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exhaust, heads, ironhead exhaust, ironhead heads, modify

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  #1  
Old 22nd May 2011
DCMC_Scooter DCMC_Scooter is offline
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Lightbulb Is there any benefit to putting 85 XR heads on an 85 XLH?

I ride an 85 XLH and have been toying with the idea of putting XR heads on it from the same gen of ironhead. I'm wondering if there is any benefit to this or would it be too much hassle for too little of any positive result. I thought it might be like putting buell heads on another type of harley motor. Any thoughts on this?

Also, I've researched shorter exhausts on ironheads. Seems like the consensus for those owning ironheads that it runs fine, but depending on how short and how big the id is on your exhaust determines where your gain and loss is, whether you gain or lose top and bottom. I know on an ironhead you want very little back pressure ( how ever you want to define the generic term). Most arguments for back pressure are from people who don't own an ironhead and may not realize the heads are designed different than say an evo. I have a standard length drag pipe. I want to cut about 12 inches off the end on both pipes, then drill billets down the rest of the length up to the first bend. My theory Is this make allow the motor to breathe more while still maintaining some slight back pressure (due to the billets). And yes of course make it louder. Not a problem for me, loud pipes save lives right?

Any feedback would be appreciated!
-SCOOTER-
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  #2  
Old 22nd May 2011
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Hi and welcome here...

If you mean 83/84 XR 1000 alloy heads, you'll need heads, barrels and rods as an absolute minimum.

Don't know about late evo Sportster, but early evo Sportster rods will do...

Patrick
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  #3  
Old 22nd May 2011
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Run some 1.75 primaries into a 2" collector with a unbaffled reversecone megaphone. Make the primaries 33-35" long, but no more then a half inch different in length from eachother. It will be loud enough and give real gains in tork.
Here is some good info http://www.drchaos.org/files/ExhaustTechnology.htm
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  #4  
Old 22nd May 2011
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Welcome to the XLForum.
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  #5  
Old 22nd May 2011
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Welcome to the forum!
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  #6  
Old 22nd May 2011
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Welcome! to the IronHead forum. Cool to have another member willing to experiment and risk.
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  #7  
Old 22nd May 2011
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Hi again, DCMC_Scooter

Basic formulae to calculate lenght and ID of exhaust pipes:

1) Pipe length in inches = 850 x ED / rpm

Where ED is 180 degrees + the arc in degrees between exhaust valve opening and BDC.

2) Pipe ID area = rpm x cylinder size in ci / 88200

Patrick
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