Is it a big deal to put a stock exhaust on a ported engine?

[Gavin67]

The ports on the engine are a oval shape, and the only exhaust I have are those stock ones with a circle shape. I can still install it, but it's not to proper shape. I am planning on getting a aftermarket exhaust that will fit properly in the near future. But is this ok to use for now?

 

[butre]

it'll be fine. won't make much power but it ain't gonna hurt

 

[FurryOnTheInside]

I only widened my ports for better torque. I have a stock exhaust for stealth reasons. Tuned expansion pipes make more noise.
I realise that I'm giving up a possible 15% extra power and some fuel efficiency by not using a tuned expansion pipe.

I opened the top and bottom of the port slightly rounder, and opened the flange of the exhaust a little bit too, to promote smooth passage of the exhaust gasses. I opened the holes in the bottom plate inside the muffler and drilled a couple of small extra holes, as well as grinding back some welds that were invading into the two tubes (although I then added a "stealth pipe" extension so that probably restricted the exhaust again).

Modified exhaust port

• FurryOnTheInside
• Aug 23, 2017

Opened the outside of the exhaust port a little rounder, and widened exhaust window a little at...

Happy Time exhaust flange

• FurryOnTheInside
• Aug 30, 2017

Opened up the end of the exhaust and made it slightly more oval, and smoothed it.
Ears bent...

Cheap exhaust, opened

• FurryOnTheInside
• Sep 9, 2017

I opened the 6mm holes to 6.7mm diameter and opened the largest hole slightly too. I ground back...