I am in the process of dualsporting an early CR500. I am fabricating a Quiet silencer. I need to quiet the noise from the expansion chamber also. Is it better to wrap it with header wrap or have it jet hot coated inside and out?
A friend and I did something like what you are saying, we wrapped the entire pipe with hi-temp header tape, formed/welded/hammered an aluminum cover (1.6mm thick) for all the outer side of the chamber and clamped in place. My friend polished it to mirror finish (I didn't like it much).
It brought down the sound level A LOT. Now it is street legal!! but not pretty...
We did this on a KTM 550.
A few years ago,I was given the leftover insulation from a rebuild on an industrial oven. I wrapped whole Xpan/chamber 1/4-3/8 thick,wrapped that with header type wrap,and finished off with the chrome-looking duct tape. Felt like it weighted 4X more than stock pipe.It was TOTALLY UNREAL how quiet it was.Never dreamed most of noise was coming thru Xpan/chamber! Actually had prob's judging power.But started looking bad after 1 ride thru mud/water.My trial was with a water cooled CR500, the fins will ring on an air cooled,so it wouldn't work as well.I hope to Xperiment some more soon.We all need to start thinking about being quieter.
I wouldn't mind if my bike was quieter. Most people only have a problem with us because they hear us.
Working off of EZ's idea, how about wrapping the pipe with insulation and having a bolt on pipe cover that was the same shape as the pipe just an inch larger in diameter. That would allow for a half inch of insulation all the way around the pipe plus when that insul breaks down it can be replaced and the whole thing acts as a pipe guard!
I guess it would be like making the wall thicker in your house. Thicker anything is harder for sound to go through. How much is the question. I guess it would depend on how thick a coating you would put on it.
A-Loop (back when they were Moose, in late '93) took a CR250 and wrapped a ($90) fiberglass pipe shell over an FMF Gold Series pipe, addded a Answer Sneaker S/A w/a homemade extended silencing chamber., blanketed the inside of the air box w/foam (neoprene?) & closed off the RH side opening, then stuffed the gap between the frame & cases w/more foam. Give Pete a call; tell 'em it was the Dirt Rider '94 (?) enduro shootout CR250.
I think that would help,but I'm not sure how much. I'ld be VERY interested in knowing how much it cut the noise back. If you try it,please let us/me know. I'm not sure Xactly what type coating u're talking about,but I would be leary if it cost big bucks because it might not be enough reduction. If U try the insulation,make sure it's made to withstand high heat. Header temps are a whole lot higher than muffler temps.
Theres an example of a CR500 converted to be street legal in my book. Denny Calvert, the bike owner and I, used Swain-Tech ceramic fiber header-wrap tape, saftey wired it in place, and fastened an aluminum pipe protector orver the top. It insulates the heat for better throttle response because the skin temperature of the pipe drops dramatically when street riding because of the additional air flow. However some of the energy is lost from the waves that travel through the pipe. So peak performance might suffer in exchange for smoother low to mid throttle response.
Check out the ceramic header wrap at www.swaintech.com