Info for building an intake

[jrlastofthebreed]

I use a metal velocity stack of about 2 inches... about a horse or so but it all adds up

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CMX?

 

[wwillf01]

No mine just came with my engine build mated with the k and n filter... from junior jackson... we tried c3 and lost hp.. not knocking maybe there is a way to tune for it but what I was told is the k and n with the stack he made created more turbulance...

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[Answ3r]

fooling around today

two different intake boots. both with no filter on the end. the one that was 6 inches long made 4hp more than the one that was 16 inches long. measuring power at the front spocket.

thought it was something to pass on.

I am pretty sure you were working on 2 stroke back then too. And I also found the same thing. Long intake kill power BIG time on 2 stroke, even more than on a 4 stroke because they fire EACH revolution instead of once in 2 revolution like a 4 stroke. That means the tuned intake lenght needs to be twice as short for the same RPM.

Also keep in mind that this tuned length will drastically affect jetting at the RPM it resonates, which in turns also has a big impact on power output. It also kind of messed up with the tuned pipe timing.
On a fuel injected 4 stroke, the effect will be a lot less felt because fueling is not vacuum/pressure related like a carburetor and you don't rely on a tuned pipe to make power.

You can "cheat" length a little by greatly tapering up the diameter like a factory airbox as soon as it's off the carburetor.

I've had best success with the factory airbox with a very vented cover with frogskin materials on the holes and try to seal the perimeter of the cover and seat/fender junction.