OD404 Posted December 3, 2009 Report Share Posted December 3, 2009 Once you overcome it's poor thermal efficiency which is the cause of its low mpg, high emissions, low torque (compared to similar piston engines of the same power) and to some extent the apex seal life issues seen on the earlier engines. Quote Link to comment Share on other sites More sharing options...
Andy P Posted December 3, 2009 Report Share Posted December 3, 2009 Once you overcome it's poor thermal efficiency which is the cause of its low mpg, high emissions, low torque (compared to similar piston engines of the same power) and to some extent the apex seal life issues seen on the earlier engines.You've summerised the reasons why despite being in love with the Rx7. I don't think I'll own one unless 1. I get a LARGE payrise or 2. I get rid of my house.Car is better. Quote Link to comment Share on other sites More sharing options...
Revolver Posted December 3, 2009 Report Share Posted December 3, 2009 The only thing that puts me off rotary engines is the need to rebuild them every so often.There are cylinder engines with worse MPG, lol - the ford GT at 4mpg.Course, a RX7 or even 8 is too much to insure for me so that's the deciding factor really. Quote Link to comment Share on other sites More sharing options...
Fish-Finger-er Posted December 3, 2009 Report Share Posted December 3, 2009 Once you overcome it's poor thermal efficiency which is the cause of its low mpg, high emissions, low torque (compared to similar piston engines of the same power) and to some extent the apex seal life issues seen on the earlier engines.Is mpg really that bad? given that its effectively a 2.6, the one i had a thrash a round in was gettin 20-25 mpg,which didnt seem that bad for a sports car with that size of engine. Torque is surely an issue with any high revving n/a engine? but revs/power level the playing field against torque, or at least thats how Ive understood it. I still think theres a lot of potential in the rotary engines, as bare in mind how many companies have been investing money into R and D for the conventional internal engine, for an extended period of time (well over 100 years) and is essentially a tweaked idea of a steam engine dating back much further(using the expansion of gases to move a piston in a linear motion and converting it into a reciprocating motion)when compared to a wankel rotary engine, which is well under half the age of the conventional engine, and by only a few companies(mazda being the main one in the last 30 years, but theyve also had to develop conventional 4 stroke engines too), it wasnt that long ago, when engine rebuilds where extremely common and fairly frequent on regular 4 stroke engines, its only recently that were seeing engines reaching 200k + without rebuilds. Quote Link to comment Share on other sites More sharing options...
Revolver Posted December 3, 2009 Report Share Posted December 3, 2009 The original limitation of the rotary engine, and the reason it hadn't been developed for a long time, is the fact we lacked the technology to make a material to go inside it. The first wankel engines had a rotor and cylinder made of a conventional metal, and after not such a long time they'd wear down so when igniting the spark would migrate into the other chambers and f**k it up.Mazda's engines use some kind of ceramic, I think, which stops this happening. It doesn't mean it doesn't happen at all though, which is why they need rebuilding. Quote Link to comment Share on other sites More sharing options...
OD404 Posted December 4, 2009 Report Share Posted December 4, 2009 No they don't Cast iron is used for the rotors and the front and rear plates. Aluminium is used for the main housings and they use steel inserts to increase the hardness (and therefore reduce wear) of the inner surface.The engine that Mazda currently has in development (dubbed the 16x) will have an all aluminium housing, but I believe they are retaining the cast iron rotors.The only time ceramic has been used in a rotary (outside a tuner using ceramic coated seals in highly tuned engines) was the R26B engine used in the 787B Le Mans car. The seals were ceramic and the housings were plasma coated in ceramic. Quote Link to comment Share on other sites More sharing options...
Revolver Posted December 4, 2009 Report Share Posted December 4, 2009 No they don't Cast iron is used for the rotors and the front and rear plates. Aluminium is used for the main housings and they use steel inserts to increase the hardness (and therefore reduce wear) of the inner surface.The engine that Mazda currently has in development (dubbed the 16x) will have an all aluminium housing, but I believe they are retaining the cast iron rotors.The only time ceramic has been used in a rotary (outside a tuner using ceramic coated seals in highly tuned engines) was the R26B engine used in the 787B Le Mans car. The seals were ceramic and the housings were plasma coated in ceramic.Ah, right...Maybe if they used ceramics it would be lighter, I understand the engine is fairly heavy lol. Quote Link to comment Share on other sites More sharing options...
OD404 Posted December 4, 2009 Report Share Posted December 4, 2009 Ah, right...Maybe if they used ceramics it would be lighter, I understand the engine is fairly heavy lol.Again, no Engine isn't all that heavy compared to others. It weighs less than a small block v8 (and that's with all its ancilliary parts in cluded). The downside to ceramics is the need for 5000miles to bed the tips into the housing in order to make a proper seal... Quote Link to comment Share on other sites More sharing options...
Revolver Posted December 4, 2009 Report Share Posted December 4, 2009 Again, no Engine isn't all that heavy compared to others. It weighs less than a small block v8 (and that's with all its ancilliary parts in cluded). The downside to ceramics is the need for 5000miles to bed the tips into the housing in order to make a proper seal...Ha, well, you'd know, lol.When you read about them you hear that they're meant to have a higher fuel usage than an ordinary cylinder engine... but I don't reckon that takes into account the fact the engine produces twice the power a cylinder engine would at the same capacity.What's engine braking and stuff like in your car? Quote Link to comment Share on other sites More sharing options...
OD404 Posted December 4, 2009 Report Share Posted December 4, 2009 They have low compression by design, so engine braking is lower (also less moving parts so less friction).I get 16mpg average from mine, there are similar power engines that do a lot better, but they need to be run a little rich to prevent detonation and knock. Quote Link to comment Share on other sites More sharing options...
Revolver Posted December 4, 2009 Report Share Posted December 4, 2009 Do you still actually have to rebuild it? I was reading about mazda's rotary engines, it said you had to rebuild the old ones every 50,000 miles, like in the mazda cosmo, but not in the renesis engine... Quote Link to comment Share on other sites More sharing options...
OD404 Posted December 4, 2009 Report Share Posted December 4, 2009 Do you still actually have to rebuild it? I was reading about mazda's rotary engines, it said you had to rebuild the old ones every 50,000 miles, like in the mazda cosmo, but not in the renesis engine...It honestly varies, I've seen stock rx7 engines (the REW) go beyond 100,000miles. The engine can go by two main causes, a tip failure which generally happens on tuned engine that have suffered from detonation which breaks the tip in one fell swoop or the tip goes just through wear so the engine loses it's combustion seal gradually (this takes forever though!). The other way these engines die is through water seal failure and it's this failure that people refer to when saying rebuilds every 50,000. The water seals can last over 100k, but not properly warming up the car, using rubbish coolant and tuning can all reduce their life. I'd say the average time is 60k and that's through the water seals going, which is a gradual process and if caught can mean a pretty cheap rebuild (compared to piston engines).The rx8's engine (the RENESIS) doesn't suffer as they've sorted the issues (partly by making it N/A). Quote Link to comment Share on other sites More sharing options...
Steve-A Posted December 4, 2009 Report Share Posted December 4, 2009 I know, its the same effect though, twice as many powerstrokes per rev.I reckon someone should do an IL4 2 stroke Have you seen some of the v4 2 strokes guys have modernised? Take one rg500 v4 500cc 2 stroke engine, drop into rgv/rs250 frame with tz 125 top ends, and you have 140kgs wet and 160hp with that crazy power band Also one day I will own a rotary powered car but it will have to be when I have a job/better job. Back on topic, realistically as others have said its a tough comparison to make. In day to day life the bike will be faster in a straight line and the car faster round bends, with average bikes, average performance cars and average riders/drivers. I love both my bike and car, they are very different experiences. Quote Link to comment Share on other sites More sharing options...
Revolver Posted December 4, 2009 Report Share Posted December 4, 2009 The rx8's engine (the RENESIS) doesn't suffer as they've sorted the issues (partly by making it N/A).Hmm...I guess you could always put a turbo on after Quote Link to comment Share on other sites More sharing options...
chrishayton Posted December 7, 2009 Report Share Posted December 7, 2009 Just like to add Thrust SSC is jet powered not rocket powered Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.