CB1100 assymetrical cam timing, lift, and duration.

[Roger the shrubber_imp]

I've been studying up a bit on our beloved CB, and one of the persistent oddities I discovered was the unusual decision by the engine design team to give the big CB some character by engineering in a little roughness. Apparently, the engine was deemed "too refined" so they retarded the intake cam timing on just two cylinders to give the bike some soul, I guess. Stranger still, they went through the trouble of utilizing a counterbalancer to make the engine smooth! Seems counterproductive.

Anyway, this assymetrical cam timing comes at a cost in achievable top end horsepower I believe, so I'm going to look into this by buying a set of stock cams and taking some measurements. My engine builder and machinist can re-profile the intake cam to a symmetrical timing configuration, perhaps even altering the duration to get more horsepower out of this powerplant. The cylinder head is also modestly configured with relatively small port area, so perhaps some improvements can be made there too.

115-125 hp seems achievable, as long as I can get the engine management system to play with these changes. Anyone else look into this or know about it?

[the Ferret]

Well the staggered cam timing was disussed on this forum ad nauseum when the bike came out in 2013, but not much been discussed lately.

Will be interesting to see what you come up with.

[Roger the shrubber_imp]

From the early to late 1990s, I built a few engines with let's just say, "more than the designed safe horsepower" (within structural limits of course) Lol...

One of them was a project Kawasaki ZX11 D1 which dyno'd almost 175 normally aspirated rwhp. This came at a substantial cost, but it was tremendous fun to ride, if not a bit challenging. Luckily, the bike's large overall dimensions and generous wheelbase made it manageable to some degree.

Looking at the stock, off the showroom floor output of some of the newest supersport bikes, this doesn't seem like particularly earth shattering performance. I'm just left wondering what I can do about the calm demeanor of the aircoooled CB motor.

[Tim_in_AZ_imp]

First Kawiboy and then you. I sense a disturbance in the force.
(In a good way.)

[Roger the shrubber_imp]

Luke..

I am your father.

[Elipten_imp]

Then father give me some dark side force!


2014 CB1100 DLX
2013 CB1100 Std
1990 BMW K75 RT

[kmoney_imp]

This could be cool. I'm betting that the cams in the are the major cork in our engines -- with the way this engine rides and it's powerband, they must be quite conservative. It'll be neat to see what your machinist comes up with.

I'm somewhat surprised that with how popular this bike has been, and how long it has been released overseas, that noone makes aftermarket cams.

[Roger the shrubber_imp]

Me too. Absolutely no internal engine mods available from my observations. This may be the nefarious side effect of stringent emissions regulations in the countries the CB was introduced into first, and weak aftermarket support especially here in the US, where the bike thus far has only had a two year run. Consider however, that there are many other bikes in the same displacement category where high revs and max horsepower output happen at the 9,500-13,000 rpm range... those bikes are supersport models, a category that the CB has nothing in common with aside from the number of cylinders. It's not that kind of motorcycle.

Any extensive engine mods will likely require changes to the fuel injection and ignition mapping, perhaps a custom ECU and possibly larger injectors, among a few. Re-profile of the cams is easy enough and is something engine builders have done for decades. In the case of assymetrical cam timing, the cam can be cut in sections, lobe centers realigned, and then rewelded, ground, and hardened.

My 1982 CB900F had fully symmetrical cam timing and an engine counterbalancer, and it had a smooth, high revving air cooled engine producing 115 HP without the need to engineer in some "character" as the designers have done with the CB1100.

[Motogeezer1949_imp]

IMO, it's a moot point. I'd love for you to do it however, and document the before and after hp

[Pterodactyl_imp]

On Kawi's thread I commented that some basic mods should get you to the 100 - 120 neddies range. That's a lot of go for an eighties style UJM. Suspension mods etc would definitely need looking at, particularly for street use. I guess the drive train and frame would be up to it.

Keep us posted.

Cheers