Thoughts on distance to expansion chamber?

[v8brick]

Here's a couple pics of my setup, if I remember right that's a 22mm carburetor off ebay. It bogs and spits at certain rpm and throttle position combinations. After reading a few posts here and modulating the throttle more conservatively it has fixed most issues. I haven't ported anything yet but I've got this exhaust on the way.

http://slappytees.com/images/motobike/6_27_08_01.jpg

http://slappytees.com/images/motobike/6_27_08_02.jpg

http://slappytees.com/images/motobike/6_27_08_03.jpg

http://slappytees.com/images/motobike/6_27_08_04.jpg

http://slappytees.com/images/motobike/6_27_08_05.jpg

http://slappytees.com/images/motobike/6_27_08_06.jpg


How far downstream do you all think the expansion chamber should be, given my intake length and carb size? I'm 200lbs and guess I'd be shooting for an all around performer, not a high speed demon as this thing sounds like it's going to explode at top speed anyway.

 

[fastboy9]

That intake is insane! I'm surprised it runs with a tube that long! Love the ram air setup though, very good!

If I was you I would have a long header pipe. Different length header pipes shift the powerband to different rpm ranges. A long header pipe (the bit before the expansion chamber) will give you more low end torque, and a short header pipe will give you more top end torque. I.E long for acceleration, short for top speed. A good way to do it is to use silicone tubing to experiment with different lengths, when your happy you can take the measurement and start some welding.

 

[v8brick]

Ok exhaust with expansion chamber is now on. I didn't have much choice on length to the expansion chamber with the tubing I had. I definitely runs better has more top end and less bog. I still have part throttle issues with the carb I'm running but it can be controlled with careful opening of the throttle most of the time. I do have some spit back through the air filter though, any idea what that could be??

http://slappytees.com/images/motobike/7_30_08_01.jpg


http://slappytees.com/images/motobike/7_30_08_02.jpg


http://slappytees.com/images/motobike/7_30_08_03.jpg

 

[Ghost0]

I run my header length around 12 inches. But remember every expansion chamber is designed different so tune to your needs. It will also depend on the gear ratio you are running. I would just start long and keep shortening it up until you get the best low end and top end combination.