Balance pipe and Dyno Hill

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If your changes to the exhaust system improve the torque characteristic of the motor, you probably won't notice an improvement in performance until you raise the overall gearing. It is very deceptive. One thing I found, is that the slightest back pressure takes the top end off the motor. If you change the valve timing to make the exhaust work harder, noise becomes a problem. The earlier the exhaust valve opens, the harder the exhaust system works. The earlier the inlet valve opens, the bigger gulp of fuel mixture you get. With my 2 into 1, I have advanced the 850 cam by 12 degrees. The tail pipe has twice the cross-sectional area of one of the two header pipes. The motor pulls extremely hard from zero, right up and through the top of the usable rev range. But every time I have raised the overall gearing, the bike has accelerated faster.
With the test runs up the dyno hill - if you improve the torque, the bike probably won't show much difference in performance unless you short-shift during the runs. If you don't have a close box, the ratios might be too wide to get an appreciable difference. The heavy crank always tries to spin up at the same rate. When you improve the torque, you increase the resistance of the crank against slowing down as you change up. You feel the improvement when you race-change up through the gears - you get there quicker.
 
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Bernhard said:
Doctor Gorden Blair of Queens University did some development work for Dunstall way back in the 1960s to find out what advantage the balanced pipe had, I believe his conclusion was 4-5 bhp gain on mid - range. Although I never noticed any difference, I also rode 2 Jap twins I had, one with balance pipe, one without, no noticeable difference. He also developed the 2-1-2 Dunstall exhaust.
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https://www.ebay.com/itm/Norton-Dun...797957?hash=item56d68db285:g:M8sAAOSwupVduHvz
 
MexicoMike said:
The info re increased power/reduced noise was published independently in several publications, including the Dunstall performance book, two years before Norton began installing the balanced exhaust. When Norton did so, they copied the design that was in the Dunstall book as far as placement of the crossover.

A quote from 1971 re the Norton engine: "By far the best system for fast roadwork is separate exhausts joined by a balance pipe up close to the cylinders." They go on to point out that a racing-type megaphone system can produce more 2-3 more HP on the dyno at 7000 RPM compared to the crossover system but the crossover system produced nearly 6 HP more than the racing system at 5500 RPM.

I'm not disagreeing with any statement here where folks observed different results; If they did, they did. I am saying that the crossover system was not some "invention" by the factory for marketing purposes. There was independent testing/use several years prior that induced the factory into incorporating it into the 850.

I can say from personal experience with a lot of competition car engine building and a LOT of dyno testing on all manner of changes, properly designed crossover pipes DO increase power and reduce noise. Nowadays they are usually use X pipes rather than the H pipes since the X provides a power boost over the H.
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I have the Dunstall book. The Dunstall crossover exhaust in my book is not like the stock Norton system.

The only way I got an increase on my dyno with the stock crossover was with restricted mufflers.
 
acotrel said:
If your changes to the ex
With the test runs up the dyno hill - if you improve the torque, the bike probably won't show much difference in performance unless you short-shift during the runs. If you don't have a close box, the ratios might be too wide to get an appreciable difference. The heavy crank always tries to spin up at the same rate. When you improve the torque, you increase the resistance of the crank against slowing down as you change up. You feel the improvement when you race-change up through the gears - you get there quicker.
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The runs are done in top Gear or sometimes 3rd to try a higher rpm range.
There's no shifting done, I hit the hill at speed(100kmHr)

Glen
 
comnoz said:
I have the Dunstall book. The Dunstall crossover exhaust in my book is not like the stock Norton system.
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I used to have headers which were big bore down to below the cross over and small bore from then on. Is that what the Dunstall book shows? They were paired with an original set of Decibels when i bought the bike.
 
I blame J.C. Whitney for the exhaust system claims...

“higher top speed”
“Lower E.T.”
“Cooler running”
“Better MPG”
“Deep, mellow sound”
“Lighter than stock”
“Lustrous chrome plated for that show car look”
 
I had a Dunstall 2-1-2 pipe set with the Gatling gun mufflers, and as I recall it was 1-5/8 throughout. Can't swear by that though. I do know that the muffler end certainly was 1-5/8 and I had to use reducers to mount them to Norton pipes.
 
I
comnoz said:
I have the Dunstall book. The Dunstall crossover exhaust in my book is not like the stock Norton system.

The only way I got an increase on my dyno with the stock crossover was with restricted mufflers.
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Interesting, the pic shown in my edition of the Dunstall book, page 22, figure 51 (and the written description associated with it) matches the OEM exhaust on the 850 as far as location/design. Wonder if there were different editions of the book?
 
ntst8 said:
I used to have headers which were big bore down to below the cross over and small bore from then on. Is that what the Dunstall book shows? They were paired with an original set of Decibels when i bought the bike.
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That is what is in my Dunstall book. And it really works for a wide powerband.

But for peak power I have never found anything that rivals individual pipes and real megaphones.
 
Thanks, they certainly went well. It’s a pity I threw them out years ago thinking they were someone’s bodge repair job.
 
comnoz said:
That is what is in my Dunstall book. And it really works for a wide powerband.

But for peak power I have never found anything that rivals individual pipes and real megaphones.
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I looked more closely at the pic in the book and the header pipe DOES narrow in diameter below the crossover pipe. I had not noticed that in the photo. SO, there were not different versions of the Dunstall book, contrary to what I had thought was a possibility.

Further, re the quote I posted earlier in this thread (#40), I did not continue reading the info in the book beyond the portion I quoted where it gives specifics. It goes on to say, "The pipe diameter should reduce in diameter from 1 5/8 inch to 1 3/8 inch immediately after the balance pipe. Correct overall pipe length is 30 inch. Any variation in length is unlikely to result in a performance gain - in fact, the reverse is true"

So the Norton implementation of the balanced pipe system looks the same at a quick glance, but, in practice it seems to have been an "economy version" of the system in the book, without the reduction in diameter of the header pipes.
 
Bernhard said:
Doctor Gorden Blair of Queens University did some development work for Dunstall way back in the 1960s to find out what advantage the balanced pipe had, I believe his conclusion was 4-5 bhp gain on mid - range. Although I never noticed any difference, I also rode 2 Jap twins I had, one with balance pipe, one without, no noticeable difference. He also developed the 2-1-2 Dunstall exhaust.
Click to expand...

Torque is twisting power and is usually measured in foot-pounds not horsepower. It is possible to have horsepower with no guts. Two-strokes are often like that - if you turn into a head-wind they die. With a Commando motor, it is about using the massive torque to better advantage because of the limit on the revs. However I think that if the overall gearing is high enough, the result is the same.
 
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I never believed in the heavy Commando crank, until I raced with it using the close box and methanol fuel. I now recognise that the motor is simply a different concept to that used in modern bikes and not necessarily worse. I believe going shorter stroke and lighter crank would be a step backwards.
 
With exhaust systems, it is more about resonance than it is about getting the gas out quicker. Where that crossover is positioned is about the length of the tuned induction tract, and it probably resonates and might act similarly to an expansion chamber. The header pipes of my 2 into 1 are about the same length as the tail pipe. And the tail pipe should resonate at twice the frequency of one header pipe. So with those lengths being that way, the system is always balanced regardless of the revs.
 
acotrel said:
Torque is twisting power and is usually measured in foot-pounds not horsepower. It is possible to have horsepower with no guts.
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Horsepower is simply: torque x rotating speed (in radians/second)
...so, if you had a completely flat (horizontal) torque "curve" the horsepower will go up in proportion to rpm.
 
MexicoMike said:
I looked more closely at the pic in the book and the header pipe DOES narrow in diameter below the crossover pipe. I had not noticed that in the photo. SO, there were not different versions of the Dunstall book, contrary to what I had thought was a possibility.

Further, re the quote I posted earlier in this thread (#40), I did not continue reading the info in the book beyond the portion I quoted where it gives specifics. It goes on to say, "The pipe diameter should reduce in diameter from 1 5/8 inch to 1 3/8 inch immediately after the balance pipe. Correct overall pipe length is 30 inch. Any variation in length is unlikely to result in a performance gain - in fact, the reverse is true"

So the Norton implementation of the balanced pipe system looks the same at a quick glance, but, in practice it seems to have been an "economy version" of the system in the book, without the reduction in diameter of the header pipes.
Click to expand...

I suspect it was as much a visual thing as anything.

Kind of like the reason Brian S. told me about going to 32mm ports. "People wanted them"
 
comnoz said:
That is what is in my Dunstall book. And it really works for a wide powerband.

But for peak power I have never found anything that rivals individual pipes and real megaphones.
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I agree with that, but I would never use megaphone exhausts for racing. Even on large race circuits, there are usually a couple of tight corners. If your motor drops off the mega in the middle of a corner and you are forced to slip the clutch, you can lose a race as you try to get the bike back under control. With a 2 into 1, you lose a bit off the top, but the gains elsewhere are worth the sacrifice.
 
With Triumphs, the crossover arrived at the same time as the skinny racing type pipes, on their road bikes. The skinny pipes alone would have been an improvement. The E3134 cams arrived with the 1953 Tiger 100 race kit. All the road bikes had fat pipes up until about 1959. My Triton 500 had the skinny pipes with megaphones when I bought it. It was unrideable until I fitted a 2 into 1 system. My friend still has my skinny race kit pipes on his 650 Triton, but with reverse cone megaphones. And being a bigger motor, still has good torque.
It is difficult to fit a 2 into 1 exhaust onto a bike which has a featherbed frame.
 
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