The Sifton 480 - Monster of all Norton cams

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JS
your modified rocker arm with the valve tip extended by 2 or 3 mm will necessitate a re positioning of the valve if a satisfactory contact is to be maintained. How are you proposing to overcome this little problem. You can only swing the valve out so far and still stay within the confines of the bore, or have you already ascertained that there is sufficient room ?
 
Snotzo said:
My comments on this topic are confined to theoretical calculations only. The practicality may well be something different entirely.
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Ron, I always enjoy your theoretical calculations here. You clearly have some serious history in internal combustion engine analysis. I've gained valuable insights from your posts here, as well as from private communications. Please keep it up. I base my choice of components and modification details as much as I can on what I think is good theory, but in the end, I have to just go try it and see what happens. One of the pleasures of this forum is the number of folks on it who provide a serious depth of both theory and experience, and are willing to share it with all of us. I'll stop now before I get all mushy. Must be the influence of that last glass of Jeffe Blonde.

Ken
 
When you fit these radical cams to a motor, do you try moving the timing forwards and backwards to find the optimum position to suit the exhaust system ? - Can it be done on a dyno or do you need to try the bike in the place where it is intended to be used ?
 
Christian - The tight lobe centers I mentioned were determined by the Norton guru of my racing days - C.R. Axtell. He offered the same cam lobes with various lobe centers. 104 deg LC was popular but tighter lobe centers were harder to install because of valve clash problems and required valves to be sunk into the head. The 103 and 102 lobe center cams were hotter and put out more HP. The Harley XR750 has 96 intake and 108 deg exhaust lobe centers (102 for each if straight up) and kicks ass on everything.

I don't use opening and closing event specs because of the longer ramps I use. I look at how the opening and closing sides and the two lobes relate to each other at larger openings. The lift of each lobe at TDC tells the same story as opening and closing events and tells it with more relevant accuracy.

Snotzo - Moving the valves away from each other is an important discussion and more needs to be said. The Commando valve layout is still based on the smaller 650SS bore. With a larger bore you can move the valves, re-angle them and go to bigger diameters. It takes someone like Herb Becker to go all out and weld a solid bar into the Commando guide bores and start all over. Once he's done it, other people can follow. The short stroke engine being built will have 81mm bores so there is room to both move and re-angle the valves. Ports can be welded and moved as well.

See the vid at 30 seconds from the beginning and note the option of welding alum tubes into the guide bore. I didn't weld tubes in this vid because I started with a special Full Auto head that started with 1/4" guide bores. But I've done the welded up tubes (or you can use solid rods) in the guide bores in another head and it works just fine. It would be great if the Full Auto head came with re-angeled guides and intake valve seats with a larger OD - that way they could use stock valves for 750s or be modified for bigger valves with larger bores (John Snead I hope you're reading this).

 
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acotrel said:
When you fit these radical cams to a motor, do you try moving the timing forwards and backwards to find the optimum position to suit the exhaust system ? - Can it be done on a dyno or do you need to try the bike in the place where it is intended to be used ?
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Why would you want to try and install a radical camshaft to suit an existing exhaust ?
 
acotrel said:
When you fit these radical cams to a motor, do you try moving the timing forwards and backwards to find the optimum position to suit the exhaust system ? - Can it be done on a dyno or do you need to try the bike in the place where it is intended to be used ?
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Well, in my case, I'm after maximum top end horsepower for landspeed racing, so I essentially picked the cam with the most lift and duration I could find, and hoped I could get it to work without valve interference. The best exhaust for top end only horsepower is two separate pipes with appropriate diameter and length for the tuning effects to work at the peak of the hp curve. No point in looking at other combinations, like 2-into-1, or megaphones, or anything else. All they do is give you either better mid-range, or a broader curve at peak hp, but you have lose a little from the absolute maximum hp in return. That's useful for road racing, but not for landspeed. Anyhow, that's my interpretation of the theory, for what it's worth. I do think there might be some tradeoffs that could be made between max valve size vs camshaft profile, like larger valves and a bit milder cam so the valves don't clash, or the opposite, smaller valves and more aggressive cam profiles, but at the moment, I need to get to the track with what I have, and see how it works. And clearly, there are gains to be had with the shorter stroke and bigger bore combinations, but there's probably a limit to that too.

Regarding advancing or retarding the cam, my limited experience with trying that on a dyno is that for maximum horsepower there's not much to be gained in most cases. The cam designers seem to have already got it right. Might be different if you're looking for a torque monster for short courses, and willing to give up some top end to get it, but I don't have much experience there.

And concerning dyno vs. track, it's pretty obvious by now that the dyno can save vast amounts of time in getting to the right setup, but there's still frequently something to be gained from final tuning at the track.

Ken
 
Not an LSR builder or racer myself but a TC/John Gregory type motor with enough reliability to do the job would be my dream machine, a Hogslayer for the Salt in black and gold.

Just dug up an old interview with Pegasus Norton builder Derek Chinn, who helped TC sort a sick motor on his final UK visit in 1978 "which did indeed reveal it was the sum of all the parts rather than trick items that made the machine fly!"

Hogslayer, Yamaha OW31 and AMA Superbikes were my motorcycling fantasies during these formative years.
 
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Building a road race machine is a very narrow field of purpose when compared to a road bike. There are fewer compromises and a much more single minded approach.

But reading Ken’s words makes me realise that build a LSR is EVEN narrower and even more single minded.

There’s a lot of appeal to building something so focused !
 
Ken,
I have absolutely no experience with any of this stuff, but have a question. When setting your bike up for max hp. at w.o.t. I imagine you have a narrow RPM range you want to stay in. I also believe you are using a 4 speed gear box. How do you compensate for weather and track conditions to avoid having 3rd gear to high and 4th gear to low in order to stay in your desired RPM. I’m guessing that changing the front and rear sprockets might help, or do you try to get a close 3rd and 4th gearset in the box?
Good luck with your build and LS attempt. I would also like to say good luck with that crazy fire/bad weather you guys are having.
Pete
 
KiwiNeill said:
Just dug up an old interview with Pegasus Norton builder Derek Chinn, who helped TC sort a sick motor on his final UK visit in 1978 " which did indeed reveal it was the sum of all the parts rather than trick items that made the machine fly!"
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Words to live by!

Ken
 
Deets55 said:
Ken,
I have absolutely no experience with any of this stuff, but have a question. When setting your bike up for max hp. at w.o.t. I imagine you have a narrow RPM range you want to stay in. I also believe you are using a 4 speed gear box. How do you compensate for weather and track conditions to avoid having 3rd gear to high and 4th gear to low in order to stay in your desired RPM. I’m guessing that changing the front and rear sprockets might help, or do you try to get a close 3rd and 4th gearset in the box?
Good luck with your build and LS attempt. I would also like to say good luck with that crazy fire/bad weather you guys are having.
Pete
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Thanks for the kind thoughts, Pete. I'll take all the luck I can get:).

I use a 5-speed box with close ratio gearing. If I were using a 4-speed, I would use the close ratio 3rd and 4th gear sets. In either case, I would end up with a 10% spread between 3rd and 4th (or between 4th and 5th) gear, with a 1.1:1 3rd gear and 1.0:1 4th gear. That's close enough that staying in the power band is not a problem. Other than that, it's a matter of changing rear and/or front sprockets to get it right for the conditions. In practice, I usually gear a little tall, and hope for a tailwind.

FWIW, it's not really a super narrow power band, even with the radical cam, big carbs, and tuned exhaust. It's just that it's centered at the high rpm end of the range.

Ken
 
lcrken said:
Thanks for the kind thoughts, Pete. I'll take all the luck I can get:).

I use a 5-speed box with close ratio gearing. If I were using a 4-speed, I would use the close ratio 3rd and 4th gear sets. In either case, I would end up with a 10% spread between 3rd and 4th (or between 4th and 5th) gear, with a 1.1:1 3rd gear and 1.0:1 4th gear. That's close enough that staying in the power band is not a problem. Other than that, it's a matter of changing rear and/or front sprockets to get it right for the conditions. In practice, I usually gear a little tall, and hope for a tailwind.

FWIW, it's not really a super narrow power band, even with the radical cam, big carbs, and tuned exhaust. It's just that it's centered at the high rpm end of the range.

Ken
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Thanks Ken
 
I suggest that believing the cam designers have got it right, might be a wrong approach. What C.R.Axtell achieved probably involved both judgement and luck. When you build a bike, it is the total package which is important. Just because you use the best individual parts, it does not mean you achieve the theoretical result, unless you optimise the way you have used them. I don't accept the assumption that most standard Commandos have the best settings for their cams or the best cam profiles. When you think about fast bikes, there are several variables which all work together to make up a pattern. They need to be optimised. You might find that if you use a 2 into 1 exhaust, you can use higher gear ratios because you have more torque. It is possible to build a motor which has a very high ultimate top end power, but because the torque curve has a sharper peak, it never reaches it's full potential during a record attempt.
 
If you look at racing two-stroke development, the balance between port timings and expansion chambers has been extremely important. But the fastest two strokes are those in which more torque has been achieved. Earlier versions use to feel as though they had stopped as soon as you turned into a head-wind. They had loads of top-end power, but there was no substance to them.
 
prob not relevant here but new to me..

https://www.accessnorton.com/NortonCommando/270-degree-crankshaft.21956/#post-327951
the rediculous loads put upon the cam chain... NOT helped when people go and fit6 higher / quicker lift cams. It was selected for use with the cam fitted as standard to the motor in the 1940s NOT for use with the rediculous high / quick lift cams later employed
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https://www.accessnorton.com/NortonCommando/270-degree-crankshaft.21956/#post-327955
the fierce nature of the new cam which driven by as it was by chain, used to thrash about within the slack allowed by the chain adjustment. This too, was giving problems. Many engines seemed to be wearing their camshaft chains excessively
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84ok

The 270 degree crank/cam arrangement dramatically increases the load on the cam chain because two valves are lifting at once. But Ken's motor and the other motor I'm talking about will have 360 deg cranks and cam chain failure shouldn't be a problem. Jwis chain is a stronger option just to be safe.
 
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Fast Eddie said:
Al, just for clarities sake here...

Ken is actually doing this stuff, he’s putting his throttle hand where is mouth is out on the salt.

He’s not just blathering on about it from behind a keyboard.

Jus’ sayin...
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Don't knock keyboards. I bet mine is faster than yours !
I have a high lift space key, variable fonts and a 0 to 1 time of well under 3 seconds (all this and no oil leaks).
 
jseng1 said:
Snotzo - Moving the valves away from each other is an important discussion and more needs to be said. The Commando valve layout is still based on the smaller 650SS bore. With a larger bore you can move the valves, re-angle them and go to bigger diameters. It takes someone like Herb Becker to go all out and weld a solid bar into the Commando guide bores and start all over. Once he's done it, other people can follow. The short stroke engine being built will have 81mm bores so there is room to both move and re-angle the valves. Ports can be welded and moved as well.
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JS, there will never be an optimum position of rocker arm to valve, so allowing for this we end up with a compromise.
It is usual to try to obtain a contact path for the valve tip of the rocker arm and the end of the valve stem, such that the path, although curved, will stay as close as possible to the centre line of the valve stem, from valve closed to valve full open. That the valve angle can be moved is common knowledge, but little seems to be understood about the resultant contact path.

The problem here is that the rocker pivot shaft is fixed, and ideally it could do with also being moved, to better compliment both the changed valve angle, and any seriously high lift cams. Those wishing to investigate this should carefully measure up a head, then lay out the rocker and valve using either CAD or a drawing board, preferably larger than life to better see the contact path.
Such a modification might be applicable to your lengthened rocker arm, the longer the arm, the more favorable the arc of the contact path

Some may say why go to all this trouble, valve angles have been changed before and nothing bad has resulted.
Fair enough, but how close has the result been to a disaster as a result of the rocker tip contacting the edge of the valve stem at full lift?

When serious changes have been made for competition at the highest level, it is part of the nature of the top competitor to be always striving for that last ounce of performance, and if a sweeter valve action can be obtained, the whole valve train, indeed the whole engine benefits.
Hopefully so also does the rider.

Posted in the hope of encouraging further discussion.
 
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