Cbr 150 Airbox Mod

[KRS1]

Found something that actually works with the airbox today - cut the rubber snorkel. The length of the rubber snorkel is tuned to the internal volume of the actual airbox itself. Much like a 4th order ported speaker cabinet, reducing the port length of a speaker cabinet raises the tuning frequency of the enclosure, giving higher output at higher frequencies (higher RPM's) The new tuning frequency is approximately one octave higher. When i stop feeling lazy i'll measure the airbox and run the dimensions through my enclosure software to get the actual frequency.

In the 1st pic below it shows the snorkel taken out completely, it runs like crap without it and sounds like a monotone barfing duck after testing.

Second step was to cut the outer half of the snorkel as seen in 2nd pic, this actually worked by giving the airbox a higher tuning frequency, and less resistance to the inward vacuum of airflow.

In the 3rd and 4th pics I attempted to insert the snorkel in backwards so the mouth of the snorkel would be closer to the wall of the airbox in attempt to create a stronger vacuum seen in the third pic, just like a speaker enclosure it didn't work, buzzed alot though !

Results: quite noticeable stronger acceleration, now when im one gear too high i can just slip the clutch and the power will come (within reason). Eventually i tried to take it one step further and cut that rubber flange going around the tube. But it works better with it intact like in the pic.

If you do it and find that it doesn't work the part number is 17240-KPP-900, keep in mind that i have an aftermarket CDI. More than likely this will also work with the Fi CBR 150 also.

Looks like i may not be needing cams and bigger piston afterall !

So what i got so far is:

1) CDI

2) Thicker plug wire

3) CR8EGP needle plug

4) Airbox mod

Going to get the stock carb bored out to around 30-32mm next if i can find jets. Changed my mind about the NSR carb.

Edited September 15, 2011 by KRS1

[VocalNeal]

Interesting.

On a PCX forum one guy said he got results by removing the comparable piece. From inspection the length of the outer section on a PCX is short like your modified one.

My NSR has holes cut in the top of the air box. Not by me.

I'd do the cams anyway just for fun.

As I know nothing about speakers theoretically is there any merit to measuring the actual operating frequency and could this be done stationary . Say using guitar tuning software Like G-Tune.

Edited September 16, 2011 by VocalNeal

[KRS1]

If you mean measure the freq of the airbox while the bike is stationary and engine running, i think its plausible since it will still hit the same rpms without being loaded to a spinning tire. I think the best indication would be the difference in how fast the tach climbs with various port lengths and enclosure volumes.

My bike is climbing faster than it use to. the 7k-8k vibrating is still there upon acceleration, but when you get there it stops now. I think the barfing duck drone when the snorkel is completely removed is do to turbulant air biting the edges of the airbox cover, so in this case i think 2 inches would probably be the shortest you could get away with, but worried the inside part of the port is going to be too short since i already tried flipping it backwards and didn't work. I'll take one for the team and see what happens though, a new snorkel is cheap enough.

ehh cams, living in an apartment sucks, i'll be at the mercy of somchai. I'd have to calculate the new shim heights and somchai aint open to suggestions. . Tell the truth though, the current mods are almost enough to keep me happy for another couple of months, just need a little tiny bit more. Probably try a lighter timing chain to shave some weight off the valvetrain, figure i can cut almost half the weight off there, then there might be enough power for the bike to handle a 2.85 sprocket ratio compared to 2.93 giving me around 155 kph. Titanium valves sound tasty.

[arnoldjr]

If you mean measure the freq of the airbox while the bike is stationary and engine running, i think its plausible since it will still hit the same rpms without being loaded to a spinning tire. I think the best indication would be the difference in how fast the tach climbs with various port lengths and enclosure volumes.

My bike is climbing faster than it use to. the 7k-8k vibrating is still there upon acceleration, but when you get there it stops now. I think the barfing duck drone when the snorkel is completely removed is do to turbulant air biting the edges of the airbox cover, so in this case i think 2 inches would probably be the shortest you could get away with, but worried the inside part of the port is going to be too short since i already tried flipping it backwards and didn't work. I'll take one for the team and see what happens though, a new snorkel is cheap enough.

ehh cams, living in an apartment sucks, i'll be at the mercy of somchai. I'd have to calculate the new shim heights and somchai aint open to suggestions. . Tell the truth though, the current mods are almost enough to keep me happy for another couple of months, just need a little tiny bit more. Probably try a lighter timing chain to shave some weight off the valvetrain, figure i can cut almost half the weight off there, then there might be enough power for the bike to handle a 2.85 sprocket ratio compared to 2.93 giving me around 155 kph. Titanium valves sound tasty.

Why not just sell it and get an NSR SP or a TZM? Double the horsepower and its a 2-stroke so super cheap. Throw a tuned pipe on it, skim the head, and a few other goodies and you'll still probably have money left over from the sale of the CBR150. My 1996 TZM did 155km/h stock and I weigh 95kg. 2 smokes are the way to go dude.

[KRS1]

Hah, funny you should mention that, i also have an NSR 150. modified exhaust, advanced ignition, modified clutch, intake/exhaust ports enlarged and smoothed, 0.75 over piston. It's a monster when it hits 5k rpm, takes off like a scalded cat and sounds like one too. You dont want to be caught off guard when the powerband hits. Need to change the head bearings though.

I'm just messing with this CBR 150 to see how far i can take it with external mods. Now i just like to freak people out on the mountains when a CBR 150 passes them up.