Dr. Blair on Dyno Hill- Place your bets!

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worntorn said:
At the moment the Dunstall system is securely on there and sounds great, right from idle up.
That part I like.
There is a significant weight reduction over stock as the tubing & silencers are thin wall. This is also a plus.
If a weld breaks or the thinwall pipe cracks then I'll be putting it under a bench.
I wish it gave equal performance to the standard Commando non balance exhaust.
I did not buy into the 1.14 second reduction in 1/4 mile et as this would put a Commando in the same league as a modern 100 HP bike such as the 1200cc Thruxton R.
An exhaust pipe ain't gonna do that!
It will be interesting to see how it performs on the 920.

Glen
Click to expand...
Oh they are thin wall alright!!
Didn't last two winters!
 
Bernhard said:
Re Dunstall cam. I strongly suggest when you build the motor to put a timing disc on a check the cam timings- Dunstall's have a habit of being out on this.
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If you change the amount of restriction in the exhaust system, where the exhaust valve opens might have an effect. With moderate cams, the exhaust usually opens at about 70 degrees before BDC. My 2 into 1 is less restrictive than some, but my exhaust valve opens at about 92 degrees before BDC. My inlet valve opens at 65 degrees before TDC. The noise is horrendous, but the motor pulls like a train.
You might get better results if you advance the cam, but you need to watch the heat factor. I use methanol fuel, so things tend to run a bit cooler My cam is advanced 12 degrees before standard settings.
If you do that the closing points of the valves might seem silly, but it seems to work well. I have a 2S Combat cam I have been thinking of using. I would advance that 6 degrees.
 
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acotrel said:
If you change the amount of restriction in the exhaust system, where the exhaust valve opens might have an effect. With moderate cams, the exhaust usually opens at about 70 degrees before BDC. My 2 into 1 is less restrictive than some, but my exhaust valve opens at about 92 degrees before BDC. My inlet valve opens at 65 degrees before TDC. The noise is horrendous, but the motor pulls like a train.
You might get better results if you advance the cam, but you need to watch the heat factor. I use methanol fuel, so things tend to run a bit cooler My cam is advanced 12 degrees before standard settings.
If you do that the closing points of the valves might seem silly, but it seems to work well. I have a 2S Combat cam I have been thinking of using. I would advance that 6 degrees.
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You might have your cam advanced, but IMO you are misquoting yourself because as you have quoted again and again on this website, you run your engine on menthol and NOT gas/petrol as does uhmmm....97% of the rest of our readers.
 
Bernhard said:
You might have your cam advanced, but IMO you are misquoting yourself because as you have quoted again and again on this website, you run your engine on menthol and NOT gas/petrol as does uhmmm....97% of the rest of our readers.
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Getting a motor to perform well, is as difficult or easy with methanol as it is with petrol The only difference is that when you use methanol, the jets are much bigger so you have more margin for error. With both methanol jetting lean without doing destruction gets more speed, but with petrol, it is much more difficult to get fine adjustment. Being British, you should know that. Getting petrol jetting right on a race bike is as insane as playing cricket. Ask any two-stroke guy. Most only ever use petrol. For them, methanol is great, but so is the wear rate.
 
acotrel said:
Getting a motor to perform well, is as difficult or easy with methanol as it is with petrol The only difference is that when you use methanol, the jets are much bigger so you have more margin for error. With both methanol jetting lean without doing destruction gets more speed, but with petrol, it is much more difficult to get fine adjustment. Being British, you should know that. Getting petrol jetting right on a race bike is as insane as playing cricket. Ask any two-stroke guy. Most only ever use petrol. For them, methanol is great, but so is the wear rate.
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For what must be the upteen time, in the Northern hemisphere we don't have a any fuel class in motorcycle road racing, so your statement is Invalid, the only sports where you can use other fuel than pump gas is speedway and on the quater mile dragstrip.
 
Bernhard said:
For what must be the upteen time, in the Northern hemisphere we don't have a any fuel class in motorcycle road racing, so your statement is Invalid, the only sports where you can use other fuel than pump gas is speedway and on the quater mile dragstrip.
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BHR allow methanol in some classes.
 
Looks like we've gone methanol. At least no one has said " There's no way a stock Norton will dyno 113 kmh on dyno hill. I'm calling BS on your numbers!"
Which is how a real dyno thread ends:)

Glen
 
gortnipper said:
113 kph is nothing. A REAL Norton would do 113 MPH ( (metric?! Nah!) on Dyno Hill. AND tighten its line.
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100 MPH is not too difficult for any large capacity four-stroke engined motorcycle, but once you reach that speed going faster takes proportionately much more power. A dyno does not take into account wind and rolling resistance. I have never had my 850 on a very large race circuit to find out what it can actually do in top speed. And I would not want to. !113 MPH plus, is to fast to get off at, unless you are a hero.
 
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I have always been of the opinion that a good 500cc Manx is capable of doing about 130 MPH on a big race circuit. A fairing adds a few MPH.
 
acotrel said:
I have always been of the opinion that a good 500cc Manx is capable of doing about 130 MPH on a big race circuit. A fairing adds a few MPH.
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If true then WOW!!
My Duc 907IE FI 2valve 900, I did 140mph (indicated) on the 101 in Nova Scotia tucked down behind the full aero & fairing...81HP
My Duc S4 Monster 916 FI unfaired 101 HP factory advert says 147mph +20HP for 7mph? I never tried over 125
Shows what a fairing will do...
 
The speed a bike can do, is only an opinion if you have never done it. When I race my 850, I am always apprehensive because it has not got a billet crank. On short race circuits, speeds are usually less than 100 MPH. That is fast enough for any get-off. I have done that and I don't like it. However fast you go, that is the speed at which you must be prepared to step off. If you do it often enough , it becomes a matter of when, not if.
 
dynodave said:
If true then WOW!!
My Duc 907IE FI 2valve 900, I did 140mph (indicated) on the 101 in Nova Scotia tucked down behind the full aero & fairing...81HP
My Duc S4 Monster 916 FI unfaired 101 HP factory advert says 147mph +20HP for 7mph? I never tried over 125
Shows what a fairing will do...
Click to expand...
The thing i like best about a fairing at those speeds is it keeps you from the feeling that your helmet is about to be ripped off your head.
 
dynodave said:
If true then WOW!!
My Duc 907IE FI 2valve 900, I did 140mph (indicated) on the 101 in Nova Scotia tucked down behind the full aero & fairing...81HP
My Duc S4 Monster 916 FI unfaired 101 HP factory advert says 147mph +20HP for 7mph? I never tried over 125
Shows what a fairing will do...
Click to expand...
Those last few mph are very costly...

especially on sleds!
 
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