Modifying Coffman Sizzler (lengthening)

[Jcary85]

Hey All,
I have a coffman sizzler installed on my mildly ported 701 with Stock head (for now). Its the shorter version of the pipe (either that, or its been cut down at some point in history). I believe the shorter version was better for top-end, but I'm more interested in low-end. Has anyone ever extended the pipe (in the middle area where the big coupler is) to get better bottom end? I'm curious how much longer the long version of the sizzler is as well.

Thanks for any help!
-Jordan

 

[Quinc]

There are some threads that show the length. But easiest thing to do would be to buy a full length chamber from @TheBuzzard

 

[Jcary85]

I kinda hate to spend more money on this thing (it’s pretty crappy/old). I have a TIG welder so I was thinking extending it might be pretty easy.

 

[Vortex]

Another way to lower the onset of the power band is to increase compression. Assuming 62t cases, you'd want to keep the 38s for the higher air velocity which will give you the off idle snap. Pair that with a low pitch prop and the current short chamber and you should have some nice air time. Just my 2ct. Low end power is kind of subjective. My experience with these motors is that they do not like to be ridden around at part throttle very much once you've modified anything internally. I assume you want the motor to rev up quick and build torque right off idle not have strong performance at 1/4 throttle.

 

[Jcary85]

Another way to lower the onset of the power band is to increase compression. Assuming 62t cases, you'd want to keep the 38s for the higher air velocity which will give you the off idle snap. Pair that with a low pitch prop and the current short chamber and you should have some nice air time. Just my 2ct. Low end power is kind of subjective. My experience with these motors is that they do not like to be ridden around at part throttle very much once you've modified anything internally. I assume you want the motor to rev up quick and build torque right off idle not have strong performance at 1/4 throttle.

Thanks! That’s great advice. Maybe ill look at milling the head or an aftermarket head and a prop as my next modifications.

 

[TheBuzzard]

there is no such thing as the shorter version. the tail cone can be cut down to make the chamber smaller. not advised! I don't have any SJ tail cones left but I do have the kawi tail cones which are longer than the SJ ones and will increase chamber volume. recommended!

 

[Req]

there is no such thing as the shorter version. the tail cone can be cut down to make the chamber smaller. not advised! I don't have any SJ tail cones left but I do have the kawi tail cones which are longer than the SJ ones and will increase chamber volume. recommended!

One thing to note on the Kawi tail cone is due to the shape you may have to run the stinger section of the chamber rotated 180 degrees to fit the tank (still had to dent a stock tank). This puts the stinger nipple on the bottom however does not seem to cause any issues, its just hard to get to the nipple when installed.

TheBuzzard: What is your take on the longer tail cone? How far down does it move the power band and how does it compare to the yamaha tail cone? My ski came with the Kawi tail so I have no frame of reference.

 

[kevbo]

Find a Kawasaki head pipe or make a 1" spacer ring for the chamber. These mods will make the pipe come on a little sooner but also reduce power. The real answer is a bored nozzle and lower pitched impeller.