Tuned intake runner lenght?

[sendler]

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.

[Olympiadis]

Wallace Racing - Automotive Calculators

[sendler]

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.

[sendler]

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.

[gone-ot]

...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).

[drmiller100]

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.

[sendler]

Originally Posted by drmiller100

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?

[sendler]

Originally Posted by Old Tele man

...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).

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.

[E4ODnut]

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?

[drmiller100]

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.