New monster racing cam with smooth ramps

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).



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.



Below is the same ramp comparison but re-aligning the beginning of the ramps so they both start at the same beginning point.

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

Brooking 850 said:

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

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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.

'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.

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 ?

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).





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.

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.

acotrel said:

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.

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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.

Ken

acotrel said:

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

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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.

SteveA said:

acotrel said:

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

Click to expand...

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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Al had a Triumph?

He kept that quiet...

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.

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.

Fast Eddie said:

SteveA said:

acotrel said:

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

Click to expand...

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.

Click to expand...

Al had a Triumph?

He kept that quiet...

Click to expand...

Oh, the irony... 8)

Here's the graph comparing the new Smooth ramp JS3 to the D+ (Sifton 460).

I'm a little confused by your last comparison, Jim. You show the "D+ (Sifton 460)" curve using flat lifters, but the JS3 with BSA lifters. The Sifton 460 cams were designed for use with radiused lifters, so shouldn't the comparison show the curves for both cams with the BSA lifters?

Also, I'm confused by your reference to the Sifton 460 as a D+ cam. I thought the D+ nomenclature was for Norris cams, like the 560-D+, Megacycle's version of the Norris cam, which is a flat tappet cam. I know you've looked into different cam grinds in some detail, so you probably have more info than I do. If you could clear up my confusion, I'd appreciate it.

I'm interested because I've been using a Sifton 460 cam in my 920 race engine for a long time now, and really like it. I also used it for a while in a short stroke 750 for road racing, but didn't like it as well as the Axtell cam in the same engine. I've never had any valve float issues with either engine, but never deliberately ran the 920 above 7200 rpm, or the short stroke above 7500.

I don't know of anyone who currently grinds cams to the Sifton 460 profile, so it's good to see you offer this version of it. I have a Norris grind (N480) Megacycle cam in the ultra short stroke 750 I'm currently building for landspeed racing, but I might have gone with the Sifton 460 instead, if I had an extra one. It's always nice to have more cam options available.

Ken

What I am showing is the lift and duration of the lifter - not the cam lobe. The Norris D cam is a copy of the Sifton 460 but its designed for flat lifters - so a Norris D with flat lifters and a Sifton D with radiused BSA lifters will give the same lift and duration at the lifter and also at the valve even though the lobes look different. The Megacycle 560 D+ is a copy of the Norris D and both of them came from the original Sifton 460 but were redesigned for flat lifters.

Nowdays the competition is tougher with the refinement of the old Yamaha vertical twin. The advent of lightweight pistons and longer rods help close that gap with by reducing stress and vibration enough to give you about 1000 additional RPM. So now we are in the 8000+RPM range and the old style cam ramps just don't cut it anymore. So three things became necessary - the lightweight BSA lifters (which I have you to thank for after you showed me the Sifton 460 BSA lifter arrangement) and the Beehive springs which give about 500+ more RPM than the RD racing springs. Finally there is the new smooth ramp which boosts the valve train RPM capability even higher to approx 9000+RPM. Even if you don't rev that high you still get better valve control and reduced wear. And if you miss a gear you don't have to worry about tangling a valve and destroying your head.

There are several 500cc international screamers fitted with JS internals that can rev to 9000 and beyond. For those motors this new smooth ramp cam is absolutely necessary. There are also several Norton 750 to 1000cc twins winning races on the international classic circuit now. Not only are they using the lighterweight parts for higher RPM but some are going to the 270 degree crank and claim improved acceleration corner to corner. The 270 degree crank puts more strain on the cam chain and the new smooth ramp helps keep the chain from breaking.

The photo below shows a flat lifter cam and a radiused lifter cam. They look completely different but the lift and duration is the same because the cam on the left uses a flat lifter and the cam on the right uses a radiused lifter.

Thanks, Jim. I didn't realize that Norris copied the profile from Sifton. I've never been able to find much info on Sifton cams. FWIW, I was told at one time that the Sifton 460 profile was originally developed for Triumph engines, and later applied to a Norton cam. Can't remember who told me that.

Ken

lcrken said:

Thanks, Jim. I didn't realize that Norris copied the profile from Sifton. I've never been able to find much info on Sifton cams. FWIW, I was told at one time that the Sifton 460 profile was originally developed for Triumph engines, and later applied to a Norton cam. Can't remember who told me that.

Ken

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In my cam studies I found that many of the Norton/Triumph/BSA cams are copies/variations of each other. I'ts easier to graft a successful cam profile from one engine to another rather than design one from scratch and you know you've got something workable to begin with. I've done something similar with the JS2 (PW3) and JS3 (Sifton 460). Both the PW3 and the Sifton 460 (D+) needed better ramps and for ramp technology I turned to the high power Harley XR750 "ML" cam (developed by Mert Lawill).

After a lot of math and computer work I came up with a cam that worked. See the Harley XR750 "ML" cam profile below (corrected for use with Norton rocker arm ratio differences etc and measured at the lifter). The outrageous XR750 "ML" cam has huge ramps that are way beyond anything you find on a Brit bike – that’s one reason they can rev to 9000RPM.

jseng1 said:

The outrageous XR750 "ML" cam has huge ramps that are way beyond anything you find on a Brit bike – that’s one reason they can rev to 9000RPM

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Hello Jim,
Will this cam be good for 75o short stroke for street?

I am almost certain the XR750 engine runs roller tappets and has a significantly greater rocker ratio than that of a Commando engine. It's a whole different kettle of fish when trying to compare an XR750 to a Commando with respect to the valve train. You can take valve motion and back it into a Norton cam profile but you really need to understand the valve train dynamics of the Commando.
I am just trying to understand how you did the correcting