The CB1100 Community Forum

Great- somebody besides me please grow a pair and rip into their engine.

I'd love to have some competition as that drives motivation and innovation.

(08-08-2018, 12:24 PM)The ferret_imp Wrote: [ -> ]Here is something I think about when I think about performace upgrades. Some of the greatest engineers or mechanics or tuners are Japanese. The CB is hugely popular in Japan. The aftermarket for the CB is huge in Japan. If much could be easily gained by massaging this motor as some would have you believe, one would think Samurider would show big bore kits, cams, larger valves etc on his website available for purchase. It was certainly like that with other Japanese bikes the entire time I was in the motorcycle industry from 1972 to 1989. Performance enhancing mods are readily available for other Japanese bikes..ZRX's, Hyabusas, GSXR's and many other bikes that don't really need it, but not being available for one that quite a few people feel could use a boost, and would gladly pay for makes little sense to me. You can buy fairings, and exhaust systems, and swingarms and wheels, and sprockets and body parts galore, any little trinket to make it prettier, or tricker than the next guys, but not one motor part offering to make it faster. Why do you think that is?

Like I said, just something I sometimes think about.

+1, Ferret, thank you for your wise read

1* If I had, lets say a 120 HP CB air cooled engine , I am more than certain, it would not be enough for some members, these would like to have a 150 HP one , and if they got it, these would say...now entire frame is too weak and other parts cannot withstand this load or mechanical stress, causing the CB to have a short life..and burns too much gas now...and would be unhappy again....and even if you had air cooled one, HEAT would be your worse enemy...
2* Some members have a big plan with engine modification backed by NO engineering +++ knowledge..so for these my advice is: put the money where your mouth is..
3* In my entire automotive life, I met only two people who have adequate knowledge about cams ++, one was my friend who used to race cars and had automotive racing shop closed to public and the other one is PowerDubs...and even he tells members what to expect + think before you start !!!

I used to port and modify small 2-stroke, carbureted engines (up to 175 cc) and believe me, 4 stroke MPI, air cooled is totally different = much more difficult animal.

Good luck to all amateur modifiers ..., stop playing engineers without eng. degree ....

If anyone thinks my statement offends you, I give permission to all moderators to delete it.

I don't think one necessarily needs an engineering degree to successfully improve an engine's output but I do agree Honda intentionally designed the CB1100 to meet a certain set of parameters given noise, emission, rideability, cost, and efficiency targets and not to absolute 10/10ths performance. I'm good with that.

Peter – I am cool with whatever comments you want to throw my way. I have known several engineers in my life and they are all opinionated maybe even a little arrogant and condescending. But to me that is not necessarily a bad thing.

I’ve already said I’m just doing this for fun and to see what I can get out of it. I promise you Honda could’ve got more out of the engine if they wanted to.

I never claimed to be smarter than them, which is why I said I am just removing the obvious bottlenecks that they had to put up with. You very likely are smarter than me as well.

But I have also been hot rodding all of my engines starting with dirt bikes decades ago, and have heavily modified many motorcycles and cars to extent that most people would not believe.

Example- I spent more money modifying my VW mk4 R32 then I paid for the car. ($3x,xxx). It was a LOT of fun. Made over 30% more power at the wheels than stock with zero loss, all gain across the rev range - quite substantial even down low. And sounded fantastic. Got better mileage when cruising as well. Every aspect of the car was changed numerous times.

Trapped 105.xx, and 13.1 all day long at the drag strip in a normally aspirated 3.2 6 cyl weighing around 3400# plus me (200 nekid). Slow compared to a bike or a turbo car- but back in the muscle car days not too shabby.

Not really understanding the hate from soo many people on the topic of CB1100 engine modifications.








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I suppose I can understand the "modding" desire from my perspective as a teacher. Most kids come into my math class having learned from other professional teachers a certain way to solve problems. For many students, that's perfectly acceptable. For many teachers, teaching a standard algorithm is as far as they want to go. It's time-tested and reliable. And that's cool. It will get most students where they want to go in school and in life. However, for me, I want my students to be fast and efficient problem solvers. I like the challenge. I invest a a whole lot of time and energy teaching them alternate ways to understand numbers and how to use advanced strategies. I love watching their faces light up when they realize they how fast they can solve problems.

That sounds incredibly interesting to me- is there a book or website you can recommend?


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(08-09-2018, 02:47 AM)m in sc_imp Wrote: [ -> ]doesnt matter really, and yes, its liquid cooled, and th erevlimiter is around... 11k? or so. BUT.. we were talking about efficiency per cc, right? were talking 30% displacement but 50% of the power. efficient. and whats the advantage: better flowing head and compression. it was a stock bike i daily rode for years... so, taking some compression out available with the liquid cooling from 14: 1 (stock) to lets say, 11;1 and aircooling the same motor, i would guarantee that it still made more hp per cc than the cb is stock tune to stock tune. I also know, that a power commander, open air filter, and aftermarket exhaust showed a 9hp increase on the 390s. they do come with really good heads out of the box, on those, it was fueling and exhaust..

lets get more apples to apples but scale it down. doing nothing more than big bore (170cc) head change, an aftermarket exhaust, and a freer flowing air filter, a grom which is aircooled 125, made by honda at the same time the cbs were/are made, so it has all the same restrictions, etc, will take an 8hp bike to 23-25 hp. with bolt ons. the biggest difference is the head. with just going to a bigger bore and a cam, you might see 12-14. Ive seen a gps verified 95mph a few times on mine. (with a stock lower end). With porting the head, which i have not yet done, there are multiple cases of other ones dynoing up over 30 hp at 180cc on an aircooled honda single and breaking 100 mph.


just because nobody has done it on this platform, doesn't mean it isn't feasible or true.

Well, just to clarify my point:

With volumetric efficiency I am refering to how much air comes into the engine per cycle vs the theoreical maximum. This is about the losses the engine has as a pump (per cycle).

Simplyfying a lot, that (with fuel, of course ) gives you torque.

Then, the quicker you can do that per minute, gives you more power.

So the CB maybe is getting as much air as it can -per cycle. I don't think there is a significant restriction in the TB if by improving this, Honda would have got the same performance with better economy: they wan't as much air in as possible without restrictions, and then they make it "driveable" with smart engine control.

Can you get more power per cc? Yes, making the "pump" to work quicker, i.e. more revs. That probably implies cooling problems, more consumption, worse reliability, or some other things that made Honda decide not to rise the redline a bit more. But I don't think the TB is the limiting factor, as it must be pretty much optimised.

Perhaps on older vehicles, due to manufacturing limitations for mass production, there were several ways to improve induction (e.g. cleaning mould split-lines on casting intake manifolds was an easy way to improve the output on the old Citroën AX ), but with modern vehicles, I don't see much marging there.

(Can you put the redline on the CB 2K rpm higher, like the "Duke"? Probably yes, but, probably honda can't do it safely without hitting emissions problems, or reliability... unless it was liquid cooled, but then, it wouldn't be the CB, would it?)

VE isn’t everything, nor is it static.

100% VE at 3k makes x, but move 100% VE to 4k and you made more power.

Use a little velocity, scavenging, resonance pulse, and push past 100%...


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Like everything, opinions differ even among knowledgeable people.

To me ideal VE means 100% cyl fill volume, no more no less.

The reality of that is none of us other than privileged lucky few who work in labs know exactly what and when that occurs unless supplied with very expensive equipment. Us mere mortals can simply guess, calculate, deduct.

But as far as the 'engine' being efficient- VE, personally I think of that being the mechanical flow limitation, before manipulation.

Meaning- you can put in more lift and more duration to get rid of a bottleneck, and the engine will naturally want to breath a certain amount of air, at a certain RPM, and make a certain amount of power- effected by the bore, stroke, valves, port angles, butterfly size, etc.

Take that same exact engine though- slot the cam sprockets and without changing a single thing other than when the cams open and close you can increase the overlap since at higher rpm you have less time to fill a cyl with atmo pressure so you use the suction of the exhaust leaving to pull in more fresh mixture.

Time it right and you can catch the edge of the intake wave right when the exhaust valve closes and let it slam in- piling up even more mix for more power- at high RPM, but you will loose power down low.

Myself- I don't call that increasing VE, I call it manipulating VE. The engine itself doesn't flow more naturally- it can have the same poor port design, valve size, single barrel carb, etc. You are just robbing one RPM to pay another. Same can be done with intake runner length, exhaust primary & secondary sizing, collector choice, etc.

I'm sure you know all this- so don't think I am trying to hold a class. Just having conversation for fun and maybe we can suck some new guys into the rabbit hole. Slippery slope.

Hi new to the forum but I found this interesting thread already.
I think the similarities of the CB1100 to the CB1300 can't be over looked. It has the same stroke, I think even the same wrist pins. It may be possible to put the 1300 pistons in with a bore and plate. The crankcases must be the same as it has the waterpump output in the casting as well as other ports found on the cb1300.
I'd imagine the CB1300 throttle bodies(36mm?) may drop on too. I read somewhere else that a full tune on the CB1300 with 41mm FCR race carbs dyno'd out at just under 200bhp!
This does move quite a way away from the ethos of the bike but man what a sleeper.

I think this bike would turbo real nice though, easy 200bhp then no question.