exhaust question for gx390

[natew121]

okay i have just about completed my marathon 4 stroke swap last step is the exhaust the question i have is . I have the old 2GP muffler in really good shape off the 2 stroke that was pulled . do you think this muffler would be to restrictive for the 4 stroke.?

[natew121]

anyone??..

[rvkersh]

I think with a little larger tailpipe it would be ok.

[sho305]

Not familiar with it, but it could be a tuned pipe inside too that might make the 4 stroke run differently. I would say make a pipe and use the clone muffler, or other lawn muffler, but that one might work ok not sure...you can try it.

[rvkersh]

Ive cut a bunch of these open, they are baffled like a 4 stoke, the tuning is done at the stinger or otherwise called the tail pipe.Take the stinger out ,enlarge the opening, and put in a 1" to 1-1/4" tail pipe. Nice and quiet. You could get a 4 stroke ezgo muffler, do the same mod. still nice and quiet.

[sho305]

There you go. 1" should be about right for a stock 390 or even a little bit smaller. The racers run 1 to 1 1/8 headers and a tailpipe after a muffler is typically smaller. I'm going to try a 1" or 7/8 etc.

[rvkersh]

Now we are on to something, I'm very interested in the clone builds.

[sho305]

I typically want nothing to do with a 9hp muffler, but if you know the guts and can change it then no problem. Cutting flow cuts power, unless you plan to run stock rpm on the clone and even then it may still be hard on it if it restricts. With G9 people sometimes get exhaust valve problems from heat in the stock engine, when running them hard with no governor. I played it safe and used a car muffler it was so cheap to buy anyway, but have done a few mods to engine and no governor in it.

[natew121]

going to attempt to mod mine this week hopefully i can get it all mounted up well have to see if i can ill take some pictures and possbile post a video up

[natew121]

my engine will most likely keep the governor for now. the exhaust i choose to go with is 1 1 1/2 inch header pipe ran back to the muffler with a 1 1/2 inch pipe for the tail pipe coming off the muffle . i think it will be just fine. it sounds really good and honestly no louder than a kawi mule maybe quiter. next mod is install a rubber exhaust hanger for viberation, and heat wrap everything .