[farna]

I've heard of the sleeve valve engine and knew how it operated in theory, but see the cut-away in action "explains" a lot more than words could! That's why it eventually went away -- too complex. The sleeves had to slide over the bores, so the outside of the bore had to be machined smooth as well as the inside. I'm pretty sure that the bores are inserts because of that -- otherwise how could they be ground smooth?

[MARTINSR]

Isn't that wild Frank? I love this stuff.

Brian

[farna]

I love some of the old wild creations too. Some things just turned out to be to impractical, like the sleeve valves. They were supposedly very efficient, more so than the typical "poppet" valves used today, but they would have been harder to modify. The biggest drawback was manufacturing cost though, which is why they were only used in high end models even back then.

That's why GM took a hard look at the Wankel. You can only get so much power from a gallon of gasoline, the rotary is no more efficient than standard piston engine. The real savings would have been in cost to manufacture -- fewer moving parts to assemble. Of course it's more compact and a bit lighter in weight, and a chassis designed specifically for it should be more efficient overall.

So there's a question -- why didn't GM tool up to build the Wankel in the mid 70s? They spent millions on development and had some machine-shop built engines running. So why did they write it all off?

[327 / 350 hp]

Hi guys,, my guess would be that the Wanklel engine was not very fuel efficient and unable to seal very well... GM was in the process then of getting more and better fuel economy ... Jim

[496CHEVY3100]

I think the rotary was dicontinued in mid 70s because of emissions the 2 rotary or 4 rotary as planned for the mid engine corvette and later for the vega fell to same regulation as air cooled VW

[boothboy]

It was because of emissions.
BB

[farna]

Emissions it was! As far as fuel it was no more efficient than a piston engine, though the weight savings and compactness would help IF the car were designed around the engine. Didn't help much for existing car designs. A further problem was that any design taking full advantage of the size and weight would be drastically different from anything the public was used to.

GM was having trouble getting emissions down -- HC was the main problem. They had it down to 1975-76 standards, but really didn't know how they were going to meet increasing standards. So they petitioned congress for a freeze on Wankel standards at 76 levels for a 10 year period to give them time to figure it out. Congress refused, and GM canned the project -- wrote millions off in taxes for the loss (you never get more than 20% of a loss back that way, if that much!).

In the meantime, Mazda came up with a simple solution -- a "thermal reactor" right after the exhaust ports. Air was injected into the "reactor", which got hot and stayed hot, to burn off HC in the exhaust system before it exited the tailpipe. Rotaries produce higher exhaust temperatures than piston engines -- 1700-2000 degrees at high rpm in 71-95 Mazda twin rotors, down to 1600 in the latest RX-8 models (due to a change in exhaust port design). Compare this to 1100-1400 degrees in a piston engine at high rpm (WOT). See more here:
http://www.rotaryeng.net/side-exhaust-port.pdf
Simple explanation:
Rotary Tech Tips: Rotary Engine Exhaust Basics

So how do I know all this? There is an AMC link!! And that's the next question... what has the GM rotary to do with AMC? I think it's an easy one for most...

[MARTINSR]

Last night I was at an auto museum and I was surprised to see that many of those sports cars, famous sports cars had motors smaller than my Rambler! And the cars weren't small, they looked to be as big or bigger but the motors were often tiny.

Brian

[boothboy]

Originally Posted by farna

Emissions it was! As far as fuel it was no more efficient than a piston engine, though the weight savings and compactness would help IF the car were designed around the engine. Didn't help much for existing car designs. A further problem was that any design taking full advantage of the size and weight would be drastically different from anything the public was used to.

GM was having trouble getting emissions down -- HC was the main problem. They had it down to 1975-76 standards, but really didn't know how they were going to meet increasing standards. So they petitioned congress for a freeze on Wankel standards at 76 levels for a 10 year period to give them time to figure it out. Congress refused, and GM canned the project -- wrote millions off in taxes for the loss (you never get more than 20% of a loss back that way, if that much!).

In the meantime, Mazda came up with a simple solution -- a "thermal reactor" right after the exhaust ports. Air was injected into the "reactor", which got hot and stayed hot, to burn off HC in the exhaust system before it exited the tailpipe. Rotaries produce higher exhaust temperatures than piston engines -- 1700-2000 degrees at high rpm in 71-95 Mazda twin rotors, down to 1600 in the latest RX-8 models (due to a change in exhaust port design). Compare this to 1100-1400 degrees in a piston engine at high rpm (WOT). See more here:
http://www.rotaryeng.net/side-exhaust-port.pdf
Simple explanation:
Rotary Tech Tips: Rotary Engine Exhaust Basics

So how do I know all this? There is an AMC link!! And that's the next question... what has the GM rotary to do with AMC? I think it's an easy one for most...

AMC had contracted with GM to purchase rotaries but GM dropped the engine.

BB

[farna]

Yep, I knew that was an easy one! A follow-on then.... for what car did AMC want the rotary?

[boothboy]

With out looking it up I'll guess Javelin or Matador.
BB

[boothboy]

Also getting back to the Wankel, I seem to remember early slipper sealing problems. Smokers!
BB

[farna]

No, not the Javelin or Matador, and all new car designed specifically for the rotary engine, to take advantage of the compact size and low weight...

The apex seals on early model rotraies didn't last long. I thought they went to a teflon seal, but a quick Google shows that they are multi-piece cast iron seals, much like piston rings, and always have been. A "carbon filled aluminum" seal is available, but factory has always been cast iron (with little leaf springs beneath). I would think the tension on the springs would be affected by combustion heat over time, and they would actually go out before the seal itself. When the apex seals (the only part that touches the chamber sides -- just like piston rings!) start to go compression starts to fail. My bro-in-law had an RX-8 that was starting to give problems. It wasn't the apex seals, but corner seals (at the ends of the apex seals) that were starting to go. The car had over 100K on it, around 135K when it started having starting issues. Costs a lot to rebuild a rotary! It could be "freshened up" with new seals, but that's just like re-ringing but not boring a high mileage piston engine. You might get another 25-50K out of it before you're back to square one -- depends on how bad it was to start with. Lots of time/money for that!

[mr4speed]

That would be the Pacer................

[Joe G]

Originally Posted by farna

Yep, I knew that was an easy one! A follow-on then.... for what car did AMC want the rotary?

Maybe for the AMX/2?