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Discussion Starter · #1 ·
I know that the only real difference between the 883, 1200,and 1340 motors is the length of the stroke and that they are all the same bore but does that mean all the heads are the Sam? I have a set of high compression 1340 heads that have been ported and polished and was curious to what if any difference between those and the heads on my evo sporty? I know the gaskets at the base of the cylinders are the same but have no idea about the heads. Im not trying to be an idiot im just a curious fellow.
 

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I stopped by a buddies today, and saw my first 1340 headed sporty. Not knowing a lot about the evo sportys...I was interested to know if there was any machining involved myself.
 

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The pushrod hole angles are way different. About the only things that are the same are the headbolt pattern and the rockerbox pattern. The valves, motor mounts, combustion chamber size and shape, and (as mentioned) the p-rod angles are too different to interchange. S.T.D. used to use the same basic casting for both, but the machining is drastically different.
 

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Four cams vs one cam. Two TOTALLY different motors!
The OP wasn't addressing the number of camshafts a motor contains, but some "interchangability" questions. To clarify, 1200XL & 1340 FX/FL pistons are the same P/N. Naturally a 55ci (883cc) bore is much smaller while it does share the same stroke as a 1200XL. The strokes of the XL and BT are different also (3 13/16" vs 4 1/4") Everything from the crankcase deck up can "bolt on" but as some have said pushrod angularity issues must be addressed if you want to run a BT cylinder head on Sporty jugs. TK.
 

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Discussion Starter · #8 ·
i figured as much with the pushrod angles. i was looking at a company called revolution performance that sells a kit that turns my 883 motor into a 90" monster sporty. obviously with some case boreing to accomadate the longer stroke and larger bore and figured if they could do it maybe i could atleast do an 80" with factory equipment. ill keep you all posted on how it goes. thanks for all the insight
 

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The pistons are NOT the same! The stroke difference requires two distinct deck heights. The sportster pistons can be used with a 4 5/8" stroker flywheel assy to make an 89" big twin.

You can stroke a sportster motor to 89" by using the same stroke, but it's more involved because of the shorter rods and base deck heights. The best way to get around 90" in a sportster is with 3 13/16" bore and no stroke. It'll rev like stock, last like stock and make a stack of power! S&S also sells a 89" bore/stroke kit, but it requires case boring anyway, cost more money and lowers the redline/longevity, making all bore 88" motors a way better choice, IMO!
 

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Threadkiller. Everything from the crankcase deck up can "bolt on" but as some have said pushrod angularity issues must be addressed if you want to run a BT cylinder head on Sporty jugs. TK.[/QUOTE said:
Here's a pic.
Not being familiar with the sportys at all...just going on what I was told.
(I had to ask "wtf" after looking at it for a minute trying to see why it looked like this one had been to the gym ).

If much interest is generated I can get some better shots next week. Yes, the angles are machined into the head for the push rod tubes..I looked.
 

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If you look at the front edge of the front head, you'll see a boss with the front motormount bolted to it. that is present ONLY on sportster heads, and S.T.D. castings. Those are clearly not S.T.D.s, so they are stock sportster heads with sportster rockerboxes. They look very similar anyway.
 

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Discussion Starter · #14 ·
66xlch any chance you would mind giving me a parts list of sorts for the way you explained how you would do it. i like the rev like stock wear like stock aspect. the sporty is going to be my daily and am even hoping to make it to the Horse stampede with it this year. it would be greatly appreciated
 

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The exhaust ports are the same, but they end up in a different place when installed due to the difference in deck height. So, a two-into-one head pipe for a big twin won't fit onto a sportser, even though the ports are they same. Close but no.

If I wanted to build a 90 or so inch sportster, I'd look at an Axtell 88" big bore cylinder kit. The Revolution kit might work well, but I have no experience with it. I do know that Revolution used (s?) some Axtell parts. If you keep the compression under 10-1, use a decent cam (too little is just as bad as too much, despite popular opinion!) it will last just fine. The real power comes from the heads. Quality porting has no downsides. It's the actual valve job and wild spring rates that detract from reliability.

The state of tune matters more than the actual size. Setting a stock motor up for maximum peak power will cause it to last like fireworks, but a mildly tuned big motor might last as long (or longer) than a stone stock version.
 

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The exhaust ports are the same, but they end up in a different place when installed due to the difference in deck height. So, a two-into-one head pipe for a big twin won't fit onto a sportser, even though the ports are they same. Close but no.
True, when addressing exhaust systems, but if a XL was sporting BT heads (or vice versa) the the "chassis'" choice of exhaust pipe would bolt right on.
 

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I'm gonna have to go back to my buddies and see this bike again...
He said heads and jugs. Now that I have been schooled to evo sportys a little I'll see if he meant something else..like just BT jugs.
 
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