Dennis,

 

I’ll try and give you a more “detailed” review of you analysis and approach in a short while (I have to dig up a drawing of the Renesis 4 port intake to look at).  However, I seem to recall that there is a valve in the air passages of the intake that rotates open or closed depending of some engine load variables.  IF my memory is correct, this value in effect halves (or doubles depending on which runner you are using for reference) the distance the pulse has to travel from port of one rotor to port of the second rotor.  At the right rpm range the value closes forcing the pulse to travel the shorter distance (or else it opens at the lower RPM range to make the pulse travel a longer circuit – or vice versa – I have to look and see if the Renesis even has such a valve – the older N/A 13Bs did have the value in order to change the effective length of the intake runners.

 

I can not tell from my hasty look at your e mails whether you took that factor (the valve changing the effective length of the runner)  into consideration or indeed, if the Renesis even has one. ?

 

Will get back to you shortly

 

Ed

 

 

OK - I'll try to stirrup some reflective comment on the list.

I'm in the middle of trying to design a new intake for my RX-8 Renesis powered RV-7A
I've been reading the tuned intake discussion posts from 2004 and 2005.  FAW theory etc.  I've tried
to apply the theories to the Mazda RX-8  4 port intake to see how it works and make sure it
agreed with the theories.  No Luck!!? 

My measurements of the cast aluminum intake show primary runners are 12.5 in. long + 2.5 inch to the center of the chamber
where the intake runners from rotor 1 interact with rotor 2's intake runners.  Add 3 inches at the other end ( engine flange) for the distance from the
manifold flange to the center of the intake at the rotor face and the total intake is 18.0 inches.  The secondaries are 1/2 inch longer at 18.5 inches. 

It appears they are using the FAW wave created as Rotor #1 intake opens to travel through the intake tubes to Rotor #2.  Total distance  from rotor
#1 to rotor #2 is 36 in. for primary runners and 37 in. for secondary runners.

Ed's post of Aug. 26,04 indicated a "E" shaft rotation of 93 deg. between Rotor #1 opening and Rotor #2 closing.  I measured the angle on an old engine and agree. 
The pulse from rotor #1 needs some opening to exit and at rotor #2 you must have some opening to enter the rotor.  I'll guess this is a total of 10 deg.  Hence we have about 83 deg of  "E" shaft rotation time for the pulse to travel from rotor #1 to rotor #2.

I want to design my intake for max. HP at 6750 rpm.  6750/60 = 112.5 rps; 1/112.5 = 0.008888rev/sec or for 360 deg rotation of the "E" shaft it takes 8.888ms.
The time for 83 deg of "E" shaft rotation would be 8.888ms*83deg/360deg = 2.05ms. (the time available for the pulse to travel from rotor #1 to #2.)
speed of sound = 1100fps or 1.1f/ms*12 = 13.2 in/ms.  So 13.2in/ms *  2.05 ms = 26.4 inch from rotor #1 to #2.  My problem is this is already 5 in./ intake shorter than the RX-8 4 port intake.  If I assume their intake is designed for 8500 rpm the calculation indicates a runner length of 21.3 inches is needed between rotor
31 and #2.  I measured the RX-8 cast al. intake to be 18 in * 2 = 36 in .

To me it appears I do not understand how the RX-8 intake really works!!  Anyone have any ideas or find an error with the logic?

Going FAW crazy!!

Dennis H.

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