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New monster racing cam with smooth ramps

Classic Norton Commando Motorcycles.

New monster racing cam with smooth ramps

Postby jseng1 » Tue Sep 05, 2017 6:24 pm

Its been 2 years in the making. Finally there is an all out racing cam with smooth opening/closing ramps to prevent valve bounce and loss of power. It started out as the Sifton 460 profile - specially designed for lightweight radiused lifters to further reduce stress and valve bounce (AKA Norris D+ cam for flat lifters). Labled "JS3 smooth ramp". This cam allows racers to bump up their cam duration and lift and reach higher RPM levels. It has more lift and duration than the PW3 (JS2) and most other racing cams (except for the Sifton 480 which is an extreme drag race cam).

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The image below shows the longer, more gradual ramp of the new JS3. The amount of jerk and stress on the valve train is greatly reduced. The opening and closing ramps of earlier Norton race cams are too harsh and can cause the valve to bounce 2 or 3 times off the seat at high RPM. Too much valve bounce will result in intake fuel charge gasses escaping out the exhaust valve - or worse yet - valve clash and destruction. The new smooth ramp changes all that and makes things better all around. Plasma Nitride surface treatment for greater reliability. Available on special request.

Image

Below is the same ramp comparison but re-aligning the beginning of the ramps so they both start at the same beginning point.
Image
Last edited by jseng1 on Tue Sep 05, 2017 9:09 pm, edited 2 times in total.
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Re: New monster racing cam with smooth ramps

Postby Brooking 850 » Tue Sep 05, 2017 8:31 pm

Does this cam need the Vv's reangled to avoid clash?
How would it suit an 880 cc motor with 10:1 CR and FA head with 1.5mm bigger intake Vv's?
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Re: New monster racing cam with smooth ramps

Postby jseng1 » Wed Sep 06, 2017 8:28 am

Brooking 850 wrote:Does this cam need the Vv's reangled to avoid clash?
How would it suit an 880 cc motor with 10:1 CR and FA head with 1.5mm bigger intake Vv's?
Regards Mike


Stock size valves would not need to be reangled with this cam. It would raise the power band in your 880 and give you more peak power provided your exhaust is free breathing, but anytime you increase the valve size with a Norton race cam without reangling them you take a risk with valve clash. Its best to reangle valves when going to a bigger diameter. Your larger valves must be getting very close to each other now unless they've been recessed into the head and recessing works against efficient flow.
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Re: New monster racing cam with smooth ramps

Postby acotrel » Wed Sep 06, 2017 7:12 pm

'This cam allows racers to bump up their cam duration and lift and reach higher RPM levels. It has more lift and duration than the PW3 (JS2) and most other racing cams (except for the Sifton 480 which is an extreme drag race cam). '

Do you actually have a problem getting your motor to spin up to over 7000 RPM ? Mine goes there and looks like going through the roof if I don't stop it. I use what I believe is a standard 850 cam (it might have slightly higher lift) advanced 12 degrees ahead of standard, with a two into one exhaust which has skinny headers and a large tail pipe. It makes too much noise, but getting it rev is never a problem. I'd be really interested to know how many guys have tried advancing and retarding their standard cams in an effort to optimise them in conjunction with their exhaust system.
I remember I previously mentioned I'd done this with the 850 cam and somebody else confirmed what I had claimed. The motor pulls like a train and spins up through the roof - need an increase in overall gearing. The reason I tried this in the first place, is that anti noise and pollution laws were around even in the 70s The guy who built the commando would have made them suitable for road use even at the expense of performance. It might be like Peter Williams trick steering for the commando, they had to change it to suit the commuters.

I note your comment about heat build-up in Commando engines when using petrol, it might be very relevant to this topic. If you advance the cam, the exhaust system gets extremely hot. I think it is because the charge goes further down the pipe before it gets stuffed back into the combustion chamber.
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Re: New monster racing cam with smooth ramps

Postby acotrel » Wed Sep 06, 2017 7:22 pm

With the Triumph Tiger 100 race kit which came out in 1953, ignition and cam timings are specified as well as exhaust pipe dimensions. And if you use the specified cams and their settings and those pipes, when you try to move away from them, the bike usually goes slower. I suggest it is an optimised system. If you change anything, you are back to square one. The same probably applies to the later Manx Nortons - optimised through racing experience ?
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Re: New monster racing cam with smooth ramps

Postby jseng1 » Sat Sep 09, 2017 12:44 pm

Acotrel - you can time cams anyway you want.

The point of this cam is to reduce valve bounce (HP loss) and strain on the valve train. This cam should be capable of 9000+RPM with beehive springs and lightweight radiused lifters (if you have an ultra short stroke that will rev that high).

See the jerk graphs below. The JS3 jerk (black line) is reduced by approx 1/2 of what it is on the Sifton 460 (D+ grind). Ignore the red line -its an acceleration curve and is not shown on the Sifton 460 graph (it came out a mirror image dipping downward and was cropped out).

Image

Image

To avoid confusion I've cropped out everything but the jerk curve (black) where it is most severe and creates the most havoc. This is a continuation of the JS2 smooth ramp process I applied to the PW3 cam which is a great and popular cam but has an abrupt ramp that is hard on the valve train and tends toward valve float at high RPM.
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Re: New monster racing cam with smooth ramps

Postby acotrel » Sat Sep 09, 2017 1:09 pm

As far as I can see, the only benefit of that cam in a conventional Commando motor would be to extended the life of the valve springs and the cam followers and tappets. Increasing revs to gain horsepower is not the best way to go with a long stroke heavy crank Commando motor. And if you decrease the stroke, the nature of the power delivery is different and requires a different handling set-up and riding style. All can be accommodated, but often the riders' anxiety and stress levels increase. If you are the only rider in a race who is experiencing that, you are at a major disadvantage. How many guys race using separate pipes with megaphone exhausts these days - it is not only due to the noise laws that we don't use them.
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Re: New monster racing cam with smooth ramps

Postby lcrken » Sat Sep 09, 2017 4:26 pm

acotrel wrote:As far as I can see, the only benefit of that cam in a conventional Commando motor would be to extended the life of the valve springs and the cam followers and tappets. Increasing revs to gain horsepower is not the best way to go with a long stroke heavy crank Commando motor.


On the other hand, shortening the stroke and increasing the revs is pretty much the only way to get a normally aspirated Commando motor to make more horsepower (not counting rocket fuels), once you've already done all the usual engine race mods. And on most of the tracks I'm familiar with (but not necessarily all), more horsepower means lower lap times.

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Re: New monster racing cam with smooth ramps

Postby SteveA » Sun Sep 10, 2017 3:08 am

acotrel wrote:........And if you decrease the stroke, the nature of the power delivery is different and requires a different handling set-up and riding style.....


I can tell you that does not apply to my 80.4 750 Short Stroke, nor have I seen anyone else claim that for an 80.4 Commando. Other have simply said.....more rpm! And in general terms, it helps to achieve more hp!

Time to stop quoting your nasty 500 Triumph experience, it isn't relevant here.
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Re: New monster racing cam with smooth ramps

Postby Fast Eddie » Sun Sep 10, 2017 10:15 am

SteveA wrote:
acotrel wrote:........And if you decrease the stroke, the nature of the power delivery is different and requires a different handling set-up and riding style.....


I can tell you that does not apply to my 80.4 750 Short Stroke, nor have I seen anyone else claim that for an 80.4 Commando. Other have simply said.....more rpm! And in general terms, it helps to achieve more hp!

Time to stop quoting your nasty 500 Triumph experience, it isn't relevant here.


Al had a Triumph?

He kept that quiet...
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Re: New monster racing cam with smooth ramps

Postby acotrel » Mon Sep 11, 2017 1:31 pm

I have had a lot of 650 Triumphs and I raced my short-stroked version for about 12 years. They are inferior in too many ways. Their only advantage is the separate cams for inlet and exhaust.
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Re: New monster racing cam with smooth ramps

Postby acotrel » Mon Sep 11, 2017 1:40 pm

I don't know how anyone could dare to race a long stroke engined Commando at Daytona. If my bike was revving like that at such high speed and for such long distances, I would be shitting myself. My theory is to never go faster than the speed at which I am prepared to crash, because with old bikes it is not 'if' but 'when'. And when I race there are certain parts of race circuits where I don't stick my neck out. That crash that Doug MacRae had at Daytona should be a warning to everyone.
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Re: New monster racing cam with smooth ramps

Postby Jagbruno » Mon Sep 11, 2017 3:23 pm

Fast Eddie wrote:
SteveA wrote:
acotrel wrote:........And if you decrease the stroke, the nature of the power delivery is different and requires a different handling set-up and riding style.....


I can tell you that does not apply to my 80.4 750 Short Stroke, nor have I seen anyone else claim that for an 80.4 Commando. Other have simply said.....more rpm! And in general terms, it helps to achieve more hp!

Time to stop quoting your nasty 500 Triumph experience, it isn't relevant here.


Al had a Triumph?

He kept that quiet...


Oh, the irony... 8)
Slimline racer 850 Commando
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