Inexpensive exhaust "silencer"... [updated]

[cliffyk]

I recently acquired a new 2020 Coleman Outfitter 400 and overall am quite pleased with it. I had the "too be expected" loose bolts (first thing I checked), all related to the final assembly conducted by the pimple-faced kid "mechanic" at Tractor Supply.--the bolts in the upper driver's side roll bar joint were just hand tight, as were those of the upper seat belt anchors--but other than that it had been pretty well assembled.

The included owner's manual  is not current; it speaks of using the choke to cold-start the motor (it's EFI, no choke),  and shows the ignition and lighting switches as dash-mounted when in fact they are on the steering column. It also direct you to remove the seat to change the spark plug--except that on this revision the cylinder tilts rearward and the cylinder head in found beneath the dump bed. Other maintenance tasks are similarly ill-described and it is generally useless.

I did find the exhaust note to be a bit strident and devised the following to tone it down a bit. I used one of those inexpensive 1" NPT female inlet B&S "muffin" mufflers that have been around for decades, and a steel 1" EMT to steel box adapters that have been available for a like time:

 

 

1" EMT has an outside diameter of 29.5 mm, the tailpipe extension on the beast is 28 mm O.D.--so I use a partially overlapped  cylindrical shim spacer of 28 ga. (0.47 mm) galvanized sheet metal to fit the EMT adapter to the tailpipe . Bedded well in muffler putty the single set screw on the adapter mounted it up quite firmly.On my first ride I found the motor to feel and sound a bit constipated--so i drilled out the 106 1/8" holes in the faced of the muffin to 9/64". This is a 26.5% increase in area [(9/64)^2 / (1/8)^2 = 1.2656]

That made the difference needed to restore proper flow without making it too loud again:It

is arguably not a pretty as some of the $100+ aftermarket alternative, but at $15 for the muffler and adapter it better fits my budget.Make sure you get the genuine B&S part (# 392989) as the 3rd party clones lack an inner baffle that makes them inherently louder than the B&S piece.

 

FWIW--I  also  removed the front anti-roll bar--and have found little to no adverse effect on handling (and arguably some positive effect)--it also got rid of an annoying  rattle from the low-quality driver's side roll bar tie-rod end. Put in an iridium spark plug too...

[update]

For anyone who cares. I have re-drilled the 106 outlet holes to 5/32" which seems to be a sweet point.

I had the beast running 45 mph (indicated, 40 by GPS) t'other day and it felt a bit "held back" so when I got home I hogged out the holes to 5/32"--another 23.4% area on top of the 9/32' holes (56% more than the original 1/8" holes). Went out today and got it going 53 mph (indicated, 47 per the GPS). Coleman and Hisun claim 38 mph top-end for the HS400 but I knew it had more than that.

So, I Think the 5/32" holes are about optimal.

I need to take the B&S thingy off and see what it can do, however it (the B&S thing) is so nicely mounted and sealed now that I don't want to mess with it...

[/update]

 

[Locking Diff]

Thanks for the info. I think I might try this on my Missimo 410