piston vs rotary engines!!??

[lietuvis91]

Did anyone read this dec issue of turbo mag? They started a series on rotary engines and they explain how they work and some issues with them in detail. I'm seriuosly considering an RX-7 now. I just wanted to know does anyone think that maybe rotary is the best way to go for drag and just high speed driving in general. They do have much less moving parts it seems so less shit that can brake! It just spured my interest in rotary and want to know if any of you guys have any experience with them, or can anyone compare from experience cylinder vs. rotary angines reliability and race potential!? What are some of the advantages or better yet biggest disadvantages of rotary engines??? And how hard are they to work on for the do-it-yourselfers as compared to piston engines???

[dayna240sx]

Originally Posted by lietuvis91

It just spured my interest in rotary and want to know if any of you guys have any experience with them,

Well, since I'm not a guy, I guess I cant answer any of your questions...

Oh well.

[Polygon]

Well, if you want to go rotary then forget the RX-7. You're looking at all sorts of reliability issues. Go with the RX-8 if you decide to get a rotary. The one thing I don't like about the rotary engine design is that you don't have a lot of rotational force like you do in a piston combustion engine produced by the crank and rods. This causes the rotary design to have a loss in torque so i wouldn't suggest one for a drag racer. However; they have a very high redline making them great track racers.

[lietuvis91]

thankx for your input guys and GALs! Sorry dayna240sx for excluding you! I have heard of the reliability issues with the rx-7, but i wonder if a race built motor would eliminate most of them or is it still just too much trouble?! The concept of rotary just seems really cool cuz it's relatively small displacement but capable of pushing some mad power! really fascinates me! Anyone alse wanna take a shot at this? Any links for some info would be appreciated!

[Moppie]

Originally Posted by Polygon

Well, if you want to go rotary then forget the RX-7. You're looking at all sorts of reliability issues.

And thats differnt from people calling Cryslers unreliable because?



The very early Rotory engines certianly didnt have the longevity of thier piston engine counter parts, but with new seals, and proper maintiance a recently rebuilt one will last for an easy 100,000ks plus.
The new engines are of course even better, and when properly maintianed will last just as long as a piston engine.
The RX8 funnily enough has yet to have been in the market long enough to have its reliability tested.


The torque issue is also a myth, you have to remember they are relativly quite small capacity engines, and do infact have a very linear power curve, which when it comes to actualy going somewhere is far more important than any peak numbers.
Any of the RX series make great drag cars, there are plenty of sub 10sec cars, and Iv seen plenty of pics in Ausie mags of rotory powered cars flying the front wheels when launching.



Maintiance for the average owner is not an issue, they all still have an ignition system, and some form of either carberation or fuel injection, and they require regular oil changes just like any other car.
There is some specialist knowledge required when getting into rebuilding the engine, but its knowledge that is readily avliable, and anyone that can rebuild a piston engine can rebuild a rotory, usualy in less time as there are less parts.


Basicly they are not any better, nor any worse than a piston engine, they are simply differnt, and anyone who tries to tell you otherwise is mis-guided and ignorant.

[Neutrino]

Moppie, polygon never said that mazda's engines are unreliable....he specified a model...and you have to agree there are a lot of rumors saing that the rx7 engines had some issues...even the mazda engineers admited them....it seemed that the biggest problem was valve overlap...problem which they aparently solved trough the repositioning of the valves in the renesis


and you know too that the 1.3L its better measured as a 2.6L.....so its displacement its not that small


also I agree with polygon....i cannot see the rotary engines being capable of as much torque as the piston ones since they lack the leverage of the rods pushing on the crankshaft's lobes

[Moppie]

Originally Posted by Neutrino

Moppie, polygon never said that mazda's engines are unreliable....he specified a model...

True, but it was still an un-qualified statement.
The cars themselves are very reliable, its only the early engines that ever had problems, all of which will have either been fixed, or are easily now fixed.

How the displacement is measured is another issue, Iv heard a variety of theorys, but yes the most common one is to double the pyhsical capacity of the combustion chambers, so yes a 13b would be a 2.6l engine. But then most people also say that the functioning of the rotory is so differnt to a piston engine that you can't really compare them on capcity.



But torque certianly does not seem to be an issue with the engines, thier design means they have to be revved higher than most piston engines to make similar amounts of hp, but that in itself is not a bad thing, its just as I said above, differnt.
But remember that a rotory engine applies a more direct force to the crank than a piston engine does, and the diameter of the rotor I suppose gives the same effect as the length of rod and crank.

[disco192]

I am yet to understand the obsession with torque. Torque is not what accelerates a car, horsepower is. Yes torque is a factor it determining the HP, but so is RPM. YOu dont see people going crazy because their car has a higher redline, poeple would laugh at them. If torque were such a big deal then why arent more deisels race cars??? BECAUSE THEY DONT HAVE VERY HIGH HP.

Now on the topic of rotaries, the port overlap of a RX7 to my knowledge has no significant affect on the performance of the engine. It is a problem due to unburned hydrocarbons that caused it to fail emmisions.

One of the other problems with a rotary engine is the seals. They are definately the weakest part of the engine. There are many companies out there working to find the "perfect seal". The problem comes with durability vs performance. They make seals that can handle very high rpm and boost, but they would have to be replaced more than you would probably like, but taking apart an RX7 engine isnt all that tough.

[disco192]

but i would get an rx7 because they look sweet and car be fixed up for drag racing or you can do some sweet drifting in it too

[dayna240sx]

Originally Posted by Neutrino

....it seemed that the biggest problem was valve overlap...problem which they aparently solved trough the repositioning of the valves in the renesis

i cannot see the rotary engines being capable of as much torque as the piston ones since they lack the leverage of the rods pushing on the crankshaft's lobes

What valves?

You cannot have valve overlap, if there are no valves...

adding width to the rotor face is like lengthening the stroke in a piston engine... the wider the rotor face, the greater the torque.

[lietuvis91]

Hey ~Ms. Rotary Bandit~
how about you put a twist on this discussion! Do you agree what everyone's saying about the rotary or .....? To me it seems like there realy isn't any reason to go with rotary other then liking the actuall cars that have rotaries. I just thought that maybe rotary had a lot more race potential and maybe more reliabitity - up to about 60k miles that is, after which they begin to die it seems! But if the biggest problem with the engine are the seals then with some r&d someone will find a way to overcome that problem. Turbo mag suggested that there are some aftermarket seals that do significantly better than stocks. Well, this is good info so far. Any rotary experts out there?

[dayna240sx]

What do you want to know?

There a three good sets of aftermarket "seals" out there... And I assume we are talking about the Apex Seals.

Mazdaspeed motorsports has come kick ass Carbon apex seals. they really aren't good on a daily driven car because they really do not seal well until reletively high RPM..

another option is the Hurley seals
http://www.hurleyrotary.com

I have used their long life seals in basic rebuilds and plan to try their self lubricating seals on my RX-3 engine.. (its goal is to see 300+K miles w/o a rebuild/oerhaul)

their race seals are also very impressive.

The third choice are the seals made by atkins rotary,

there is another brand out there made by "rotary aviation" which i believe is the same as atkins..

they claim 700% greater bending strength and 33% harder seals than all other seals... I have never used them, but they sound tempting...

I have a nice chart in my RE handbook where you can calculate the forces on the apex seals, the extra "bending" would make a longer lasting apex seal, and cause less wear on the rotor housing...

what else would you like to know?

As far as i am concerned the Apex seal issue has been fixed for years.... really ever since they killed the 6mm apex seal in the early 12a's...

[Neutrino]

well the diameter of the rotor gives the torque in a rotary engine but you cannot make a direct analogy with the torque aplied by a rod in a piston engine


the rods in the piston engines aply 100% of the force to the point with most leverage (crankshaft lobes)

on the other hand inside a rotary the force its spread all over the face of the rotor and not on its apex where it would have the most leverage


dayna about those intake and exaust ports...i called them valves just because they do the same thing as in a piston engine and i'm very used to the therm valves....but nevertheles all the info i found on the rx7 atributed its poor gas mileage and problems to the overlap between the intake and exaust ports

and disco 192....torque is every bit as important as horsepower for perfomance...you don't belive me try autocrossing.....you hit a hairpin turn you drop out of the powerband and you'll see how long it takes to bring the rpm back up

[disco192]

Well unless you are going slower than 15 mph i dont see why you would be in the bottom part of your powerband anyway.

And what you are trying to say is low end power, not torque. Torque does not accelerate a car, horsepower does.

[Moppie]

Originally Posted by Neutrino

you hit a hairpin turn you drop out of the powerband and you'll see how long it takes to bring the rpm back up

A little tip, try changing gear