[arsenic]

I think there's a thing on APE Racing that smaller ports actually increase HP. Now I can't find it

[neonjeffie]

thanks for the insight. im gonna check with my engine builder and get another opinion. i think i'll just clean em up good annd smooth it all out. ive done car heads but not a bike one.

[Tmod]

I think there's a thing on APE Racing that smaller ports actually increase HP. Now I can't find it

+1

Found this at a different site and it follows right along with your statement.

Don't overlook the valve seat angles and the angles on the valve.

To go fast and win races, you need horsepower! To make horsepower, you you need a high flowing, high velocity, efficient induction system. Minimizing port volume, while keeping enough cross sectional area to provide enough cfm to produce maximum horsepower and high rpm torque, along with great throttle response, is what makes an efficient induction system and a strong running engine. When looking at a flow sheet from a ported cylinder head, you see that numbers increase as valve lift increases. This is because the valve becomes less and less of a restriction as it leaves the seat. But don't be fooled from the high number at peak lift. Lets say it's 310cfm @.700" lift, with a 220cc intake port. Well unless your doing some serious racing, your not running a valve train that's going to produce that kind of lift. If your building a street engine or a mild race engine, you will probably be limited to say .550" to .600" lift, in which case you're probably moving around 275-285cfm with the same port. These numbers are still respectable; however, the valve is only at peak lift for a short amount of time. With that being said, the area of the lift curve in which you want to see improvement is mid lift numbers from .250" to .450" lift. The valve will spend most of it's time at these points, so improvements here is where more horsepower will be made. High flow numbers are important, but even more important is port swirl, port velocity, and of course a good port volume to airflow ratio. Any large port will move a lot of air, but the smaller port moving just as much air will create a flatter torque curve and be more effective with high velocity and great throttle response (important in bracket racing).

[Astro4x4]

Some info on high velocity head porting.

http://www.mototuneusa.com/