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Ironhead Sportster Motorcycle Talk (1957-1985) For all those that wanna talk about Ironhead Sportster Motorcycles

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  #31  
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Quote:
Originally Posted by kitabel View Post
So, THAT'S why they use big cams: to lower the compression!
Nope it's the opposite.

Long duration cams need the compression ratio to run/work.

Or did you forget your Smiley?
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  #32  
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Long duration cams need the compression ratio to run/work
Like the KR!
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  #33  
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i have a set of brass 2 pc.intake clamps by Arlen Ness i bought new back in the 80's.best clamps i've ever had.they'e attached to a Super B.strong enough to hold that big long carb without a brace.his sales pitch for those clamps was a picture of him standing on a carb with one foot.
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  #34  
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You can't make enough compression on a side valve.
They have their own miserable compromises.
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  #35  
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Quote:
Originally Posted by kitabel View Post
So, THAT'S why they use big cams: to lower the compression!
Depends on the term "big" I guess.

At lower RPM's (read kick starting speeds) cams having very late closing intake valves don't make good compression.

In fact at the lower rev range when the engine is running they are still down on many "small" cams like P's and PB's.

What this means is you can start the bike more easily but you lose torque at the lower RPM's.
At higher RPM's this is negated by the inertia effect of the incoming charge, so, no woriies.

If you want to reclaim some of that torque the normal course of action is to increase the static compression ratio.

I'm seeing over 210 PSI cranking pressure on my current race engine despite running Andrews X grinds. This is with JE pistons and the heads have been decked. Cylinders were left alone but lapped into the heads.

I've got 60 thou clearance on the valves. So far, that's been good.
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