Dr. Blair on Dyno Hill- Place your bets!

maylar

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Speaking of Dyno Hill -

I have one that I call Plug Chop Hill. Same kind of deal, an uphill stretch of highway a few miles from home. How would one determine the grade of a hill? My GPS doesn't have an altimeter.
 

gortnipper

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Speaking of Dyno Hill -

I have one that I call Plug Chop Hill. Same kind of deal, an uphill stretch of highway a few miles from home. How would one determine the grade of a hill? My GPS doesn't have an altimeter.
You could always take a roofing square and a spirit level out there and measure in a few places and average.

Make sure someone puts up a video of you doing that... ;-)
 
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Al is right about the calibration
How do we know that you are not eating a load of pork pies between each run??? :rolleyes: :D
To some extent that is happening, but it all comes out in the wash, as we say in house construction.
The Dunstall 2-1-2 had the weight advantage of no centre stand (4.5 lb) plus 3.5 pound lighter silencers.
This 7 lbs is very close to the amount of my Covid weight gain since testing the balance set a few months ago.
Calibration done :)!

Glen
 

850cmndo

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I've been running this setup, 2-1-2 with Dunstall mufflers, off and on for over 40 years never expecting to see this much attention paid to them. I can't say that I went into it with an expectation of better performance. I'm not of that sort. I'll admit up front what got me off was the "cool factor". There are damn few things that sound like a Norton wearing this getup. You have to be behind one to get it. Think of the Bullit mustang in the movie chase. They and the whole center stand fiasco are another story. One day I'll put the works back on.
 

WZ507

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Speaking of Dyno Hill -

I have one that I call Plug Chop Hill. Same kind of deal, an uphill stretch of highway a few miles from home. How would one determine the grade of a hill? My GPS doesn't have an altimeter.
Regarding your question about how to determine grade here is another option.

There is a phone app named "Ski Tracks", that is a free down load and provides reasonably nice information in plots or tabular form about altitude changes, speed profile of a run, map of where you are/were, etc. Just turn it on to “Track” and it begins recording and will keep recording until you turn it off, e.g., if you turned it on to record a morning’s worth of skiing it will track every trip you make up and down the mountain along with all the relevant details of the runs (total elevation up, total elevation down, . steepest grade, max speed, etc. After you turn it off you can go into "Analysis" and see all the particulars of the run(s). I think it will provide exactly what you want to know as you will have accurate elevation and distance change, from which grade can easily be determined.
 

maylar

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Right, dinn think of that. There's an Android altimeter app too.
 
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Same here. Will download that app and get some numbers from Dyno hill, just for fun.
I measured the grade with a 4' hand level in 3 places and all came out about the same, 12.5 degrees.
I was curious as to how it compared to our major mountain grades, which are 8% at the most.

Glen
 
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I was reading yesterday about Croxford riding against Kenny Roberts when Roberts had one of the first Goodyear wets on his bike. Ron Tommbbs had them on the Hendesron Matchless in the sixties. They were the first gum-ball tires we saw. What changed almost immediately was the angle of lean on the bikes - increased considerably. In those days it was almost impossible to lean a Manx. When the guys fitted 18 inch rime to use the better rubber, the footrests came closer to the road.
So what? You can ALWAYS raise the footrests!!!!
 
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I will try this system on the 920 when it is running. Who knows, it might work better on that engine?
The interesting thing is the reality vs advertising.
The Dunstall catalogue claim of a 1.14 seconds et reduction , or an 11.5 second et by adding this exhaust to a stock Commando, did not materialize for me.
That number is pretty wild as it equates to roughly doubling the horsepower of a standard Commando.
The other claim that was sometimes made is " 5 HP added to the midrange "
That seemed quite possible.
In reality the system made a little less midrange power than a standard non balanced Commando exhaust.
At least it is light in weight!
Because it is thin wall, it's bound to be light in weight, but the thin wall does mean that durability is much reduced.
Oh well, gotta put up with that to trim the weight.
Checked out just how much weight is saved last night.
The stock system is .080" wall whereas the Dunstalls is .060" wall. However, the Dunstall uses more pipe and larger pipe.
In fact, the Dunstall ( pipes only) is 5 oz heavier than stock Commando.

So it's a performance mod that is a bit heavier and makes a bit less power but is far less durable plus requires replacing the excellent Commando centre stand with a crap stand.
In fairness, the Dunstall silencers are probably lighter than stock Commando. I have pattern Dunstall type here and they are lighter than the open pea shooters.
I won't use them though as I have some Emgo 16" reverse megaphones that are about half the weight of the Dunstall pattern silencers.

Glen
What didn't come out in that road test was that Dunstall installed a big valve mod in the engine.
 
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What didn't come out in that road test was that Dunstall installed a big valve mod in the engine.
No, the 1.15 second claim wasn't from a road test, it was from the Dunstall 1974 Catalogue. It clearly states that this power gain is created just by replacing the stock exhaust with the Dunstall/Blair exhaust.
Note the relatively slow 1/4 mile et quoted for the stock bike.
Is this the time for a bike fitted with stuffed up overly restrictive Black caps?
If so there would be a big improvement with the Dunstalls or any freeflowing silencer type exhaust.

Glen

 
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In the article, the trap speed difference and the ET difference do not correlate! It would take at least 13-15HP additional HP to make that much of an ET difference but only around five to make the trap speed difference. Trap speed is a much more reliable indicator of engine power than ET. I suspect they diddled around a bit with the launch on the "stock" bike and did the best they could with an experienced drag racer (and smallest guy they could find) on the modded bike. ASSUMING the tests were done at the same drag strip on the same day, that's the only thing that can explain the difference,. ;)

Five HP with only an exhaust change MIGHT be possible (assuming jetting was appropriately adjusted); 13+ is absolutely not.
 
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The key point from the so called road test was thatthe system only worked with the so called dunstall decibel silencers. I did try using pea shooters eventually but then found it worse than stock. There might have been some slight mid range improvement with the full system but certainly nothing on top end. Perhaps if my system had sealed it would have worked better. in the end it went inthe dustbin.Am amazed that Glenn has one that has survived I think it came out in 72 and was prior to the 850.
 
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In the article, the trap speed difference and the ET difference do not correlate! It would take at least 13-15HP additional HP to make that much of an ET difference but only around five to make the trap speed difference. Trap speed is a much more reliable indicator of engine power than ET. I suspect they diddled around a bit with the launch on the "stock" bike and did the best they could with an experienced drag racer (and smallest guy they could find) on the modded bike. ASSUMING the tests were done at the same drag strip on the same day, that's the only thing that can explain the difference,. ;)

Five HP with only an exhaust change MIGHT be possible (assuming jetting was appropriately adjusted); 13+ is absolutely not.
Jetting AND cam timing.
 
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If we take the ad claim at face value, one could fit the Dunstall system onto the stock 750 Norton that won the Cycle Superbike Seven shootout.
You could expect to reduce its 12.69 second et by 1.15 seconds to 11.54 seconds, similar to a 100 bhp Thruxton R or equivalent.

That is quite a claim!!

Glen
 
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