We strapped the Fat Boy to a Super Flow cycle dyno and ran it. The motorcycle
accelerated from 40 mph to 80 mph-which is approximately 2,550 rpm to
4,575 rpm-and it produced a corrected horsepower of 65.7 and a
corrected torque of 75.5 foot/pounds.
the motorcycle was turned over to my team. We randomly picked a set of
Quantum 4-valve heads, rocker boxes, covers, and intake parts off the
shelf. We also chose a set of pre-made exhaust pipes that fit this
motorcycle. All the pieces are available unchromed as well. The inside
of the pipes were sprayed with a heat-resistant paint and set aside for
future use. A crane Hi-4 single-fire ignition with a matching crane coil
was also selected.
you are not a motorcycle technician, I strongly recommend you consult
the Harley-Davidson shop manual on how to dismantle the top end. Start
by removing the negative battery terminal, drain the fuel, remove
tanks, exhaust, heads, etc.
NOTE: When installing Quantum 4-valve heads on 1984 and 1985 Evolution
big twin engines, you must use late style 1986 and up base studs (H-D
part number 16387-85) or equivalent. Take care to set them all at the
If you are careful and do not
move or break the seal on the base gaskets, you should not have to
change them unless you want to. You can use a head bolt and spacer to
hold the cylinder in place while you do the rest of the work.