SlowMoe Posted March 23, 2011 Author Report Share Posted March 23, 2011 All of that is over my head, but I have a hard time grasping the blow down "area." I thought you were trying to cut the piston to match the existing exhaust port so that it opens the whole top of the port at exactly the same time. Yes, my interest initially was in finding out the effect of using a flat roof, as I had devised a way to modify the piston to cause the port to open at the same time, giing the effect of using a flat roof. Then I began to ponder what other effects this mod would have on the engine, and realized that you could also gain a good amount of mean port area to allow the combustion gasses to escape at the same time, without changing the exhaust duration. I'm just saying that to me you could probably gain a good bit of power if your engine was deficient in blowdown time/area without narrowing the powerband as much as actually cutting the roof higher Quote Link to comment Share on other sites More sharing options...
mopar1rules Posted March 24, 2011 Report Share Posted March 24, 2011 Imo, w/cutting them pistons like you described, I think you still are shortening the power stroke and increasing the port duration, as the piston crown's edge is what dictates the timing, as when it opens or closes ports off. So, if that piston crown timing edge has been altered in any way, so has the port timing and power stroke. At least I think so. Quote Link to comment Share on other sites More sharing options...
RZBansheeMan Posted March 24, 2011 Report Share Posted March 24, 2011 I get what Slow is saying.. I don't think it would increase duration the way he is wanting to "profile" the exhaust edge of the piston, My taking on it is with a flat crown edged piston and a round exhaust port roof the blow down area is starting small and gradually getting bigger.. So instead of using a flat roof and risking ring snag, He is theorizing slightly "profiling" the piston edges to match the round roofed port to get the blow down to start happening all at once, trying to get get better peak numbers I'm assuming without adding duration and causing ring snag. If you will..kind of like "unshrouding" .. Is the way I see it. Mike Quote Link to comment Share on other sites More sharing options...
mopar1rules Posted March 24, 2011 Report Share Posted March 24, 2011 Mike, I think I'm following you. SlowMoe is just pretty much increasing area, w/o altering the port roof/duration. Quote Link to comment Share on other sites More sharing options...
SlowMoe Posted March 24, 2011 Author Report Share Posted March 24, 2011 (edited) Bingo!!!! More area plus a stronger pulse from the port "popping" open. Edited March 24, 2011 by SlowMoe Quote Link to comment Share on other sites More sharing options...
AKheathen Posted March 25, 2011 Report Share Posted March 25, 2011 oh, yes, i stand corrected "time/area" still tired right now, but this is one thing i'm seeing, that we generally speak in durations, in terms of degrees, but really, it is time/area. although you are not actually changing duration, you are still manipulating the time/area of the port "duration"....... so, what i am saying, is that it may still have something like a 188, or whatever your cylinders are at, but manipulation of the time/area can change the actual output to be different than the degrees suggest. for example, that 188* can be shaped to run like 190*, or 186*.... i know you like examples, so here is a great one showing just this- the serval cylinders. everyone looks at the numbers, and grunt enthusiasts tend to jump for joy, and proclaim that they are built to be and "shine" as more of a low-mid torqer than advertized. others, are seeing it as a little on the low side to believe the claims fully. in reality, time/area has been aptly set so that it can definitely turn the revs, and pull up top, yet have the strong mid-low, as it was designed. now, don't get me wrong, i'm sure there is something to be had with the more abrupt "popping" as you put it, but you will likely see it as a result of higher compression, and the blow-down should be increased as a result. i believe that if you do not account for it in this way, you may find that it will actually be a bit more peaky than expected, but you can factor it with your transfers to broaden the power back out. and, as you mentioned, scalloping for testing the transfers' time is not an issue with you to see, without irreversibly cutting on the transfers themselves. you can also open it up and cut again, so you can test both ways, as well. Quote Link to comment Share on other sites More sharing options...
SlowMoe Posted March 25, 2011 Author Report Share Posted March 25, 2011 oh, yes, i stand corrected "time/area" still tired right now, but this is one thing i'm seeing, that we generally speak in durations, in terms of degrees, but really, it is time/area. although you are not actually changing duration, you are still manipulating the time/area of the port "duration"....... so, what i am saying, is that it may still have something like a 188, or whatever your cylinders are at, but manipulation of the time/area can change the actual output to be different than the degrees suggest. for example, that 188* can be shaped to run like 190*, or 186*.... i know you like examples, so here is a great one showing just this- the serval cylinders. everyone looks at the numbers, and grunt enthusiasts tend to jump for joy, and proclaim that they are built to be and "shine" as more of a low-mid torqer than advertized. others, are seeing it as a little on the low side to believe the claims fully. in reality, time/area has been aptly set so that it can definitely turn the revs, and pull up top, yet have the strong mid-low, as it was designed. now, don't get me wrong, i'm sure there is something to be had with the more abrupt "popping" as you put it, but you will likely see it as a result of higher compression, and the blow-down should be increased as a result. i believe that if you do not account for it in this way, you may find that it will actually be a bit more peaky than expected, but you can factor it with your transfers to broaden the power back out. and, as you mentioned, scalloping for testing the transfers' time is not an issue with you to see, without irreversibly cutting on the transfers themselves. you can also open it up and cut again, so you can test both ways, as well. Exactly! If you read back I came to this realization a few posts back. When the engine is below peak rpm the cylinder is filling and bleeding before the port closes. The lower the duration the faster it will close and seal in pressure at a low rpm. Even though this mod wouldn't change the duration per say, there willl be more area for the pressure to bleed out before the port closes, causeing a narrowing of the powerband. On the other hand above peak rpm there will be more area for the pressurized pipe to feed the cylinder so your overrev would be improved. Man I wish I had a dyno Quote Link to comment Share on other sites More sharing options...
mopar1rules Posted March 25, 2011 Report Share Posted March 25, 2011 Man I wish I had a dyno don't we all? lol Quote Link to comment Share on other sites More sharing options...
bigborebanshee Posted March 25, 2011 Report Share Posted March 25, 2011 those 2 stroke books are intersting but again they have a lot of outdated therior's in them BUT are an EXCELLENT read if you are into this stuff. are they going to teach you how to port the holy hell out of your stockers MAYBE BUT its still going to be up to you to get it all to work. Those theories and methods are outdated. They are still effective but as the methods became more understood,cheaper and faster ways were discovered to maximize the output.Aftermarket sleeves,Cylinders,Coolheads,not to mention all of the different piston configurations. Technology has made these old methods obsolete and newer methods/ theories have surpassed the output and reliability of the originals. Quote Link to comment Share on other sites More sharing options...
J-Madd Posted March 25, 2011 Report Share Posted March 25, 2011 Those theories and methods are outdated. They are still effective but as the methods became more understood,cheaper and faster ways were discovered to maximize the output.Aftermarket sleeves,Cylinders,Coolheads,not to mention all of the different piston configurations. Technology has made these old methods obsolete and newer methods/ theories have surpassed the output and reliability of the originals. Have you read the Gordon Jennings and A.G. Bell books? I respectfully disagree with your statement. Port duration, dome shape, ignition timing, pipe design, carburator design, intake design, etc and how each will affect power output is mentioned in those books. Quote Link to comment Share on other sites More sharing options...
bigborebanshee Posted March 27, 2011 Report Share Posted March 27, 2011 Have you read the Gordon Jennings and A.G. Bell books? I respectfully disagree with your statement. Port duration, dome shape, ignition timing, pipe design, carburator design, intake design, etc and how each will affect power output is mentioned in those books. I was referring more to the methods than theories.Those books are fundamental in understanding 2 stroke principals/cycle. Quote Link to comment Share on other sites More sharing options...
SlowMoe Posted April 6, 2011 Author Report Share Posted April 6, 2011 Bump for teh wisdom Quote Link to comment Share on other sites More sharing options...
misterww225 Posted July 17, 2013 Report Share Posted July 17, 2013 Hmmmmm... http://bansheehq.com/forums/index.php?showtopic=114131 Quote Link to comment Share on other sites More sharing options...
trickedcarbine Posted July 18, 2013 Report Share Posted July 18, 2013 Holy thread mining! Vito's super stock pistons....... The concept is old. It is also a cheap cop out vs. just getting a real port job. Quote Link to comment Share on other sites More sharing options...
misterww225 Posted July 18, 2013 Report Share Posted July 18, 2013 Holy thread mining! Vito's super stock pistons....... The concept is old. It is also a cheap cop out vs. just getting a real port job. Neg. Vito's super stock pistons are cut straight across to simply advance the exhaust timing. There is extra "meat" in the piston land on these. The concept discussed here is an old method to effectively make the exhaust port top flat for a wide portion of that exhaust port. "More area plus a stronger pulse from the port "popping" open." -SlowMoe Quote Link to comment Share on other sites More sharing options...
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