Big valves or small valves

Joined
Jul 25, 2015
Messages
1,184
Country flag
A step down from Carb to intake can work wonders.
I don't think the science has been explained. It's one of those things that just seems to work, although perhaps not on every engine type.
This gain with an oversized carb and step was discovered by the BSA Goldstar experimental tester Roland Pike, quite by accident. An assistant brought the wrong carb for a Goldstar, I believe it was a 350 and he fitted a 500 carb. The bike made extra power on the dyno. The mistake was discovered so they tried blending the manifold to the oversized carb ( step removed)
The extra power disappeared.
Put the step back in and the power came back.

Glen
That is interesting and there are probably more unexplaineds tobe generated by the internal combustion engine.
 

MichaelB

"Sons of Arthritus"
VIP MEMBER
Joined
Jan 14, 2004
Messages
1,703
Country flag
A step down from Carb to intake can work wonders.
I don't think the science has been explained. It's one of those things that just seems to work, although perhaps not on every engine type.
This gain with an oversized carb and step was discovered by the BSA Goldstar experimental tester Roland Pike, quite by accident. An assistant brought the wrong carb for a Goldstar, I believe it was a 350 and he fitted a 500 carb. The bike made extra power on the dyno. The mistake was discovered so they tried blending the manifold to the oversized carb ( step removed)
The extra power disappeared.
Put the step back in and the power came back.

Glen
Yes this is weird.
Dyno Dave has mentioned several times about winning a shoot out with his Combat with 32mm carbs / manifolds and stock RH1 head with 30mm (or is it 28.5) ports.
 
Joined
Jun 30, 2012
Messages
10,951
Country flag
Ceertainly worth thinking about as peak hp is not the goal for my original 50odd year old 750 engine.
Why do so many people want Nortons to be something they are not ? A 650SS is an excellent motorcycle when you use it in the way the designer intended. When I built my Seeley 850, I never really believed in it. However I do now. I have never raced with a better motor. It does everything right.
 
Joined
Dec 22, 2006
Messages
6,283
Country flag
or "Autobahnfest" , like they say in Germany.
Something a Norton will never be. Not even the new ones.
If, for sake of the argument, an 850 Commando had 100 HP from the factory out, we would still have the same discussion: " I like what I have, but would be happier if I had more.." ( power)
A different approach would be to accept what you have and try to use it more efficiently.
I believe it is a typical American way of thinking:
If in need, don't use less, but produce more..
The Americans do love power and so do Canadians, Brits, Australians and Europeans.
The Australians created the GM LS engine which added huge power to a fairly lazy American V8.
The Europeans are building and selling loads of 500-700 BHP production SUVs. Also the 200+ HP BMW 1000rr, Ducati Panigales and loads of other ultra powerful machines.
They have been doing this for a very long time.
In 1960 Enzo Ferrari stated " Aerodynamics is for those who don't know how to build engines"
The Brits love to hop things up too. There is a long history there. Vincent wasn't the first but he was one of the more successful British hotrodders.
He hotrodded his street machines to produce a model that went faster than any other production vehicle-on two wheels or four.

Canadians- for hotrodded Nortons look no further than Herb Becker, although there are plenty of other CDn hotrodders.

The problem with the Commando is that the Brits had already been busy hopping up the 1948 design engine for 2 decades when the first Commando appeared. They had almost tripled output in twenty years.
Same with the trans, although it dates back even further than the engine design. It was initially designed for 15 HP machines, then modified as power levels doubled and then doubled again to 4x original design level. . It's a wonder it stands up at all!

So the approach Ludwig has taken with weight reduction vs increased engine output makes good sense with the Commando.

Glen
 
Last edited:
Joined
Jun 30, 2012
Messages
10,951
Country flag
That is interesting and there are probably more unexplaineds tobe generated by the internal combustion engine.
What actually works can often be different from the theory. But there is always an explanation. Why do oval bodied carbs or flat slide carbs help some motors make more horsepower ?. To me that seems an insignificant difference.
I think with my bike, the cooling effect of the methanol works better with the bigger carb because the gas speeds are lower within the carb. Methanol gives more power due to it's high latent heat of vaporisation. It is a chemical supercharging effect. Of course the other thing is you can have the jetting wrong and still get good power - just not the best.
 
Joined
Jun 30, 2012
Messages
10,951
Country flag
You mean like those folk that change the chassis to something completely different ? And fit modern gearboxes ? Etc ?

Shouldn’t be allowed right ?!
The only ways motorcycle racing can be justified, is it improves the breed and provides enjoyment. Production racing is extremely boring but it sells motorcycles to people who fantasize. You have a choice - maintain your beautiful road-going commando or go the whole hog and race. The in-between stage is not good.
Nigel, I have read about your bike. If i had it, I would not keep my licence for long and in Australia, if you lose one licence, you lose them all. On public roads I drive a car and even that has a six speed close ratio gearbox. The joke is there is nowhere I can drive it in the way it was intended to be driven. When I drive it, my gear changes are 1st, 2nd, 4th and 6th.
 
Last edited:

ashman

VIP MEMBER
Joined
Jul 11, 2010
Messages
4,138
Country flag
I love my HOTROD Norton its light as, handles great in the Featherbed and the work within the motor is good enough for me, but even better now with the 1200 Thruxton S with a few mods to the exhaust and new Ikon shocks as well new tyres, I ride it hard all the time and handles pretty good, more torque than the hot Norton, the best of two worlds a hot rod old bike and a modern bike with little maintenance and can log up a lots of miles without any problems between service and both bikes get the attention where ever I go, but the Norton is showing its age but it does get more attention as its no show pony and shows its been ridden.
But the Norton has had a lot of work done to the porting, cam and crank I am still running the original valves, why replace when they are doing the job, guides have been replaced a few times when needed, still have the original seats for the valves, the Norton has always been a reliable bike for me and only miner things have let me down in the 46 years like broken chain, one coil and 2 EIs failures one while 100 miles from home and its never really leaked oil in all the time I have owned only minor seepages every so often that get fixed as soon as they start as gaskets do get old, so the old stock valves work for me.

Ashley
 

Chris

VIP MEMBER
Joined
Jan 21, 2008
Messages
1,362
Country flag
Al as Brooking says lol.
No Commandos being built!
Same reason Slippery Sam stopped winning the production TT.
 
Joined
Apr 22, 2020
Messages
1,024
Country flag
Wouldn't the 930 Amal be the right choice for Norton owners that really want that performance edge between stop lights. LOL

I like modifying things. It's not for everyone, but I think a lot of people still do it without talking a lot about it.

So, in closing I have a set of Amal 930 carburetors I would gladly trade for 33mm Keihin CRS carburetors. Any smaller is better takers out there?

Oops, was that off topic? OK valves... Yes everyone that has a 4 stroke should have a couple per cylinder of at least OEM size.
 
Last edited:
Joined
Apr 13, 2021
Messages
117
Country flag
Where were all the Commandos ?

I think I was there. I seem to recall Peter Stevens Motorcycle Shop ran a very nice Triumph T140V that year.
we had just bought one and it was good to see it going around although not really competitive
al
 
Joined
Jun 30, 2012
Messages
10,951
Country flag
When Ken (Fullauto) came to visit me, his 850 Commando was beautiful. But it had a single carb conversion. I can see sense in doing that, but if I had a road going Commando, I would keep it looking as standard as possible. 'Beauty is in the eye of the beholder'. To me, my Seeley 850 is a dog's breakfast. I hate Velocettes, but I once saw a Clubmans' which was to die for. It was nut and bolt perfect. You do not often see old bikes like that these days. That sort of attention to detail takes a certain mentality which I do not have.
In my opinion, people who own road-going Commandos are simply custodians, Commandos are like what genuine featherbed Manx Nortons are to the people who own them. And they suffer from the same problem - modification.
 
Joined
Jun 30, 2012
Messages
10,951
Country flag
When historic road racing began in Victoria in 1973, the excuse was 'to preserve the old racing bikes'. It has destroyed more good bikes than it ever preserved.
 
Top