Custom exhaust for an 11 hp honda Gx340

[kartsandatvs]

Hello guys, I am adapting a 11 hp honda gx340 on a 4 wheeler, and need to build a custom exhaust, the internal measurement of the round pipe is 1 inch, any ideas on the length ? could it be the same as on the 5.5 hp hondas or the 6.5 hp clones, thanks

 

[mckutzy]

What length do you need? The other clones are a different shape in the exhaust port.

 

[danssoslow]

There are several manufacturers of big block Honda exhausts that might help you on length, and more importantly the diameters. Typical rules apply, long for torque/low end tuning, short for horsepower/high end tuning.

 

[kartsandatvs]

Thanks for your replies, was asking for the length because Im gonna be fabricating this pipe myself probably using 1 1/4 by 1 1/4 square tubing to respect the internal 1 inch and even giving it more breathing space, cant bend 1 1/4 round tubing myself, but its not difficult to make some cuts on the square tubing with some mig welding , this is a picture of a pipe I made for a 6.5 hp honda clone using 1 x 1 square tube with probably a 3/4 x 3/4 internal "diameter" and screwed the original silencer at the end. Thanks and my goal would be torque not really speed , so any ideas on a standard length would be appreciated.

 

[OzFab]

Somehow, I don't see square tubing being very efficient; you have to consider aerodynamics: Gases move faster through smooth, radiused bends but, start to go a bit haywire around tight, sharp bends, slowing down the scavenging effect &, in turn, hurting horsepower.

My best advice to you is to find a local shop that does tube bending (maybe even an exhaust shop) & ask if you can raid their scrap bin to find what you need...

 

[kartsandatvs]

Great idea Fabroman , hope the have something in the 1 to 1 1/14 internal diameter range, maybe 1 1/2 inch would be to much for an 11 hp engine, what do you think ? any ideas on length maybe a foot and a half (18 to 20 inches) thanks for your replies

 

[mckutzy]

For this, one could use just regular non galv black pipe, cut and weld the sections like you have done with the square. Should get a better response too.
It doesn't take much to do, if you have made the square one. This should be nice and easy.

 

[danssoslow]

http://www.robertsonstorquetubes.com/honda.htm#hondagx390sus

Looking at the bottom of this page, the largest inner diameter used is a 1.025 (at the head) and that's going to be for an open class (read: very modified) engine. I'm not sure what what the i.d. of the 1 1/4" tubing you plan on using is; but I'd at least follow this manufacturer as a maximum i.d. guidline. Go too large, and you will loose velocity, which is not a good thing.

 

[kartsandatvs]

Thanks for your replies

 

[OzFab]

Go too large, and you will loose velocity, which is not a good thing.

You want at least the header section to be as close to the same size as (but not smaller than) the port as possible