turbocharged cb550 bobber

[swansmaa]

scored a rough old bike a wile back, and now im getting around to building something out of it. Its a 1975 honda cb550f. The plan is to build a hardtail bobber, thats boosted with a draw through single carb setup. The main goal is to build a fun and unique bike on a tight budget.



got it stripped down and chopped up the frame a little


start of building the intake. making 1 of 2 flanges


made the intake collector. turned out alright


intake flanges


mmmmm pie


2 runners done. chop saw and angle grinder got a good workout

better shot of the collector. cut the pieces with a cutoff wheel and mig'ed em up

 

[swansmaa]

the bike now sits as a roller. im happy with how its looking

 

[coyote13]

On board for this. What carb are you running?

 

[SONICJK]

Nice first couple posts!
I am watching, welcome to DTT>

 

[swansmaa]

On board for this. What carb are you running?

ive got a 30mm mikuni that im gonna start out with. might have to switch to something larger

 

[MJPriceisright]

whoa. looks fun.

 

[Sonreir]

Yeah... you're gonna want a much bigger carb. VM44, maybe?

 

[MJPriceisright]

Yeah... you're gonna want a much bigger carb. VM44, maybe?

yepppp.. the roof on a vm30 carb is like 500cc or so right?

 

[swansmaa]

yepppp.. the roof on a vm30 carb is like 500cc or so right?

the way i understand it, using a turbo is like cheating on carb size since the air is being forced (sucked in this case) through by the turbine. I agree that larger would be better, but this one might work out for now.

 

[canyoncarver]

This will be unique for sure.

 

[Sonreir]

yepppp.. the roof on a vm30 carb is like 500cc or so right?

VM30 is good to around 30 horsepower. So a single VM30 would be too small for this engine even in naturally aspirated configuration.

the way i understand it, using a turbo is like cheating on carb size since the air is being forced (sucked in this case) through by the turbine. I agree that larger would be better, but this one might work out for now.

Too small of a carb will act as a restriction on the turbo. The restriction will take the form of a low pressure zone your turbo will have to overcome to continue to provide the correct amount of boost. It kills efficiency. In the case of a turbo, poor efficiency often translates to additional heat. Additional heat means increased likelihood of detonation and/or pre-ignition.

 

[Sonreir]

More on the topic, here, if you're interested:

http://www.dotheton.com/forum/index.php?topic=39814.msg475052#msg475052

 

[bradj]

Ill watch kool project

 

[swansmaa]

More on the topic, here, if you're interested:

http://www.dotheton.com/forum/index.php?topic=39814.msg475052#msg475052

good read, what did you end up boosting with the turbo in that picture?
Back to the carb, I was expecting a loss of efficiency from a small carb but not increased temps. my turbo inlet is right around 41mm ID before it necks down to the compressor wheel, so I would think a vm40 or so would be ideal. I do have a vm38 that I could borrow from another machine. I plan on running all stock internals on the 550 for now, so we will see how it goes.

 

[kopcicle]

Depending on your local parts sources a BS38 from a XS650 (still a little small) or a BS40 from a Suzuki Savage . Good places to start because other than having to make your main jets (get out the drills ) CV carburettors are very forgiving in a suck through ...

~kop

 

[swansmaa]

CV carburettors are very forgiving in a suck through

well thats good to know, I was worried that the false vaccum created on decel in a draw through arrangement wouldnt work out well with a diaphragm carb.

 

[swansmaa]

well ive made a little progress, slowly but surely. decided to build an exhaust header that was a little more direct, thats all done now. intake mani is off for powdercoating right now. Also, I just won these. 40mm flatside (Ill only be using one) So she should be able to breathe.

 

[Rich Ard]

Rad. I'm in.

 

[DV2000NJ]

This is interesting. I'm in as well.

 

[swansmaa]

got the carbs in the mail today, and my buddy finished up powder coating the intake so i made a little progress.

new megaphone/log style header is all welded up, painted with high temp black, and wrapped in header wrap. Forgot to take pics while building it, but im happy with how it turned out.

got a buddy to machine me a steel oil galley plug with the metric male threads and an 1/8" pipe thread tapped into it. Much stronger than drilling/tapping the hollow aluminum plug. The T fitting feeds the turbo oil inlet and an oil psi gauge.

Intake is powdered high temp black and bolted up to the cylinder head.

new carb: gotta make a couple slight mods but it should work out well. 40mm flatslide mikuni, with plenty of main jets/ pilots/needles available thanks to the snowmobile world.

got a few more things to give some attention to, and i'll be pretty close to seeing if it will run.