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My R75s did a lot of mileage offroad and one of the things I always wanted was more responsive midrange and trials type plonking power. (The /5 was better for that IMO). Back then there were plenty components if you wanted to make a mega monster, but nothing to enhance the low end (or at least, nothing available in outback Australia).

I got most of what I wanted by fitting Mikunis (straight off a Suzuki T500, jetting almost bang on), and getting the local Mt Isa Mines workshop to roll me up a stainless steel silencer to my spec (actually ideas cribbed from Phil Irving ). The /5 heavy flywheel helped I'm sure.

I can't help thinking that these days there's probably a cam that will help, but I can't see one anywhere. I always liked the tweak we could do with some of the old British bikes of using a hotter cam for the exhaust and a mild inlet (eg 3134s on Triumphs exhaust), or grinding the exhaust cam follower flatter on some singles.

So let's hear the opinions, or even better, info from those who have tuned a bike for low and midrange.

This is what MI sells as an Enduro cam for later bikes: http://www.motoren-israel.com/product_i ... shaft.html

It is bassicly an R50/5 to R60/6 cam with a bean can nose.

Keep in mind that the R60 9.2 to 1 engine was the pingiest engine BMW made and I believe the cam was the culprit.

Find out what BMW did to the R65 Mono - it lost 2hp to the LS at the same rpm,but peak torque was lowered from 6,500rpm to 3,500rpm. It has a lot more bottom end than the LS,with a pretty good top end too,it pulls a taller final drive to the LS,so acceleration is down.

Jim Cray gets good results with twin plugging gas flowing, some minor mods to the air box and setting the head height so the squish band works. All done without any cam changes, when these are added in you can start to increase Bhp and torque, but possibly at the expense of bottom end grunt

See this before and after dyno chart and look at the modified engine torque curve, this gives a very nice engine on the road, bur hardly a trials bike!

Usual hot-rodding "tricks" apply – but kinda in reverse !
BMW provides the model,
i.e. BMW sport models used larger carbs, bigger valves, and etc to produce improved top-end HP & performance.
Standard models produced somewhat less HP but delivered more torque at low and mid rpm.

Intake and exhaust systems also play an important part in the torque delivery / peak vs HP equation.
Typically a smaller diameter exhaust and a longer system length
enhance low-mid torque delivery & lower torque peak
as does longer intake tracts.

Cam profile is a consideration, too, but the stock 308 should be a suitable choice.

Most folks readily buy into the sales rap of more HP.
Tuning for rapid torque delivery and a usable torque peak makes a lot of sense.
Looking forward to see what you come up with.

What Vansen said plus a little more compression!

It's been a while since I've done serious engine mods - mainly to British singles.

Here's what I did to a Velocette Venom to get plonk, a decent midrange, without losing much if anything of the top end.
Cyl head of the Viper (350cc) for the smaller inlet port. Opened the port up slightly, but concentrated on straightening it and cutting down valve guide intrusion on inlet. Used gaskets to bring the CR down to standard.
Matched the carb to the port and made the induction length 8" if I remember right.
Ground the exhaust valve cam guide follower flat like the Thruxton, but left inlet standard.
Used the heavier flywheels of an MSS but got them balanced by Geoff Dodkin. Polished to a mirror finish - don't think it helped, but looked good
Long megaphone exhaust with narrower taper than usual for the time.
It worked nicely. I lived in the Highlands of Scotland with lots of winding narrow singlelane roads and this gave a bike with great response. The ability to plonk along was invaluable when riding on snow and ice. (Used to ride year round)
Much of this was adapted from the spec of the Velos used for 24 hour races (Montejuich etc)

So left to my own devices, I'd probably do something similar with the BMW, but tricks like modifying cam followers wouldn't work, I'd need to get a cam modified. It would be simpler if one was available off the shelf.

George Ryals wrote:...'69 BSA 441 Victor Special...

I had the motocross version with Ceriani fork. When giving it heaps, sometimes the clutch would be reluctant to disengage, or would slip when the lever was freed even though everything worked perfectly on the bench. I figured the mainshaft was bowing under pressure causing the clutch pushrod to bind, so I cut the clutch pushrod in the centre, case hardened the ends, and put a suitable size ball bearing between the 2 cut parts. This stopped the binding. (You may already know this or don't have the problem)