Bill,
There is some one currently tuning a 2" intake - I think 16" may be a little
short. How did you measure the length e.g.  centre of diameter?
What diameter is the 16" primary runners.
What is the diameter of all the other runners.
Diameter may help in guesstimating the runner length i.e. reduced diameter =
increased velocity.

George ( down under)

> I have been studying the intake system on my 6 port RX-8. It is MUCH more
> complicated than I anticipated. Not only does it have an Auxiliary Port
> Valve (APV), it has a Secondary Shutter Valve (SSV) and a Variable Dynamic
> Effect (VDI) valve.
>
> I've attached a diagram from the service manual, it may help some, but the
> system is so complicated, it does not explain it all by any stretch.
>
> Let's back up a bit and talk about the six different runners coming from
> the housings. On the front and rear housings there are primary and
> secondary runners. In the center (intermediate) housing there are two
> side-by-side runners, one for the front rotor and one for the rear rotor.
>
> The first valve in the system (starting from the block) is the APV. The
> APV looks like it works just like the port valves in the RX-7. A servo
> twists two of these in the block. This, I can deal with. I'll just lock
> (probably epoxy) them in the high-speed position.
>
> The other two valves are going to be more of a challenge as they are
> located in the intake manifold that I plan to do away with and replace
with
> a simpler, lighter, replacement manifold designed for high speed only.
>
> The SSV is the next valve in line. The SSV enables (or disables) the
> intake runners from the secondary ports on the front and rear housings. It
> connects the front secondary runner to the front rotor intermediate
housing
> runner at about the 13 inch point. At the same time, it connects the rear
> secondary runner to the rear rotor intermediate housing runner.
>
> I think I want my replacement manifold to emulate an open SSV. I suspect
> that the auto engine disables these "late" timed secondary runners to
> improve the idle, but I could easily be wrong. (Please let me know if I
> have it wrong.)
>
> Moving further upstream in the intake is the VDI. Its operation is
> difficult to explain clearly, but I'll give it a shot. When the VDI is
> closed, the rear intermediate runner joins with the front intermediate
> runner at about the 19 inch mark. The primary runners (front and rear)
join
> in about an inch further upstream, essentially the same point. When the
VDI
> opens, the front and rear intermediate runners join together at about the
> 13 inch mark, (just after the SSV.) This also joins the front and rear
> secondaries at this 13 inch point, if the SSV is open.
>
> I'm assuming all the valves are open at the high-power setting. (Please
> correct me if I am wrong about this.) If I want to emulate this with my
> replacement manifold, I would:
>
> 1) Make 16 inch runners for the primary ports.
>
> 2) Make 13 inch runners for the secondary ports and the intermediate
> housing ports.
>
> 3) Combine the secondary runners with the intermediate runners into a 6
> inch "mixing" runner.
>
> 4) The primary runners would then join with the mixing runner.
>
> 5) Plumb it all to the throttle body.
>
> Has anyone done this before? Am I on the right track/


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> Bill Dube <LED@Killacycle.com>
> http://www.killacycle.com/Lights.htm
>
>


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