Cams comparison

I have never seen an objective comparison of the various Commando and earlier cams on this forum. It might be interesting to hear from people who have used each type in 750cc Commandos. - The effects on midrange power and top end, exhaust type and gearing, and usable rev range. For myself, I have absolutely no idea what any of them do. I suspect the cam is my 850 is 650SS. I simply adjust everything else and work around it.
A few reports might be helpful.

Did Peter Williams ever publish any tuning notes ? The only tuning notes I have for Nortons are 'Tuning For Speed' and Paul Dunstall's. When Yamaha two-strokes were being raced in the 1970s, the Yamaha development papers were available from the American engineering societies. Both Phil Irving and Peter Willams were professionally qualified engineers, who would normally publish their findings.
Most mechanics probably never publish anything.

There must be some Peter Williams notes somewhere since he is credited with the PW3 cam profile. A claimed top speed of 160 mph all tucked in is a bit amazing and hard to believe. I'll post here if I find anything else.

Also, regarding Joachim‘s cam, the PW3 often gets bad press, now, I’ve never used a PW3 myself, but Mick Hemmings swore by the PW3 as does Norman White (who describes it as ‘the only cam to consider’) and it was designed by PW himself… so it really should not be a bad cam. And then we have Joachim‘s evidence, how can anyone argue against his before and after graphs?

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Peter Williams and his father also designed all of the various S cams, other than the original SS. That was designed by Doug Hele for road use and it is very good in that application. According to those who used the Hele SS cam for racing, it also worked well there and won a lot of races.
I suppose that the SS cam might have an advantage on a course with a lot of tight corners whereas a higher lift longer duration cam would excel on a higher speed track.
I believe all of the Peter Williams cams were designed more with racing in mind than for street use.

Glen

je roule avec un pw3 depuis 4 ans , plus de couple et de punch, mais comme l'overlap est plus grand le bruit d'échappement est trés fort

pyer said:

je roule avec un pw3 depuis 4 ans , plus de couple et de punch, mais comme l'overlap est plus grand le bruit d'échappement est trés fort

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English:
been driving with a pw3 for 4 years, more torque and punch, but as the overlap is greater the exhaust noise is very loud

According to the man with the dyno, the PW3 vs stock loses about 6 hp in the midrange and gains 3 hp at the top.
The result would feel extra strong as comes onto the cam, coming from lowered torque vs stock in the middle to extra torque vs stock at the top.

Glen

worntorn said:

According to the man with the dyno, the PW3 vs stock loses about 6 hp in the midrange and gains 3 hp at the top.
The result would feel extra strong as comes onto cam, coming from lowered torque vs stock in the middle to extra torque vs stock at the top.

Glen

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That'd easily fool a butt dyno

worntorn said:

According to the man with the dyno, the PW3 vs stock loses about 6 hp in the midrange and gains 3 hp at the top.
The result would feel extra strong as comes onto the cam, coming from lowered torque vs stock in the middle to extra torque vs stock at the top.

Glen

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That is more what I would have expected from a later cam. I don't like a strong surge of power as the motor comes onto the cam. It can make the bike more difficult to ride smoothly in fast open corners. The 2 into 1 exhaust seems to maintain a strong power curve without bumps. But some power can be lost off the top if the system is restrictive due to noise rules.

A loss of 6 BHP midrange to gain 3 BHP at the top might not be a good way to go if the gearbox is not close ratio. With wider ratios more midrange is needed. - Depends a bit on the circuit. If the motor is continually well on the boil 3 BHP extra at the top might be OK. I think it was at Silverstone that PW was faster than the TZ750s.
I am surprised the Norton factory was not more methodical - they employed some very good guys.
The Japanese did not seem to be shy about sharing secrets.
It would be interesting to know how the Manx was developed by Joe Craig.
I used to have Triumphs - Nortons seem to be much better.

acotrel said:

A loss of 6 BHP midrange to gain 3 BHP at the top might not be a good way to go if the gearbox is not close ratio. With wider ratios more midrange is needed. - Depends a bit on the circuit. If the motor is continually well on the boil 3 BHP extra at the top might be OK. I think it was at Silverstone that PW was faster than the TZ750s.
I am surprised the Norton factory was not more methodical - they employed some very good guys.
The Japanese did not seem to be shy about sharing secrets.
It would be interesting to know how the Manx was developed by Joe Craig.
I used to have Triumphs - Nortons seem to be much better.

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How do you know if the 'Norton Factory' was methodical or not? What is your assertion based on? What do you mean by 'Norton Factory'? I guess we are talking the period after AMC, who purchased Norton in 1953, and went bust in 1966. So realistically I guess you mean the Norton Commando period from cradle to grave between '67 and '76. Over that period the relevant 'factories' were operated under the Norton Villiers banner, and then the Norton Villiers Triumph organisation, a forced marriage.

In the 1970s Norton road bike development was supported by the Norton 'Experimental Department'. And the John Player race team effort was supported by the Thruxton race shop. Different organisations with different responsibilities.

If you are talking about the race shop you are really talking about a few guys in a shed at Thruxton. Talk to Norman White, he might tell you how they worked. They had a dyno, they built engines, they tested them on the dyno and on the local race track and every weekend of the race season in the hands of Norton employees and racers. They made modifications, they made adjustments, they wrote stuff down! They created drawings when needed to make stuff repeatable. Sounds methodical to me, but who knows.

Norman might also tell you that Peter Williams came up with a new cam profile every couple of weeks! And that some of them worked on the dyno, and some of them worked on the race track!

Evidence suggests most of them were variations on a 2S/4S theme. Small improvements rather than radical changes I suspect, with the occasional damp squib. As far as I can see they had no responsibility to feed their development work to the experimental department and by that I mean, no responsibility to develop anything for road use!

The PW3 profile has no direct relationship to PWs time at Norton, being a later development by Peter as a private individual, a development aided by computing technology that was not available in the early 1970s. Do get a copy of Peter's book.

And try to imagine British industry as a loose association of individuals, some trying to do things they were not responsible for, just because they wanted to! Managed by people who had no idea what the engineers and others that worked for them were doing most of the time! Certainly that better reflects the parts of British industry I worked in over 30 years.

worntorn said:

According to the man with the dyno, the PW3 vs stock loses about 6 hp in the midrange and gains 3 hp at the top.
The result would feel extra strong as comes onto the cam, coming from lowered torque vs stock in the middle to extra torque vs stock at the top.

Glen

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Maybe the man with the dyno could be more specific! Engine build spec, capacity, stroke and compression etc.
What rpm does it lose 6bhp at? Where is it neutral? And where is the extra 3 bhp?

I would say that most people who have raced with a PW3 would not recognise the reported characteristic.

For me personally it is a great cam for building power from 5 to 7000, particularly 6 to 7 change up and repeat. When run through a close ratio box with 34 or 36mm carbs and an open separate exhaust system and compression between 10.25 and 10.5:1 and Fullauto ports and a light crank, rods and pistons and pump fuel. (doubtless a little more compression would be OK too)

If your dyno man reports a mid range hole at 4000rpm, I'm hardly aware of it!

Remember, it is great race cam, but for me, it's not a road cam, for which use the 650SS derived standard cam you refer to.

The man with the dyno is Jim Comstock and he provided all relevant info at the time. I have reposted that info a couple of times.
This was a PW3 that went into an otherwise stock 850. The power loss was through the mid range where most road bikes spend the most of their time. I can't recall the exact rpm numbers at the moment. I didn't commit them to memory as the results were such that this is not a modification I'm ever going to do.

He wasn't telling people not to use the PW3 for racing or even for roaduse.
It was clear that for road use the change from a stock cam to a PW3 with no other changes is a detune, unless you mostly run at very high rpm on the road.
People still do add a hot cam on its own and often are very happy, even with the midrange reduction. That's alright too, it's all just for fun!
When we were kids on bicycles we clamped baseball cards onto the front forks and let them make noise on the spokes. We knew that this mod made our bikes faster. It sure felt that way at least!

We had one member here who was running a single mikuni and a PW3 . He liked the single mikuni as he didn't like revving over 5k. He swore that the PW3 was helping the below 5 k performance. The dyno says otherwise, but he was enjoying it, so that was the right setup for him.

Glen

acotrel said:

A loss of 6 BHP midrange to gain 3 BHP at the top might not be a good way to go if the gearbox is not close ratio. With wider ratios more midrange is needed. - Depends a bit on the circuit. If the motor is continually well on the boil 3 BHP extra at the top might be OK. I think it was at Silverstone that PW was faster than the TZ750s.
I am surprised the Norton factory was not more methodical - they employed some very good guys.
The Japanese did not seem to be shy about sharing secrets.
It would be interesting to know how the Manx was developed by Joe Craig.
I used to have Triumphs - Nortons seem to be much better.

Click to expand...

Hours on the dynos and on the track tuning seem to work for Joe. Having tons of experience helped and he was methodical in his approach, just on a short budget.

Carl H said:

Norton: Riding back from the brink

Not for the first time Norton faces an uncertain future after a recent financial scandal. But as a history littered with racing triumphs and comebacks proves, motorcycling’s coolest brand has a habit of surviving. Mat Oxley reports

www.motorsportmagazine.com

Hours on the dynos and on the track tuning seem to work for Joe. Having tons of experience helped and he was methodical in his approach, just on a short budget.

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I found the magazine article interesting. I often wondered about the combustion chamber in the Manx. The ones I have seen usually have a squish band which goes right around the circumference,, The squish band in the Commando engine is only near the inlet valve. The comments about combustion conditions and running as lean as possible, tally with my own thinking and practice.
I suggest the handling of the feather-bed frame is a big plus. With 19 inch wheels and it's rake it is almost impossible to get more trail. The main difference I found when I road a Manx, was the oversteer when it is gassed in corners. Developing that handling would not have been easy. I watched Duke race the Gilera against the Manxes on an airstrip circuit - he simply passed around them at the ends of the straights, in big swoops. The Gilera did not need to be fast in corners.
Francis Beart's book 'A single purpose' is interesting, but still does not give much away about tuning.
When methanol is used, tuning is much easier, and the heat problems are diminished.

worntorn said:

The man with the dyno is Jim Comstock and he provided all relevant info at the time. I have reposted that info a couple of times.
This was a PW3 that went into an otherwise stock 850. The power loss was through the mid range where most road bikes spend the most of their time. I can't recall the exact rpm numbers at the moment. I didn't commit them to memory as the results were such that this is not a modification I'm ever going to do.

He wasn't telling people not to use the PW3 for racing or even for roaduse.
It was clear that for road use the change from a stock cam to a PW3 with no other changes is a detune, unless you mostly run at very high rpm on the road.
People still do add a hot cam on its own and often are very happy, even with the midrange reduction. That's alright too, it's all just for fun!
When we were kids on bicycles we clamped baseball cards onto the front forks and let them make noise on the spokes. We knew that this mod made our bikes faster. It sure felt that way at least!

We had one member here who was running a single mikuni and a PW3 . He liked the single mikuni as he didn't like revving over 5k. He swore that the PW3 was helping the below 5 k performance. The dyno says otherwise, but he was enjoying it, so that was the right setup for him.

Glen

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Glen, that just confirms that to make a camshaft work, you usually have to address other relevant parameters. Just changing the cam is rarely a magic bullet, and often unhelpful. I know you know that.

But yes indeed, if it makes the individual happy who are we to tell them they shouldn't be?

Though I observe that many would not tell you if they weren't happy. And personally, what I use is always the best choice .

I run the JS2, which is very similar to a PW3 cam. I run 9.5:1 compression (I am debating moving up to just past 10:1), beehive springs, BSA lifters, and RH10 conversion tubes. The JS2 is a big improvement over the stock Norton cam. It is a different power delivery experience, my opinion of the 850 was it made peak torque way too early. It felt like a tractor, and it was not the experience I wanted. The JS2 cam moves that power up 1000 to 1500 RPM. It makes great power around town, I cruise at 3000 to 4000 rpm and at 4000 RPM the power really comes on and pulls hard through 7500 rpm, and I really do not care to see what it makes past 7500. I will say this experience makes me want to build a short stroke bike at some point, and makes the 850 feel a bit more like a 750.

The PW3 is a fairly significant departure from the stock Norton cam, it moves the peak torque on an 850 up to the 4000 to 4500 range and revs to upwards of 7500 rpm. While I think it is a great street cam, it is not a drop in cam. And I suspect if you optimize for it, you will make a bit more than 3hp on the top end.

maaseyracer said:

I run the JS2, which is very similar to a PW3 cam. I run 9.5:1 compression (I am debating moving up to just past 10:1), beehive springs, BSA lifters, and RH10 conversion tubes. The JS2 is a big improvement over the stock Norton cam. It is a different power delivery experience, my opinion of the 850 was it made peak torque way too early. It felt like a tractor, and it was not the experience I wanted. The JS2 cam moves that power up 1000 to 1500 RPM. It makes great power around town, I cruise at 3000 to 4000 rpm and at 4000 RPM the power really comes on and pulls hard through 7500 rpm, and I really do not care to see what it makes past 7500. I will say this experience makes me want to build a short stroke bike at some point, and makes the 850 feel a bit more like a 750.

The PW3 is a fairly significant departure from the stock Norton cam, it moves the peak torque on an 850 up to the 4000 to 4500 range and revs to upwards of 7500 rpm. While I think it is a great street cam, it is not a drop in cam. And I suspect if you optimize for it, you will make a bit more than 3hp on the top end.

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The peak torque with the stock 850 is at 5000 rpm, peak power at 5800 rpm.

4500 is where the PW3 loses 6 bhp against stock ( on dyno).
Other changes can be done to fill that back in. I suspect it would take a lot of compression alone to do it. A point or two would get some of it, but then you can also add compression with the stock cam and it will hang onto more of that increased compression in that range.
Going from Jim's dyno testing on these bikes, 4 to 5000 rpm is pretty much owned by the SS cam. Above that others prevail.


You might be ok at 10 to 1. My 920 is at 9.8 to one with the stock cam. In theory it should cause pre ignition more readily than a bigger cam at that compression as it hangs onto more compression. So far it has worked well, no pinging that I can hear. The acid test will be climbing a long grade on a hot day.

Glen

worntorn said:

The peak torque with the stock 850 is at 5000 rpm, peak power at 5800 rpm.

4500 is where the PW3 loses 6 bhp against stock ( on dyno).
Other changes can be done to fill that back in. I suspect it would take a lot of compression alone to do it. A point or two would get some of it, but then you can also add compression with the stock cam and it will hang onto more of that increased compression in that range.
Going from Jim's dyno testing on these bikes, 4 to 5000 rpm is pretty much owned by the SS cam. Above that others prevail.


You might be ok at 10 to 1. My 920 is at 9.8 to one with the stock cam. In theory it should cause pre ignition more readily than a bigger cam at that compression as it hangs onto more compression. So far it has worked well, no pinging that I can hear. The acid test will be climbing a long grade on a hot day.

Glen

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Interesting about the torque, I would have assumed it peaked much sooner, I have not studied dyno charts on these things.

I think I will be fine at 10.25:1 Plenty of clearance to the head and I am timed at 28 degrees, if it gives me any trouble I will time to 27 or 26 degrees, if I have issues there I will go back to 9.5:1.

maaseyracer said:

Interesting about the torque, I would have assumed it peaked much sooner, I have not studied dyno charts on these things.

I think I will be fine at 10.25:1 Plenty of clearance to the head and I am timed at 28 degrees, if it gives me any trouble I will time to 27 or 26 degrees, if I have issues there I will go back to 9.5:1.

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Works Norton 750 short strokes ran around 10.25:1. I have stuck with around that in the engines I have built in the '70s and after 2010. Personally, I think it is a better place to be than 11:1 for a road racer, apart from anything else it isn't too demanding on fuel spec. Clearly, others who make a lot of effort to get more compression disagree.

(I run a 750 short stroke with around 10.25:1, JS2, beehives, long rods, unmolested Fullauto Head with standard sized valves, 36mm Mikunis, open separate exhausts. Timed between 28 and 30 degrees, and it will run on 98 octane pump fuel. I normally rev it to 7500, but it may go to 8000 occasionally. This is a pretty well-balanced and rideable road race engine. For road use I would run a standard cam profile, probably compression about where you have it and maybe 34mm Mikunis, or maybe 33 FCRs, and drop the rpm range. Oh, and most likely an 89mm crank with the 77mm bore.)