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| Shaving piston top instead of raising exhaust port http://www.kawi2strokes.com/forum/viewtopic.php?f=16&t=7783 |
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| Author: | Agent H2 [ Thu Feb 13, 2014 9:46 pm ] |
| Post subject: | Shaving piston top instead of raising exhaust port |
I once had an H1 that had pistons that had been carefully beveled, ground and shaped on the top facing the exhaust port. I am assuming this was someone not wanting to ruin a stock set cylinders? Looked like a piston with a I had forgotten about this but talk of cutting pistons jogged my memory. Anyone ever hear of such a hack? |
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| Author: | ThreePipesSmokin [ Thu Feb 13, 2014 9:54 pm ] |
| Post subject: | Re: Shaving piston top instead of raising exhaust port |
I've heard of it and it "does work", but: *you can't get more than about a millimeter of height change *you can weaken the piston by taking off too much *you can create hot spots (and deto) by creating sharp steps *it's just not the right way to do it, IT'S A RIG! 
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| Author: | Ja-Moo [ Thu Feb 13, 2014 9:59 pm ] |
| Post subject: | Re: Shaving piston top instead of raising exhaust port |
It's a hack, it was to do non destructive testing for minor changes. You don't get any more port area, that is what makes the difference. |
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| Author: | denisj [ Thu Feb 13, 2014 11:58 pm ] |
| Post subject: | Re: Shaving piston top instead of raising exhaust port |
I am pretty sure there is a bunch of information on this in the 2 stroke tuners handbook http://www.amrca.com/tech/tuners.pdf |
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| Author: | Agent H2 [ Fri Feb 14, 2014 9:10 pm ] |
| Post subject: | Re: Shaving piston top instead of raising exhaust port |
Yes, a hack. I kinda thought that on first glance when I saw it. |
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| Author: | H2RTuner [ Fri Feb 14, 2014 10:04 pm ] |
| Post subject: | Re: Shaving piston top instead of raising exhaust port |
If I am correct on the type of mods you are describing, I would think they were somewhat the same as, but not as radical as some of the early chain saw engines, and, older, very early two stroke designs, before loop scavenged engine porting came about. Some of those old things had a heck of a lump on the top of the piston, with a ski slope aimed down from the top of the lump, twords the exhaust side of the cylinder. The lump was there to stop some of the short circuiting between the transfer and exhaust ports, and, it worked very effectively to steal a lot of power. Nope, they didn't work well at all, compared to the loop scavenge stuff we work with today. |
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| Author: | P.K. [ Sat Feb 15, 2014 6:44 am ] |
| Post subject: | Re: Shaving piston top instead of raising exhaust port |
This "hack" is described in A. Graham Bell's book Two Stroke Performance Tuning. http://3cyl.com/mraxl/manuals/bell/performance-tuning-graham-bell.pdf#page=31 |
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| Author: | H2RTuner [ Sat Feb 15, 2014 3:30 pm ] |
| Post subject: | Re: Shaving piston top instead of raising exhaust port |
Yes, Gordon did outline a testing only procedure, but, that shouldn't be brought over to full time use, it is only a basic, less than what should be done development trick only. Nobody is forcing anyone else to do it any way other than they wish to do it. Do go HEAD ON with it, and, when the engine locks up suddenly, and, you are spit off the bike over the handlebars, you will then know the exact meaning of "HEAD ON". |
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| Author: | Ja-Moo [ Sat Feb 15, 2014 4:48 pm ] |
| Post subject: | Re: Shaving piston top instead of raising exhaust port |
Actually no one is going to do it, Bill just wanted to know if anyone had heard of it..... 
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| Author: | Agent H2 [ Sun Feb 16, 2014 6:12 pm ] |
| Post subject: | Re: Shaving piston top instead of raising exhaust port |
Gumby speak true. |
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