Re: Ring gap over port, port width.

Graham Motzing /
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after seeing this DT i'm'a say fuck the baby ports and go as wide as you can, especially if adding aux ports is complicated by stud spacing and cylinder design.

you see a lot of dirtbikes where the Aux ports kinda do the same thing as the 'snooter' ... they are up high and get covered 1/2 way with the power valve. I think they are functioning more to evacuate blowdown gasses and blast the return pulse, and only marginally effective at evacuating the transfer-charged loop scavenge process.

I.e at low blowdown, low exhaust scavenge efficiency, where the loop process is pressure driven by the crankcase, the big open exhaust is more effective, and at high blowdown, where the pipe is driving the process, the aux ports are more effective.

I DO like that when you run bridges/aux ports you can put the lube holes in your piston and keep better cooling contact when the piston drops to BDC. I think that makes a huge difference vs. it running dry from exhaust burning off the oil film at TDC. I'm curious if cutting a couple very small vertical from the case up to, and just short of, the bottom of the exhaust port, would have any positive effect in this regard... it would reduce surface area contact, but it might draw and hold more oil for better lubrication.

or maybe even a little horizontal wiper shelf groove that the piston could expose at TDC... i dunno. crazy thoughts.

I'm still learning a lot about how exhaust characteristics contribute to piston heating on the exhaust side, especially at midrange where the exhaust pulse is reverberating while the piston is still partially covering the port.

This vespa polini motor that i built is seriously making me reconsider some of my long held assumptions about mismatched timing, blowdown, and pipe.

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Subject Written By Posted
  Ring gap over port, port width.Topic by: Alex Degnes Alex Degnes 07/01/14 03:02AM
  Re: Ring gap over port, port width.Re: #CrazyWayne™ rocks. #CrazyWayne #CrazyWayne™ rocks. #CrazyWayne 07/01/14 03:17AM
  Re: Ring gap over port, port width.Re: Graham Motzing Graham Motzing 07/01/14 10:03AM
  Re: Ring gap over port, port width.Re: Flagrant - Flagrant - 07/01/14 11:46AM
  Re: Ring gap over port, port width.Re: Alex Degnes Alex Degnes 07/01/14 05:35PM
  Re: Ring gap over port, port width.Re: #CrazyWayne™ rocks. #CrazyWayne #CrazyWayne™ rocks. #CrazyWayne 07/01/14 05:49PM
  Re: Ring gap over port, port width.Re: Alex Degnes Alex Degnes 07/02/14 03:48AM
  Re: Ring gap over port, port width.Re: #CrazyWayne™ rocks. #CrazyWayne #CrazyWayne™ rocks. #CrazyWayne 07/02/14 06:07AM
  Re: Ring gap over port, port width.Re: JBOT Admin JBOT Admin 07/01/14 11:44AM
  Re: Ring gap over port, port width.Re: Flagrant - Flagrant - 07/01/14 11:48AM
  Re: Ring gap over port, port width.Re: Graham Motzing Graham Motzing 07/01/14 12:07PM
  Re: Ring gap over port, port width.Re: #CrazyWayne™ rocks. #CrazyWayne #CrazyWayne™ rocks. #CrazyWayne 07/01/14 12:03PM
  Re: Ring gap over port, port width.Re: JBOT Admin JBOT Admin 07/01/14 12:29PM
  Re: Ring gap over port, port width.Re: Graham Motzing Graham Motzing 07/01/14 01:47PM
  Re: Ring gap over port, port width.Re: Alex Degnes Alex Degnes 07/01/14 03:16PM
  Re: Ring gap over port, port width.Re: Alex Degnes Alex Degnes 07/01/14 03:06PM
  Re: Ring gap over port, port width.Re: Alex Degnes Alex Degnes 07/01/14 03:37PM
  Re: Ring gap over port, port width.Re: #CrazyWayne™ rocks. #CrazyWayne #CrazyWayne™ rocks. #CrazyWayne 07/01/14 05:18PM
  Re: Ring gap over port, port width.Re: JBOT Admin JBOT Admin 07/01/14 04:35PM
  Re: Ring gap over port, port width.Re: Blake MD No PM Plz Blake MD No PM Plz 07/01/14 04:41PM
  Re: Ring gap over port, port width.Re: Alex Degnes Alex Degnes 07/02/14 03:52AM
  Re: Ring gap over port, port width.Re: Alex Degnes Alex Degnes 07/02/14 07:32AM
  Re: Ring gap over port, port width.Re: Alex Degnes Alex Degnes 07/02/14 07:33AM
  Re: Ring gap over port, port width.Re: Alex Degnes Alex Degnes 07/02/14 07:40AM
  Re: Ring gap over port, port width.Re: Graham Motzing Graham Motzing 07/02/14 09:33AM
  Re: Ring gap over port, port width.Re: Alex Degnes Alex Degnes 07/07/14 01:09PM

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