Tuned intake runner lenght?
 

So, I want to make a tuned runner for my 2011 Honda CBR250R motorcycle with it's fuel injected single. Has anyone seen a web site with a good calculator? This bike already has a huge airbox and air filter and a pronounced tuned runner extending into the clean side of the air box. It might already be as good as it can get for fuel economy but I have no idea what the tuning frequency currently is. It might be as high as 8,600 rpm where a big power peak develops whenever an after market exhaust is fitted. I might like to extend it to get the tuning to match my 65 mph cruise rpms of 6,000 and accept whatever reduction in peak hp at higher speeds that result.

wow! 1 square inches by 14 inches long for 6,000 rpm. It looks like the stock tuning is indeed closer to 1.5 square inches at 9.8 inches long for a peak of 8,700. I would have to make a major mod to find room for 4 more inches of length. Would probably have to add a 90* elbow. I wonder what the gain in torque at 6000 would be if I bother to try.

The throttle body is actually 1.77 square inches. 38mm diameter. His calculators don't allow to fix the area and calculate just the length vs rpm. I assume that the stock 1.77 square inches will still fairly closely follow theory for a 14 inch runner resonating at the desired 6,000 rpm. The over sized cross area only serving to broaden and round off the peak slightly.

...look here too: http://ecomodder.com/forum/279769-post37.html

...also, this book: Two-Stroke Tuner's Handbook, by Gordon Jennings, 1973, H.P.Books (ISBN 0-912656-41-7).

your elbow would have to be a GENTLE curve or it will screw up the reverb - look at the exhaust pipe, not the header, for an example.

also, tuning the intake ONLY works at WOT. Do you need more power at a lower RPM?

And you can get second and third harmonics to work as well.

I'm trying to get the highest efficiency at cruise rpm which would often be 25% throttle so there is some disruption at 4 inches from the valves. But it would also be nice in competition to lower the first torque peak from the current 6,000 rpm and get the most efficiency for 90% load pulse and glide either side of 6,000 as opposed to the power band from 6,000 to 8,700 as it is now. I can also play with the cam timing as the gears are taper fit and can be timed anywhere. Shaving the head to raise compression from the stock 10.7:1 is also not out of the picture eventually. Will a closed pipe have a second harmonic or only odd order harmonics of 1,3,5?

Is the frequency of the intake determined only by the length, independent of the cross section for a normal range of areas which have apparently been optimized at 1.7 square inches for red line 10,500 rpm.

That's a good link. Up to now the only information I've found on intake tuning was highly technical. This calculator might be a bit general, but it is certainly a good starting point. I didn't see any mention of incorporating the runner length and diameter with a plenum size to take advantage of the Helmholtz principal. Has anyone seen any similar type calculators that will give ball park figures for that kind of set up?

with part throttle, you cannot get intake tuning, or exhaust tuning for that matter.

Tuning an intake for part throttle cannot be done, and should not be a goal as you are missing the point of it all.

If it were me, and I wanted better mileage, I'd put longer gears in it to where I can lower the rpm and use more throttle.