What cam do you have and why?

WZ507 said:

Fast Eddie said:

Thanks, but that's not much clearer really. The graphs shown overlay different cams to compare. It would be clearer to overlay the same cam with different follower grinds.

Click to expand...

Fast Eddie,

The plot below, provided in a personal communication from Comnoz and presented here with his permission, addresses your desire to see the 312A lobe with different followers in a single plot.

Unrelated to the above is a general observation about the broad spectrum of cam lobes people employ and have commented on here – and thanks to all for sharing your builds/thoughts. So step back, blur your eyes a little bit and bear with me for a moment to consider what has been presented. Considering all of these lobes, and ordering them from closest to stock to wildest, we’ve done a good job of incrementing our way through the continuum of cam profiles from the mildest of profiles right up to just south of the D+ and the N480 (which are very large full race profiles). And of all the lobes evaluated here, in general, nary a bad word has been spoken about any of them, nor has there been any real concession that low end or mid-range torque was sacrificed to achieve more top end power - just smooth unrelenting yank from down low to up high. Perhaps the only reference to sacrifice relates to the poor old 2S, which has historically been the whipping boy for top end performance occurring at the expense of mid-range torque. So we’re just one big happy family that is pleased with our cam selections.

Just my $0.02, but I nevertheless remain amazed how pleased the majority of people are with the larger lobes for street use. Thanks again for sharing all your comments.

Click to expand...

That's great, and very clear, thank you.

It still looks like such a small difference to me though.

I find it hard to believe that most riders could tell the difference in a 'blind test'!

worntorn said:

WZ507 said:

Just my $0.02, but I nevertheless remain amazed how pleased the majority of people are with the larger lobes for street use. Thanks again for sharing all your comments.

Click to expand...

I think it comes down to the fact that most people like to be happy with their choices and will overlook shortcomings to get there. Please forgive the Vincent analogy below, but since it comes from the great Phil Irving it might be of interest.

Forty years ago Phil Irving wrote a letter to the editor of the MPH about this same subject. At that time and still today many people replaced his MK1 standard cams with Lightning cams for their touring bikes.
He designed ( and hand ground the first sets) the MK 1 cams for maximum grunt on a hill when loaded (extra power below 4,000 rpm) and later on designed and ground the first MK2 or Lightning cams for speed record attempts ( extra power above 4k , but some loss below 4 k)
Since a road Vincent spends almost all of it's time below 4 k rpm, those who installed his Lightning cams were actually detuning their Vincents according to Phil.
Nonetheless, I've met many current Vincent owners who have switched from the gruntier MK1 cam to the peakier Lightning cam and claim increased power everywhere.
It's pretty much impossible to tell them otherwise, even though their claims of all over power increases are incorrect, according to the man who designed the engine, cams and all.

Glen

Click to expand...

Glen,

Perfect! I don't think it could possibly be said more succinctly. Everyone's got their way eh?

I might add though that changing cam(s) alone may very likely render a loss of performance (per the Phil Irving citation) in some section of the useable power range but in my cases cited, other things were done including increased compression which will help improve lower end performance lost due to greater cam duration.

worntorn said:

WZ507 said:

Fast Eddie said:

Thanks, but that's not much clearer really. The graphs shown overlay different cams to compare. It would be clearer to overlay the same cam with different follower grinds.

Click to expand...

Fast Eddie,

The plot below, provided in a personal communication from Comnoz and presented here with his permission, addresses your desire to see the 312A lobe with different followers in a single plot.

Unrelated to the above is a general observation about the broad spectrum of cam lobes people employ and have commented on here – and thanks to all for sharing your builds/thoughts. So step back, blur your eyes a little bit and bear with me for a moment to consider what has been presented. Considering all of these lobes, and ordering them from closest to stock to wildest, we’ve done a good job of incrementing our way through the continuum of cam profiles from the mildest of profiles right up to just south of the D+ and the N480 (which are very large full race profiles). And of all the lobes evaluated here, in general, nary a bad word has been spoken about any of them, nor has there been any real concession that low end or mid-range torque was sacrificed to achieve more top end power - just smooth unrelenting yank from down low to up high. Perhaps the only reference to sacrifice relates to the poor old 2S, which has historically been the whipping boy for top end performance occurring at the expense of mid-range torque. So we’re just one big happy family that is pleased with our cam selections.

Just my $0.02, but I nevertheless remain amazed how pleased the majority of people are with the larger lobes for street use. Thanks again for sharing all your comments.

Click to expand...

I think it comes down to the fact that most people like to be happy with their choices and will overlook shortcomings to get there. Please forgive the Vincent analogy below, but since it comes from the great Phil Irving it might be of interest.

Forty years ago Phil Irving wrote a letter to the editor of the MPH about this same subject. At that time and still today many people replaced his MK1 standard cams with Lightning cams for their touring bikes.
He designed ( and hand ground the first sets) the MK 1 cams for maximum grunt on a hill when loaded (extra power below 4,000 rpm) and later on designed and ground the first MK2 or Lightning cams for speed record attempts ( extra power above 4k , but some loss below 4 k)
Since a road Vincent spends almost all of it's time below 4 k rpm, those who installed his Lightning cams were actually detuning their Vincents according to Phil.
Nonetheless, I've met many current Vincent owners who have switched from the gruntier MK1 cam to the peakier Lightning cam and claim increased power everywhere.
It's pretty much impossible to tell them otherwise, even though their claims of all over power increases are incorrect, according to the man who designed the engine, cams and all.

Glen

Click to expand...

A good post Glen and very relevant.

I imagine that very few people would strip a motor and only replace the cam. I think most people would do other stuff at the same time, replacing some worn out stuff, raising the CR a tad, replacing worn out valve gear, etc.

So, on top of the self convincing / placebo effect that inevitably is at work, its quite probable that the other stuff they do, increases the mid range, and kinda substitutes for that lost by the bigger cam.

The net result is they still feel the same good mid range as before, and increased higher end pull.

So I'd say most people, myself included, never really compare a cams effect 'back to back' against another.

Plus, as other have posted already, folk have different perceptions....

I was working on my Triumph racer in the Dresda race shop once and got chatting to a customer. My Triumph racer had about .460" of lift as I recall, was 840cc, radical squished head, etc. and made around 72rwhp at the time. The guy was asking about the power etc. but seemed more interested in telling me what a rocket ship his bike was, which after a little probing tuned out to have a fairly stock pre unit T110 lump. "Its awesome" says our hero, "but I never take it over 4,000". I've nothing against T110 motors, but I wouldn't describe the sub 4,000rpm performance as rocket ship like... We clearly had different kinds of awesomeness in our minds!

Degans had another customer once who had him build a 'race motor' for the street (against Degans advice). Matey was unhappy and thought something was wrong. It turned out the motor was a flier, he just wasn't revving it and the reduction it low end pull was all he could feel.

Muddy waters ...

Fast Eddie said:

That's great, and very clear, thank you.

It still looks like such a small difference to me though.

I find it hard to believe that most riders could tell the difference in a 'blind test'!

Click to expand...

Eddie,

Consider the following. The lobe profiles of the 312A, the Axtell #3 and your JS1 are essentially the same, with the exception that the 312A is designed for a flat tappet and the JS1 is designed for a radius tappet. You love the performance of your JS1 over the stock cam. When you look at the area under the curve in the 312A plots you’ll see that the curve area of the flat tappet cam is ~ 17% greater than the CDO cam, and the curve area of the 312A with the 4” radius lifter is on the order of 11% greater than the CDO cam, so significant increases for both. I don’t want to draw analogy between curve area and actual engine output as there are many other factors to consider, but you know 1st hand that a 17% increase in curve area, via the duration and lift increases of your cam, in combination with the other critical parameters of your build result in a very satisfying riding experience. Perhaps taking a bit of the curve area away may not be a big deal, but would certainly move you somewhat in the direction of the stock cam. How much? I wish I knew.

I think the bottom line is what Comnoz referred to previously in this thread, namely that performance differences between flat vs radius follower is attributable to shortening the effective cam duration via the radius follower, which in turn reduces the overlap area, which in turn moderates performance to some extent. But again back to your question, "to what extent?"

Your intuition regarding the average rider using the seat-of-the-pants dyno might be correct in that one might be hard pressed to distinguish between the performance of an engine fit with a 312A/flat and a 312A/radius follower cam system. Don’t know, never had the benefit of evaluating such systems. But……….. perhaps someday we can goad Comnoz into building a test mule for our enlightenment, where everything remains constant, cams are stabbed in, tested and changed out. Doesn't hurt to dream such thoughts! After all he must have plenty of idle time on his hands for such an undertaking right?

worntorn said:

I think it comes down to the fact that most people like to be happy with their choices and will overlook shortcomings to get there. Please forgive the Vincent analogy below, but since it comes from the great Phil Irving it might be of interest.

Forty years ago Phil Irving wrote a letter to the editor of the MPH about this same subject. At that time and still today many people replaced his MK1 standard cams with Lightning cams for their touring bikes.
He designed ( and hand ground the first sets) the MK 1 cams for maximum grunt on a hill when loaded (extra power below 4,000 rpm) and later on designed and ground the first MK2 or Lightning cams for speed record attempts ( extra power above 4k , but some loss below 4 k)
Since a road Vincent spends almost all of it's time below 4 k rpm, those who installed his Lightning cams were actually detuning their Vincents according to Phil.
Nonetheless, I've met many current Vincent owners who have switched from the gruntier MK1 cam to the peakier Lightning cam and claim increased power everywhere.
It's pretty much impossible to tell them otherwise, even though their claims of all over power increases are incorrect, according to the man who designed the engine, cams and all.

Glen

Click to expand...

More times than I would care to admit -I have been the guy with the hot cammed Norton heading up the pass, revving along at 6000 rpm in third gear while stock cammed bikes are easily staying ahead of me in fourth gear at a nice comfortable RPM.

It took a lot of dyno runs and a long time to get over the "bigger is better" when it comes to cams. That even applies to full roadrace motors and land speed record bikes.

Even with the 12a cam in Sir Eddies rocket -Paul had to detune the motor a bit with longer exhaust to be able to accelerate after the 3 to 4 shift. With the short exhaust the powerband was not wide enough to stay in the power when making the shift to 4th at 100 mph. It needs a closer ratio transmission. Jim

I have used flattened cam followers in 650cc Triumph motors and haven't noticed any difference in performance. In those motors when race cams are fitted and exhausts with mufflers are used, the usable rev range is from 4,000 to 8,000 RPM, however even below the cam spot there is usually a bit more go. When you use megaphones, you are left with NOTHING under 4,000 RPM. Surely when you fit flat followers with a cam which was designed for use with radiused followers, as the cam turns the initial lift rate is increased, however as the cam reaches full lift, the lift rate and closing rate are decreased. So the valve is less likely to be chucked down the hole or break off as it snaps shut ? As far as maximum lift is concerned, isn't that determined by the distance from the base circle to the nose of the cam, as well as the tappet clearance ? How does the shape of the cam follower affect that ?
A race cam is a street bike is usually good fun, if you are an adrenalin addict. However a race bike taken to extremes can be a pain in the arse, especially on relatively tight circuits. I found that the faster you try to go, often the slower you usually end up going.
My 500cc short stroke Triton was beautiful on Phillip Island, it would power on forever simply getting faster, and passing many other bigger bikes as it reached the ends of the straights. The problem is that on a race circuit, you sometimes have to stop and go around corners. Perhaps there might be a market for 12 speed gearboxes for Nortons and Triumphs ?

The last four cylinder Gileras in the 60s had 7 speed gearboxes - wouldn't that be lovely ? You could be so bloody aggro !

'Even with the 12a cam in Sir Eddies rocket -Paul had to detune the motor a bit with longer exhaust to be able to accelerate after the 3 to 4 shift. With the short exhaust the powerband was not wide enough to stay in the power when making the shift to 4th at 100 mph. It needs a closer ratio transmission. Jim'

Try a 70 MPH bend when the motor falls off the power band and you are too chicken to touch the clutch. Because you know that if the revs rise, the bike will probably twist itself sideways and chuck you off. So you wait until the bike is around the corners and upright - then where are all the other guys ? In the wet, it is even better.

comnoz said:

Sir Eddies Rocket is running a 312a cam with radius ground stock lifters.

It revs to 10,000+ with oversized steel valves and stock pushrods -no valve bounce or float till 10,300. Jim

Click to expand...

Offset radius aren't they? - a world of difference. I was talking about regular radius compared to flat.

jseng1 said:

comnoz said:

Sir Eddies Rocket is running a 312a cam with radius ground stock lifters.

It revs to 10,000+ with oversized steel valves and stock pushrods -no valve bounce or float till 10,300. Jim

Click to expand...

Offset radius aren't they? - a world of difference. I was talking about regular radius compared to flat.

Click to expand...

Actually it's a little more than just an offset radius. It's a variable radius.
It opens the valve faster and closes the valve slower.
No loft, no float and no bounce -but still the same area under the curve.

comnoz said:

jseng1 said:

comnoz said:

Sir Eddies Rocket is running a 312a cam with radius ground stock lifters.

It revs to 10,000+ with oversized steel valves and stock pushrods -no valve bounce or float till 10,300. Jim

Click to expand...

Offset radius aren't they? - a world of difference. I was talking about regular radius compared to flat.

Click to expand...

Actually it's a little more than just an offset radius. It's a variable radius.
It opens the valve faster and closes the valve slower.
No loft, no float and no bounce -but still the same area under the curve.

Click to expand...

Jim,
asymmetrical ??? or two radius change in transitioning on the lifter?
Cheer,
Tom
CNN

Eddie, my motor was basically the same before the rebuild with a rebore and general freshen up, the only changes being the micro polishing, ceramic coating of everything and Jim Comstock's conical valve springs. Essentially, only the cam was changed. No change in compression ratio, not even a clean up of the ports, but the difference in performance is quite marked. Where I really noticed it was, cruising at 70 MPH and backing off to 60 or less, opening the throttle to regain the speed lost is MUCH stronger with the PW3. I was having a bit of a thrash the other day, had a bit of open road, gave it the berries to about 5000rpm through the gears and thought, "Gee this is pulling hard in third", went to change up and realised I was already in top. Such is the difference.

This really is the finest motorcycle that I have ever owned, of any make or model. It is deeply satisfying and I just cannot get enough of it. No matter how long I ride during the day, when I get back to my place, I have to keep going and do a few favourite local roads before i get home. I've done nearly 5000 miles on it in about four months. It really is my everyday bike.

Fullauto said:

Eddie, my motor was basically the same before the rebuild with a rebore and general freshen up, the only changes being the micro polishing, ceramic coating of everything and Jim Comstock's conical valve springs. Essentially, only the cam was changed. No change in compression ratio, not even a clean up of the ports, but the difference in performance is quite marked. Where I really noticed it was, cruising at 70 MPH and backing off to 60 or less, opening the throttle to regain the speed lost is MUCH stronger with the PW3. I was having a bit of a thrash the other day, had a bit of open road, gave it the berries to about 5000rpm through the gears and thought, "Gee this is pulling hard in third", went to change up and realised I was already in top. Such is the difference.

This really is the finest motorcycle that I have ever owned, of any make or model. It is deeply satisfying and I just cannot get enough of it. No matter how long I ride during the day, when I get back to my place, I have to keep going and do a few favourite local roads before i get home. I've done nearly 5000 miles on it in about four months. It really is my everyday bike.

Click to expand...

5,000 miles in 4 months... strewth, I'm jealous!

Before stripping mine, it had stock CR, stock cam, and a single Mik. It pulled OK, but nothing special and totally ran out of puff at about 5,000rpm.

So I'd say your PW3 is delivering the goods.

I guess your head may flow a little better than my stock RH10 did too ? :wink:

Nice looking bike yer got there Ken. What it really needs is one of Matts cNw chrome front mudguards, much tidier than most I reckon.

Looking forward to hearing you thoughts after running the CR carbs BTW...

CanukNortonNut said:

comnoz said:

Actually it's a little more than just an offset radius. It's a variable radius.
It opens the valve faster and closes the valve slower.
No loft, no float and no bounce -but still the same area under the curve.

Click to expand...

Jim,
asymmetrical ??? or two radius change in transitioning on the lifter?
Cheer,
Tom
CNN

Click to expand...

It's an offset, decreasing radius cut. It does make for asymmetrical valve motion.

I ground a pile of Phenolic lifters, mapped them and run then in my cam analyzer program before I found something that looked smooth enough to run at 10,000 rpm.
That was after I modified my lifter grinder with adjustable levers and linkage to change the radius as the lifter moves across the stone.
Then when I found a grind that looked promising I replaced the stone wheel with a diamond wheel and ground a real set of lifters to run in the spintron. It was pretty educational.

Is the closing radius the larger on the offset lifters? Seems you would want acceleration on opening and deceleration on closing.

Danno said:

Is the closing radius the larger on the offset lifters? Seems you would want acceleration on opening and deceleration on closing.

Click to expand...

comnoz said:

jseng1 said:

comnoz said:

Sir Eddies Rocket is running a 312a cam with radius ground stock lifters.

It revs to 10,000+ with oversized steel valves and stock pushrods -no valve bounce or float till 10,300. Jim

Click to expand...

Offset radius aren't they? - a world of difference. I was talking about regular radius compared to flat.

Click to expand...

Actually it's a little more than just an offset radius. It's a variable radius.
It opens the valve faster and closes the valve slower.
No loft, no float and no bounce -but still the same area under the curve.

Click to expand...

The best cam Axtell ever developed for the Nortons, which he called the "Allegro" at the time, had assymetric lobes, with the opening profile different from the closing profile. He had trouble getting anyone to grind them, because doing so required cutting the standard cam grinder wheels down to a smaller radius to do the slightly concave profile on the closing ramp. As I recall, the idea was that because you had spring pressure helping close the valve, you could let it close more rapidly than you could open it. The grinding wheels were expensive, so the cam grinding shops were reluctant to modify one just to grind a few cams for Axtell. That's one of the things that motivated him to finally get his own cam grinding machine. I was never able to convince him to sell me any of the Allegro cams. The only place I know of that they were used was on Ron Wood's bikes, but there might have been others. That was along time ago, so I can't guarantee that my memories are always correct in the details.

Sounds like Jim is getting a similar effect with his assymetric lifters. Clever idea, that. If you wanted to experiment, you could just pull the cylinder to change lifters, with no need to split the cases to change cams.

Ken

Only hearsay, however I was told years ago that a main reason for dropping valves was when the cam allowed the valve to snap shut too suddenly - probably fatigues the stem. It would probably apply more to the large valves in British single cylinder motors ? I do know this, the exhaust cam profile and the exhaust configuration are at least as important as the shape of the inlet cam, as far as performance is concerned