Intake modification

I have a 2003 YZF450 that I am in the process of replacing a broken 3rd gear in the tranny. Since having it apart I noticed that the intake surface on the cyclinder is very rough and has casting flaws. In the past I have polished the intake on 2-strokes with very good results.

My question is: Do you think it would help if I cleaned up and polished the intake? Or am I better off leaving it alone?

Thanks in advance!


IF all you do is to smooth out the rough edges and knock down the odd little casting blob here and there, you'll help it some.

BUT....DO NOT alter the shape or size of any area of the intake port without a full understanding of what the results will be, or the results you get may not match your expectations. In particular, avoid any changes to the shape of the valve pocket (the area between the valve guide and the seat), and the dividers that separate the three individual runners. You can smooth over any steps, misaligned laps, and inconsistencies, but don't change the shape or shift the partitioning edge left or right, or move it farther down the port. Changing the shape of the runner entries has an effect not only on mass airflow, but on the terminal flow of the fuel/air charge as it enters the chamber, and you don't want to mess with it unless you have a lot of time and money, or someone who knows what works has told you how to handle it. Leave the bored recess around the valve guide alone, too.

In "polishing', don't go beyond a smooth, sanded finish. That type of surface helps retain the boundary layer of air against the port walls, and helps keep fuel droplets from contacting them.

The Casting Marks Can Be Taken Out But It Is Recommended To Keep The Surface Rough To Break Up The Fuel Charge. Ive Been Doing Head Work For Many Years And It Keeps Changing According To Flow. I Recently Saw A Head Done By Yoshimura And They Filled In Alot Of The Bottom Runners And The Back Side Of The Valve Runner. Best To Be Done On Flow Bench. Thanks They Do Not Polish Exhaust Anymoore Either

Thanks for your replies. I will take your advice and only clean up the casting marks.

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