MAF143
Super OPE Member
- Local time
- 10:42 PM
- User ID
- 16099
- Joined
- Mar 30, 2021
- Messages
- 143
- Reaction score
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- Location
- North Central Ohio
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I'm working on a Husqvarna 445 for a friend and have a question about a region on the piston that opens the upper transfer ports to the crankcase between the strato air transfer and the opening of the transfer port to the combustion chamber.
As the piston is going up in compression the blue area short circuits the upper transfer port to the crankcase right before the strato ports are opened to the transfer ports by the red area. And as the piston is coming down in the power stroke, the blue area opens the upper transfer port to the crankcase via the hole in the piston after the stratos charged the upper transfer tunnels with air. I see what happens and when it happens, but I'm not sure what purpose it serves and how this timing and the size of the hole in the piston acts to improve the functionality of the saw.
Just trying to understand what this passage is for, how it works, and why is it there? My brain may be able to understand if someone explains it to me but I'm not even close to smart enough to figure it out on my own...
I'll be widening the exhaust and mildly porting this saw just for fun (it's a clammy), but I would like to understand what this blue area does and how it may effect adding duration to the intake. I'm thinking of increasing intake duration from 142* to 155* or so. Also blowdown on this saw was very short, only 12*.
Are there any other saws with this piston port that I can read up on? I couldn't find anything similar in my searches, but that may be cuz I'm not really sure what I'm searching for... rookie here, but very curious...
![Piston B4 marked.jpg Piston B4 marked.jpg](https://opeforum.com/data/attachments/404/404875-1420f1873f6d43f0025e8307c271bc5f.jpg?hash=FCDxhz9tQ_)
As the piston is going up in compression the blue area short circuits the upper transfer port to the crankcase right before the strato ports are opened to the transfer ports by the red area. And as the piston is coming down in the power stroke, the blue area opens the upper transfer port to the crankcase via the hole in the piston after the stratos charged the upper transfer tunnels with air. I see what happens and when it happens, but I'm not sure what purpose it serves and how this timing and the size of the hole in the piston acts to improve the functionality of the saw.
Just trying to understand what this passage is for, how it works, and why is it there? My brain may be able to understand if someone explains it to me but I'm not even close to smart enough to figure it out on my own...
I'll be widening the exhaust and mildly porting this saw just for fun (it's a clammy), but I would like to understand what this blue area does and how it may effect adding duration to the intake. I'm thinking of increasing intake duration from 142* to 155* or so. Also blowdown on this saw was very short, only 12*.
Are there any other saws with this piston port that I can read up on? I couldn't find anything similar in my searches, but that may be cuz I'm not really sure what I'm searching for... rookie here, but very curious...
![Piston B4 marked.jpg Piston B4 marked.jpg](https://opeforum.com/data/attachments/404/404875-1420f1873f6d43f0025e8307c271bc5f.jpg?hash=FCDxhz9tQ_)