RZ/RD 350 & Misc. 2-Stroke Tech BBS

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PostPosted: Sat May 19, 2018 7:29 pm 
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Gus the crank guy wrote:
how wide is the band?


squish area should be about 50% of bore area

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PostPosted: Sat May 19, 2018 7:46 pm 
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That's a bit much, you would need a ton of clearance


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PostPosted: Sun May 20, 2018 5:12 am 
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You can bathtub stuff out quite a bit if needs be. Tall and bowl like is pretty old fashioned.

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PostPosted: Sun May 20, 2018 5:42 am 
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Gus the crank guy wrote:
That's a bit much, you would need a ton of clearance


no it's not. it's 50% of the area, not 50% of the bore diameter. if you have a bore of 70, the width of the squish area is about 10mm.

and why would squish area have an effect of the clearance ? it only has an effect on the volume of the actual combustionchamber.-bowl which accordingly must be changed. Or not because better squish allows higher compression-ratios.

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PostPosted: Sun May 20, 2018 11:16 am 
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Math (and comprehension) are hard. :smt004

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PostPosted: Sun May 20, 2018 11:21 am 
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That makes no sense, if 50% of the area is 10mm how would you get 100% at 20mm, 100% is all of it. 50% of a 70mm bore is 35 divided by 2 which is 17.5mm. the wider the band width the more clearance it needs.


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PostPosted: Sun May 20, 2018 11:34 am 
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I understand what your saying on volume or area, the way to do squish is a percentage of the bore not the area, you would also need to remove the area of the Piston from the area of the head, I'm not a politician to try and do a smoke and mirrors on things, I would not say 50% it just confuses people give them a number they can relate too not percentages


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PostPosted: Sun May 20, 2018 6:30 pm 
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Gus the crank guy wrote:
That makes no sense, if 50% of the area is 10mm how would you get 100% at 20mm, 100% is all of it. 50% of a 70mm bore is 35 divided by 2 which is 17.5mm. the wider the band width the more clearance it needs.


eeuhm ... a circle with a 10mm radius has a surface of Pi*R^2, or Pi*100. a circle with a radius of 20mm has a surface of Pi*400 -> double the bore but 4 times bigger, because in a circle-surface, the radius is squared !

Gus the crank guy wrote:
I understand what your saying on volume or area, the way to do squish is a percentage of the bore not the area, you would also need to remove the area of the Piston from the area of the head, I'm not a politician to try and do a smoke and mirrors on things, I would not say 50% it just confuses people give them a number they can relate too not percentages


percentage of bore or percentage of area is just a way of name-calling, it gives different numbers, but the result should be the same.
If I (and everyone else I know of, that talks about squish-area's on fora worldwide I read) talk about area, we do not talk about the actual surface of the combustion-chamber or the piston if it is domed, we talk about the area of the bore-surface, so the area of a flat circle. Why should you talk about percentages and not about numbers ? because percentages are universal, numbers are not. so a 50% squish area is a value that is true for anyone that wants good performance from any 2-stroke, from a 50cc to a 500cc cylindre : it is true for all of them. If you talk about a number, it is only true if you know what bore it is for.

free for all that want to use it, an excell I made : http://users.telenet.be/jannemie/JanBro ... c%20B.xlsm
squish velocity gives exact same result as Prof Blair in his books. password protected to avoid messing it up. password is x (just the letter x) in case you would want to change/add something. the password is also embedded in the macro of the "autograph" button, as that needs the password temporarily removed. so if you want to change it, you also have to change it in there.

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PostPosted: Sun May 20, 2018 6:44 pm 
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That's exactly what I'm saying, I understand exactly what your saying, but to people that have normal lives and don't want to excel in calculious it makes no sense, tell them for hi rpm road racing 9-10mm width with .050 clearance, and cut the squish at 13* with a Banshee piston or 9* for a blaster piston works pretty good, if your more into torque power a little wider but the wider it gets the more clearance you'll need and everyone understands it, formula bores people especially if it's not a total race motor and that how you make a living.


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PostPosted: Sun May 20, 2018 7:03 pm 
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Gus the crank guy wrote:
That's exactly what I'm saying, I understand exactly what your saying, but to people that have normal lives and don't want to excel in calculious it makes no sense, tell them for hi rpm road racing 9-10mm width with .050 clearance, and cut the squish at 13* with a Banshee piston or 9* for a blaster piston works pretty good, if your more into torque power a little wider but the wider it gets the more clearance you'll need and everyone understands it, formula bores people especially if it's not a total race motor and that how you make a living.


you talk about numbers, nowhere in this topic, the bore is mentionned. Is it standard ? does he have Athena 68mm cylinders ? I don't know but my number is correct. You don't know but still you give a number which may or may not be correct.
setting up squish requires calculating, so just a tiny bit more calculating won't hurt anybody. and now with my excell, there is no excuse at all :smt002

and why should clearance increase if the width of the squish increases ? that makes no sense at all. it's not that the crank/rod will stretch more simply because the width of the squish is bigger. in an ideal 2-stroke, there is absolutly no volume between piston and head under the squish-area because the piston would come infinitly close to the head without touching it at TDC/max RPM.

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Last edited by JanBros on Mon May 21, 2018 4:48 am, edited 1 time in total.

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PostPosted: Sun May 20, 2018 8:19 pm 
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Good enough isn't for some people. Me for one.

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PostPosted: Sun May 20, 2018 10:12 pm 
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Squish velocity increases the longer it travels, if you go from a band that's 10mm wide to one that's 14mm wide the temp rises alot, you have to increase the clearance to keep velocity under control


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PostPosted: Sun May 20, 2018 10:14 pm 
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Most Athena cylinders are 68mm


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PostPosted: Sun May 20, 2018 10:37 pm 
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I just read that you said why would squish clearance need to be raised the wider the band? Are you serious? Maybe that's why I don't use that math you provided, I have a Dyno and I have 50 sets of domes I know why the seize for no apparent reason and I know what works and what doesn't


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PostPosted: Mon May 21, 2018 4:44 am 
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Gus the crank guy wrote:
Squish velocity increases the longer it travels, if you go from a band that's 10mm wide to one that's 14mm wide the temp rises alot, you have to increase the clearance to keep velocity under control


no, you retard your ignition. higher velocity = higher burning speed.

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