Norris cam Magnum 70
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lcrken
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It's a pretty serious cam for a 750. The intake lobe is basically the same as their 750D all-out racing cam, but the exhaust is a milder profile from their Super Street cam. It's still a lot of lift and a lot of duration. Probably has great top end power in properly built engine. Might be a bit fussy in a street 750 for around town putting. Milder exhaust profile also helps reduce risk of valve interference in big valve heads. With that much lift and duration you'll definitely have to check for piston-valve clearance, valve-valve interference, and valve spring bind when you set it up. Should make a good race bike cam, though.
Ken
Ken
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Was just lurking until Ken stated this Mag-70 cam is on similar scale as Norris D [D= drag race?] and may not be desirable for timid civilized use. This confuses me as I see the hottest vintage engines idle reasonably on cold starts and easy control rolling through crowed pits areas. My '68 Ranger P!! drag only wonder went BLATT! not varrRROOOM on short throttle blips yet was a short shifting HD like treat for low end torque to waddle through school lots or deep sand lanes no problemo even in top gear no throttle even climbing grade. It was extra fun with soft steady kettle drum like 600 rpm at lights - so the hot rods of the era, 2 & 4 stroke triples would glare down at me on 50cc size bike and go varrRRoOOMM and let out clutch still on throttle for a short lerch forward to invite a contest, which generally I cut short with just a BLATT! with slight clutch release w/o throttle to whiplash head to tires blur too fast to focus on til 2 bike lengths later in less that a blink. I'd bet this Magnum 70 might work a treat to live with if valve train and CR to handle it. Drive train and tire wear may be the real issue to consider in traffic to pass - not bogging stalling easing around. May tame it to taste by advancing cam degree some too.
BTW DynoDave Comeau has CNC set up to profile cams fast w/o much tedium so might be good to alert him to send cam to add to his reference base.
BTW DynoDave Comeau has CNC set up to profile cams fast w/o much tedium so might be good to alert him to send cam to add to his reference base.
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lcrken said:
Assuming Ken's lift # are at the valve.... then it looks very close if not identical to this web cam: http://atlanticgreen.com/images/cam930.gif
A local roadracer uses it and it is very strong especially with a rather "free flow" exhaust. ... a touch hotter than a combat
Chris
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Hi Dave
Thank you
Everytime I find a cam I look at your site! Thanks for all your help.
You may notice that Steve A has chimed in about his short stroke?
He called in Sunday & appears not to have a cam for his engine yet
Might give it a bash in my 850
Thanks Ikren Thanks Hobot.
Time to get my roadbike back on the road
all the best Chris
Thank you
Everytime I find a cam I look at your site! Thanks for all your help.
You may notice that Steve A has chimed in about his short stroke?
He called in Sunday & appears not to have a cam for his engine yet
Might give it a bash in my 850
Thanks Ikren Thanks Hobot.
Time to get my roadbike back on the road
all the best Chris
SteveA
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Chris said:Hi Dave
Thank you
Everytime I find a cam I look at your site! Thanks for all your help.
You may notice that Steve A has chimed in about his short stroke?
He called in Sunday & appears not to have a cam for his engine yet
Might give it a bash in my 850
Thanks Ikren Thanks Hobot.
Time to get my roadbike back on the road
all the best Chris
Chris, you have too many projects.... :wink:
750 long stroke, 960, 850! Nah, it needs to be tried in a 750 short stroke first....
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I've a Norris D which needs heavier-longer springs and lighter valves- retainers not to coil bind,float or clash with the lift- rpms the cam was intended to breath at. I think my ole P!! had similar, idled nice and low 600 rpm and would cough-stumble if throttle snapped - for ~.5 sec till ~1000 rpm for BLATT! response, clutch in free wheeling or fully engaged going nowhere in street tire smoke cloud w/0 any front brake applied. Magnum770 reported installed in Production Racer so might look up what their details were but there's better valve kit available nowadays like Beehive springs and 6 mm stems. Might also look up the mass of proddie flywheel as both P!! and Peel had about 5 lb less which helped avoid the sluggish varrRROOMMM response for more of BLATTTT! If you can snap throttle to WOT and back fast as ya can from 1000ish rpm and not shoot tach needle right past 7000 into upper redzone, then ya ain't experienced what's possible in Norton push rod clunker. Fast rising torque curve allows reversed controls delight, extra throttle slows ya down and backing off thrusts harder hooking up unless short shifting to mimic a touring Harley.
lcrken
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SteveA said:
Steve, I think they were primarily referring to using their high performance spring kits, which included springs, titanium retainers, and spring seats, as opposed to using stock springs. That was what cam grinders back then typically specified as necessary for their higher performance cam grinds. The other common warnings were to check for spring bind, retainer-to-guide clearance at full lift, and valve-to-piston clearance.
Other mods like rocker lightening, aftermarket pushrods, bronze guides, bigger valves, and so on were not things cam grinders normally required for their cams to work. They did sometimes include recommendations for mods like high compression pistons and free flowing exhausts to get maximum benefit from hotter cams, but not as a condition for using them.
This particular cam profile is for flat tappets, so no follower radiusing required, unless you wanted to do so to make the valve lift profile a little milder.
Ken
lcrken
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SteveA said:Steve, I had some thin stem inlet vales in '75/'76, in cast iron guides they didn't last long!....they came from Thruxton....
So who is doing them now? and I hope they supply them with the right collets....see above....
Kibblewhite Precision Machining (KPMI) at http://www.kpmivalvetrain.com/ will make their Black Diamond valves for Nortons in 7 mm stems on request, although they only show them in their listings for Triumphs. They supplied the 7 mm valve kits for Nortons that Kenny Dreer used to sell. They will also make them in custom sizes, or in titanium if you so desire. They can also supply matching spring retainers and collets, and bronze guides. I've had them make Black Diamond valves for Norton intakes with 1 5/8" heads to suit the RH7 heads, and they are very easy to deal with.
Ken
lcrken
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acotrel said:
Drag racing, landspeed racing, and roadracing on long courses like Daytona.
On more typical roadrace courses, I'd agree with you. Really good midrange and good enough top end power, with 5 or 6 speed gearbox and well set up bike can work better on tighter courses than going for max top end power. Not sure what sort of tracks you race on, but at some US tracks like Daytona, serious top end power is esssential for good results.
Ken
SteveA
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lcrken said:
It is an interesting one Alan, and KC has indicated it is the mid range of his long stroke he finds really useful.....but as I have said before...I am building a short stroke....different anyway...and a whole box of gear is going to be essential...now...does it make sense to be building a short stroke and tending to build for mid range, when top end might be its forte anyway....
As for UK tracks, we tend toward the tight ones anyway...and my own history includes the last Norton I raced which as a long stroke 850 made mid range by the bucket anyway but...in the Rickman chassis I still got better results on the airfields we used in the day...long open tracks...which is where I think I am best!
And my more recent history includes two GSXR750s, 6 speed box, all top end and more or less no mid range and a rev limiter set around 13K.....compared to a Commando this is all a bit different...
If Chris will consider letting me use the cam we are discussing I might like to give it a try, with a good valve train, maybe the JS radius A65 followers, beehives etc. A bit milder in use perhaps that way and then allow the thing to rev over 8K with lower risk of the valve train throwing up...
Do I want to build a Commando motor to be like a GSXR750?, not really, but by going short stroke it aint going to make the mid range of a long stroke anyway, and it is certainly not going to make comparable mid range to a 1007 or 960 that I will ride against in 1300 twins, so I might as well go for top end!
Anyway a cam can always be changed if you don't like it.....I am pretty much committed to 80.4mm now with crank and rods....
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