Also posted on RM forum...

I've been looking into some tech info on intake manifold design and runner length. What do you guys think of this http://www.grapeaperacing.com/...s.pdf

Runner length = ((Effective cam duration * 0.25 * Pressure wave speed * 2) / (Peak power RPM + Reflective Value)) - 0.5 * Runner diameter

What do you consider to be the effective cam duration? 720 - (Advertised duration - 10,20, or 30 degrees?)
What do you use for pressure wave speed? 1200,1250,1300 ft/s?
What pressure wave / reflective value do you tune for? 3,4?
Do you consider this to be a good equation for Honda engines?

For my engine making peak power at 9000 rpm, using a effective cam duration of 445 degrees, 1300 ft/s wave speed, 1.75" diameter runner, and using the 3rd pressure wave, its comes out to 9.36" for the runner length. BUT that includes the distance from the head to the valve which is 3.12", so the actual intake manifold runner length would calculate to 6.25" long. Make it a 2" diameter runner and its 6.58" long. By going off that equation, I'm thinking of a manifold with runners that taper from 2" diameter to stock size with runners that can be adjusted from 6" to 7" long to get an exact tune on the dyno would be great. 4" diameter plennum with a 70mm TB also.

What do you think about the way the runners enter the manifold? One engine builder / genius said to make them come in flat with the manifold and not to put velocity stacks inside.

Thanks

 

Also, whats a good explaination why the manifold runners are shorter than ITB runners?

 

Anyone? Thoughts?

I've got the answer to the manifold vs ITB's question.