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

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PostPosted: Tue May 22, 2018 5:42 pm 
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My bike weighs 277 with no fuel, my stock stroke is 85 rwhp, but I have a 7mil on the bench with a lil more compression vforce 2 reeds (better than 3's) and 39 flat slides I should be over 100 so we'll see how that works 😎 yes sir I will


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PostPosted: Tue May 22, 2018 5:43 pm 
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Gus the crank guy wrote:
if someone asks about it he or she is maybe just getting to understand it, to throw that formula at someone was ridiculous, and not even tell him the angle I thought was kinda being like ha ha figure that out, but maybe I'm wrong. I'll say this jet it rich as hell you run that squish to tight you'll seize that thing bigger than shit. Out


you didn't tell an angle either ... and you didn't ask about the bore ...
as any well-informed tuner will now : squish should be paralel to the piston.
it's almost impossible to have too much squish velocity. the higher the squish velocity, the faster the mixture burns. A very welcome advantage of that is that you can retard your ignition. Anything than can de done that helps with retarding the ignition is a good thing and one should always aim to do this : the shorter the burning, the shorter time the piston is exposed to heat (you seem to have heating problem's with high MSV ... but you never wondered why ?) also if you do not retard, your highest preasure comes to soon and you run the risk of detonation. Maybe that's why you try to jet it "rich as hell" but maybe for once you should try to setup yor ignition correct...

gas comming in contact with with a solid surface tries to cling onto it : it forms a boundary layer and that layer is a good insulator against heat radiation from the combustion. the downside of high MSV is that the turbulence can also disturb this boundary layer. which would be a bad thing. But it still is a whole lot better than detonation, and high MSV is very good against detonation as the shockwave of detonation is a thousandfold higher than the MSV turbulence. When detonation occurs, it happens at the end of the combustion when preasure is high and temperature of unburnt mixture is heated up by radiation. High MSV though also flings parts of burning mixture through the whole combustion chamber all the way to the edges, igniting all mixture BEFORE detonation factors are reached.

30m/s is the minimum MSV you should aim for.

and one final argument PRO tight PARALEL squish : if there is no room for mixture, there is no mixture that can detonate.

so there you have my reason's for saying what I said, I'm very curious as to yours for what you are saying. And I definitly want to hear you reasons as to why a wide tight squish would heat up the engine !

I'm sure you have some knowledge and experience, and can built an engine, but I'm also sure you are practising "old-school 2stroke wisdom" probably still relying on Gorden Jennings book. That IS a good book, you get a good understanding of how the engine works etc, but it is outdated long time ago, and certainly don't follow his specific time-area exhaust charts.

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PostPosted: Tue May 22, 2018 6:28 pm 
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I'm not gonna argue with you or anyone else I try to get along with everyone, I believe in my Dyno not math. unless it's for clearance, I make crankshafts, cast my own cylinder's just so I don't need to rely on anyone else, I will listen to everyone and take it under advisement until my Dyno say's that doesn't work, our lil group of 4 2stroke guys do pretty well, I'm 58 years old have no business road racing just ask my daughter but it's fun, I would not ride a 4stroke but look at this as a challenge, TDR is in my class and those pesky TZ's but like my buddy says they may out brake you or out corner you but they aren't gonna out motor you and that's why I do it so with that I'm off to the next race I'll post how it went, have a great day my friend we'll just agree to disagree on this one but probably not on all the rest, I showed my buddy the Piston on that Chernobyl post and said look at that, he said uuugh how tights his squish?


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PostPosted: Tue May 22, 2018 6:40 pm 
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have fun at the track, that's what it's all about :smt023

still would like to hear your explanation though :smt002

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PostPosted: Tue May 22, 2018 7:06 pm 
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Oh for sure in the process of moving


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PostPosted: Wed May 23, 2018 10:49 pm 
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Question and Smoker will do, I think people take things the wrong way, if you don't agree with me then F off, but oh well, I will be doing another 784 build because we cast our own cylinder's, machine Billit heads, have a ton of domes to choose from and have Wiseco making special pistons so next year's bike will be R6 frame and a big 2 stroke I'll keep peeps posted


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PostPosted: Sun May 27, 2018 1:56 pm 
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Theres are so many variables and so many combinations that work better than stock but there are some to avoid.

Looking at the squish band from above is 2 circles, bore or squish band outer and band inner. Area, pi times radius squared, between the 2 gives your percentage. The piston probly has some radius and you will probably cut the band strait in the head because its easier so it wont be perfectly parallel. It will just be a few thousandths difference but you want to if a little off be wider to the inside.

The squish band is a nozzle blowing to bore center. What im reading is Gus has a band this wide and if he goes tighter than .05 " it causes problems. I hear too fast squish velocity can cause detonation so maybe that's it. Im reading Jan say run it tighter its more efficient. A racebike at high rpm's like Gus he would have to also narrow the band, bigger inner diameter, bigger nozzle, slow the velocity. If i'm even on the right track. On the street it might be a good combination at lower rpm's. On the other hand if its running good don't f with it. It would be good to put some real numbers to all this. Compression ratio port timing fuel all change thing up


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PostPosted: Mon May 28, 2018 1:31 am 
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Somewhat, if you have a wide band and it's tight you will seize that thing bigger than shit, I assume most RZ's are every so often rode pretty hard, probably not like mine unless your racing it, there's a post about a chernobyl club, I showed my buddy and he said well it was rich enough how tight was his squish? To get the effect of a tight squish squeeze 2 fingers together and take an air nozzle and pull the trigger you will blister your fingers to no end ( don't do it) the longer (wider) the band is it must be offset by more clearance, but if you have way too much clearance it will feel like the jetting is off mid range and you won't get it to clean up, I just told the guy what I use on A 68mm bore and the clearance


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PostPosted: Mon May 28, 2018 4:43 pm 
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Gus the crank guy wrote:
if you have a wide band and it's tight you will seize that thing bigger than shit


repeating yourself over and over doesn't make it more right. Still no explanation what so ever :smt015 .

I'm certainly not pretending to know everything, but when someone with the knowledge "closest to everything as possible" explains stuff, I read and learn. and I take any explanation of Jan Thiel or Frits Overmars or Wobbly over Gus the crank guy. They have worked on the best 2-stroke engines ever made (yours does not come close Gus, not even by a lightyear - mine either, but at least I'm not bragging about my stuff). if you ever reach (or even come close to) 15.2 BMEP in a 2-stroke, you have bragging rights, until then it's all talk but no walk.

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PostPosted: Mon May 28, 2018 5:01 pm 
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There's always that little piece from Neels Van Niekerk about squish. Scott Clough thinks enough of it to include it on his website. How many here use/used his software?

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PostPosted: Mon May 28, 2018 5:44 pm 
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What is your msv? Do you have a number you shoot for, what do you use to measure your BMEP


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PostPosted: Mon May 28, 2018 5:48 pm 
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Gus the crank guy wrote:
What is your msv? Do you have a number you shoot for, what do you use to measure your BMEP


If I claim here 10 times that high crankcase-comprssion is good for high power at high rpm's , does that make it true ?
I have no problem discussing this further, but for once, let's discuss what you claim, instead of only focussing on what I say - a discussion is bi-directional. I'm done explaining until you come up with a reasonable explanation for your claims.

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Last edited by JanBros on Mon May 28, 2018 6:19 pm, edited 1 time in total.

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PostPosted: Mon May 28, 2018 6:18 pm 
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I have measured crankcase pressure on a 250 and it's about 1 pound, are you gonna answer my question or not


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PostPosted: Mon May 28, 2018 6:20 pm 
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Gus the crank guy wrote:
I have measured crankcase pressure on a 250 and it's about 1 pound, are you gonna answer my question or not


what do you think ?

JanBros wrote:
I'm done explaining until you come up with a reasonable explanation for your claims.

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PostPosted: Mon May 28, 2018 6:32 pm 
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Ok what ever, in the future just simple answers work best, until then I don't give a damn what you think your entitled too, I'd prefer you just said thank you have a nice day. But I'll leave you with this, I forget the year but we were racing for a world title in watercraft and even you know water requires a lot of hp well the factory seadoo and Polaris were there and ole Maurice head of seadoo is beside himself, how is this local guy beating the factory? Because they don't know everything, but it was cool to see Kel Caruthers ask my buddy how are you getting that done, after a discussion he said ok, next race he gave the thumbs up, guess it worked... Now you go figure all that out and you don't need a dumb answer as I'll never look at this post again, see you at the races or do you not race anything


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