Dr. Blair on Dyno Hill- Place your bets!

The US told Norton that the bikes would not be allowed in unless they complied with these new low decibel regs.
80% of Nortons production had been going to the US, so they had to comply even though it killed the performance of the bike.
We followed suit in Canada, bikes had to be hushed down to nothingness.
I can remember getting checkup slips for too much noise with my ES2.
My 955 Daytona triple makes a bigger racket idling than the ES2 did full bore, but the authorities don't seem to care nowadays.

Glen

maylar said:

Curious if anyone's tested an Interstate with the low pipes (not black caps). My buddy's combat interstate can't keep up with my 850 MKII and I have no idea why.

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Yes, I tested a set of those and they were godawful.
The speedometer went backwards on the hill, deceleration instead of acceleration. It turned the 850 Norton into a 650 BSA, or worse!

Glen

maylar said:

Curious if anyone's tested an Interstate with the low pipes (not black caps). My buddy's combat interstate can't keep up with my 850 MKII and I have no idea why.

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He has a Combat, if you want to stay in front maybe don't tell him about the silencers

Glen

worntorn said:

He has a Combat, if you want to stay in front maybe don't tell him about the silencers

Glen

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Maybe it has 'very' raised gearing

trident sam said:

Maybe it has 'very' raised gearing

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No, he has a 19T compared to my 20. He should theoretically blast by me but the truth is I leave him pathetically in the dust. I'm not sure where he got the silencers from but they are the correct looking "cigar" style.

maylar said:

Curious if anyone's tested an Interstate with the low pipes (not black caps). My buddy's combat interstate can't keep up with my 850 MKII and I have no idea why.

Click to expand...

Hi here is my take on what went on back then.

I owned a new 73 Mk1 850 with low pipes ham can RH4. This would pick the front wheel up just with throttle in both 1st and 2nd gears. Top speedo 120 on the clock.Real flyer.
This was followed within 12 months by a new 74 Mk2a with airbox black caps and RH10 head. No edge to this, no throttle snap and 10mph slower. At the time not impressed but kept it for 40yrs so I must have mellowed to the Mk2a.

None of the Norton guys would explain why there was less urge.

My own take is Norton had to quieten the Mk2a down hence the headwork and blackcaps but tried to get a bit back with the airbox.
Just did not get it all back, but with 30mm inlet ports and down from 260 to 230 main jets how could they.

Moving from Mk2a to Mk 3 added a load of weight so they went back to the bigger inlet ports and parallel manifold


None of which you would advertise at the time.

Best Commando I have driven/ ridden was not an 850 but a K plate 750 that was as fast with a Watsonian sports chair on as a good 850 Mk 3 was solo.
Never did understand why, but we tried 3 differant Commandos all 850s before we put the 750 on the outfit. (Wallace and Grommitt outfit at East Fortune Norton weekend in 2000). Who ever built the engine did a good job as it just got used and did not need spannering.

The MK3 extra weight is only 30 lbs, the e start. Adding an Alton e start to an earlier stock bike results in a bike that weighs the same as a MK3, +- a couple of pounds.
That weight isn't helpful for performance, but it's not a big factor, about 2 tenths of a second on et.

Glen

worntorn said:

These are the Emgos I tried.
They are very light, straight thru and quite harsh sounding.
The bike dropped 2 kmh vs the open peashooters.

Glen

https://fortnine.ca/en/emgo-reverse-cone-megaphone-muffler-shorty-chrome-80-84030?pk_cid=14215329279&pk_campaign=pla-301293093341&pk_source=google&pk_medium=paid&pk_content=126198455992&gclid=Cj0KCQjwwNWKBhDAARIsAJ8HkhfYaQBaYOZKAi86Pj-GP9KU6suqZ5nrBeFzNUMsdwVYKxfHUzFN6kUaApjFEALw_wcB

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these would be dunstall lookalike by emgo.
still quiter than the peashooter opened up

maylar said:

Curious if anyone's tested an Interstate with the low pipes (not black caps). My buddy's combat interstate can't keep up with my 850 MKII and I have no idea why.

Click to expand...

Maybe he doesn’t know how to ride it, meaning keeping it above 4,500rpm all the time ?

worntorn said:

Yes, I tested a set of those and they were godawful.
The speedometer went backwards on the hill, deceleration instead of acceleration. It turned the 850 Norton into a 650 BSA, or worse!

Glen

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Thanks, Glen. My buddy's Combat Interstate is recently rebuilt and runs superbly. His plugs are an envious shade of brown. George is a big guy and packs about 80 lbs. over me, and we've always attributed the differences in performance to that. But if those cigar silencers suck, I'm gonna suggest that he substitute some peashooters and give it a go.

Fast Eddie said:

Maybe he doesn’t know how to ride it, meaning keeping it above 4,500rpm all the time ?

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He's been riding a combat motor for 45 years. He knows the engine's characteristics well. Maybe the lazy Boyer MKIII advance plays into it too?

worntorn said:

The MK3 extra weight is only 30 lbs, the e start. Adding an Alton e start to an earlier stock bike results in a bike that weighs the same as a MK3, +- a couple of pounds.
That weight isn't helpful for performance, but it's not a big factor, about 2 tenths of a second on et.

Glen

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The cNw e-start adds a net gain of about 11 lbs. over stock, not including replacing the bronze clutch of an 850 with aluminum backed Barnett's. It wouldn't affect et (I don't think?) but throttle response is noticeably quicker with the reduced rotational weight in the clutch/primary.

I suppose any weight gain affects et but the change with 11 lbs or 25 lbs added is so little you would never notice it for road riding.
On the other hand , the power drop with restrictive silencers is noticeable immediately.
Where did my motor go?

Glen

maylar said:

Thanks, Glen. My buddy's Combat Interstate is recently rebuilt and runs superbly. His plugs are an envious shade of brown. George is a big guy and packs about 80 lbs. over me, and we've always attributed the differences in performance to that. But if those cigar silencers suck, I'm gonna suggest that he substitute some peashooters and give it a go.

Click to expand...

There are at least 2 versions of those Interstate silencers.
Some are open and loud, other are severely restricted with baffles. I have the restricted type here.
I suspect the originals were of the open type.

The power to weight ratio for you on your bike vs George on his bike is-
You on your bike 670 lbs
670 ÷ 60 crankshaft HP = 11.16 lb per HP.
George on his bike
750lbs ÷ 65 bhp = 11.53 lb per HP.
So at the point where the Combat has its best shot, it is still trying to move more weight per HP.
This would be a split second before a shift only.
When at 5000 rpm the 850 has 53.3 bhp.
The Combat has something less than a standard 750 which has 45.7 bhp.
So let's be generous and estimate 44bhp @ 5000 rpm for the Combat

Now the numbers are-
You
670÷ 53.3 = 12.52 lb per HP
George
750÷44= 17 lb per HP.

I don't think George is ever going to keep up unless he buys a Hayabusa!

Glen

They have been tested.
The sound level is even lower than with the baffled Interstate silencers.
The power level is better than with those silencers, but not much.
It actually felt quite good rolling on the throttle at 3 k rpm but once above that performance suffers.
On the hill it managed a sad 102 kmh at top, a far cry from 113 with separate open peashooters.
That is the difference at just 4k rpm. I didn't measure it, but as the revs increase it is clear that the restrictive vs non restrictive power difference gets much greater.
This bike normally rips past 6500 rpm in 3rd.
With the Blackcaps on it managed 5800 rpm in third and then I ran out of road.
There really is very little top end power and the midrange is gutted as well.

Glen

worntorn said:

There really is very little top end power and the midrange is gutted as well.

Glen

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Plus they are futt bugly.

Just about everything is ugly next to a Pea Shooter, One of the best looking exhaust ever....

And , if of the open variety, also the best performing of this test group. That is, as long as they are stuck on the end of plain vanilla separate stock headers.

Glen

I run the AN "Norton" stamped peas. They are loud. AN has since offered what they claim are quieter peashooters.
Anybody tried them?

worntorn said:

And , if of the open variety, also the best performing of this test group. That is, as long as they are stuck on the end of plain vanilla separate stock headers.

Glen

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Glen
Viking make "big bore" (1 5/8") headers - any views as to the wisdom of this?
English bike makers have historically, in my view, suffered from an over-eagerness to enlarge the exhaust (ports (sometimes 2 per cylinder), headers, etc) but continue to have stiflingly small inlets and carbs.
Will the big pipes actually result in better performance - at usable revs?
Cheers