with 176,000 km is more than half way to being really well used, not "really low" mileage. I had a toyota land cruiser with 365,000km on rebuilt engine and 800,000 km on the body though. Where do you live that 110k miles is low mileage? How many miles is a lot to you? How/why are people driving that much?
    - eric_h 12y ago
      > in canada it is unusual to see cars with more than 300,000 km on them That's largely because of the need to salt roads in the canadian winters - yearly, excessive exposure to salt water drastically limits the possible lifetime of a car. The further away from cold weather requiring salted roadways you get, the longer cars last.
      - snowwindwaves 12y ago
        So in developed countries that don't have icy winter roads most people are driving cars with more than 300,000 km on them? I'm really curious where the parent lives that people are investing so much in the longevity of a vehicle. By the time they get to 300,000 km even if they aren't rusty they are usually 20 years old and things like drivetrain start to go and the vehicle is not worth the cost to keep up the required maintenance.
        eric_h 12y ago
        Certainly not most, but definitely more.
        jccooper 12y ago
- msandford 12y ago
  > okay, they're way more reliable than Subaru engines... Are Subaru engines really unreliable? I was under the impression that as long as you kept the power output under about 300 wheel horsepower that the entire drivetrain is pretty reliable.
  - busterarm 12y ago
    Everything about Subarus are pretty bulletproof -- except the engine. But you're mostly right. They will last if you leave the car 100% stock. Just don't modify them. Ever.
- geoelectric 12y ago
  IIRC, the turbo issue was the usual one around heat stress, and a turbo timer went a long way towards easing that.

busterarm 12y ago

2nd Generation Turbo RX7 owner here. Rebuilt 13B engines before. The reliability of the engine itself is way misunderstood. They aren't more or less reliable than any other engine (okay, they're way more reliable than Subaru engines...). The problems are with heat and lubrication. The early RX8s had a flawed design. 2nd and 3rd Gen RX7s had problems with their OMPs and terrible electrical problems. 2nd gens have really weak alternators stock. Turbos usually fail before engines do. Honestly the engine itself is awesome. Yes, if you lose a seal it will screw your engine (but usually the housings & rotors are salvageable). Piston engines throw rods and screw your whole car. If you bypass the OMP and run premix and actually do proper maintenance on your car, they will last. My 10AE has over 110k miles on it and has not blown up yet -- probably has another another 40k on it before it'll be ready for a rebuild. I still am on the stock OMP (it's an S4).

caboteria 12y ago
Glad to see their longevity is improved. I had a '74 RX-4 and the conventional wisdom at the time was that you'd get 70-80k miles before you'd lose compression on one of your tip seals. My dad got 80k on the first motor so we weren't too bummed. We changed the motor for a new one and it was still going strong when the body rusted away so badly it wasn't worth fixing. Fun car, though.
mattlutze 12y ago
This book[1] on the Wankel history considered 150k miles the life expectancy for the 13B, less than for previous motors. They're really cool motors, I'm in that boat with you. How they work means forced-induction doesn't necessarily impact engine life the same way FI on piston/crankshaft motors. That the piston motor is just going to last longer not needing or before it needs major restoration. A mildly interesting point is that heat isn't an easily mitigated factor, unless we're talking the exact use cases in the OP article -- generators, which run in a very controlled RPM band. Same when we talk about UAV engines or other electricity-generation applications. So, you can engineer the motor to be efficient at those rotation speeds WRT heat management and fuel efficiency. 1: https://books.google.de/books?id=IB2lMFqTTl8C&pg=PA117&lpg=PA117&dq=wankel+life+expectancy&source=bl&ots=_3t9jAEzs5&sig=Ymz3dkAEy-ibxmTPrVJmLh_CKYs&hl=en&sa=X&ei=yDc6VfnFCsuwsQGVxoGoBg&ved=0CDsQ6AEwAw#v=onepage&q=wankel%20life%20expectancy&f=false https://books.google.de/books?id=IB2lMFqTTl8C&pg=PA117&lpg=P...
yason 12y ago
My 10AE has over 110k miles on it and has not blown up yet -- probably has another another 40k on it before it'll be ready for a rebuild. That's really low. I don't think I've ever bought a car with only 110k miles on it...
- snowwindwaves 12y ago
  in canada it is unusual to see cars with more than 300,000 km on them, so a vehicle with 176,000 km is more than half way to being really well used, not "really low" mileage. I had a toyota land cruiser with 365,000km on rebuilt engine and 800,000 km on the body though. Where do you live that 110k miles is low mileage? How many miles is a lot to you? How/why are people driving that much?
  - eric_h 12y ago
    > in canada it is unusual to see cars with more than 300,000 km on them That's largely because of the need to salt roads in the canadian winters - yearly, excessive exposure to salt water drastically limits the possible lifetime of a car. The further away from cold weather requiring salted roadways you get, the longer cars last.
    - snowwindwaves 12y ago
      So in developed countries that don't have icy winter roads most people are driving cars with more than 300,000 km on them? I'm really curious where the parent lives that people are investing so much in the longevity of a vehicle. By the time they get to 300,000 km even if they aren't rusty they are usually 20 years old and things like drivetrain start to go and the vehicle is not worth the cost to keep up the required maintenance.
      - eric_h 12y ago
        Certainly not most, but definitely more.
      - jccooper 12y ago
msandford 12y ago
> okay, they're way more reliable than Subaru engines... Are Subaru engines really unreliable? I was under the impression that as long as you kept the power output under about 300 wheel horsepower that the entire drivetrain is pretty reliable.
- busterarm 12y ago
  Everything about Subarus are pretty bulletproof -- except the engine. But you're mostly right. They will last if you leave the car 100% stock. Just don't modify them. Ever.
geoelectric 12y ago
IIRC, the turbo issue was the usual one around heat stress, and a turbo timer went a long way towards easing that.