NoPistons -Mazda Rx7 & Rx8 Rotary Forum

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- Rotary Engine Building, Porting & Swaps (https://www.nopistons.com/rotary-engine-building-porting-swaps-55/)

- - Intake Runner Length (https://www.nopistons.com/rotary-engine-building-porting-swaps-55/intake-runner-length-45795/)

know I've asked some people before; but I'd just like the input of more people.

We'll just say I'm building an All-motor rotary racecar...

Large 4port Streetport (think bridgeport, minus the bridge) built enough to make make and handle power to ~10k. 4 38mm TB's, 1.25" intake runner diameter.... how long does the over-all length of the manifold need to be (stacks to port-face)? I'm looking for a nice broad powerband (car will get a lot of street use) but I've also got manifold simplicity and under-hood room to think about.

Any input appreciated; and please give a little input, not just "18inches". ~CE

Well, since it's getting lots of street use, you're gonna have to compromise. I would say use two different lengths of runner. Have the primary ports come on around 6k, and the secondaries come in around 9. It'll lessen your absolute power, but the band will be widened.

That's my theory anyway, check out "the club" for more info:

http://www.rx7club.com/showthread.php?t=19...STOCK+PORT+AREA

Quote:

Originally Posted by Liquid Anarchy' date='Mar 8 2005, 03:34 PM

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Where do you want the peak torque. makes a big difference. I have some measurements somewhere that correlate some racing beat dyno plots to actual measurements. YMMV, but 2" moves you about 500 RPM up or down on peak. This could mean 15HP more at 5000 or 20 more at 9000, depending what you really want.

Not entirely helpful I know, but I'll try and dig out the measurements as a starting point, then you need to design things so you can add/subtract a few inches here and there off the trumpets.