Part One: The Exhaust Port

[XP_Slinger]

Would be easy to mark with a sharp pencil, even if you can’t get all of it because of the rings it would still help

Agreed. The more I think about it the more I’m liking the idea. Like a flat roof (efficiency wise) without the risk of snagging the ring.

 

[XP_Slinger]

Doesn’t mean I’m gunna go tear my saws apart and do it. But by theory it should help

Neither am I, but I’m going to try it on my 254, been goofing around with that saw. Perfect candidate because the exhaust is already where I want it, no need for a change in timing.

 

[XP_Slinger]

If your engine already has enough blowdown, you're going to do a lot of work for nothing. I tried it on a couple of racing bike engines that already had good blowdown and it didn't change anything. However, when the engine needs it, the mod is worth about 2 extra degrees of blowdown - the more curvature of the port roof, the more effect it has.

I shine a bright light through the sparkplug hole and then keep nipping the edge of the piston crown until the entire port cracks open at the same moment.

I see what you’re saying. But what I’m going to do won’t change my blowdown, won’t be grinding on the piston at the top of the port. Just matching piston to port arc as you described. At least that will be my goal...lol

 

[Deets066]

I see what you’re saying. But what I’m going to do won’t change my blowdown, won’t be grinding on the piston at the top of the port. Just matching piston to port arc as you described.

Won’t change your numbers, but will act like you did

 

[XP_Slinger]

Won’t change your numbers, but will act like you did

You just sparked a thought. I bet compression will drop a little given the larger area that has to close.

 

[Terry Syd]

I bet compression will drop a little given the larger area that has to close.

Removing the washers from under the sparkplug and compression release will probably get it all back.

 

[Deets066]

You just sparked a thought. I bet compression will drop a little given the larger area that has to close.

Removing material from piston would reduce comp too. But not enough to worry about

 

[Bjorn]

This is interesting.

 

[MustangMike]

Good stuff, but on a chainsaw you typically want a megaphone shape in the exhaust port as the exhaust gas is rapidly expanding.

The volume of exhaust is typically about 10X the volume of intake.

 

[Bjorn]

Good stuff, but on a chainsaw you typically want a megaphone shape in the exhaust port as the exhaust gas is rapidly expanding.

The volume of exhaust is typically about 10X the volume of intake.

Hi. I think The exhaust expanding would be the same in a saw as in a bike engine.

 

[MustangMike]

The difference being a bike would be more like a piped saw, where the exhaust pulls the exhaust out. Some bikes will also have header type exhaust.

With a chainsaw only generally having one cylinder and a tin can style muffler, it changes things.

 

[Bjorn]

Here is a beatiful exhaust port.

 

[Lightning Performance]

Here is a beatiful exhaust port.View attachment 230977

https://opeforum.com/threads/post-up-your-ported-cylinder-artwork.3409/page-61#post-1036060

 

[BonScott46]

Here is a beatiful exhaust port.View attachment 230977

Hybrid?

 

[Canadian farm boy]

Hybrid?

Yes. That’s the roughed in port. This is the same port finished

 

[Lightning Performance]

Yes. That’s the roughed in port. This is the same port finishedView attachment 230983

Shinny

 

[Canadian farm boy]

Shinny

Finished it with 220 grit emery cloth.

 

[BonScott46]

Yes. That’s the roughed in port. This is the same port finishedView attachment 230983

Purdy.

 

[CJ Brown]

Finished it with 220 grit emery cloth.

Beautiful work as always Mike.

 

[I Know Something]

I haven't seen this anywhere. Or missed it? With these custom exhaust sizes and shapes, what you guys using for gaskets? Modify the existing or some bulk roll?