trenace
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posted August 13, 2004 11:09 AM
Connecting rod length for 10R?
Does anyone happen to know the connecting rod length for the 10R?
Thanks!
  
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swft
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posted August 13, 2004 07:09 PM
I guess not...
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trenace
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posted August 13, 2004 07:35 PM
I'm interested to know, because it's striking how much higher piston speed the 10R is rated to run at redline vs the 12R: 4690 fpm (!!!!!) vs 4180 fpm.
Now, the 12R has a not-good rod length / stroke ratio of 1.575. Which I think would contribute to yet-higher piston speeds not being acceptable.
But I don't know.
It would be interesting knowledge either way: is the 10R able to accept this high piston speed despite having no longer rods than the 12R does?
Or, did Kawasaki choose to go for longer rods as part of the program of getting the 10R's redline up to 13 grand despite having a stroke almost identical -- just 0.4 mm shorter -- than the 12R?
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Jammer
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posted August 13, 2004 08:05 PM
I would say - long enuf - it seems to work OK!!!!!!
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dougmeyer
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posted August 14, 2004 08:57 AM
 Edited By: dougmeyer on 14 Aug 2004 09:58
Rod length does not have any bearing on piston speed. Only stroke does.
Rod length effects rod angularity and thus piston to wall thrust loads and internal friction.
Doug
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trenace
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posted August 14, 2004 10:50 AM
Edited By: trenace on 14 Aug 2004 11:54
Actually there is an effect on momentary piston speeds, with greater peak speeds with worse ratios of rod length to stroke while same average speed: but this was not my point and seems no major point and may have little relevance to durability.
I was not saying longer rod length decreases average piston speed: of course not. That is simply a function of stroke and rpm, nothing else. But by decreasing side loads and friction longer rods may allow tolerance of higher piston speeds, if other factors also allow.
As another point, sort of a related illustration, engines with the same abysmal rod/stroke ratios as say a 12 stroked to 60 mm, can be very long-lived while running at much lower piston speeds. A bad (very low) ratio by itself is not inherently self-destructive.
But run a 12 stroked to 60 mm, with the resulting bad rod/stroke ratio, at piston speeds equal to or even a little less than a stock10R, if this has ever shown durability like a stock motor I'm unaware of it.
Spin a stroked 12 to the same piston speeds as a 10R and I predict a short life. For that matter, spin a stock 12 to the same piston speeds as a 10R and I predict a short life. Why does the 10R do better here, what can we do to improve the 12 in this aspect?
Engines designed ground-up for very high piston speeds, e.g. F1 engines, run rod/stroke ratios more like 2:1, though that's not the only reason why.
Anyway, maybe no one has the answer, as it doesn't seem to be a published figure.
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dougmeyer
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posted August 14, 2004 12:16 PM
Edited By: dougmeyer on 14 Aug 2004 13:17
Trenace,
Interesting assumptions, but not borne out in actual practice. Muzzy has been running and selling 60mm stroke ZX-12's for 4 years now. We have several 62.4 mm cranks in service and our 1427 cc (60mm stroke) Pro Stock engine routinely spins higher than a ZX-10r's redline. No piston failures which might indicate an overload, to my knowedge.
By the way, what's a "momentary" speed? If it's momentary, there is no speed, right? I think what your heading for is the lengthing of the dwell time at TDC and BDC with the longer rod effecting the piston speed because more of the time spent at TD and BD is spent at zero velocity. Would that not suggest that a longer rod (less angularity) would increase the acceleration necessary to get the requisite average velocity?
Just askin'.
Doug
Oh yeah, I think that, within reason, physical packaging ("tallness" of the engine) might be a very important factor in choosing rod length.
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trenace
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posted August 14, 2004 12:57 PM
Edited By: trenace on 29 Aug 2004 23:47
Well, there have been a number of stroker kits that have gone only a few thousand miles for their users, when used as street bikes. Have any you know of shown the tens-of-thousands of miles durability typical of street bikes, which I suppose the 10R also will though admittedly that isn't proven?
(The Gixxer also has piston speeds somewhere around here and has reasonable street durability. I don't know its rod length either.)
I'm not saying the stroker 12's can't go a season of drag racing, for most guys, before rebuilding, I know they can -- I'm saying that I personally don't believe, you may disagree, that a stroker ZX-12 will show the engine life on the street that I would expect a ZX-10R will, if run to the same piston speeds, if run to the 12's usual redline. Nor as many runs on the strip either.
On the "momentary" point, it's not the best language, though I could say as time approaches zero speed still exists, regardless of how closely one approaches zero, or for that matter at any "point" in time kinetic energy is still conserved and therefore velocity still exists: so if I discuss speed while the crank is at 90 degrees for example and refer to this as "momentary" speed, I hope the slight infelicity of that isn't a problem.
That is what I meant: average speed is the same, but speed at different points in the crank's revolution differ with differing rod lengths.
Your acceleration question made me think about it (something that is an on and off thing, more off than on  ) as I hadn't considered accelerations before nor remembered anything on it, and on thinking about it, I realize that I had it backwards in the above post. It was right that momentary piston speeds -- is there a better expression for this? -- differ with different rod lengths, but actually it's the long rod that gives (slightly) higher piston speeds at the 90 degree point. Not the short rod. However, the long rod has the longer dwell time and therefore lesser acceleration around TDC and BDC. So, those lesser accelerations place less stress on the bearings, which is the problem area. Perhaps this is the real advantage with regard to ability to tolerate rpm corresponding to high average piston speeds.
An engine being less tall is always good, I wouldn't think designers ever actually want a taller engine. Designing for long connecting rods is I think always with recognition that it's at the cost of needing a taller block, or higher placement of piston pin bosses, or both.
Anyway, Doug, if you ever, as I'm sure you will, have a good chance to measure a 10R rod I'd like to know, thanks! Though it's easy to not remember at the time or simply have other things to do. As well as definitely all further thoughts you have on this.
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swft
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posted August 25, 2004 05:40 AM
This deserves a bump...
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Y2KZX12R
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posted August 25, 2004 05:47 PM
Thanks Swft, I hadent seen this thread before.
Good thinking going on in here.
Rods are funny, and results with putting longer rods in engines is generally over rated. I think mags like HotRod have caused this over the years.
Having seen and been part of some dyno testing on just this topic a few years back, i can tell you that on some engines, longer rods dont make much if any real world difference. I admit this testing was done with automotive racing engines and not bike engines, but...
The mean piston speed is what I believe you are refering to. Its true a longer rod keeps the piston at the top and bottom longer. Its also true that the piston velocity mid stroke is higher with a longer rod. After all you cant stretch more total time into one complete cycle. So if more time is spent at the bottom and top then, well, you get the point.
This is where ring seal comes into play. Rings dont like going over certain speeds in the bore. Go over the magic number (rings all differ here) and you loose seal. Port the piston and you get some sealing back. (to a point)
Another note, optimal timing varries with different rod lengths. This is amaizing to see on a dyno. holding an engine at 6000 rpm and doing a timing curve chart for that rpm reveals that the curve on each side of optimal timing drops off faster (much) with longer rods than shorter ones.
This makes tuning a short rod engine easier. Its slightly more forgiving if its not timed and "jetted" perfect. But when the longer rod engine is optimized for fuel and timing it can quite often make more power, assuming all other things are the same.
I have also seen smallblock fords fall off on power up top with longer rods.
And also different fuels that have very different cylinder pressure rise rates respond differently to rod length. diesels for instance need Looooong rods to keep the piston up top a long time as cylinder pressure slowly (relative to racing gasoline engines) rises and builds.
Look at the rods and rod stroke ratios of the old multi chamber steam engines from the 1800's.
The other extreme is an F1 engine.
Then there is mechanical advantages as well, like doug said, less cylinder wall loading with a longer rod. The turn around time is increased. Less "felt" G force on the rod bolts from a gentler stop and start.
Less harmonics in the crank. Longer main bearing life.
But wait theres more... 
____________
Y2KZX12R
CompetitionCNC.com
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swft
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posted August 26, 2004 06:24 AM
Wow, this is getting interesting! I love 'applied physics'!
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