Looking for 50hp German Cam

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Pinhead
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Looking for 50hp German Cam

Postby Pinhead » Tue Mar 29, 2011 9:42 pm

I'm trying to find a German 50hp cam to fit into a '79 CB650 for my 100MPG project. Does anyone want to part with one, or possibly trade for a '79 stock US cam?

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Volker_P
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Re: Looking for 50hp German Cam

Postby Volker_P » Wed Mar 30, 2011 1:06 am

How many do you need? I'm basically not selling any engine parts but I'll swap with all undamaged 63hp cams I can get! I have only one really intact 63hp (36mm lobes) in my engine, but might have three or four 50hp (33mm lobes) in good shape.

Possibly I should not tell you that the mpg rather went up than down as I went to the unrestricted cam some time ago. :roll: I think Ibsen and Robert found the same.

However in any case it may be more simple to first trying to get one without overseas shipping.
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Pinhead
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Re: Looking for 50hp German Cam

Postby Pinhead » Wed Mar 30, 2011 3:54 pm

My theory is that with the cylinder head modifications that I've done, I'm losing more fuel out the exhaust during overlap than the bike did originally (the PowreLynz and ST Valves flow more at low-lift values than the stock configuration). The 50 hp cam should have much less overlap than the 63hp version.

I may try using more restrictive mufflers to see if the theory holds true. If the more restrictive exhaust produces a net gain in MPG, it would be a strong indicator that my exhaust is over-scavenging the cylinder and sucking air/fuel out of the exhaust before the exhaust valve closes.

I do have a spare 63hp cam that came with my eBay cylinder head...

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Volker_P
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Re: Looking for 50hp German Cam

Postby Volker_P » Thu Mar 31, 2011 1:08 am

All right, I just wanted to mention. I am basically interested in that 63hp cam if everything is smooth and shipping and taxes conditions won't turn that into a nightmare. Never tried that so far.
A CO content measurement may be used to verify unburned components in the exhaust. However there might be other reasons for that, too. Nevertheless a direct comparison with/without partly plugged exhaust might be suitable to provide a quick answer here.
I'm somewhat surprised as I'd rather assume that this kind of turbulence should in general slow down the flow.
Although illumination is from the wrong side for that, maybe my old picture helps to get an idea on the overlap: Image
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cb650
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Re: Looking for 50hp German Cam

Postby cb650 » Thu Mar 31, 2011 1:23 am

I wonder how the 50 hp cam compares to a 550 cam?
Did you clean the tank out?!?!?!?!

Pinhead
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Re: Looking for 50hp German Cam

Postby Pinhead » Thu Mar 31, 2011 3:57 pm

The rough texture on the ports and valves makes the port "act" like it has a smaller CSA when there are low-flow requirements which helps maintain velocity. Also, the ST pattern on the valves reduces laminar flow, which actually speeds flow over the surface of the valve.

Surface Turbulence
In August of 1988, Surface Turbulence became standard on all Metric Mechanic engines. By using Surface Turbulence we've been able to lean out the engine and burn much of the wasted (emissions) fuel. This has also reduced the fuel input into the engine by 10 - 15% under moderate (part throttle) driving conditions and up to 25 - 30% under full load (wide open throttle). Surface Turbulence in an internal combustion engine is generated by causing a rhythmic tumbling action over a surface or object. This tumbling, set in motion by a surface turbulence generator, accomplishes the following:

    It re-homogenizes the fuel and air.
    It reduces laminar flow.


Instead of air dragging, it now tumbles over the surface of the valve - like a layer of tiny spinning ball bearings. Over such a surface, the main stream can now move at full speed. Also, as air flows over these ramps, the fuel mixture hits the backside of the valve and is kept homogeneous by the tumbling that the grooves generate. Having fewer heavy particles, the homogeneous mixture burns more completely. So, the effect is that the "boundary layer" which is normally lost in airflow with a conventional valve, now has an airflow gain of 2% - 4% by using the HiFlo ST Valve.

On a conventional intake valve, as fuel leaves the fuel injector or the discharge Venturi of the carburetor, it is atomized into the "main stream." This mixture is either taken into the cylinder through the opening created by the valve and the seat, or the mixture runs into the backside of the valve. Fuel hitting the backside of the valve is then knocked out of suspension. Because the air flowing over the face of the valve is moving so slowly, fuel particles tend to adhere to the valve's surface. Eventually there are sufficient fuel particles collected on the valve to grow heavy enough to be shaken off the valve, due to a beating action against the seat. Or they get swept off by the "main stream". Since these heavy fuel particles aren't very combustible, they're wasted in part!


Judging by that picture, though, the cams have pretty close to the same overlap.

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Volker_P
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Re: Looking for 50hp German Cam

Postby Volker_P » Fri Apr 01, 2011 1:13 am

Thanks for the link. However I don't like the explanation there because it is wrong. Typically a rough surface will not really impact laminar and tend to slow down any other kind of flow. Unless roughness induces a laminar/turbulent transition because the turbulent boundary layer is much thinner than the laminar one.
I assume that's what this turbulence stuff does in the low rpm range together with keeping smaller fuel droplets in the air and increasing mixture quality that way. For high rpm, probably just the latter effect is remaining.
But that's just a guess from my limited knowledge. One may check out engineering literature for reliable info.
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Pinhead
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Re: Looking for 50hp German Cam

Postby Pinhead » Fri Apr 01, 2011 1:52 am

Volker_P wrote:Thanks for the link. However I don't like the explanation there because it is wrong. Typically a rough surface will not really impact laminar and tend to slow down any other kind of flow. Unless roughness induces a laminar/turbulent transition because the turbulent boundary layer is much thinner than the laminar one.
I assume that's what this turbulence stuff does in the low rpm range together with keeping smaller fuel droplets in the air and increasing mixture quality that way. For high rpm, probably just the latter effect is remaining.
But that's just a guess from my limited knowledge. One may check out engineering literature for reliable info.


That's how I understand it as well.


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