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The Sifton 480 - Monster of all Norton cams

Discussion in 'Norton Commando Motorcycles (Classic)' started by jseng1, Nov 17, 2018.

  1. Madnorton

    Madnorton VIP MEMBER

    Joined:
    Jun 9, 2008
    Surely if you lengthen the rocker arm, then the valve spring rating or fitted pressure need to be adjusted to compensate. Not only is the ratio increasing the amount of spring pressure due to the additional valve lift, but also this needs to be considered working back to the lobe. What the spring pressure is on the valve side, is not what the nose of the lobe will experience, as the ratio is not 1:1.
     
  2. 84ok

    84ok

    Joined:
    Aug 10, 2014
    do norton valves rotate like in typical mainstream air cooled aviation engines?

     
  3. jseng1

    jseng1

    Joined:
    Nov 26, 2009
    Snotzo said “the longer the arm, the more favorable the arc of the contact path. “

    That’s a good point. What we’re really trying to do is get more lift out of the cam and extending the rocker tip with a special tappet as shown in the photo on page 1 is a very easy way to do it. Moving the rocker spindle has been done but its a LOT more work and you run into problems with the pushrods getting out of line and wanting to rub the pushrod tunnels. When going this far its a given that the valves will be reangled and that’s a well beaten path. Proper alignment with the valve tip can be achieved be cannibalizing a rocker tip (moving/extending the rocker tip hole for measuring purposes only) and aligning it as in the vid posted on page 2.

    Madnorton - Yes with a longer rocker arm the spring pressures and loads on the cam lobe will be increased but the increase will be nearly the same as the stock rocker setup using a higher lift cam. In other words, stresses will be about the same if the valve ends up with the same lift and duration. But you can go further with the extender rocker arm.

    So far it looks good but it hasn’t been tried. A land speed racer or all out roadracer would be good test beds. I can think of a couple people who are open to this idea and I have communicated with them. Now its up to them or anyone else who reads this.
     
  4. acotrel

    acotrel

    Joined:
    Jun 30, 2012
    I am not intending to criticise. What Ken is doing interests me. From my own experience with playing with a top end motor, I have found it is possible to create a motor which will pull forever, but never get there quickly enough. It depends on the shape of the torque curve and the gearing. The problem is with any exercise such as this, you only have limited track time. You can use a dyno, but you are still supposing until you actually riding the bike. A close ratio box can keep you in the power band, but maximum torque might occur over a very narrow range, depending on how radical the cam is. If it occurs over a 2000 RPM range within the power band . . . ? In an extreme situation such as a land speed record with a commando, you are getting into the same sorts of problems you have with two-strokes in road racing.
    I think Ken's approach of buying the best available top-end cam and developing it, is the correct one. But what I find difficult to get my head around is the precision of the torque measurement on the dyno. I suspect the shape of the torque curve might be a most important factor.
     
  5. Madnorton

    Madnorton VIP MEMBER

    Joined:
    Jun 9, 2008
    Surely in this case the actual precision of the whole torque curve measurement on the dyno is irrelevant, as also mentioned the gearing is a factor along with the revs that the engine will be using for the majority of the run, this portion of a torque curve would surely be the only area of interest. Agreed, a dyno is supposing, though useful for prediction - need to start somewhere, but test runs could be done elsewhere prior to the flats run and these runs could be useful to determine the revs, fueling and speed which would then give an area to look at in more detail and build upon.

    The lift on the 480 is it really needed, it might be a case of losing some to get the engine to rev to 9000rpm. I know of one case in the 4 wheel industry where the cam lift alone was reduced by 2mm against the owners wishes, and the car produced more revs and slightly more power. Moving valves and using larger valves great, but surely it would get to point where the cylinder walls will disrupt the flow into the cylinder.

    With the 480 modified, is the seated pressure realistic, it would suggest way to high at 150lbs, this level would need a very light spring rate to stop power being sapped on lift. I run a cam between 0.400 the sifton lift and only use 59lbs seated using standard springs and on the dyno last month it did not bounce or lose control. Over 3500 miles and the valves are not recessing either. There must be drag cars out there using cams with more lift and rev to way over 9000rpm, I know the cam profile overall is different, but I bet they do not use 150lbs seated, and they rev way higher than 10000rpm and use heavier valves. The rev range we use these days is considered insignificant these days by valve spring manufacturers.

    This will be one interesting machine when running, shows much promise, hopefully enough records are kept to record each individual change and what the result of each change produced. At 9000rpm, despite all the above I reckon the exhaust system will be the critical key to making all above work.
     
  6. Snotzo

    Snotzo

    Joined:
    Mar 12, 2013
    I do not know whether the Megacycle 480 cam is a replica of the Sifton 480, or their own profile to give the same valve lift, but I have run a dynamic simulation for a Sifton 480, using Prof. Blair's 4StHead software, and with a 42 mm steel intake valve, BSA type radius followers, and a single beehive (or conical, as you prefer) valve spring.
    At 9000 rpm all was still functioning correctly with no valve bounce or component separation. Seated spring pressure was 125 lbs.
    This software package not only computes the inertia of all the moving parts, but includes the flex of all the moving items of the valve train, and this DOES include camshaft flex.(Note JS). A Titanium valve would simply increase the safety factor, or add something to the rev limit if required.

    The exhaust side is rather different because the valve has first to overcome the high in cylinder pressure before opening, and here the pushrod will be subject to serious loading, with considerable flexing as a result. In the flexed position, the pushrod behaves similar to a spring, and eventually it will revert or spring almost back to it's starting condition, and if in so doing it should catch up with the valve, it can push the valve to lift further than designed to do, and thereby ending up in a condition known as 'float', which will also include component separation.

    This is a very short explanation of the valve train events, but it should serve to notify those interested that it is rather more than a guessing game to get all the performance ducks in line so that they behave well and in unison.

    All the above is relevant only to the Sifton 480, I have no data for the Megacycle 480, so results with that profile could well be very different.

    Re seated spring pressures, I can turn back to the last work I did with V8's, and a quick search revealed that valve lifts were 18 mm plus, and spring seated forces were 325 lbs. Drag racers are now lifting valves more than 25 mm, and tripple valve springs are used, but their saving grace is - they only have to last for an extremely short run, a matter of a few seconds, then the engine is quickly torn down and critical components replaced before the repeat run.

    One final point re acotrel and his fascination for 2 into 1 exhaust systems. Alan, this discussion is basically concerning a high power Commando engine, and quite simply single exhaust pipes are the only way to go if max.power is the goal. Forget about two strokes, they were never ever championship contenders with coupled pipes. Despite the short power bands of the early Japanese motors, they were still winners, so the torque, however little it was, must have been adequate.
     
    Dances with Shrapnel likes this.
  7. Snotzo

    Snotzo

    Joined:
    Mar 12, 2013
    Madnorton,
    leaving aside considerations of your road machine, and staying focussed on the high power development that JS is working on, the lift of the valve, in particular the intake valve, depends upon the aims of the designer. For a high performance application the target will be to maximise the intake of fresh charge, assisted by the pressure difference that exists across the valve.
    Exhaust gas residuals exit the cylinder with considerable energy, thereby creating a lowering of pressure within the cylinder across the overlap period, such that the pressure difference with atmospheric, ensures a very favorable situation for the intake process.

    To maximise on this situation, the valve duration and lift will be selected so that the opening and timing points will be acceptable for the performance target, and the lift will be such that the valve is open for a reasonable lengthy period, so that full port flow potential is available.
    To ensure this latter is available, the valve must inevitably lift more than 25% of the seat inner diameter, but the problem comes when having reached this much valve lift, the rate of lift has to be slowed down in order that the valve can then eventually start to close. Typically, valve lift designs for high performance applications will feature accelleration rates such that the maximum accelleration is reached before the valve has lifted 25% of it's total lift, following which design is focussed on slowing the rate down so that at peak lift the change to closing the valve may take place as smoothly as possible.

    Many ways have been tried to eliminate the lifts that are inevitable with such designs, but to date no one has found a way to lift the valve to the 25% position, hold it there for X degrees, then return it to it's seat, at least, not for a high performance application.

    Your comment re the importance of the exhaust system may well be very significant. It's first obvious duty is to afford the efficient removal of exhaust gas residuals, but tied in with this is the control by design of the pressure wave fluctuations to ensure that the cylinder is most efffectively scavenged, and a negative pressure condition exists during the overlap period across the engine speed range where maximum power is required, and the deeper the negative the better. This can be a very complicated subject in it's own right.

    In short, there is no precise formula that will provide all the answers to the many questions that might be raised, but rather there are a lot of different combinations that can produce the same end result, more or less.
    You pay your money and take your pick, it's that easy - and it's that difficult !

    Good luck JS with your project, I hope you'll keep us informed of progress.
     
  8. Madnorton

    Madnorton VIP MEMBER

    Joined:
    Jun 9, 2008
    It is indeed, hopefully the changes will be recorded in detail, and results recorded. You don't get something for nothing when constrained by an envelope of parameters to work with and modify within limits or physical boundaries. I think that the project will succeed, once they zone in on the targeted area of where they wish for this performance is to be utilised. I can't see any reason why it is not going to work, it will just be which combination they choose, hopefully the simplest one.
     
  9. Hillbilly Bike

    Hillbilly Bike

    Joined:
    Oct 18, 2018
    There's more to engine power than lumpy cams.. I run a 650 Triumph in land speed racing...My bike held the modified production push rod gas paved track record for 4 years and was first bike in it's class over 130 MPH...This summer a friend and competitor upped my record from 133 to 135 ...But I wasn't there so I say he had a tail wind ;);)...
    The engine is quite mild compared to my competitors..Sifton 390 cams ,Mikuni 34MM flat slides ,low for Triumph 10.5 compression and 34 inch straight pipes...No long intakes or trick exhaust......The engine never runs over 7000 rpm..It's reliable and literally the bike comes off the trailer and runs it's best...No jetting changes despite air density changes, no slipping clutches, no problems..
    The tricks are in the combustion process..Raised intake port floors, tight piston quench and a somewhat lean fuel mixture..Avoiding high RPM mean avoiding the need to buy a $2000 crankshaft to avoid the eventual Triumph crank failure when making good hp at over 7500 rpm... On an accurate Superflow dyno it makes 55 rear wheel HP and more importantly, 46 ft lbs torque at 5100 rpm and at 7000 rpm there's still 40 ft lbs of torque..
    I use a stock 4 speed...on a 1-1/2 mile track the bike is in high gear at just over 1/4 mile....The bike is easy to ride, no tachometer, the rider just gets into high gear,gets into the best tuck for a naked frame bike and holds the throttle wide open...
     
    KiwiNeill likes this.
  10. KiwiNeill

    KiwiNeill

    Joined:
    Jul 25, 2011
    Hillbilly Bike
    sounds like a properly sorted, hot rodded bike using well chosen components that work in harmony to great effect. Excellent results, is that your bike in the avatar?
     
    kommando likes this.
  11. jseng1

    jseng1

    Joined:
    Nov 26, 2009
    The Megacycle 480 cam has .436" lift and is supposed to be a copy of the Sifton 480.

    290 dur @ .040" with 7/8 radiused lifters

    280 dur @.050" with 7/8 radiused lifters

    294 dur @ .040" with 1-1/8 lifters radiused lifters

    284 dur @.050" with 1-1/8 lifters radiused lifters

    312 dur @ .040" with flat lifters

    302 dur @.050" with flat lifters


    The Sifton 460 (D+ or JS3) has about the same duration but less lift at .395" and was used in Norton factory dirt track motors with BSA 7/8" radius lifters.

    Running the 480 last year with used (tired) dual racing springs ended up with a bent valve at around 7500RPM.

    The HD XR750 race engine has an even bigger cam than the 480 and uses 200lbs pressure on the valve seat with roller lifters.
     
    Last edited: Nov 30, 2018
  12. Hillbilly Bike

    Hillbilly Bike

    Joined:
    Oct 18, 2018
    Yes, about 3 years ago when it ran 128 mph...My rider on the bike, me in hat...It's all about harmony...the intake, cam and exhaust needs to work together..Different builders have different ideas, some work out, some don't...I knew very little about Triumph tuning but it seemed to me what I was told to do seemed out of date.... I'm just using my Triumph as an example here, Nortons in theory have a superior head design using less valve valve angle and a more shallow combustion chamber..This gives a faster burn with less total ignition timing and will also influence cam specs...
     
  13. acotrel

    acotrel

    Joined:
    Jun 30, 2012

    Your comment about not revving over 7000 RPM interests me. My friend has a 650cc Triton which is never revved over 6,300 RPM. It is the only Triumph engine which has survived from the 60s in our local road racing. I rode the bike once at Calder Raceway and blew off one of the fast guys in a straight line, who was riding an H2 Kawasaki two stroke with chambers and which was the full bit. The Triumph astounded me the way it pulled such high gearing and accelerated so hard. Everything the owner ever does to the motor of that bike is about improving torque.
    I don't know that I fully agree that separate pipes are best for top-end power. If a 2 into 1 pipe has no restriction after the collector and the lengths are OK , the top end power is still there undiminished. The advantage lies in the torque profile. In a land speed situation, what holds you back is wind resistance. If you have top end power with no substance, you might find the revs dropping as you hit bumps in the air. In that respect a heavy crank might be better than a light one.
     
  14. Madnorton

    Madnorton VIP MEMBER

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    Jun 9, 2008
    The more I think of this I really do think it will succeed, unlike a tuned engine for a race track that will operate throughout a rev range on different tracks etc this is all out speed - this is a parameter that a design and changes can be made by doing away with the parameters not needed. With 50 years of knowledge of those gone before, though relatively complex but not impossible to achieve. the engine design to achieve the aim can be visuallised and built. The thread title I find now somewhat irrelevant, it should be 'cam for the fastest speed possible' - with the 'modified' Sifton the spec is most probably going to end up way different to what the sifton spec was originally and thus effectively a new cam design using the sifton as a blank.

    I am really looking forward to the finished engine, if it does just does one run out and back then it will be worth all the effort.
     
  15. Snotzo

    Snotzo

    Joined:
    Mar 12, 2013
    Acotrell
    from your above posts it's obvious you know very little about high performance engine development, but most forum members will know this already, so your continued comments about the merits of a 2 into 1 exhaust system for an out and out high performance engine, will be treated as irrelevant
    In any case, since you appear to disregard it, the original post was featuring a Sifton 480 cam as a possible fitment to a Commando engine.
    NOTE Commando, not Triumph. If you want to continue with your Triumph reminiscences, please take your posts to the part of the forum that caters specifically for them, where you and Hillbilly Bike can discuss your maladjustments to your hearts content.
    Gas paved track record HB ? We've run a pushrod 500 single at the Isle of Man Classic TT that was officially timed at 140.1 mph, so you still have quite a way to go.

    Madnorton, the problem most will face when attempting to build a motor such as JS is working on, is the ready availability of a cam that appears to be capable of doing what the engine builder wants. JS has chosen to go with the Megacycle 480 for want of a better starting point, and quite possibly a way forward from this design will reveal itself through subsequent testing. As you can appreciate, one off's are not that easy or cheap to obtain, and a start has to be made somewhere. He's already modified the closing ramp somewhat, so that has to be verified by test as being a correct and worthwhile mod. His main problem may well come from the fixed lobe separation, so a certain amount of historical know how will undoubtedly be applied in order to make a correct selection.
    Regarding actual maximum valve lift, 480" is not that great. There is no reason why anyone with sufficient interest could look at lifting the intake valve at least 100 thou higher. It certainly can be done, but as you correctly remark, the extra lift may not in the end be worth anything in performance, and possibly only aggravation in use. The Sifton 480 and I assume the Megacycle 480 have already been sucessfully used on many previous occasions, so for JS at this moment in time it's possibly a case of "better the devil you know than the devil you don't know"
     
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  16. Hortons Norton

    Hortons Norton

    Joined:
    Oct 12, 2007
    A 650 Triumph below 6,300 rpm blowing off a built H2 750 triple in a straight????? You will never get me to believe that! lol lol
     
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  17. Fast Eddie

    Fast Eddie VIP MEMBER

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    Oct 4, 2013
    Perhaps the triple rider was 400lbs... and stuck in first gear... with a flat tyre...
     
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  18. KiwiNeill

    KiwiNeill

    Joined:
    Jul 25, 2011
    Hortons Norton
    probably due to high gearing, improved torque and a 2-1 pipe, hot tip for every vehicle known to mankind I heard, but I think Fast Eddie has it right, just too polite to mention the broken chain...
     
    Last edited: Nov 30, 2018
  19. Hillbilly Bike

    Hillbilly Bike

    Joined:
    Oct 18, 2018
    Naked frame ,standing start 1-1/2 mile running within the rules of land speed racing modified production..Perhaps you need to bring you single to the the LSR tracks in Maine or Bonneville to show us your speed? Picture of said single with timed speed certification?
    Yes, this Triumph talk is out of forum but may serve a bit of info for others, sorry to offend you, have a good day...
     
    KiwiNeill likes this.
  20. kommando

    kommando

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    May 7, 2005

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