Chris,

I had the cut off  RX-8, 4 port manifold at the Rotary Roundup.  The second rotary valve above where you  and I cut the intake manifold off is approximately 13 inches from the engine intake port.    With the throttle wide open that valve would be open and connect all the intake tubes together.  Most "tuned" length suggestions I've seen in the past have been 20 to 25 inches. From talking to people using these lengths they don't feel they have increased power due to the dynamic effect.

If I were building a "tuned" intake I'd duplicate the 13 inch length used by Mazda in the RX-8 intake.  As you can guess that would put the intake "box" on top of the engine.  With a James cowl it will be very tight above the engine.  For my first intake I am building a rectangular box that will be brazed to the intake just above the injectors.  It will extend forward and bend down as it goes forward.  I have a 65 mm Mustang throttle body I plan to use at the front end.  I'm about half finished with it and if I ever get to where I can easily post pictures I'll send some.
 
Sorry for the slow response.  I've got plenty of excuses but don't think any are good enough!

Dennis H.

the mallorys wrote:

After talking to everyone at the Rotary Roundup, I came away thinking I was going to use the bottom half of the stock Renesis intake, then put curved pipes up and over the engine and put the plenum on the right.  Now that I have it cut and sitting in front of me, I am wondering about the lenght of the tubes.  The botom half already gives me about 7.5 inches of tube.  Then if I go over the top, I'm looking at another 16 inches. 

 

My question for today:

 

Can I just put the plenum right on top of the intake manifold, and run the pipes up into it.  There is 3.75 inches between the top of my manifold and the fuel rail holes.  I could attach the rail to the top of the plenum, and I wouldn't have to mod the fuel rails at all.

 

I seem to remember the consensus was that the length of the tubes didn't seem to matter all that much.

 

What do y'all think?

 

Chris

 

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