Actual Rotary Displacement Request

j9fd3s · 05-31-2011, 02:08 PM

i have thought about this, and there are a few ways to look at it, none of which is that great IMO. my thoughts started with howard colemans assertion that 255hp in an 159CID engine will have a lot of cylinder pressure. which might be true in a PISTON engine, but the rotary is different enough that we can cast some doubt.

first off, the Mazda rotary is a 4 stroke engine. there are 4 distinct strokes, and there are 2 TDC's and 2 BDC's, just like a piston engine. unlike a piston engine these 4 strokes happen in a different physical location from each other.

also unlike a piston engine, the mazda rotary takes THREE rotations of the eccentric shaft to have a power event on all the working chambers in the engine. a piston engine needs two rotations. this is why the displacement game is apples and oranges.

mazda rates a 13B with 360 degrees of eshaft rotation, 2x654cc (13B, 12A is 573), if you rate a piston engine on 1 turn of its crank, a 350 chevy becomes a 2.85 liter engine....

so its easy to rate a rotary on 2 turns of the eccentric shaft, which gives 4 working chambers worth, 4x654cc or 2.6. in the real world this seems to be close.

however what about those other 2 chambers? we count all 8 cylinders on a v8, but ignore a one third of the engine when we do the 255/159CID calculation. 3 rotations of the shaft is 654cc x 6 = 3924cc.

apples to oranges... a rotary piston engine IS different than an uppy downy motor, and this is one of the fundamental ways.

mike

05-31-2011, 02:08 PM	#3
j9fd3s Rotary Fanatic Join Date: Mar 2008 Posts: 123 Rep Power: 18	i have thought about this, and there are a few ways to look at it, none of which is that great IMO. my thoughts started with howard colemans assertion that 255hp in an 159CID engine will have a lot of cylinder pressure. which might be true in a PISTON engine, but the rotary is different enough that we can cast some doubt. first off, the Mazda rotary is a 4 stroke engine. there are 4 distinct strokes, and there are 2 TDC's and 2 BDC's, just like a piston engine. unlike a piston engine these 4 strokes happen in a different physical location from each other. also unlike a piston engine, the mazda rotary takes THREE rotations of the eccentric shaft to have a power event on all the working chambers in the engine. a piston engine needs two rotations. this is why the displacement game is apples and oranges. mazda rates a 13B with 360 degrees of eshaft rotation, 2x654cc (13B, 12A is 573), if you rate a piston engine on 1 turn of its crank, a 350 chevy becomes a 2.85 liter engine.... so its easy to rate a rotary on 2 turns of the eccentric shaft, which gives 4 working chambers worth, 4x654cc or 2.6. in the real world this seems to be close. however what about those other 2 chambers? we count all 8 cylinders on a v8, but ignore a one third of the engine when we do the 255/159CID calculation. 3 rotations of the shaft is 654cc x 6 = 3924cc. apples to oranges... a rotary piston engine IS different than an uppy downy motor, and this is one of the fundamental ways. mike