Opening tertiary ports at high RPM?
 

OK,
I am new to rotory engines in general and spent some time trying to understand how they work.

I have seen threaads talking about the tertiary ports only opening at certain RPMs. How is this possible? Isn't opening and closing of a port decided by the rotor's position?

IE: isn't each port open/closed every time the rotor turns? How can one be off until higher RPMs?

The ports themselves don't open - they're just there. However, no intake air is provided to those ports until valves in the intake tract are opened. The RX-8 has a complex intake manifold system that governs air flow into the engine.

Here's a crucial thread to read to understand how this works: the S-DAIS thread . Also, do a search in this forum section for "s-dais", and you'll find a bunch of threads discussing this topic.

Regards,
Gordon

Yes, the famous S-DAIS thread with the famous "122,74 mph optimal speed for intake air" that remains unexplained...

Holy crap! It's IKnowNot'ing! Where have you been?

It won't be long before I can find out where that speed comes from. Give me 15 weeks of PDE and it shall be done. :D

That number applies to the max speed of air for Helmholtz tuning. That is the speed that air should be entering into a Helmholtz plenum at the tuning point. The max speed through the intake runners should be no more than .6 mach at the hp peak which is roughly 456 mph or so at sea level on a 60 degree day (You need a frame of reference). 122.74 mph translates to 180 feet per second. Go look up Helmholtz formulas and you'll see 180 f/s. Basically the main air intake tube going into the plenum (or airbox) needs to be much larger than each individual intake runner and this is how you figure out diameter. Length is another issue.