Part One: The Exhaust Port

[paragonbuilder]

I don't understand the question. If you don't need the extra blow down, then the mod doesn't do anything. I tried it on a couple of racing bikes that already had significant blow down and noticed no change, nada, zip, zero.

If you do need the extra blow down, then the mod can work. Instead of raising the exhaust port two degrees, you shape the piston crown to the curvature of the exhaust port roof. That gives you the needed blow down PLUS you retain two more degrees of TRAPPING EFFICIENCY and two more degrees of the POWER STROKE.

It takes a fair bit of work to get the shape right. You shine a bright light in the spark plug hole and then use a flat needle file to trim the edge of the piston. Just keep trimming the dark spots until the entire port cracks open at the same time.

I like a nice curve on the top of the exhaust port. By using this mod, I can use the curve I want and actually gain more port area on opening than if I used a flat roof.

I guess what I'm saying is plan for it from the start. If you want 20 degrees blowdown then set the exhaust at 18 degrees, this gaining more trapping efficiency.
I'm not talking about doing it after you have it where you want it.
If it doesn't work you can toss a new piston in and raise the exhaust 2 degrees.
I'm going to try this at some point.


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[rattler]

 

[Mastermind]

View attachment 68602

Nice looking work Mike.

 

[rattler]

Nice looking work Mike.

Thank you Sir.

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[Deets066]

View attachment 68602

Good looking port, all the way out

 

[rattler]

Good looking port, all the way out

Thank you Feets. You got one on the first or second page that is down right slick .

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[Deets066]

Thank you Feets. You got one on the first or second page that is down right slick .

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Craytex is your friend... and then a white buffing wheel on the fordom, with buffing compound

 

[rattler]

Craytex is your friend... and then a white buffing wheel on the fordom, with buffing compound

Thank you Deets sorry. I have never used Craytex but have the white compound with a price of green scotch brite.

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[Deets066]

Craytex is expensive but works well. Doesn't last long either.

The white buffing wheel with compound is key to getting the mirror finish.
But as posted earlier it isn't really necessary, but I'm still gunna do it

 

[Chainsaw Jim]

This is polished with a double cutter burr and that stihl lubricant spray. It's odd shaped because the ring gap is too close on one side leaving only the other side to widen.
Once I get it ground nice and smooth I wet it with the spray. The wet burr gobs up with aluminum dust and begins to polish at the right speed and pressure. The shine shows up about as fast as you can grind carbon off.



If I want mirror shine I'll chuck up a polishing bit and use a compound.

 

[Deets066]

WD 40 leaves a nice finish with a single cut burr

 

[rogue60]

Ok fellas, bear with me on the drawing as I'm not the artsy type. But, anyone try a shape like this? Would give a flat area for rapid release of pressure and potentially better scavenging vs an oval but the ring would be safe. Not as optimum as flat all the way across but maybe a way to get part of the flat advantage. Justathinkin on this flat thing and the idea popped in my head
View attachment 68356

This kind of exhaust port has been around for many years generally speaking is the last stage of a power valve to open ,thats when things start to get interesting if you are the one holding it on the stopper ...

 

[XP_Slinger]

This kind of exhaust port has been around for many years generally speaking is the last stage of a power valve to open ,thats when things start to interesting if you are the one holding it on the stopper ...
View attachment 68771

Excellent info and thanks for posting the pic. You say that's a power valve cylinder, wonder if that would translate to a saw that would have crap low end but scream like hell up top. Definitely not a personality I would want in a work saw if it falls flat on its face at 9,000 rpm. I still may sacrifice a cylinder to try it to a lesser extreme shape wise

 

[Mastermind]

I wanna build a jug with a power valve......

 

[rogue60]

I wanna build a jug with a power valve......

No way not in chainsaw no need for em..All power valves basically do is restrict the motor from say low to mid so you can get traction.
Guys looking for max get up and go will actually pull the power valves out in say like drag bikes/hill climbing etc..

 

[Mastermind]

No way not in chainsaw no need for em..All power valves basically do is restrict the motor from say low to mid so you can get traction.
Guys looking for max get up and go will actually pull the power valves out in say like drag bikes/hill climbing etc..

Don't pee on my silly iders. lol

 

[junkman]

Something like this ?

Hullo

 

[junkman]

No way not in chainsaw no need for em..All power valves basically do is restrict the motor from say low to mid so you can get traction.
Guys looking for max get up and go will actually pull the power valves out in say like drag bikes/hill climbing etc..

What about guys falling timber with long bars that need bottom end starting grunt ?

 

[Deets066]

Or runnin a long bar period, using the dogs

 

[rogue60]

What about guys falling timber with long bars that need bottom end starting grunt ?

Yeah I guess but power valves in a terminology sense is kind of misleading they don't actually add power.
More a restrictor they hold power back by blocking off the exhaust port, most all of them nowadays are tunable with heavier or lighter springs /less or more washers etc..
I can't say myself I have ever picked up a chainsaw and pulled the trigger and thought man wish I had less power down low this thing spools up way too fast!.