What cam do you have and why?

Status
Not open for further replies.
One correction here; one of my builds of the Commando racer used a cam I found in a parts bin which was marked "RX" and I was told it was a Norris RX. DynoDave profiled it and posted same with the comment that it had "a bit more overlap than the PW3".

I would have no reservations about running this cam in a street Commando.

What cam do you have and why?
 
When I was a kid, I fitted race cams to a range of road bikes - they were always good for an adrenalin rush. However when I went road racing I learned some very hard lessons. My friend was always into extreme motors and I inherited one of his bikes. It had jumped on him at Bathurst in the 1950s and broke his arm and leg in the one incident. When I raced it, it turned me into an instant dud.
 
As stated above, I campaigned a 750 Commando racer with maybe 9.5 or 10:1 compression, squish and a Megacycle 560-020 cam, and I would have no reservations with doing the same for a snappy street build. I ran it with 3" radiused lifters.
Plotting courtesy of Dyno Dave
What cam do you have and why?
 
Fast Eddie said:
acotrel said:
What cam do you have and why?
Click to expand...

THAT is one fine looking motorcycle !!
Click to expand...


I beg to differ , what an ugly piece of garbage , lines are all to pot . Red is for the ITALIANS . And it aint got the hystericalorg Honda emblem . AND its bigger than 125cc . :lol: :lol:
For the money they spend on their RC69 reps youcould do a 74 Ago MV grand prix bike . :twisted: ( yea thats a CB 750 with no thru flow on the cylinders . :x


Cant a pack of half assef gits out here get together and put together something to stop these cheap tinny Jap Suckers having it ALL THERE OWN WAY !?

Thinking last night what an overweight gutless p o s the original GS 1000 was ( and what a joke the GS 750 ) .

IF theres any Myopic Anglophile en masse here , Ive got the makings of the engine in the shed , we'd need a practised welder & ditto machineist .
On a teth there budget , with a bit of scavengeing and collectivism ,we should have the barstewards in our sights . But youll only get the champagne when theyre trashed .

No halfassed knowall pessimist type aussies , unless theyve got machineshops and know how to shut up and GET SOMETHING DONE , or I'll go homen Do It Myself .

Hondas walking all overthem . Cant even put a British Bike Together Right , and dunno how the d*^#well go , ANYWAY . :shock: :wink:
 
p.s. those things all pretzled & the cam chains fell out , blowing of BSA Triumph , So They DIDNT try it again , at DAYTONA with those. NOTE BSA Won it in 71 ! :lol: :lol: :lol: WHOS for a TWIN !?
 
Dances with Shrapnel said:
As stated above, I campaigned a 750 Commando racer with maybe 9.5 or 10:1 compression, squish and a Megacycle 560-020 cam, and I would have no reservations with doing the same for a snappy street build. I ran it with 3" radiused lifters.
Plotting courtesy of Dyno Dave
What cam do you have and why?
Click to expand...

The difference between flat and 3" radius lifters do not make anywhere near as much difference as I had expected!

Is it just me?

Please feel free to correct my ignorance here, as I am interested to know more.
 
From JimC's cam thread:

cams-t12813-105.html

comnoz said:
The next step up is the #312A grind run with 4 inch radius lifters. it has duration numbers slightly longer a stock cam with considerably more lift and a little more overlap than the stock cam. It likes a 9.5 to 1 compression ratio and works well with the stock exhaust. It is the setup that is in my bike now.

What cam do you have and why?


Then we get to the hot street grind. It is the same #312A but with flat lifters. An increase in duration and overlap make it come alive over 4500 rpm. It likes compression between 9.5 and 10-1. With the extra overlap -it responds well to exhaust tuning.
This was also the cam that I used with best results on the shorter roadrace courses. It revs freely and has a fairly wide powerband.

What cam do you have and why?
Click to expand...
 
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.
 
Well it looks to me like there is a lift increase from a shy 36k to ~37k, with more overlap by going from 4" radius to flat lifters.
 
Yes there will be more duration (and overlap), I'm just interested in understanding how much. And, how much difference this makes to the characteristics of the engine.

The graph shown earlier by Shrapnel seemed like a very small difference, but, as I understand it, it makes a big difference to the power delivery characteristics of the engine.

However, the peak lift cannot change irrespective of the amount of radius... can it...?
 
Fast Eddie said:
The difference between flat and 3" radius lifters do not make anywhere near as much difference as I had expected!

Is it just me?

Please feel free to correct my ignorance here, as I am interested to know more.
Click to expand...

I've got nothing for you on this Fast Eddie. The curves do not look unreasonable to me. And when looking at the difference between cross-over at lifts for the RX cam with and without radiused lifters, it looks about the same as the compared to the difference between cross-over at lifts for the WC12a cam. The RX comparison used a 3" radius lifter whereas the WC12a comparison used a 4" radius lifter. From as best as I can see, both cams indicated about a 0.020" to 0.030" reduction in lift at cross over when employing radiused lifters.
 
Fast Eddie said:
Yes there will be more duration (and overlap), I'm just interested in understanding how much. And, how much difference this makes to the characteristics of the engine.

The graph shown earlier by Shrapnel seemed like a very small difference, but, as I understand it, it makes a big difference to the power delivery characteristics of the engine.

However, the peak lift cannot change irrespective of the amount of radius... can it...?
Click to expand...

The peak lift does not change. The Y axis of the 2 plots are scaled differently, in the 312A 4" rad follower plot the Y axis scale moves in 0.060" lift increments whereas in the 312A flat follower plot the scale moves in 0.050" increments.
 
The difference in the area under the curve changes a bit when going to a radius lifter, but that is not what makes the difference in how they run.

It is the considerable change in degrees of overlap that makes the difference. Jim
 
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.
 

Attachments

  • What cam do you have and why?
    312A flat and radius lifter.webp
    69.4 KB · Views: 328
WZ507 said:
I nevertheless remain amazed how pleased the majority of people are with the larger lobes for street use.
Click to expand...

We're a bunch of gear-heads! (or, like me, a Jr. Gear Head) :mrgreen: :mrgreen:
 
Adding a radius to lifters for a cam designed for flat lifters - or running a cam designed for 1-1/8" radiused lifters with tighter 7/8" radiused lifters will reduce the duration and increase the overlap between lobes. This is usually done when slightly oversize valves are installed without re-angling the guides and you have a potential valve clash problem. It's a cheap quick fix solution and gives you more valve clash room. This is OK for street bikes that don't rev too high but its not a good idea for a race bike or a cafe bike thats run to red line because the reduction of duration (while keeping the same lift) increases the acceleration and pushes the valve towards the valve bounce zone. The ramp is effectively shortened and you have a situation that leans in the direction of the PW3 cam with its shorter ramps and valve bounce potential. Its better if you only tighten the radius of the exhaust lifters because the lighter ex valve has less chance of valve bounce. Most of the Norton cams are already to close to valve bounce problems at high revs.

Its a trade off of problems depending on what's more important in each case. It will add torque but reduce the top end.

For example - Changing from 1-1/8" radiued lifters to 7/8" radiused lifters will reduce the duration by about 4 degrees and reduce the lift at overlap by about .006" (JS1 cam).
 
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
 
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
 
Status
Not open for further replies.
Back
Top