Muffler vs srtaight pipe

[Cooter]

My muffler on my 400 broke so I put a straight pipe on it to ride this last weekend. It almost seemed to run better with the straight pipe. I was wondering if this is in any way harmful for the motor or just my hearing. If anybody had any bad experiences with a straight pipe I would like to know. Thanks.

[Go Go Diablo]

For sure I'm not a muffler expert, but here is my 2 cents.

When I started making mufflers for the 400/444, Barrie mentioned that he saw a Hus Ski Service Bulletin about installing some additional holes within the muffler by taking the end caps off and drilling into the inlet pipe. If I remember correctly, it may have also said to punch out the end cap of the exhaust pipe. Both modifications would improve HP of the motor. I suspect they felt there was too much back pressure being created. So when I made the mufflers, I added some extra holes in both pipes.

Years back when I made the Diablo muffler, I talked with several people about making them first with specific questions around the baffle designs. The message I heard was consistent that a 2-cycle motor needs a certain amount of back pressure to operate correctly and too little back pressure could cause a motor to run hot and burn pistons. That makes sense I guess as you relieve back pressure and create HP, the engine may be working above it's designed power output.

Both points are about getting the proper back pressure within a muffler in order for it to not only run properly, but also operate within it's rated horsepower.

I'm very curious about what others think.

Bruce

[JeffC]

I have tested the water a little on the mufflers. The original mufflers work well but I have found by using the same muffler design, that one baffle with larger holes in it and instead of a cap on the end installing a larger diameter 2 inch long tube inside the muffler gives you a little more kick. Providing you adjust your carburetor to compensate for more air flow.

[Cooter]

Thanks for the replies. Hey Bruce, is the muffler I got from you a couple of years ago the same as you just made or are there some differences. I added a extra support on mine but the pipe between the flange and muffler broke. I plan on cutting it apart and putting a new pipe on it so maybe I can reduce backpressure in it then.

[Go Go Diablo]

There are some differences and I believe the one being made now is better than those reproduced earlier.

[Barrie2777]

The muffler should be supported to the head of the motor and not bolted to the base. Doing this allows the muffler to vibrate with the engine and thus eliminate the brake you experienced.

[Vintage srx]

Barrie can you please post a picture of how your muffler braces go to the head . Thankyou !

[Cooter]

Thanks Barrie for posting picture of muffler bracing. You were right I braced mine off of motor mount bolt which is seperate from motor and probably caused it to break. Considering my JLO idles as smooth as the paint shaker at the Sherwin Williams Store it was doomed for failure