CB350/4 racebike project

[GregT]

I've been slowly working away on this for a customer here in NZ. Built to our pre '72 rules, it's out to 454cc. Web cam and springs, shotpeened 400 rods, 400 crank. Z650 24mm carbs cut down to fit will go on. Dyna S ignition.Z1 caliper grafted on. Big disc on home made carrier. Honda CB250R wheels. Home made rearsets etc.But I used this to have a go at hydrofoming some curved megaphones. RHS pretty well done as pic, still to have silencing elements inserted.It should go pretty well - and look a little different too.

[steve murdoch]

Greg, that is very cool.
MV Augusta or Magni style.
You must be tempted to run at least once through the gears without the silencers?
I will probably hear it over here.

[Rob S.]

Is that a '72?

[spyug]

Any idea of the probable horsepower ? I only ask as a recent episode of Café Racer TV showed a similar build and the builder claimed a doubling of stock horsepower to around 46 or so. I wonder how much you can get out of these little mills.

Interesting design on the pipes but I would think more suitable for a street application. How is the weight in comparison to stockers?

Cheers.

[kingofvenus]

Kool. Couple yr's back at a show somebody had a 305 superhawk with one of those motors (coulda' been a 400 too) swapped into it, looked like it was stock from honda.

[GregT]

Is that a '72 ? Ha. well, within the eligibility criteria of our rules, yes...good question,lol.
Weight, very light, They're 20 gauge sheet - .9mm.
Yep, for max power a 4:1 would have been the way to go...BUT, have a look at the later CB400 pipes and realise that there's a big oil filter housing right where you want to put the collector. That's why the 400 pipe is a twisted bunch of snakes...I didn't fancy building one thank you. Anyway the owner's girl friend said she fancied seeing four pipes on it...
Probable HP, I'd hope somewhere in the high 40's low 50's at the wheel. It's light and well braked and most of our local circuits are quite technical and fairly short so it's going to be a fun ride.
Noise..The owner's local circuit has a strictly enforced 92Db limit measured about 40m off the track edge. i'm confident there's enough silencer volume i can get it legal.
Forgot to mention that I've found an alternative oil pump capacity increase solution. The usual way to do this - dating right back to Kaz Yoshima - is to surface grind a CB750 pump rotor set to match a machined pump body. This will gain you about 2.5mm of rotor width which will increase the pump capacity emormously. The supply of CB750 pump rotors is as you may imagine, getting a little low these days and as they seem to be hardened steel, precision surface grinding is required to adapt them. Honda CBX550 pumps are the same rotor OD and are quite wide. They are also made from sintered Iron which is then hard chromed. So they machine very well indeed with normal lathe tools. So it was an easy job to cut the pump body for the wider rotor and machine one side of the CBX rotors to suit. I'm quite happy to be running bare sintered iron against one side face of the oil pump body. We'll see what sort of pressure it gives when I fire it up.

[GregT]

Well it's still not finished due to more than a few other bikes sneaking in front of it in the queue. The owner wanted to put it in the show associated with the Southern Classic Festival this weekend - so it got a bit more done on it...
Cleans up pretty...

[GregT]

And the other side.

[steve murdoch]

Did you have to make a caliper carrier as well to fit your Kawi rotor?
The big brake looks good.
Your rearsets look Raaskish. Probably stronger.

[Buffalo Bill]

Sweet bike!
Do the wire spokes have to be tuned for equal tension?
Be like tuning a round harp.

[GregT]

Did you have to make a caliper carrier as well to fit your Kawi rotor?
The big brake looks good.
Your rearsets look Raaskish. Probably stronger.

yeah, there's a caliper carrier in steel made to suit the Z caliper. Rearset footrests are over the counter cheapos, rearset carrier plate is 6mm alloy, pedals 5mm alloy

Sweet bike!
Do the wire spokes have to be tuned for equal tension?
Be like tuning a round harp.

recognised scrutineering technique is run a screwdriver round looking for a dull note - which is a loose spoke....


It got quite a lot of comment at the show. If I wanted to use up my time building pipes, I probably could......