OMC's 4-Rotor Wankel Racing Engine - The Real Story

[Rotary John]

Hi John
What's the issue with horizontal crank and oil lubed versus vertical and fuel oil lubricated?

There are 2 basic types of rotary engines. Oil cooled rotor and charge cooled rotor. In the oil cooled type, oil is circulated inside the rotor to cool it. With a pressurized oil system, the engine can use Babbit bearings like most automotive engines. Oil cooling requires oil seal to prevent the oil from escaping into the combust chamber and burned. It also requires an oil pump and cooler to reject the heat gathered from the rotor cooling. All of this adds to the weight, increased friction Hp., cost and complexity. The upside is the intake charge can be inducted directly into the chamber resulting in very high volumetric efficiency. The orientation of the crank has no bearing on the engine other than for oil return. Most of the automotive rotary engines are oil cooled, aka Mazda.
The charged cool rotor uses the intake charge to pass thru to rotor to cool it. This eliminates the requirement for oil seals, the oil pump and cooler and the sump. Because of no pressurized oil system Babbit bearings can not be used and roller and/or ball bearings are required to support the rotor and crankshaft. The upside is a much simpler and less costly engine. The down side is a significant reduction in volume metric efficiency due to the torturous path the charge must take to get to the intake chamber and the heating of the charge as it cools the rotor. In addition oil must be mixed with the gas to lubricate the bearings. Once again the crank orientation makes no difference.
Thus for outboard use the weight, cost and simplicity makes the charged cool rotor the best choice.
Hope this make sense.

[Rotary John]

As a side note to the above about oil cooled engines. OMC actually started it's development work with the oil cooled rotor type. We had a 100 CID 2 rotor running as both an outboard and a stern drive producing in excess of 200 HP. The cost of the outboard version was significantly higher that the current 2 strokes. The I/O version competed with the cost of the automotive engines currently being used. In addition the 200 HP engine allowed the dog house to be removed and a full width rear seat with the engine under it. Because of the weight reduction it would out perform a V-8 in all be top end speed. Because the volumes of the I/O could not justify the tooling and the outboard version was too expensive, the oil cooled program was dropped.

[powerabout]

There are 2 basic types of rotary engines. Oil cooled rotor and charge cooled rotor. In the oil cooled type, oil is circulated inside the rotor to cool it. With a pressurized oil system, the engine can use Babbit bearings like most automotive engines. Oil cooling requires oil seal to prevent the oil from escaping into the combust chamber and burned. It also requires an oil pump and cooler to reject the heat gathered from the rotor cooling. All of this adds to the weight, increased friction Hp., cost and complexity. The upside is the intake charge can be inducted directly into the chamber resulting in very high volumetric efficiency. The orientation of the crank has no bearing on the engine other than for oil return. Most of the automotive rotary engines are oil oiled aka Mazda.
The charged cool rotor uses the intake charge to pass thru to rotor to cool it. This eliminates the requirement for oil seals, the oil pump and cooler and the sump. Because of no pressurized oil system Babbit bearings can not be used and roller and/or ball bearings are required to support the rotor and crankshaft. The upside is a much simpler and less costly engine. The down side is a significant reduction in volume metric efficiency due to the torturous path the charge must take to get to the intake chamber and the heating of the charge as it cools the rotor. In addition oil must be mixed with the gas to lubricate the bearings. Once again the crank orientation makes no difference.
Thus for outboard use the weight, cost and simplicity makes the charged cool rotor the best choice.
Hope this make sense.

Thanks John


These days lighter engine means an OMC V8 is normal weight, perhaps today a boosted oil cooled rotary would fit right in?

[WaterZebra]

There are 2 basic types of rotary engines. Oil cooled rotor and charge cooled rotor. In the oil cooled type, oil is circulated inside the rotor to cool it. With a pressurized oil system, the engine can use Babbit bearings like most automotive engines. Oil cooling requires oil seal to prevent the oil from escaping into the combust chamber and burned. It also requires an oil pump and cooler to reject the heat gathered from the rotor cooling. All of this adds to the weight, increased friction Hp., cost and complexity. The upside is the intake charge can be inducted directly into the chamber resulting in very high volumetric efficiency. The orientation of the crank has no bearing on the engine other than for oil return. Most of the automotive rotary engines are oil oiled aka Mazda.
The charged cool rotor uses the intake charge to pass thru to rotor to cool it. This eliminates the requirement for oil seals, the oil pump and cooler and the sump. Because of no pressurized oil system Babbit bearings can not be used and roller and/or ball bearings are required to support the rotor and crankshaft. The upside is a much simpler and less costly engine. The down side is a significant reduction in volume metric efficiency due to the torturous path the charge must take to get to the intake chamber and the heating of the charge as it cools the rotor. In addition oil must be mixed with the gas to lubricate the bearings. Once again the crank orientation makes no difference.
Thus for outboard use the weight, cost and simplicity makes the charged cool rotor the best choice.
Hope this make sense.

RJ - You should write a bio book on the OMC Rotary.

[Instigator]

Have you seen this John?

Looks/sounds very impressive.

Have heard of similar before but don’t think any have made it through prototype stages.

The good is, the man behind the design has the background and knowledge.


https://www.cycleworld.com/story/mot...bike-unveiled/

[Rotary John]

Have you seen this John?

Looks/sounds very impressive.

Have heard of similar before but don’t think any have made it through prototype stages.

The good is, the man behind the design has the background and knowledge.


https://www.cycleworld.com/story/mot...bike-unveiled/

Yes I have heard of it before. The engine company has been making rotaries for many years; primarily drone engines. I suspect the bike will be a flash in the pan (cost) and if it dominates will be banned. I seem to recall a similar situation.

[Rotary John]

Thanks John


These days lighter engine means an OMC V8 is normal weight, perhaps today a boosted oil cooled rotary would fit right in?

If I remember the 3.5 L V-8 weighed around 235# and produced 450HP. The rotary powerhead was just over 2 L, weighed around 130 # and produced around 300 HP. Knowing what I know today and with todays materials, I believe the same rotary could produce 450 HP weighing less than 100#. Problem is no one today is interested in boat racing to invest the monies required.

[Instigator]

The designer ran Norton Motorcycles successful, multi race winning rotary bike program.
Norton went belly up and new owners finished driving them in the dirt.

One of my classic bike mags had a great, in-depth, multi page story on the new bike/motor.

It is cooled through the crank and he made the rotors wider instead of larger diameter like Mazda did.
He thought that was a mistake on their part.

He is getting 220 hp+ from 700 CC’s.

Agreed on seeing how deep new owners pockets are.

Yes I have heard of it before. The engine company has been making rotaries for many years; primarily drone engines. I suspect the bike will be a flash in the pan (cost) and if it dominates will be banned. I seem to recall a similar situation.

[Rotary John]

Mazda made the rotors narrower because of emissions. With a W/E ratio of around 4; (rotor width/eccentric value) is the most efficient to reduce the surface to volume ratio; ie. Hydrocarbon emissions. In addition, Mazda used side ports and the intake area in not dependent on rotor width. Thus a narrower rotor gave proportionately more intake are per displacement.
Norton uses a peripheral port directly into the rotor hsg. and making them wider allows a larger intake port (more intake area) w/o changing port timing. They weren't worried about emissions on a race bike.

[powerabout]

Mazda made the rotors narrower because of emissions. With a W/E ratio of around 4; (rotor width/eccentric value) is the most efficient to reduce the surface to volume ratio; ie. Hydrocarbon emissions. In addition, Mazda used side ports and the intake area in not dependent on rotor width. Thus a narrower rotor gave proportionately more intake are per displacement.
Norton uses a peripheral port directly into the rotor hsg. and making them wider allows a larger intake port (more intake area) w/o changing port timing. They weren't worried about emissions on a race bike.

Would dfi on a rotary make a big improvement in emissions to try to get the fuel away from all that surface area?

[Rotary John]

Direct injection has been tried and helps some on the intake side, but you still have the fuel quench problem on the combustion side. At some point, alternatives to the rotary due to the cost to achieve emission results are more economical. I believe the future of the rotary is as a range extender in electric vehicles, size, weight, lack of vibration. The engine could be optimized to run at a specific RPM driving a generator or specialized uses where power to weight/size are critical.

[Mark75H]

John, as always, thank you for the education on this subject.

[powerabout]

Direct injection has been tried and helps some on the intake side, but you still have the fuel quench problem on the combustion side. At some point, alternatives to the rotary due to the cost to achieve emission results are more economical. I believe the future of the rotary is as a range extender in electric vehicles, size, weight, lack of vibration. The engine could be optimized to run at a specific RPM driving a generator or specialized uses where power to weight/size are critical.

so what we need is a ceramic rotor so it becomes an adiabatic engine, no heat loss?

[Bob V]

John, as always, thank you for the education on this subject.

[Lake X Kid]

If I remember the 3.5 L V-8 weighed around 235# and produced 450HP. The rotary powerhead was just over 2 L, weighed around 130 # and produced around 300 HP. Knowing what I know today and with todays materials, I believe the same rotary could produce 450 HP weighing less than 100#. Problem is no one today is interested in boat racing to invest the monies required.

How do you quantify cubic-inches/liters for a Rotary engine?

A) One rotor has 3 combustion surfaces/heads. Therefore, (per each rotor) 3 x combustion chamber area = cubic-inches/liters.

B) One rotor/combustion chamber. Therefore, each rotor is only designated as only having 1 combustion head. 1 x combustion chamber area = cubic-inches/liters.

I am wrong to think the rotor engine should be classified as example A. Giving the rotor engine & the conventional combustion piston engine equal footing in engine size comparison.

Example B, seems to me, to give the rotary engine an unfair advantage in racing classification against piston engines.