Topic: CB500 combustion chamber volume

[tvs avery]

Hi all, new member from northern va. I hope I've put this in the right section. As the title states I was wondering what the cb500 chamber volume is. It seems to me that because of the reduced bore diameter and interchangeablity between the cb500 and cb550, one could put the former head on the latter and get a bolt on compression increase. That would save a bunch of machine work (and cam timing?)for folks (like yours truly) looking for that upgrade. Is this possible? It seems someone would have done it already, but I couldn't find any examples. Would the CR increase be enough to be worth the trouble? The only problem I could see would be the 500 valves being smaller and inhibiting performance in that regard.

[dave500]

the 500 and 550 heads are the same,,same valve size.

[tvs avery]

So the chamber volume is the same size as well? Despite the difference in bore?

[tvs avery]

the cb500 bore is 56.00mm vs cb550 58.5mm. So there must be a difference in chamber volume, and so there would be a difference in CR right? That is, a cb500 head on cb550 jugs and vice versa. Whether or not it would be big enough to warrant doing it is a different story.

[bryanj]

Heads are the same, a minor alteration in piston machining would compensate for the overbore

[dave500]

the 500 and 550 head even have the same part number,you might mill the head slightly,what for?you chasing more power?higher compression is mostly used where a hotter cam is used to compensate for the increased overlap,youll decrease the dynamic compression with a hot cam so you may need to compensate by increasing the static ratio somehow,eg,,domed pistons or mill(shave)the head,increasing a stock engines compression much usually results in you having to retard the igniton to stop it pinging,so thats a backward step.

[tvs avery]

Thanks, I thought it was too easy. I'm putting my engine back together with a 650 cam and Im buying an extra head to port, I thought if I could bump the compression at all I would, not to mention the 500 ones seem to be going for less on ebay. As far as pinging as a result of static CR increase, I thought that could be resolved with just using higher octane fuel? (to a point)

[dave500]

to a point yep,just clean up a standard head,dont try and make the ports larger,just rid the factory dags and match port those inlet manifolds to the head,they can be way out of whack,the 650 cam isnt really a hot cam either compared to what aftermarket grinds you can buy,you want torque for easy street riding,and an engine that actually idles without blipping the throttle and will pull the standard gearing from lower rpm.