90FXRS

On modified motors, high horse and torque, will more horse and torque be generated venting the heads on a twin cam to atmosphere or breathing through the intake?

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R_W_B

I'm guessing the heads, but check with some of the more known builders for a definite comfirmation. I don't think Darkhorse does anything but cranks but they are a division of Hoban Brothers which offers a complete machine shop service. They might could give some insight on that.

Hoban Brothers Cycle Service
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Also I know that Rev-Performance does head work so they could give some insight on that.
Twin Cam Cylinder Heads

I don't think they polish heads anymore. That went out years ago once they discovered the rough surface on the ports helped atomization to the point that the friction was a mute issue. But they definitely still port them.
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Also if you call this guy on the phone ( you will have to leave a short message and he will call you back) he is Mr. Harley knowledge when it comes to performance. His shop is only 40 mins or so from my place. He knows all about cams, porting etc and the dyno results thereof.

http://www.docsperformancetuning.com/

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"Our lives begin to end the day we become silent about things that matter." ~Martin Luther King Jr.
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dolt

If I understand your question correctly, the answer is venting the heads to the atmosphere or intake will have no impact on HP/TQ. Having said that, common sense should tell you that venting crankcase oil mist back into the combustion chamber has some negative effects that are eliminated by venting to the atmosphere.

90FXRS

That was what I was thinking. TCs breathers do a better job of removing oil from the mixture than the older Evo-style breathers, but there is still some in the mix.

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There's NO Substitute For Cubic Inches!!!

R_W_B

Oh I obviously misunderstood your question. I thought you meant opening up the ports some.

Some guys rig up a catch can on their bikes. I've seen this done on cages also. It really doesn't have any measurable effect on power (as previous post said,) but it runs a little cleaner. In the real old days we just had valve cover or rocker breathers. But these tend to spew a fine oil mist out and is a constant cleaning issue.

__________________
"Our lives begin to end the day we become silent about things that matter." ~Martin Luther King Jr.
"Reality is merely an illusion, albeit a very persistent one."~Einstein

the draggin

It would seem a real benefit to vent to the atmosphere if you are using synthetic oil since it does not burn like "dino" oil. If I was going for full power potential I'd vent to the atmosphere, just my two cents........

FLTR2008TRIKE

There is no power gains with a vent system to the outside. With that being said, you gain a cleaner combustion chamber which will aid in keeping the carbon build up down.

I run a catch can system on my 117"

FishHunter

No.
Some folks have had us drill/tap for 1/2-13 breathers as were in the Evo's.
Never have witnessed any dyno evidence of gains either way.

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"If a street Harley doesn't have torque, how much horsepower it makes, simply does not matter."