Topic: How to get 60bhp from a cb550?

[simonuk]

Hi
I have a 1978 cb550k3 and want to use it as a trackday bike and for classic thunderfest (time trial) events. I can improve the handling and reckon that if I can find a right side conversion to double disc it the bike should stop ok.

However it needs more performance and I was looking at fitting a dynoman bore kit , perhaps 600cc and the CR carbs. I have dyna ignition and four into one exhaust system so...  my question is how much power have people seen with this sort of setup? is it driveable with the cam fitted etc etc?   Thanks a lot for your help, not a lot of info here in the uk that I can find.

Cheers
Simon

[scottly]

The conversion to twin front discs is fairly simple: source a second left disc, rotor, and caliper assembly and bolt it up, after flipping the caliper on the arm. Some shimming under the fork leg mounts may be required. If you are retaining the stock speedometer drive, it's a bit more complicated...
With regards to 60 hp, have a read here:
http://forums.sohc4.net/index.php?topic=83748.0 

[turboguzzi]

bwaller races a big bore 600/550 motor, plenty of info in his main thread

rene from holland achieved close to 70hp from just 500cc but that was a very extreme state of tune done by a professional. Rene will not like me saying that, but that motor was a bit finicky. I stopped short at 62hp or so from a 500c.c. too self tunning it in my shed with very good reliability. So yes, a 60hp 600 is doable, and power should be pretty usable.

if dynoman's 600 kit is intended for the street, you better check what compression ratio is claimed those pistons.
for racing you'd want to be upwards of 12:1, this is key for obtaining crisp power. 

[bwaller]

Increasing displacement certainly will help, but spending your money on the cylinder head will get you to 60hp faster. If you want one stop shopping, contact MRieck. Proper porting, o/s valves, a good cam and larger carbs will get you there. Of course as TG mentions building a tight engine with increased compression is part of the package.

My wifes 592cc street bike with 10:1CR, mild cam and porting, with stock carbs produces 51rwhp. My 572cc race engine nudges 72. Be prepared to open your wallet.    

[simonuk]

Thanks all
Reckon I'll go with a bore kit and carbs to complement my ignition system and will take a look at the head work, although i'm in the uk so it would need to be diy or somebody over here to do it.

Cheers
Simon

[turboguzzi]

davies motorsports are developing/running a 500/4 racer (same head as 550) in the UK. they dont often post here so better look up their site.

[simonuk]

That's really helpful, I'll take a look, thanks
Simon

[Leino]

I live in Finland and have had several heads worked by MRieck... distance is not an issue in the world we are living today.

[simonuk]

Regarding the carbs, I note you can get a Mikuni VM setup for a cb750 using twin carbs, its claimed they give power and response. Has anyone ever done that on a 550 with similar results? Is there any kind of manifold made?

Cheers
Simon

[bwaller]

If it's for the street or the odd trackday, buy a set of Keihin CR26mm.

[Howell]

rene from holland achieved close to 70hp from just 500cc but that was a very extreme state of tune done by a professional. Rene will not like me saying that, but that motor was a bit finicky. I stopped short at 62hp or so from a 500c.c. too self tunning it in my shed with very good reliability. So yes, a 60hp 600 is doable, and power should be pretty usable.

Hello , here's René from Holland, still reading these topics.
TG our Honda CB500 produced a reliable 65 rwhp.
Our tuner made a 'test' engine which produced a 70 rwhp , but wasn't reliable.
He is still trying to get this engine reliable, but that is not easy with the low budget parts we use.
During our last raceyear we focussed on saving weight and that makes a bike also faster.