New product release - smooth ramp PW3/JS2 cam

jseng1 · Jul 14, 2016

Here's a comparison of charts showing the acceleration/jerk/stress load created by the cam - the acceleration/jerk is what beats up your valve train and causes valve bounce.

Top chart is the new JS2/PW3 smooth ramp with the acceleration/jerk only coming up to about 3 (black line).

New product release - smooth ramp PW3/JS2 cam

The earlier design PW3 type cam below has nearly twice the acceleration/jerk/stress going over 7 (black line). The jaggedness in the acceleration/jerk graph is the result of this cam being copied and having uneveness in the cam master plate.

grandpaul · Jul 14, 2016

Am I the only one that want's to know what ALL of the colored traces represent?

Thanx.

WZ507 · Jul 14, 2016

grandpaul said:
Am I the only one that want's to know what ALL of the colored traces represent?

Thanx.

jseng1 said:
Here's a comparison of charts showing the acceleration/jerk/stress load created by the cam - the acceleration/jerk is what beats up your valve train and causes valve bounce.

Top chart is the new JS2/PW3 smooth ramp with the acceleration/jerk only coming up to about 3 (black line).

The green curve is cam lift
The red curve is velocity which peaks at the steepest slope of the lift (green) curve
The black curve is acceleration which peaks at the steepest slope of the velocity (red) curve
The blue curve is jerk which peaks at the steepest slope of the acceleration (black) curve

jseng1 · Jul 16, 2016

If you look at the data curve in WZ507's post above you see that the max acceleration/jerk occurs near the bottom of the slope. Imagine yourself as a kid on a slide - coast downward in free fall till you feel the G forces hit your butt as you go through the swoop at the bottom. You may bounce back up after you're on the flat part at the bottom. Its the same way with cams. When closing - the more you can spread out the curve near the bottom - the more you will reduce the stress and unwanted bounce (which can tangle valves). This "swoop curve" is most critical in the .020" to .060" lift range. Above.060" you are mostly coasting and below .010" you are in valve lash territory anyway. Below is the new smooth ramp JS2 compared to one of the most abrupt PW3 copies I have - showing the difference in the swoop.

You don't see many problems from slamming the valve train open - pushrods rarely fail and rocker arms don't break. Too much acceleration can create loft but the big problem is when the valve hits the seat and the spring has to stop extending (and starts flopping up and down). When this happens the cam will flex - and this is a big problem with Nortons because the cam is so long. When the cam springs back it pushes the valve train and lifts the valve back up off its seat about 1/32" of an inch in some cases - bouncing the cam along the last .010" or so of the closing ramps and making the last bit of ramp almost useless.

One solution is to add a central cam support (1/2 shell bronze bearing on the bottom side). Hardly anyone does this. So the next best thing is to ease the closing of the valve as I have done.

Now look at the "gentle" HD xr750 ramp comparison below (designed by Mert Lawwill). This ramp swoop is even broader because those motors see 9000 RPM. I don't go that far but you get the idea.

acotrel · Jul 16, 2016

Jim, - What sort of power characteristic is your new cam designed to deliver ? i.e. does it produce a very distinct power band when it is used in a near standard bike with separate exhaust pipes ? Top end OR midrange improvement ? And what max revs is it designed to deliver ? I'd also be interested to know what timings you use for IO btdc , IC atdc, EO bbdc, EC atdc ? And have you tried moving it's timings backwards and forwards to see where it is optimised to suit separate pipes (a 2 into 1 pipe is obviously different) ?
I like all your theoretical stuff, however what does your cam actually do ? I've read a bit on this forum about PW3 cams, however I still don't know the differences in power characteristics compared with a standard cam. And I am not talking about dyno figures. What I am interested in is how cams actually perform when used in a bike on a race circuit.
I've read a bit about Kenny Cummins bike. It has minimum offset on the fork yokes, which would make the steering very quick, yet still seems to be set up for Daytona. Makes me wonder if the motor is set up to produce a lot of top end, or is it producing more midrange and pulling higher gearing ?

jseng1 · Jul 16, 2016

acotrel said:
Jim, - What sort of power characteristic is your new cam designed to deliver ? i.e. does it produce a very distinct power band when it is used in a near standard bike with separate exhaust pipes ? Top end OR midrange improvement ? And what max revs is it designed to deliver ? I'd also be interested to know what timings you use for IO btdc , IC atdc, EO bbdc, EC atdc ? And have you tried moving it's timings backwards and forwards to see where it is optimised to suit separate pipes (a 2 into 1 pipe is obviously different) ?
I like all your theoretical stuff, however what does your cam actually do ? I've read a bit on this forum about PW3 cams, however I still don't know the differences in power characteristics compared with a standard cam. And I am not talking about dyno figures. What I am interested in is how cams actually perform when used in a bike on a race circuit.
I've read a bit about Kenny Cummins bike. It has minimum offset on the fork yokes, which would make the steering very quick, yet still seems to be set up for Daytona. Makes me wonder if the motor is set up to produce a lot of top end, or is it producing more midrange and pulling higher gearing ?

There's too many other variable factors such as intake length, ex pipes, porting, stroke etc to lay it all on the cam.
The performance of the smooth ramp JS2 would be very near to the PW3. But it would be easier on the valve train and allow much higher RPM before running into valve bounce -even though the power characteristics would be similar. Its a race cam that will raise the RPM band power range over a stock cam in a similar way as the 4s. Mellower than the 2s and the D+ but hotter than the Axtel #3 & NR. Thats as good a description that I have to offer.

I don't use intake/exhaust openings and closings anymore. I just use lobe centers - an even split of 105 each to a more ideal 103 intake and 107 exhaust or anywhere inbetween. Its a much easier technique and all you really need to do is set the cam timing so the intake lift is .025" higher than the exhaust lift at TDC and all comes out right. That and shooting for .040" valve clash clearance.

Snotzo · Jul 17, 2016

jseng1 said:
Here's a comparison of charts showing the acceleration/jerk/stress load created by the cam - the acceleration/jerk is what beats up your valve train and causes valve bounce.

Top chart is the new JS2/PW3 smooth ramp with the acceleration/jerk only coming up to about 3 (black line).

The important point to consider about the design of the ramps is best examined by looking at the velocity trace. If all has been correctly managed, when the engine has reached it's normal (?) operating temperature, component expansion and flexure will combine to place the actual leaving of the valve from it's seat right in the knee bend of the velocity trace, at approx. the 8 degree marker on the base line. This would be the ideal, but how is this to be managed with a ramp height of approx. 50 thou, when normal tappet settings cold are likely to be only half of this, and possibly appreciably less. A tappet clearance of 10 thou would place the actual valve lift off right at the beginning of the velocity ramp where the accelleration rate is extremely high. Between 10 and 30 thou clearance will end up somewhere along the flat plateau of the velocity ramp.
On the closing side the ideal is to lower the valve down onto it's seat at some point along the flat plateau of the velocity trace of the closing ramp, but again this requires a tappet clearance somewhere between 10 and 30 thou to manage the valve closing to meet this requirement.

JS, I'll be interested to hear your recommendation for tappet settings.

jseng1 · Jul 17, 2016

Snotzo said:
...If all has been correctly managed,...will combine to place the actual leaving of the valve from it's seat right in the knee bend of the velocity trace, at approx. the 8 degree marker on the base line. This would be the ideal, .....
On the closing side the ideal is to lower the valve down onto it's seat at some point along the flat plateau of the velocity trace of the closing ramp, ....

JS, I'll be interested to hear your recommendation for tappet settings.

I looked at the actual cam profile/ramp drawings which are more accurate and easier to read than the cam data graph. At about .008" tappet clearance (hot), the valve leaves the seat at about 35 degrees from beginning of cam lift (0).

The vertical lines on the graph below are distanced at about 22 degrees. This would put the beginning of valve lift close to the black arrow in the image below. I think this is where you are saying valve lift should begin (opening/closing sides are symmetrical).

acotrel · Jul 17, 2016

Jim, you have obviously already tried your new cam in a bike. Would you please describe the set-up you used in terms of inlet port diameter, exhaust pipes type, and let us know what the power band was like, - i.e. at what revs did it come on song, and did it make the motor more top end or more torquey, if compared with a standard cam.

acotrel · Jul 17, 2016

The reason I am asking the question is that I have no intention of buying a billet crank, thicker cases etc. which would allow an increase in the top of the usable rev range. Many hot cams give more power by increasing the revs. In my case the bottom end is certain to fail if I go down that path. If your cam fattens up the midrange power as well as, or instead of raising the top of the rev range, that would be good. It would mean the overall gearing could be increased to give the bike more legs towards the ends of the straights on race circuits.

jseng1 · Jul 18, 2016

acotrel said:
The reason I am asking the question is that I have no intention of buying a billet crank, thicker cases etc. which would allow an increase in the top of the usable rev range. Many hot cams give more power by increasing the revs. In my case the bottom end is certain to fail if I go down that path. If your cam fattens up the midrange power as well as, or instead of raising the top of the rev range, that would be good. It would mean the overall gearing could be increased to give the bike more legs towards the ends of the straights on race circuits.

Like any race cam - it will raise the powerband higher in the RPM band compared to a stock cam. The increase in torque you're wanting comes from increased displacement, but heavier pistons will increase stress in the same way as higher RPM. An increase of power either high or low will add stress to the cases/crank.

If you're worried about your crank and cases, then your best option is to use the lightweight pistons and longer rods to reduce the stress.

For my inlet and ex pipe specs - they are all available in my race manual with drawings etc. These are proven specs from Leo Goff, C.R. Axtell and from the Norton factory racing dept.

Brooking 850 · Jul 19, 2016

Here is a power and torque curve to answer the question on midrange and or power at any RPM values.
RH10 head with standard size Vv's
Standard length manifolds with Amal Mk1 Premiers 32mm
Standard crankshaft.
JS rods and pistons 0.040" oversize.
Early model JS2 cam
2 into 1 exhaust 1 1/2" headers
As it shows, there is 50ftlbs of torque to the rev limiter, very torquey motor, so ideal for short track racing and will hold good pulling power at wider throttle openings, ie for longer tracks.
Doesnt necessarily need a 5 or 6 speed gearbox, although there is a 5 speed in the bike, quite high first gear, and has no issue pulling off the line without slipping the clutch.
Wind it up to 5000 rpm , drop the clutch and go!!!
Although the printout doesnt show it, still makes good power low down in the rev range.
url=http://s1228.photobucket.com/user/Brooking850/media/HD%202%20into%201%20Test%201_zpskqz1lakg.jpeg.html]

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acotrel · Jul 19, 2016

Thanks for that - it is very interesting. I would have thought that peak torque would occur at higher revs than that. What always puzzles me is the relationship between gearing, horsepower and torque. I usually try to change up below 7000 RPM, however the bike accelerates faster with the close ratio box than with the wide ratios. I sense that max. torque with my bike must occur somewhere around 6000RPM, but as I've raised the overall gearing the bike has become quicker towards the ends of the straights. The difficult part is that the response to changing the gearing is unexpected. I would have thought that lower overall gearing would give quicker acceleration coming out of slow corners. I am not used to riding such a torquey bike with such a heavy crank .
Do you race your 850 regularly and how do you gear it for various circuits ? The methanol fuel I use might make a minor difference, however I'd still like to compare.

Brooking 850 · Jul 20, 2016

Alan, I run a 5 speed box, have modified the rear drum brake hub so I can change rear sprockets for different tracks quickly , the minimum tooth count is 44 (standard Commando is 42) I run a 44, 45 or 46.
Front sprocket is a 21 .
Makes maximum torque at 4700 rpm with 56 ftlbs of torque at 6500 rpm and still over 50 ftlbs of torque at redline of just under 7500 rpm.

No need to rev it over 7000 and yes I race it regularly in three different classic classes plus track days throughout the year.
I run avgas.

Disclaimer: Due to others opinions of dyno results and how they are achieved, the power and torque figures are for my use only as a data base, however , where the curves are in relation to each other and both in relation to the rev range is the reality and of the most use!!!

lcrken · Jul 20, 2016

That's a nice looking torque curve. Should be a fun bike to ride on the track, particularly the short twisty ones, as well as having good top end power for the longer tracks.

Ken

Brooking 850 · Jul 22, 2016

Yes Ken , very good and a helluva lot of fun to ride.
Surprises a lot of guys on more moderns in pre 1989 races as well.
Regards Mike

jseng1 · Jul 27, 2016

Brooking 850 said:
Here is a power and torque curve to answer the question on midrange and or power at any RPM values.
RH10 head with standard size Vv's
Standard length manifolds with Amal Mk1 Premiers 32mm
Standard crankshaft.
JS rods and pistons 0.040" oversize.
Early model JS2 cam
2 into 1 exhaust 1 1/2" headers
As it shows, there is 50ftlbs of torque to the rev limiter, very torquey motor, so ideal for short track racing and will hold good pulling power at wider throttle openings, ie for longer tracks.
Doesnt necessarily need a 5 or 6 speed gearbox, although there is a 5 speed in the bike, quite high first gear, and has no issue pulling off the line without slipping the clutch.
Wind it up to 5000 rpm , drop the clutch and go!!!
Although the printout doesnt show it, still makes good power low down in the rev range.
url=http://s1228.photobucket.com/user/Brooking850/media/HD%202%20into%201%20Test%201_zpskqz1lakg.jpeg.html]

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Here's an interesting comparison of dyno graphs. Brookings 850 above to Bern's 850 below. What makes it interesting is that both are 850 race engines with identical internal performance components - JS lightweight high compression pistons, longer bushless Carrillo rods, JS2 cams, beehive valve springs with standard size valves. The dyno curves show the difference in power band and RPM with Bern's going all the way to 8400 RPM. This shows what a difference porting, ex pipes (2 into 1 or twin megas), intake and carbs can make. Mikes clearly being the motor with power lower in the RPM range.

acotrel · Jul 27, 2016

Due to my monetary situation I cannot afford to race these days, so my 850 has only been raced a few times. I know from the last time that I raced it - it has the potential to win. To my mind it is very unusual - I'm not used to using such a torquey motor in a light frame that handles so well. Jim Schmidt is correct about his long rods and light pistons - that is a very good way to go. One day I might be rich again and buy them. The thing about the Seeley is that I've found I can brake a third of the way into a corner, then get straight back onto the gas while the bike is cranked over - the bike then turns tight around the corner. It means I get under and get the run on larger capacity bikes which tend to run wide coming out of the corners. It is probably no more that 15 metres head start, however it makes a big difference to your speed at the end of the straights. The steering geometry probably would not suit many riders - you have to have your mind way ahead of the corner. So it is probably a bit dangerous for some. I wouldn't use it on a big circuit - the steering is too quick.
I noticed from Kenny Cummins write-up on his Seeley that he also uses reduced offset on his fork yokes and I think he rides at Daytona - might be scary ?

lcrken · Jul 27, 2016

acotrel said:
I noticed from Kenny Cummins write-up on his Seeley that he also uses reduced offset on his fork yokes and I think he rides at Daytona - might be scary ?

Reduced offset in the yokes increases trail, and makes the bike more stable at speed, not less. Maybe you meant something else?

Ken

jseng1 · Aug 1, 2016

There has been some confusion and misinterpretation of the cam profile images in this thread. I have tried to put that right and explain things in a direct simple way at:

http://www.jsmotorsport.com/technical_JS2-PW3.asp

New product release - smooth ramp PW3/JS2 cam

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