SlowMoe Posted March 22, 2011 Author Report Share Posted March 22, 2011 I wouldn't chop my piston up like that. Builders have been "chopping up" their pistons for decades. You just have to be smart about it. Quote Link to comment Share on other sites More sharing options...
BigRed350x Posted March 22, 2011 Report Share Posted March 22, 2011 Builders have been "chopping up" their pistons for decades. You just have to be smart about it. I am clearly not qualified for that sort of modification then. Quote Link to comment Share on other sites More sharing options...
okbeast Posted March 22, 2011 Report Share Posted March 22, 2011 Builders have been "chopping up" their pistons for decades. You just have to be smart about it. So was this a question thread? Or you just showing us this old-school piston chopping technique Quote Link to comment Share on other sites More sharing options...
AKheathen Posted March 22, 2011 Report Share Posted March 22, 2011 well, i feel the piston scallop, or similar, is sort of a "boost bottle" topic for me. yes, it is a way of getting a duration, or manipulating a port to act other than it is cut, but the ill effects are in the squish. if you have ever seen a vortec piston, and heard one slap, you would understand just how important even squish is. now, i believe you can get your desired effect, or at least a portion of it by doing so, but advise against it. one thought i had on this topic, is to evenly cut the other side. not sure if the squish effect will counter any gains, though. scalloping methods have been all but dropped, since a better method (skilled porting) has become readily available. more knowledgeable porters are the norm now-a-days, rather than back-yard guesstimaters, so it's not often you find someone doing it professionally. also, don't be surprised if abnormal wear develops....... Quote Link to comment Share on other sites More sharing options...
88banshee Posted March 22, 2011 Report Share Posted March 22, 2011 (edited) omfg...... didn't you get banned? i know you should have....for good reason, too. the problem with you and this site.....is you..... it's not about trying to hide info conspiracy theories, etc, but the way you just jump out of an @#!*% to @#!*% on everyone and get mad that someone came within @#!*% distance. no, we do not want any @#!*% info you are willing to share, since it is most likely as distorted and @#!*% up as what you do/did on this site. if anyone took what you said as fact, and put it to work, and spread it around, the high likelihood that it is somehow incorrect could cost this site's members tens, of thousands of dollars in @#!*% -up recovery expenses. i will give an honest answer to your question...... no, i have not done it, nor will i ever square off the top of the ports, for reasons already mentioned. can you? of course you can, and it will run, just make sure there is a nice chamfer on it, and don't expect it to make more than a pass or day, whatever, and keep throwing rings at it. don't get butt-hurt when the whole rotating assembly gets transplanted to the trash. you may just find that .002% or more hidden power...... good day sir what a dick. someone should pop you in the mouth for that i would but i live two thousand miles away. and i have tried to talk to porters and they are like ya no they keep everything quite so they make the money Edited March 22, 2011 by 88banshee Quote Link to comment Share on other sites More sharing options...
SlowMoe Posted March 22, 2011 Author Report Share Posted March 22, 2011 Well obviously it won't do anything to actually benifit the squish, but in a real world situation is it actually going to cause a problem? I mean how many cc's of fuel is that cutout actually going to displace? IMO not enough to make a difference. And as far as reliability is concerned, Vito's is still putting their name on a product that is manufactured with such a cutout and subsequent altering of the squish band. IMO if there were any chance of a reliability issue they would not be selling it. Just my opinion. But think just for a minute the actual amount of blowdown area you would add by cutting your piston like this. 1-1.5 mm average acrosss the port could be an 8-10% increase in the total blowdown area of an already ported cylinder, without messing with the duration, not to mention the possibility of creating a significantly stronger exhaust pulse.... All speculation aside, I guess it would be something that would have to be tested in a real world situation, and although I am not going to recommend anyone try it, I think it would be interesting to see the results. I mean Vitos got 5 hp, that's pretty significant.... Quote Link to comment Share on other sites More sharing options...
J-Madd Posted March 22, 2011 Report Share Posted March 22, 2011 Cutting the piston is great to experiment with different durations (and maybe port shapes?? as your trying to to). That way you don't ruin the CYLINDERS you're experimenting with. When you find the duration (or shape?) that works on the piston; you can then alter the exhaust port and use an uncut piston. I know of a stock stroke Cub that picked up 10 hp on the dyno by cutting the piston. As far as I know he is still running the cut pistons and has yet to raise the ports (as he originally planned.) Do you have a dyno to test this on? Quote Link to comment Share on other sites More sharing options...
SlowMoe Posted March 22, 2011 Author Report Share Posted March 22, 2011 Cutting the piston is great to experiment with different durations (and maybe port shapes?? as your trying to to). That way you don't ruin the CYLINDERS you're experimenting with. When you find the duration (or shape?) that works on the piston; you can then alter the exhaust port and use an uncut piston. I know of a stock stroke Cub that picked up 10 hp on the dyno by cutting the piston. As far as I know he is still running the cut pistons and has yet to raise the ports (as he originally planned.) Do you have a dyno to test this on? Ahhhh I knew someone else out there had sense. I have a dyno near my house but with the way I work plus my family it would be tough to do any testing. Not to mention I'm selling the bike BUT this is something of great interest to me. I'm going to try to make a better sketch of what I think would be the best way to do this mod. Gimme a few. Quote Link to comment Share on other sites More sharing options...
SlowMoe Posted March 22, 2011 Author Report Share Posted March 22, 2011 This is a more realistic example of how the cut would look. Quote Link to comment Share on other sites More sharing options...
SlowMoe Posted March 22, 2011 Author Report Share Posted March 22, 2011 Ok now I would like to demonstrate what effect this modification would have on the blowdown area. In this picture the area above the red line represents the total blowdown area. Now in this picture the red line represents the piston crown as it is approximately 10% through the blowdown phase. Notice the area of th port that has been uncovered by the stock piston vs that of the modified piston. From the looks of this crude diagram you have 100% or so more blowdown area at this point. That means that you have (theoredically) double the pressure bleed inside the cylinder. Now your blowdown phase is roughly 30% complete. At this point your modified engine still has roughly 25% more blowdown area Ok now you are at the end of your blowdown phase and the transfers are just starting to crack open. Your blowdown area advantage at this point is roughly 10%. So realistically you have between roughly 100% and 10% more blowdown are more with the modified piston s the stock piston, which could be expressed as a mean (average) number which I forgot how to determine, but let's say conservatively that we have a mean gain in blowdown area of 20%. That, in my opinion would be very significant indeed when coupled with the possible effects of the amplified return pulse...Again, this is only my theory. Quote Link to comment Share on other sites More sharing options...
AKheathen Posted March 23, 2011 Report Share Posted March 23, 2011 what a dick. someone should pop you in the mouth for that i would but i live two thousand miles away. and i have tried to talk to porters and they are like ya no they keep everything quite so they make the money bring it on internet tough guy..... in real life, if you ever did show, you would probably piss your pants about the time i say "my turn" you are a newb, and it shows..... to save the long rant, stay tuned to my bhq tour thread, and hit me up when i'm coming through, and we will see if you have half a nutsack. oh, and standing up for a guy who was supposedly banned, long before you signed up, and you no nothing about....that's pretty ruhtardid Ok now I would like to demonstrate what effect this modification would have on the blowdown area. In this picture the area above the red line represents the total blowdown area. Now in this picture the red line represents the piston crown as it is approximately 10% through the blowdown phase. Notice the area of th port that has been uncovered by the stock piston vs that of the modified piston. From the looks of this crude diagram you have 100% or so more blowdown area at this point. That means that you have (theoredically) double the pressure bleed inside the cylinder. Now your blowdown phase is roughly 30% complete. At this point your modified engine still has roughly 25% more blowdown area Ok now you are at the end of your blowdown phase and the transfers are just starting to crack open. Your blowdown area advantage at this point is roughly 10%. So realistically you have between roughly 100% and 10% more blowdown are more with the modified piston s the stock piston, which could be expressed as a mean (average) number which I forgot how to determine, but let's say conservatively that we have a mean gain in blowdown area of 20%. That, in my opinion would be very significant indeed when coupled with the possible effects of the amplified return pulse...Again, this is only my theory. took me a second to visualize what the pics were, lol....anyways, yes, you are increasing blow-down time, but that is because you are increasing exhaust duration the same. i can see what you are saying at the beginning of the blow-down, but remember on the flip-side, that it terminates with more blockage, due to the crown shape. i have analyzed both subjects for some time in the past. on the flat roof subject, i considered working in a gradually steepening chamfer, that will act like a more rounded roof on the rings, but the over-all shape/effect of the port can hold a flatter opening. only downside would be that the port could become "dangerous" for ring snag as the cylinder/chamfer wears, and i am unsure as to what the wear pattern might hold, so monitoring would definitely be in order. about the scalloping- if you use a higher quality piston, it is already cast/forged/milled to close strength tolerances, so both scalloping the crown, and boost porting a 3rd window are both risky, because the piston was not designed to have that, and material is usually not present where it is not needed, so you are weakening it. older and cheaper pistons may have more material to work with, to keep down on flawed qc and final product failures. now, the vitos power piston specifically, it's not really what i would call a high quality, but that aside, they did design the piston to account for the scallop, so the question is eliminated in that area, and same goes for the boost ported wsm piston. the 5hp comes simply because the scallop is a simulated exhaust porting change to the stock cylinder. you take the same amount out of the roof of a stock cylinder, and you have the same port timing effect, and probably a slight amount of power and tune over the scalloped piston. i'm not trying to kill-joy, just pointing some things out. Quote Link to comment Share on other sites More sharing options...
armyvet Posted March 23, 2011 Report Share Posted March 23, 2011 (edited) bring it on internet tough guy..... in real life, if you ever did show, you would probably piss your pants about the time i say "my turn" you are a newb, and it shows..... to save the long rant, stay tuned to my bhq tour thread, and hit me up when i'm coming through, and we will see if you have half a nutsack. oh, and standing up for a guy who was supposedly banned, long before you signed up, and you no nothing about....that's pretty ruhtardid took me a second to visualize what the pics were, lol....anyways, yes, you are increasing blow-down time, but that is because you are increasing exhaust duration the same. i can see what you are saying at the beginning of the blow-down, but remember on the flip-side, that it terminates with more blockage, due to the crown shape. i have analyzed both subjects for some time in the past. on the flat roof subject, i considered working in a gradually steepening chamfer, that will act like a more rounded roof on the rings, but the over-all shape/effect of the port can hold a flatter opening. only downside would be that the port could become "dangerous" for ring snag as the cylinder/chamfer wears, and i am unsure as to what the wear pattern might hold, so monitoring would definitely be in order. about the scalloping- if you use a higher quality piston, it is already cast/forged/milled to close strength tolerances, so both scalloping the crown, and boost porting a 3rd window are both risky, because the piston was not designed to have that, and material is usually not present where it is not needed, so you are weakening it. older and cheaper pistons may have more material to work with, to keep down on flawed qc and final product failures. now, the vitos power piston specifically, it's not really what i would call a high quality, but that aside, they did design the piston to account for the scallop, so the question is eliminated in that area, and same goes for the boost ported wsm piston. the 5hp comes simply because the scallop is a simulated exhaust porting change to the stock cylinder. you take the same amount out of the roof of a stock cylinder, and you have the same port timing effect, and probably a slight amount of power and tune over the scalloped piston. i'm not trying to kill-joy, just pointing some things out. interesting thread.As far as porting goes,i wouldnt advise against it if one doesnt have a clue as to what they are doing.But since i have been doing all my stuff for the past 20yrs or so,i have no problem gettin her done.Thats the fun part of building performance.Those are the true ones the are passionate and are willing to learn what makes things run and not just by maxin out daddys credit card paying some yo yo to do it.Its not some type of black art.Some of you guys need to play nice,its ok to disagree without name callin. Edited March 23, 2011 by armyvet Quote Link to comment Share on other sites More sharing options...
SlowMoe Posted March 23, 2011 Author Report Share Posted March 23, 2011 (edited) took me a second to visualize what the pics were, lol....anyways, yes, you are increasing blow-down time, but that is because you are increasing exhaust duration the same. Actually the way I describe doing it you don't increase exhaust duration at all. You are increasing blow down area, not time. The port will still open and close at exactly the same time due to the "hump" in the middle of the cutout. It will open at the same time as before you cut the piston, but it will open much faster. i can see what you are saying at the beginning of the blow-down, but remember on the flip-side, that it terminates with more blockage, due to the crown shape. i have analyzed both subjects for some time in the past. on the flat roof subject, i considered working in a gradually steepening chamfer, that will act like a more rounded roof on the rings, but the over-all shape/effect of the port can hold a flatter opening. only downside would be that the port could become "dangerous" for ring snag as the cylinder/chamfer wears, and i am unsure as to what the wear pattern might hold, so monitoring would definitely be in order. about the scalloping- if you use a higher quality piston, it is already cast/forged/milled to close strength tolerances, so both scalloping the crown, and boost porting a 3rd window are both risky, because the piston was not designed to have that, and material is usually not present where it is not needed, so you are weakening it. older and cheaper pistons may have more material to work with, to keep down on flawed qc and final product failures. now, the vitos power piston specifically, it's not really what i would call a high quality, but that aside, they did design the piston to account for the scallop, so the question is eliminated in that area, and same goes for the boost ported wsm piston. the 5hp comes simply because the scallop is a simulated exhaust porting change to the stock cylinder. you take the same amount out of the roof of a stock cylinder, and you have the same port timing effect, and probably a slight amount of power and tune over the scalloped piston. i'm not trying to kill-joy, just pointing some things out. Although cutting the piston in the manner described will obiously cause a weakening to some extent, Idon't believe the edge of the piston is as critical of an area as others on the piston; when was the last time you heard of a piston failing at the edge? It'd like I said earlier I have cut as much as 3mm off the crown at the edge near each of the 4 transfers and ran the snot out of it like that with no issues. Not that I would ever recommend anyone else do the same. And I agree that the cut piston won't flow 100% of the gas that a port cut to the same area increse would, however I believe it would be close. At this point I believe both of our arguements are based on speculation however I do believe there is more real world eidence supporting my case. I would love for someone to actually test this. Edited March 23, 2011 by SlowMoe Quote Link to comment Share on other sites More sharing options...
SlowMoe Posted March 23, 2011 Author Report Share Posted March 23, 2011 Another possible benifit of cutting the piston as I described: Think back to the scenario where the port is barely cracked open, and there is considerably more exhaust open area, only now imagine the piston in the upstroke at an RPM greater than the exhaust port/ pipe combo peaks at there is still some positive pressure inside the expansion chamber trying to force fresh mix into the cylinder. That return pulse has a larger area to pass through and theoredically it will fill the cylinder better and create a stronger, longer overrev. It could however be argued that this may be negated by the decrease in the return pulses' duration and the fact that below peak rpm there will be more area for the early pulse to bleed back out of the cylinder, meaning less power before peak, in a way creating a similar effect as increasing exhaust duration, but without decreasing the power stroke, therefore leaving more available torque throughout the rpm range than actually raising the port. Hmm. So 1. Should cause pipe to come on later 2. Should cause peak power to rise 3. Should allow better overrev Quote Link to comment Share on other sites More sharing options...
J-Madd Posted March 23, 2011 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. Quote Link to comment Share on other sites More sharing options...
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