I expected this drop.  For reasons of not wanting to enter a prolonged and fruitless discussion on rotary engine manifold design, I will not explain why this drop is desirable : )

Oh; come on – gives us the 25 words or less version – well; maybe 50 words. We promise no prolonged and fruitless discussion.

Al

Damn, I'm such a sucker for that line.

Most gear heads already understand that successful intake tuning is the art and science of maximizing and managing the energy represented by the moving mass of air in the manifold as it accelerates and decelerates.  But, there are some less obvious subtleties at work in the Mazda rotary manifold. 

I believe Mazda's intent on the 2nd gen NA rotary was to intentionally restrict the flow on the primary ports so as to increase the velocity in the larger secondaries.  This goal is also aided by opening the secondaries a bit sooner than the primaries (gets the train moving early).  Note that porting (enlarging) the primaries or making the primary runners larger may be counterproductive here so the time honored tradition of "bigger is better" will lead you the wrong way.  The resultant higher velocity in the secondary runners is then used to increase VE with the later closing secondary port.  So why not close up the primaries completely and get even higher velocity in the secondary?   It's all about finding the point of diminishing returns.

Tracy  (way past 50 word limit)

 

Tracy's analysis sounds reasonable to me.  Its clear that Mazda expected some benefit in going to the trouble and expense of keeping the primary and secondary runners and port timing different.  I had wondered why they would have the secondary port open before the primary port (6 port engine) and I think Tracy's hypothesis is probably correct - at least it makes sense. 

 

I ported both my primary and secondary to the same port timing and concluded that since the ports now had the same timing that I could merge the secondary and primary ports with minimum adverse effect.  My testing will hopefully show that to be correct.

 

 

Ed Anderson
RV-6A N494BW Rotary Powered
Matthews, NC

 

There is a good chance your approach will work fine.  Mazda's attempt at this juggling act was flawed due to the horribly dirty path in the secondary aux ports on the NA manifold & block.   I think that is why my turbo block (much cleaner ports) worked about as well as my earlier 6 port block, even though the later port timing on the 6 port is theoretically better.   

 

Tracy