Milling a predator 212 head.

[DieselTech]

As a cart engine, you can go nuts, everything is in the back. If she blows, it's all behind you and just a wee bit embarrassing, nothin' hurt.
On a bike you have to be a little more conservative.

Your honda, is it a gx160 or gx200? I was curious about its cylinder head. Does it have a round exhaust port or the goofy predator style port?

 

[Chainlube]

Your honda, is it a gx160 or gx200? I was curious about its cylinder head. Does it have a round exhaust port or the goofy predator style port?

Yea, it's that same goofy "D" shape as yours. It's a 200 which means 196cc. The regular B&S 4t that looks like the Honda with the OHV has a round exhaust port.

 

[rusty.western.flyer]

An exhaust port will often flow more in a "D"than "o" shape. The air on the outside of the curve has to travel more, and tends to separate more, so you shape the port accordingly.

 

[Chainlube]

An exhaust port will often flow more in a "D"than "o" shape. The air on the outside of the curve has to travel more, and tends to separate more, so you shape the port accordingly.

That's some good information, thanks. With these little engines, and pretty much straight through port job, would the port shape be much of an affect on the flow?

 

[rusty.western.flyer]

The short side radius, CSA (cross sectional area) and curtain area ratios are the most important. It's very easy to make a port large, but in N/A applications, that doesn't always equate to power. I'd have to put one on the flow bench to make any accurate statements on that particular head, though.

 

[DieselTech]

That's some good information, thanks. With these little engines, and pretty much straight through port job, would the port shape be much of an affect on the flow?

I know a bias intake port design, will greatly out flow other port designs. Paul's Karts has some good videos on it. It has something to do with the high velocity intake stream on 1 side of the port & the low side velocity on the other side of the intake stream. The port itself is higher on 1 side of the port. But it has to do when the high velocity intake stream/gas meets the low side velocity of the intake stream at the back of the valve bowl,which helps to create bowl swirl, which in turn increases flow.

 

[DieselTech]

Lmao something like that!!! Paul's karts explained it in detail better than I can.

 

[Chainlube]

The short side radius, CSA (cross sectional area) and curtain area ratios are the most important. It's very easy to make a port large, but in N/A applications, that doesn't always equate to power. I'd have to put one on the flow bench to make any accurate statements on that particular head, though.

These little engine we're not really increasing the port size but more or less just straightening them out. Even though the low side curve is gone, what happens to the high side curve, where the valve stem is at? Does the flow expand into that area?

 

[DieselTech]

These little engine we're not really increasing the port size but more or less just straightening them out. Even though the low side curve is gone, what happens to the high side curve, where the valve stem is at? Does the flow expand into that area?

I know paul mentions something about the valve guide helping with flow. He mentions that most people mow the guide off when porting. He said it's bad for valve stability for 1 & 2 it decreases with flow/mixture or port swirl.

 

[DAMIEN1307]

The valve guides are not there as decoration...I can't believe that some folks would just "mow the guide off"...lol...lol.