Author Topic: Step in the exhaust port  (Read 541 times)

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Offline Cut4fun .

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Re: Step in the exhaust port
« Reply #20 on: May 28, 2014, 05:56:13 pm »
I worked on a P100 that had a 1/4" grove cast into the top of the exhaust port roof/cylinder plating. It was oem, never learned the reason why Partner did this but is suspect it was to start the  blowdown event earlier while still maintaining the torque associated with low exhaust height...
Adam

I swear I remember some folks trying that on racesaw builds too.
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Offline aclarke

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Re: Step in the exhaust port
« Reply #21 on: May 28, 2014, 05:59:05 pm »
Tim, might be worth testing this stepped port theory in the near future with some AM jugs? I'd be game on contributing a cylinder or two plus the machining if any other members would be interested in doing the work involved with swapping jugs and testing. Maybe try a few other ideas with the same jugs...

Offline 1manband

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Re: Step in the exhaust port
« Reply #22 on: May 28, 2014, 07:13:14 pm »
panheads also ironheads to '86, had them as cast from the factory.... the exhaust pipes, were clamped on the outside of the exh spigot of the head. 

-joe
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Offline sharkey

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Re: Step in the exhaust port
« Reply #23 on: May 29, 2014, 07:39:29 am »
Here is an interesting article that explains the process.  http://www.circletrack.com/enginetech/ctrp_1008_intake_reversion/

Offline 1manband

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Re: Step in the exhaust port
« Reply #24 on: May 29, 2014, 04:43:05 pm »
Here is an interesting article that explains the process.  http://www.circletrack.com/enginetech/ctrp_1008_intake_reversion/

good read.   

in the older bikes....exactly that.

there used to be an aftermarket part, made for evo's that claimed to prevent this.  cone shaped thing....placed into the exhaust pipe.  thing is, evo's did not have that problem.

-joe 
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Offline mdavlee .

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Re: Step in the exhaust port
« Reply #25 on: May 31, 2014, 12:04:15 am »
There's a west coast shop that puts them in work saws also. Not sure if they really help or hurt. I've not done any yet in any saws. Figured I don't need that last 2-5% for cutting firewood.

Offline KilliansRedLeo

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Re: Step in the exhaust port
« Reply #26 on: May 31, 2014, 04:39:32 am »
Tim, might be worth testing this stepped port theory in the near future with some AM jugs? I'd be game on contributing a cylinder or two plus the machining if any other members would be interested in doing the work involved with swapping jugs and testing. Maybe try a few other ideas with the same jugs...

Adam, I'm game for that! I was just toying with another idea, and I have a saw ready for a top end. PM me with a number and I will give you a call to discuss. I can also supply a couple of AM jugs.
"When the people fear the government...you have tyranny....When the government fears the people....you have liberty"

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Offline farmboy

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Re: Step in the exhaust port
« Reply #27 on: May 31, 2014, 04:39:33 pm »
I cut one in a Husky 55, widened and polished w/DP muffler.  Runs good but haven't run a stock one to see difference. 
Shep

Offline KilliansRedLeo

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Re: Step in the exhaust port
« Reply #28 on: May 31, 2014, 05:08:24 pm »
I'm thinking about something else to try also, if I can figure out how to do it. I would like to try a pair of crankcase stuffers in a 365/72 saw. Sort of like the 575/76 have. Anyone have any ideas?
"When the people fear the government...you have tyranny....When the government fears the people....you have liberty"

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Offline aclarke

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Re: Step in the exhaust port
« Reply #29 on: May 31, 2014, 07:46:53 pm »
Didn't husky add a plastic stuffer onto one of the 3 series Saw crankshafts?    You can also machine a ring that presses onto each crank half and fill the "voids"  between the Bell and Big end pin with epoxy.  Marcel Vincent and others have used this method on race saws and it works well. 

I think the 372 would respond well to this but the port timing might have to be altered slightly to deal with the higher crankcase pressure.


 

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