CB550 Re-build to the max

[Bodacious]

Forget Ti valves in a SOHC head. Side thrusts cause them to seize in the guides.

Now I'm confused. Are we talking 350 4 or twin or a 500/550 or all of the above?

By all means red everything there is to red and then start with the basics. For the motor you have, what are the max safe RPMS based on mean piston speed. A 350 twin has a long stroke crank - for its size and the 550 isn't a high rev machine either. If you want revs, you start with a short stroke crank and then you work out what bore size works with that stroke to get the engine size you want. With say 1.5:1 bore:stroke on a 500, that means you have to use 4 valves and all of a sudden you realize that Honda and Yamaha et al already did that.

If this was 1970, when I was an engineering student and designed a 4 cylinder 16 valve DOHC 500 street bike in a chrome moly frame, it would make sense. In 3014 - not so much.

So then you ask yourself what the objective is. Is it to develop a given motor to see what works and what doesn't within some reasonable cost boundaries, or is it to jump ahead to try a combination of parts that you don't know if they work?

Let's say you were to define the project along the lines of: To develop a 1970 era motorcycle engine to maximize power within reasonable cost constraints. That way you develop a series of improvements to test on a dyno that can be published. That will not get you through a PhD thesis review but for an undergrad project it might work.

The best place for design ideas is the SAE.

Thank you very much. This is the kind of stuff that is helpful. Sorry about any confusion here, hopefully I can clarify: I am focusing on the 550 for the build. I have a 350 and should probably have a separate thread for it. As for the 550, I am right now trying to upgrade the immediate combustion related hardware while I have the engine completely broken down. From there I will be tuning the 550 and getting a good benchmark for HP and torque to consider what options I have to increase power. I will then use these measurements to work backwards, determining where my power is made, how the components effect the output, and where I am still losing etc etc. I intend to do a cylinder by cylinder breakdown and determine the performance of each individually.

 

[canyoncarver]

There is a guy named Mike Reik (sp?) who is well known on the SOHC4 forums. He's a guru with these old SOHC heads and valvetrains. Lots of folks send their heads to him for a full workover. I'm not suggesting that you do that, just that he'd be one of the guys I'd find when asking these kind of questions.

It's one thing to learn it all from scratch if you want to do it yourself but you are in school for a reason. Kind of Teazer's point as well I think. Learn as much as you can about what has already been done then work to improve on it from there.

 

[coyote13]

Mike Rieck* (mrieck is his username)

 

[teazer]

Just as an FYI, I'm sure there are differences from one cylinder to the next, but I think you will find that that is a second order type effect. Look at articles that examined friction losses and pumping losses for a head start before you look at combustion efficiency, volumetric efficiency, gas flow etc.

For basics, looks ta old books by Ricardo and Weslake and later by AG Bell and Vizard. Perfomance bikes did an article on friction and pumping losses. Then there's the old stalwarts "Speed and how to obtain it" and "Tuning for Speed" both equally old and still relevant.

 

[focusinprogress]

for what it's worth, the cb650 motor has many commonalities with the cb550.....it's well known that combining some cb650 parts and cb550 parts you can make a pretty spectacular engine combo. It's also known that certain year GSXR1000 rods (factory forged H-beam) are identical in length, pin diameter, and crank bearing diameter as factory cb650 rods. The common "hybrid" engine build these days is GSXR rods with "836cc kit" pistons meant for a cb750, cb550 cases bored to house moddified cb750 liners bored for the 836cc kit, cb650 crank and head. makes 90hp +/-

"Paulages" on sohc4 forums has done a few hybrid builds and has a very informative thread on the topic.

 

[Hot500]

For information about high performance rods and pistons check out Davies Motorsport in England. These guys built a 500/4 racer for the Isle of Mann TT a few years ago. Their goal was 75 hp (about 30hp more than stock) and they used special rods and lightweight 2 ring pistons.

http://davies500four.typepad.com/

These items were to be for sale, however I can't find any reference to these parts on their website. Drop them an email.

If money is no object you can buy the complete bike for about $40,000.

 

[smarsh]

There is a guy named Mike Reik (sp?) who is well known on the SOHC4 forums.

+1, there are endless references to the high quality of his work and magic.
There are also a ton of threads over on SOHC4 regarding 650&550 interchangeability, porting, and other places to realistically look for performance gains. Strap on your reading glasses.

http://forums.sohc4.net/index.php?topic=13519.0
http://forums.sohc4.net/index.php?topic=56904.msg689122#msg689122
http://forums.sohc4.net/index.php?topic=17374.25