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dave thomas
Total Likes: 3
Original Post (Thread Starter)
#825117 09/28/2020 11:28 PM
by dave thomas
dave thomas
Hi all, does anyone have performance data on the different cams available ? My DBD engined bitsa has touring profile cams but I wondered if there were any graphs / data comparing these with Scrambles or Clubmans profiles ? First hand experience would be good too
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by Rich B
Rich B
I don’t have any graphs, but I do have a DB with DBD head and 1038 Concentric with scrambles cams. IMO, it makes the engine a torque monster for real world riding. Little flat on top end, but that is ok, I don’t need to go that fast.

The engine pulls well from 2500 - 6500 RPM.
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by Magnetoman
Originally Posted by dave thomas
While we’re on the Scrambles theme, what are the differences between 42/46 and 46/46 ?
So, Clubman vs. Scrambles. Again, there's the issue of a silencer, such as it is on a Clubman, and a straight pipe on the Scrambles.

Surprisingly (to those who haven't looked at the curves), there is relatively little difference. The difference in maximum hp would be important on a track, but perhaps less so for a bike ridden on the road.

Clubman: 28.5 hp @ 5000 rpm; 36.5 hp @6000 rpm; 39 [email protected] 6500 rpm; 40 hp @7000 rpm
Catalina: 32 hp @5000 rpm; 37.5 @6000 rpm; 39.5hp @ 6500rpm

Note that there was a steady increase in the highest hp over the period of development, and there is variation even with the same cams, so I'm quoting results from the latest curves I have. Basically, with Scrambles cams you give up a little at redline, but gain at lower rpm.

It's a personal decision, but I'm not planning on riding at the IoM so I never intend on any my engines seeing anything close to redline. Given that, for me, Scrambles cams seem the way to go. Interestingly, the only dyno curve I have for a Competition model shows 41.7 hp. @ 7000 rpm. That model was built by the factory with Scrambles cams (the curve is actually for the bike I own, and when I rebuilt the engine I found Scrambles cams in it)..
1 member likes this
by Stuart Kirk
Stuart Kirk
Greetings everyone,
Here's a little "real world" seat of the pants input, as if the world we live in is real. Back in the eighties, my old '63 DBD had road race cams, a 1038 concentric, 10to1 MC forged piston and a pattern silencer, basically a straight through glass pack. It was tractable but kind of soft up to around 3500 where it hit a little flat spot but then about 4500 it came on really strong and would rev headlong to 7000 and more. The cam effect was quite gratifying and the concentric really helped civilize the lower rpm behavior. But maybe not so great for everyday use even though that's exactly how I used it back then, even did a 400 mile day once.

Right now, I have a set of scrambles cams in my '55 CB34 engined dirt bike with the small port (32mm) head, 32mm concentric and the same type of pattern silencer, but no tach so I can't really tell you any rpm's. But, I can say that it makes lots of low and mid range torque and will rev if you wish, just not quite as willingly. Of course, the smaller carb and port reduce its top end performance.

So this isn't really an apples to apples comparison of top end thrills but should give you an idea of what to expect below the 5000 rpm level MM's graphs start at. The scrambles cams will give you lots of low end tractability and satisfying top end performance.
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