Exhaust porting

Mxfan
Posts
7
Joined
12/2/2012
Location
El Cajon, CA, USA
Edited Date/Time 12/5/2012 10:14pm
I noticed that my Yamaha Yz250 has an oval exhaust port, and the exhaust pipe is round. This leaves two ledges where the two meet. Does anyone know if these are important to leave alone, or can they be blended into the pipe flange? If its done, how does it effect performance?
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kawimoto_615
Posts
60
Joined
10/18/2011
Location
Roseville, CA, USA
12/4/2012 11:41pm
leave it, its supposed to be that way. almost every bike is... what you can do is remove all the carbon and get rid of the flaws. then go through and make it look as shiny as possible.
DTHA70
Posts
336
Joined
9/25/2008
Location
Surprise, AZ, USA
12/5/2012 10:14pm
i always take the edges off of the exhaust sub port area within the exhaust port, make edges nice and round, take away and casting flaws, major edges, bumps etc and polish the hell out of it.
1
7/25/2025 5:13pm

What’s the purpose of polishing it? 

TDC
Posts
394
Joined
8/4/2023
Location
HTown, TX, USA
7/25/2025 6:17pm

What’s the purpose of polishing it? 

Smoove reduces deposits. Intake no polish, as it will grab fuel droplets. 

Better to focus on matching cases and cylinder boost port base. A little epoxy and a little grinding, as to maintain a good average width foot print. This is common for shops to find easy broad power gains and throttle response. That's if there are ledges creating turbulence. Simply tape off the rod area and vacuum out the metal shavings after. More YAT

2

The Shop

Nairb#70
Posts
3979
Joined
2/25/2020
Location
Ivoryton, CT, USA
7/26/2025 4:31am

Has anyone ever tried extrude honing their exhaust?

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