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Author Topic: turbocharged cb550 bobber  (Read 37616 times)

Offline coyote13

  • Posts: 1152
Re: turbocharged cb550 bobber
« Reply #30 on: Oct 03, 2013, 11:46:59 »
Well freaking done man.
Half the fun's in the get there...

Offline SONIC.

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Re: turbocharged cb550 bobber
« Reply #31 on: Oct 03, 2013, 12:35:28 »
Are you doing the welding with a torch?

Offline mlinder

  • Posts: 377
Re: turbocharged cb550 bobber
« Reply #32 on: Oct 03, 2013, 12:46:57 »
You've probably said somewhere already, but how much boost are you running?

Offline Mike Lawless

  • Posts: 150
  • 2006 HD Softail Deluxe - 2014 Triumph Bonneville
Re: turbocharged cb550 bobber
« Reply #33 on: Oct 03, 2013, 15:22:21 »
An observation on your intake system...
As someone with a fair amount of knowledge on turbocharged small engines, I feel I can offer some constructive criticism. Draw through systems have been used successfully on air cooled VW engines (my area of expertise) for decades. Your intake would function much better as a "plenum" style. Short tubes, or velocity stacks attached directly to the head, all connected by a larger horizontal tube with the turbo blowing into that. Something like that can fit much tighter to the engine and give you some room. It'll certainly work the way you have it, just not as good. You will want to smooth the entry into those tubes in any case.
You also need to make sure the turbo is designed for a draw thru application and has internal shaft seals between the hot side and the cold side. Many OEM turbos don't have seals. Most are designed to be for "blow thru" applications where the fuel is introduced downstream. You DO NOT wanna know what happens when fuel and air enter the exhaust system, which it can, through the shaft bearings. Especially when you are straddling that thing with the turbo close to your jewels.
Just an opinion. Take it for what it's worth.
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Offline Sonreir

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Re: turbocharged cb550 bobber
« Reply #34 on: Oct 03, 2013, 15:29:59 »
How do you get around fuel pooling issues with a draw through and plenum?  I was always under the impression that you should go from turbo straight to manifold in a draw through setup....
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Offline Mike Lawless

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Re: turbocharged cb550 bobber
« Reply #35 on: Oct 03, 2013, 15:37:59 »
That is definitely an issue, but typically not much of a concern when the plenum is so close to the head. The heat keeps the fuel vaporized unless the thing is pig rich. Also having the bottom of the plenum at least at the same height as the bottom of the intake ports would be nice.

In my opinion, a draw through is compromise anyway. It is the least expensive way to go, which is why it's popular in the air cooled VW world.
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Offline Sonreir

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Re: turbocharged cb550 bobber
« Reply #36 on: Oct 03, 2013, 16:07:35 »
In my opinion, a draw through is compromise anyway. It is the least expensive way to go, which is why it's popular in the air cooled VW world.

I hear that.
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Offline swansmaa

  • Posts: 21
Re: turbocharged cb550 bobber
« Reply #37 on: Oct 03, 2013, 16:51:57 »
Are you doing the welding with a torch?
nope, most of the welding is mig. The downpipe had a funky coating on it that made the weld splatter kinda weird.

You've probably said somewhere already, but how much boost are you running?
the wastegate on it opens around 6psi, so I'm gonna start with that.


Your intake would function much better as a "plenum" style.

constructive criticism appreciated! A plenum would have been a whole lot easier to make. The main reason I did it the way I did was to avoid fuel puddling like sonreir is talking about, but it does make sense that the heat from the cylinder head would take care of this. I was also worried that the plenum would favor either the two center cylinders, or the two outer ones. After seeing so many more manifolds constructed this way, is must not be a big issue either.


You also need to make sure the turbo is designed for a draw thru application and has internal shaft seals between the hot side and the cold side.
Are you refering to piston-ring style vs. carbon seals? the carbon seal is what you are supposed to have for draw through. This turbo currently has piston-ring type seals. These don't always work with draw through, because when the throttle is closed at high rpm you get lots of intake vacuum. this vacuum sucks oil through the ring gap in the piston-ring type seal, and oil enters the intake. I'm taking the "run it and lets see what happens" approach before I do anything about it. Might be fine, might burn a little oil, or it might smoke like a freight train and foul the plugs constantly.

as for a/f mixture entering the hot side of the turbo; it would have to go through the compressor piston-ring seal, through the center section, and then through the hot side piston ring seal. I don't plan on running much boost so i don't expect this to happen.


oh, and I 100% agree on the blow through vs. draw through thing. The only reason I'm going draw through is for simplicity of design and cost.
« Last Edit: Oct 03, 2013, 16:56:58 by swansmaa »

Offline Mike Lawless

  • Posts: 150
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Re: turbocharged cb550 bobber
« Reply #38 on: Oct 03, 2013, 18:39:31 »
All that really matters is that you have fun with it. Even at 6PSI the thing is gonna make a bunch more power. As an example, my air cooled VW drag racer dyno'd at 260hp, normally aspirated with 14-1 compression out of 2.3 litres. Ran 11.30 at 118 in the quarter as a full weight street car. Add a fairly modest turbo (blow thru) and drop the compression down to 10-1, and the thing makes close to 500hp and ran 9.85 at 143mph in it's last outing at 15 psi. At 7psi, it made around 400hp and ran low 10s. 

Besides, maybe the plenum style intake could be a project for another day once you get this version scienced out.

So, RUN IT!!
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Offline swansmaa

  • Posts: 21
Re: turbocharged cb550 bobber
« Reply #39 on: Oct 03, 2013, 21:12:58 »
All that really matters is that you have fun with it. Even at 6PSI the thing is gonna make a bunch more power. As an example, my air cooled VW drag racer dyno'd at 260hp, normally aspirated with 14-1 compression out of 2.3 litres. Ran 11.30 at 118 in the quarter as a full weight street car. Add a fairly modest turbo (blow thru) and drop the compression down to 10-1, and the thing makes close to 500hp and ran 9.85 at 143mph in it's last outing at 15 psi. At 7psi, it made around 400hp and ran low 10s. 

Besides, maybe the plenum style intake could be a project for another day once you get this version scienced out.

So, RUN IT!!

forgive me for being ignorant, but what is it that gives the plenum style an advantage (other than space savings and simplicity)? Thats the best thing about these projects, I can have fun with it and learn more for the next project.