CBR 250 RR Performance Exhausts

[Coyote]

I got a BEET Racing zaust, dont really feel much though after I installed it it did feel a bit lighter going through the mid-range. Just sounds a hellll of a lot better!

Where did you get it from?

Found this: http://www.beet.co.jp/honda/hornet250.html
The CBR page didn't have much, but hasn't the Hornet got the same motor?

[TwoSeven]

You dont need to change much on the cibby to get the max performance out of it.

The standard honda headers are spot-on design wise (as they are on all the cibby models) - if you actually measured up a yoshi unit, you'd find its exactly the same dimensions, but made of a lighter material. What you need to do is remove the flat spot at 5k and extend the top end slightly as the standard bike is tuned for 180km/hr.

To do this, you need to change the Megaphone to a smaller one. For those that dont know what that bit is, its the tapored bit that goes into the end-can, On a cibby its about 50mm long, you need to make it about 20mm but with the same start and end diameters (have a look at a roo can, its got a perfect megaphone on it - but the end can really needs a baffle) - Have a look at the new gsxr1000 for a radical megaphone design- its all megaphone and no zorst (but they use a power valve to vary the zorst length).

A much more cheaper mod to make for the bike is to move to a 520 pitch chain and sprocket (its a big for the poor chap to do, so keep the details of the sprockets when we finally works them out and sources them for you). It will and about 2 ft-lbs of torque to the bike.

[Coyote]

To do this, you need to change the Megaphone to a smaller one. For those that dont know what that bit is, its the tapored bit that goes into the end-can, On a cibby its about 50mm long, you need to make it about 20mm but with the same start and end diameters (have a look at a roo can, its got a perfect megaphone on it - but the end can really needs a baffle) - Have a look at the new gsxr1000 for a radical megaphone design- its all megaphone and no zorst (but they use a power valve to vary the zorst length).

Had a look at the pipe, not sure where this megaphone is, and I couldn't find a pic of a roo pipe

[TwoSeven]

On the pipe there are three allen bolts holding the end can on. From memory the megaphone is there (its what the bolts are screwed into). However, its very small on the two nifty, so it may not look like one at all.

Here is a pic of my old roo can before I sold it (was too noisy to use). On the right side, you'll see an alan bolt sticking out of a little dome. That dome is the megaphone (very small). Go compare that to the big triangle thing on the gsr 1k.

[HDTboy]

If you want torque or a decent bottem end then back pressure is good.

Reducing the back pressure moves the meat of the powerband up the rev range.

I still maintain that back pressure is bad. If you want torque or a decent bottom end, remove all back pressure and run milder cams.

Reducing back pressure helps exhaust scavenging by not having as much positive pressure at the exhaust valve

[Ixion]

Hurrah for the BSA M20. No back pressure and very mild cams.Let's all switch to side valves. I like side valves actually, very underrated. I reckon a turbocharged sidevalve would open a few eyes.

In reality you need back pressure . Cam timing and lift (and valve curtain area) has to be determined by the gas flow at peak revs. Milder cams means no top end. But unless it's a racer you need to plug that gaping exhaust hole a bit at lower revs. Or all your nicely sucked in mixture is going to whistle straight out again. Thats where back pressure comes in. A good zorst will give more back pressure at low revs than at peak. Sort of a poor mans VTEC. Open pipes always SOUND louder, people think they are getting more power, but it's just an illusion

[TwoSeven]

The M20 actually does use back pressure. The expansion chamber is half way down the pipe actually uses back flow - thats pretty much how 2-stroke expansion chambers work as well. Just they've made it more precise in modern bikes.

i happen to like the m20