luder_5555

not to stire up the fight over how to put out fires, but...

in the thread about the rx8 that causght fire. everyone kept saying that the oil and fuel in the cat was ingiting. i thought that the rotorys didn't have cats, and that is wht they get suc bad mpg cause they just run super rich and the extra fuel ignites in the exhaust.

i could be wrong, but i could have sworn that that is what it said when i was reading about them...

Just as the shape of the Wankel combustion chamber prevents preignition, it also leads to incomplete combustion of the air-fuel charge, with the remaining unburned hydrocarbons released into the exhaust. While manufacturers of piston-engine cars were turning to expensive catalytic converters to completely oxidize the unburned hydrocarbons, Mazda was able to avoid this cost by enriching the air/fuel mixture and increasing the amount of unburned hydrocarbons in the exhaust to actually support complete combustion in a 'thermal reactor' (an enlarged open chamber in the exhaust manifold) without the need for a catalytic converter, thereby producing a clean exhaust at the cost of some extra fuel consumption. World gasoline prices rose sharply at the time Mazda introduced their Wankel engine, making the cleaner exhaust/increased fuel consumption tradeoff an unwelcome one for consumers.

thats from wikipedia

so they either changed it for the rx8 or i'm really confused... especially cause there was one guy who really sounded like he knew about them, and i believe he ever refered to the cats as the culprit for the fire


sorry i had to make a whole thread just for this, but the other one was closed because of the bickering about how to put out a fire. and don't bring that s**t in here either

Chrisbert

Yes, they have CATs. One reason for the bad MPG is they send unburnt fuel down the pipe to keep them cooler so they meet requirements for the life of the CATs.

AngryTurtle

This is probably from the late 70's when the engine was first being made.

rockville

Wankels get bad gas mileage because they have a lot of combustion chamber surface area vs the volume of the chamber. That means a lot of heat from the combustion is absorbed into the walls of the chamber and in turn absorbed by the cooling system.

xmatt

Yes, they do have cats. In fact one of the typical FD mods is to replace the cat with a straight pipe because the it tends to cause more backpressure and trap more heat. That said, it can make it, um, challenging to pass emissions tests thereafter.

57udl3y

every street legal car you see that isn't from the 70's i think i forget what the abbreviation is otherwise i'd look it up, has a cat unless someone replaced it with a test pipe

MikeyCB

Late 80s RX7s had 3 cats, which when they failed, cost tonnnnns to replace.

xmatt

Yeah, actually I should have said that even the FD had 2 cats. The "precat" was the one that was notorious for clogging up, trapping heat in the turbos and causing engine failures. Everybody replaces that with a straight pipe.

luder_5555

ok, well the way wiki was saying ir, they just had that extra gas to burn off anything, it does make more sence that they would have a cat

J5sense

My 1989 RX-7 GTU had 3 cats. that i replaced with one test pipe after the cats clogged up. i remember they where crazy expensive to replace!