Wanna Talk About Port Shapes?

We talk a lot about compression, port timing, muffler mods, etc. We don't talk too much about the shape of the port, and how the shape relates to performance.

Here's a few pics of an 064 I just did.......and there's some pics of another 064 jug in here too. I sanded through the plating when I was getting the transfer off the second 064 jug.

This pic really shows the difference between a "performance shape" and a stock port. Notice how the corners have been opened up to increase time area.........but the port height is unaffected.



In this pic the rough in of the intake port is nearly complete......I'll tighten the corners a little more and work on out to my marks. Notice that this port is only a little wider than stock, and at the stock height. It should be plain to see that this port will be more conductive to flow than a stock port.



Here is a stock 064 intake port for comparison.



And here they are side by side.

 

Now, for the transfer ports.

Here's a shot of the stock ports.



And here's a fully finished transfer.

Notice the corners. They are even tighter than the intake port. When the transfers first crack open, you want to be fully flowing across the entire area of the port.



Here's another shot that shows how tight the corners are......and that shape is carried back into the port a good ways.



Here's another......note the lower opening of the transfer. I don't open this down as far as I once did. I just take the lip off to prevent fuel puddling.

 

Same treatment on the exhaust port.......just raise it to the height I want, and tighten the corners up a bit. Not as much as on the intake though. The rings ride across the exhaust port so you want a nice arch to the port to keep from beating the rings up.



Here's another thought. In a two stroke engine, it's all about the time/area of the ports went it comes to performance. You can widen the port to gain T/A, or you can raise it. If the rings travel across the exhaust would it be wiser to get the T/A you want by setting the height, or widening the port?????

 

Here's the last pic I have for now.

I don't normally enlarge the exhaust flange area on these saws. It's plenty big enough. I just deburr, and smooth it out. It's more important the match the muffler, heat shield, and gasket to the jug perfectly than it is to hog stuff out and weaken the flange.....

Note the arch across the roof of the exhaust port.........easy on the rings is key here.

 

Perfect thread since some have been asking about what porting is. Ill be watching and admiring.

What tools do you use for grinding Randy?

 

A picture is worth quite a few words here Bryan.

 

What would you recomnend for someone that just does a few muffler mods now and then? Ive destroyed dremels and the cheap HF knockoffs (they actually lasted longer).

I cant justify a foredom setup like that!

 

Square ports for the intake and transfers. I wish all the old race saws stuff wasn't gone. Good pictures of port shapes and stuff like that from way back. I like those bridge ports you put in that 64 cylinder.

 

HF has a Foredom knock off that's pretty good. The handpieces suck.......but the Foredom handpieces fit.

 

Just a little extra transfer area.......and it aids in directing the flow. I do that on most two port engines.

 

I was digging for finger port pictures but I can't find any.

 

Here you go.......

Finger ported 064.

 

3120

 

MS460

 

How does a finger port work?

 

It's just a extra transfer port.

 

I have some pictures of 288 cylinders on my computer. I have 2 46 cylinders to port soon and I may do a set of fingers in one.

 

Im learning a ton here. Been wanting to see some finger ports..
Hey Randy.... You da man !

 

No, I ain't.......

But I have friends that are.......and I pay attention.