tuj

I'll admit this question is mostly curiousity, but does anyone know if the port sizes for intake and exhaust are the same on the center housing as they are on the end housings? The reason being, I'm curious if two center housings would provide the same intake and exhaust flow as 1 end + 1 center. Its probably obvious where I'm going with this... 3-rotor.

I don't really intend to build one, but I'm curious as to its feasibility. Some people have suggested that a 3-rotor with all side ports is not possible, but if I recall correctly, the 20b was side-intake, perhipheral exhaust. Does it not seem feasible to build a 3-rotor Renesis with a custom e-shaft?

rotarenvy

well I can't answer the technical part of your question but recently I read that mazda is re-entering le-mans (SP?) with a 3 rotor renesis so I guess it is possible.
I wonder how much the parts or a engine costs

rotarygod

The center ports do not flow the same as the side ports. First of all on the intake side of it, the center port (primary) timing is different than the side ports of either engine. The high power engines have 2 ports on the side housings. If you were to build a 3 rotor based on the Renesis center housing, the center rotor would not have the extra port. The low power version of the engine does only have 1 port per each side housing but it's opening/closing timing is not the same as the center housing, nor is it's intake runners the same or the same size. Again, they wouldn't flow the same nor would their timing be the same. It gets much worse on the exhaust side. The outer ports while supposedly the same port timing as the center exhaust ports, have much larger better flowing exhaust runners. They have twice the area. If you were to use an additional center housing for a 3rd rotor, the exhaust would only flow about half as much as the other rotors. As you can see there are a number of problems with trying to build a 3 rotor Renesis this way. By no means is it impossible. The 20B had a larger front intermediate housing that was the same 80mm width as each rotor housing. This allowed the ports to be configured as needed for even flow. This same approach could be applied to the Renesis if a new housing were manufactured. From there all that would ahve to be done is to install a new main intermediate housing exhaust sleeve to keep the exhaust ports separated. It could be done but Mazda or someone else would have to cast a new housing. This would not be cheap or easy.

Mazda is NOT using a 3 rotor Renesis. It is a 13G based all peripheral port engine. The term Renesis is merely being used since the current rotary is known as a Renesis. It is still old engine technology. No side ports here.

tuj

Thanks RotaryGod, you rule. I suspected the port sizes would be different after comparing pictures of the 20b intermidiate housings and seeing that they were not identical.

It seems very interesting that the intake timings are different between the end and intermediate housings. Do you think there is a performance-based reason for this, or did they change the center housing timing because the runners are physically smaller? I know its kind of apples to oranges, but I have never heard of a piston engine that used two different cam profiles for the each of the intake valves; they always both follow the same lobe. You'd think that the engine would benefit from symmetrical airflow, but perhaps since the ports would be directly opposed to each other, this would decrease the velocity of the intake flow? Then again, wouldn't the two streams colliding at the center of the rotor be ideal for even dispusion inside the chamber?

I guess I could understand if the timings were different to create overlap between say the center intake and the end exhaust, to maybe achieve some kind of cross-flow effect, but the Renesis has essentially zero overlap right?

While I know that all-peripheral port engines have better hp than the side-intake port engines, I'm curious as to whether or not the all-side port engine has the potential to make high hp? IIRC, the NA-tuned 13b made something around 120 hp, and 315+ for a bridge-ported engine. Maybe 370 for a full pehipheral port? The Renesis is making ~240 with full-side ports. Is there potential for a full-side port motor (ie bridge-ported on both the intake and exhaust) to make as much as a peripheral port? And if not as much peak hp, wouldn't having more precise control over the port timings / flows offer better hp at lower rpms than the peripheral port and still have substantial hp? Obviously the new all-side port motor has better emissions, and a full peripheral port sacrifices everything but top end. Still, I wonder what the potential of the Renesis is in racing trim?

rotarygod

The port size differences between the primary (center) ports and the secondary/auxillary ports in the side housing have always been different in the rotary. This has been true back to the early '70's. Nothing new here. Understand that in the Renesis, the outer ports do not always receive air. They have valves that close them off independently of the rest of the intake system. I've never seen a multi valve piston head do that either. The rotary is very unique. FWIW: Mazda first used variable port timing (valve timing) in the rotary as early as 1982, over a decade ahead of the same principle in piston engines was applied to passenger cars!

The problem isn't really with the size of the intake ports. It's all about flow. When you make a rotary port larger to increase it's flow, you also change it's timing. This is sometimes counterproductive as timing may be increased to the point that max port efficiency is higher than the intended powerband but suffers where the engine drives at the most. But hey, it flows more. More is only better when you need it.