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Old 03-02-2011, 04:57 PM   #76
Weaverman
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Yes, it's the acceleration that increases.
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Old 03-02-2011, 05:28 PM   #77
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Originally Posted by Weaverman View Post
Yes, it's the acceleration that increases.
So does ring flutter become a factor with higher piston acceleration or does the slow start from stopped tdc help here?
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Old 03-02-2011, 06:38 PM   #78
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Yeah, but they start the same...delusional Dynojet numbers.
Except to boneheads, dynos are not about the numbers themselves. They are about comparatively analyzing runs on the same dyno.
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Old 03-02-2011, 06:51 PM   #79
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Originally Posted by supershaft View Post
Except to boneheads, dynos are not about the numbers themselves. They are about comparatively analyzing runs on the same dyno.
Lets try and keep to the theory and forget the "bonehead" remarks please.
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Old 03-02-2011, 09:04 PM   #80
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I'm still getting my head around this but the speed max does not have to increase.
An increase in speed average will do it. Increasing acceleration would achieve this.
That makes sense, but I don't know enough to know if that's the case.

Out esteemed colleague has suggested otherwise.



edit: okay, just getting caght up in this thread and noticed WM's additional information.


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Old 03-02-2011, 09:23 PM   #81
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Where do you find the Carillo/Venolia combo? Sounds interesting, and I'd sure like a higher CR for the riding I do. Plus, I don't have to burn soft coal where I live! Remember, BMW was considering many factors when they made their choices.
WM, If you've got the time, click on "Rebuilding a 92 R100GSPD" in my sig line.

Venolia 1050 pistons mated to modded '77 R100S "squish band" heads at approx 12:1 (measured pressures, not cc'd). Torque, mid range power and fuel efficiency are all up by significant margins.

Now if only I could find a way to control distorting cylinders that have been bored too thin to maintain dimensional stability...

It never ends.

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Old 03-02-2011, 09:27 PM   #82
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Lets try and keep to the theory and forget the "bonehead" remarks please.
Oops! I didn't mean that larryboy was being a bonehead. I was making fun of all kinds that just can't get past the numbers.
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Old 03-02-2011, 11:10 PM   #83
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Oops! I didn't mean that larryboy was being a bonehead. I was making fun of all kinds that just can't get past the numbers.

I got it, been a good topic to read on. The initial poster doesn't seem aware that a Dynojet factors in 20% more which should read about 39 HP at the wheel, not the inflated 'factored' dyno sheet. An 85,000 mile twin isn't putting 48 HP to the ground...since we're talking numbers.
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Old 03-03-2011, 04:09 AM   #84
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[QUOTE=Stagehand;15305970]Yeah me too, even if I dont understand a thing and just like the way the words sound

Chuckled when I read this; that's me too.
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Old 03-03-2011, 06:41 AM   #85
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Originally Posted by larryboy View Post
I got it, been a good topic to read on. The initial poster doesn't seem aware that a Dynojet factors in 20% more which should read about 39 HP at the wheel, not the inflated 'factored' dyno sheet. An 85,000 mile twin isn't putting 48 HP to the ground...since we're talking numbers.
I'm fully aware of differences between the various dyno numbers. I've not seen anything that suggests a dynojet factors in 20% over factory crank numbers..... I know that there is usually a 10% diff between a SAE number and the dynojet number.. and have seen 15% differences between a dyno dynamics unit and the dynojet number. What engine dyno did BMW use to figure out their numbers ? Maybe my drivetrain losses are less than others because I use the magical super synth lube LOL... (just kidding btw)

either way..maybe not correct to compare to the factory crank numbers..but this was a baseline..from which I hope to optimize a few parameters...and then at some point..go back on the same dynojet dyno...to see how it did...
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Old 03-03-2011, 08:34 AM   #86
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Originally Posted by larryboy View Post
I got it, been a good topic to read on. The initial poster doesn't seem aware that a Dynojet factors in 20% more which should read about 39 HP at the wheel, not the inflated 'factored' dyno sheet. An 85,000 mile twin isn't putting 48 HP to the ground...since we're talking numbers.
So are you saying that all Dynojets read high or just their inertia dynos? I have always thought that their inertia dynos read high. Where did you get the 20% number from?
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Old 03-03-2011, 09:37 AM   #87
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Anotherguy - Agree. And I doubt the engineers really ever get it WRONG. They just might not have designed it exactly the way everyone wants. Engineering is definitly one of those pursuits where you can't please all the people all the time. [b]BTW, it's really the BIG bore that's limited by flame front speed, not the small bore.[b] More of a benefit of smaller bores, and part of the reason Ferrari builds V12s.

And let's not think about the times the bean counters win the war, and management tells the engineers to use the rod or other piece already in production.
It's a small bore with a wide included valve angle that needs a big dome to get even moderate compression that benefits the most from long rods.The flame front has to travel far more than the bore radius leading to some serious advance to get peak cylinder pressure at the right time. Lots of shrouding going on in that hole.Harley,BMW,Guzzi and the like. Check the rod length on an R1,GSXR ect. Mostly pushrod stuff,why would you waste a DOHC on a narrow bore? Dual pugging is cheaper and less costly in the long run and achieves the desired result.

And a calibrated DynoJet will give good HP numbers. I've run SuperFlow SF-901,FactoryPro EC997 and Dynojet from 100 to 250i. Favorite is the EC997. The SuperFlow is an awesome tool but difficult to use for motorcycles. Harleys are the easiest to mount to the 901 but not close to easy. When all is said and done the numbers only matter at the bar. Results speak far louder than numbers. The proper use of the tool is what you seek. As I alluded to earlier it's the area under the curve that gets the job done and the only way to see that is a dyno printout no matter where it comes from.
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Old 03-03-2011, 09:40 AM   #88
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I've not seen anything that suggests a dynojet factors in 20% over factory crank numbers.....

Didn't say that, they're measuring power at the wheel and their software gives you back 20% for parasitic losses. If you're on a Dynojet you need to take away 20% from what they tell you. Look around the 'net, it's pretty common knowledge.
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Old 03-03-2011, 09:56 AM   #89
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Didn't say that, they're measuring power at the wheel and their software gives you back 20% for parasitic losses. If you're on a Dynojet you need to take away 20% from what they tell you. Look around the 'net, it's pretty common knowledge.

ok.not 20% over factory..but still..I've not seen anything that says a dynojet gives back 20%.... I'll go look around the internetz to see..but what you are saying is that dynojet numbers should in theory be close to or greater than the factory crank numbers? (assuming drivetrain loss is 20%)..(in a non-locking automatic..for sure....manual..maybe 15% losses).
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Old 03-03-2011, 10:03 AM   #90
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ok.not 20% over factory..but still..I've not seen anything that says a dynojet gives back 20%.... I'll go look around the internetz to see..but what you are saying is that dynojet numbers should in theory be close to or greater than the factory crank numbers? (assuming drivetrain loss is 20%)..(in a non-locking automatic..for sure....manual..maybe 15% losses).

Yes, they get you back to a crank reading...a little misleading, but the whole tune on the same dyno still works and is a great tool. Do you really want to go looking for power with 85,000 on the clock?
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