HEADS UP!!!

Site upgrade in progress... Core site functions are working, but some non-critical features/functions will be temporarily unavailable while we work to restore them over the next couple of weeks.

Please post any bugs you encounter, but before you do, check to see if it's already listed.

Thanks for your patience while we work to improve the community.

Sign in to follow this  
Followers 0
FriscoKLR

Physics\design of the '08/'09 shorty can horsepower

7 posts in this topic

Just picked up a 2009 450f, have it in the garage next to my clapped out '06. What in the design of the shorty muffler on the '09 450f's can cost that much horsepower compared to the '06?

Share this post


Link to post
Share on other sites

Its got a bunch of cones in it, thats all I know, if you look someone had a picture of one cut open a while back.

Share this post


Link to post
Share on other sites

The 06 silencer (and pretty much every other mx silencer) is just a straight through core, which provides very little resistance to the exhaust and thus little back pressure which equals good power. The 08-09 silencer has perforated cones inside, cause resistance to the flow and back pressure to the exhaust system, which is bad. Here's a cutaway of the 08-09 silencer:

89103034.y06uA26j.YZ450FMuffler1.jpg

Share this post


Link to post
Share on other sites

It's restrictive, simple as that.

If it were a well designed baffled muffler, it would have been much less so. There is resonant chamber technology in common use the would have possibly made it quieter AND increased the power output, but they ignored it for the frankly antiquated approach they chose:

YZ450%20MUFFLER.jpg

Share this post


Link to post
Share on other sites

Thanks for the quick replies. Does the yellow restrictive cone fit into the cylinder below it or is the cylinder from an older silencer for comparison?

The stocker came with a brand new ProMoto Billet spark arrester end cap on it. Think I'll give cutting it out a shot before dropping $350+ plus on a new slip on.

Share this post


Link to post
Share on other sites

The can slides over the core below it in the same manner as any typical silencer does. The yellow cone runs down the center of the perf core.

So whereas in a normal fiber packed silencer the exhaust flows straight out with very little restriction, the "shorty" puts two perforated cones in the path of the exhaust and forces some to flow through the perforated ends of the cones, some to go around them, and some directly into the packing due to the pressure created ahead of the cones. It's the kind of thing that was done in cheap custom mufflers for British bikes in the '60's. :excuseme:

Quite often, the add-on end cones like PMB, DRD , etc., that add a spark arrestor require the removal of the second (yellow) cone. The spark screen itself does not impact performance negatively in any way that I've ever noticed.

Share this post


Link to post
Share on other sites

I have the PMB SA also.

http://www.thumpertalk.com/forum/showthread.php?t=727517&highlight= Recently I bashed out the inboard cone. Thanks to 'ray' for the idea.

http://www.thumpertalk.com/forum/showthread.php?t=915420&highlight=

I swear it was a huge improvement. I also repacked the silencer and replaced the stock air filter with a twin air at the same time so those improvements may have contributed.

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!


Register a new account

Sign in

Already have an account? Sign in here.


Sign In Now
Sign in to follow this  
Followers 0