As some of you know, though I don't generally like to let anyone else touch my bikes, I lent my XR1200
to Zippers so that they could experiment with cams, heads, motor work, and of course an 88" build during the summer of
2009 and winter 2009-2010. I could have dabbled, but this way there should be a wider array of aftermarket stuff for the guy
who just has to have MORE POWER.
The objective of the 88" build was not a high HP, extreme build. The goal of this motor build
was to put together a pretty bullet proof, high TQ, wide power band 88" XR1200 motor. Compression was a very workable/reliable
9.8. The stock XR1200 heads were CNC ported with the combustion chamber reshaped for the 88" motor, slightly larger valves
but nothing radical, and the cooling oil flow retained. Cams are .630/.585 like in some of their other Sportster builds. The
end result is a motor that should last, builds power early, and holds about 100 ft-lbs of TQ for a nice wide band. The goal
of this build was not a peak HP, high RPM race engine but a build that behaves on the street, pulls stumps, and drops right
in to a stock engine without fuss. And boy does it. You can ride it smoothly at any RPM, idle through parking lots, and lift
the front wheel at will.
Here are a few thoughts if you are thinking of a higher cube, higher power build.
First of course, going to 88" requires boring the cases for the larger cylinder spigots. Which makes some crank work easy
while the cases are split. Personally, I would not do a 88" build without having the trueness of the crank checked, and having
the crank pinned/welded. The trueness of even stock cranks can be suspect, and I believe that the higher TQ of this build
will twist stock cranks which would lead to a destroyed motor.
A second thing is that none of the current aftermarket
pipes made good power with this build. All of the ones they tried, including the Termignoni, would not build good peak power.
No surprise, but the current batch of pipes are optimized for a stock XR1200 build. To get the nice strong and flat TQ
curve that this build produced, Zippers experimented with a number of head pipes and exhaust cans. The best performance came
with a D&D head pipe and an experimental exhaust can. That's a long way of saying that the 88" build makes great power
but that exhaust selection has a huge impact on the final power numbers. No matter which exhaust one picks though, it's still
a sweet build!
For a guy who wants MORE POWER and doesn't want to worry about engine life or always having to find
good high octane gas, this build starts easily, runs smoothly, wasn't prone to pinging, and will pull your arms out of their
sockets if you don't pay attention when you grab the throttle. Too bad it's not legal for the race series...