American Motorcycle Dealer AMD 207 October 2016 | Page 20

1

The single chain-driven camshaft is described as “lighter, mechanically
less complex and creating less friction and noise.”

2

Two spark plugs per cylinder: one entering from the top of the
head, one from the side.

3

The number of ‘Big Twin’ engines Harley has designed, including the
EL of 1936

3.937” x 4.375” The bore and stroke of the 107-inch M-8;
the 114 inch Twin-Cooled variant has a 4.016” bore and 4.500” stroke

less complex, creating less friction and
noise.
Weighing the same as the lowerpowered engine it replaces, the
power-to-weight ratio of the ‘Eight’ is
another of the significant factors in
delivering increased power - there can
be no doubt that even as you read this,
the aftermarket will be busy working
on lighter weight, higher strength
components to push that ratio way
further.
The 107-inch version of the ‘Eight’ is
said to accelerate 11 percent quicker
0-60 mph (equal to a two to three bike
length improvement), and 11 percent
quicker from 60-80 mph in top gear
(equal to a one to two bike length
improvement), compared to the Twin
Cam High Output 103.
The 114-inch version is said to
accelerate 8 percent quicker 0-60mph,
and 12 percent quicker 60-80mph
than the Twin Cam 110.
Heat has always been the big issue for

the Twin Cam. Harley describe the
‘Eight’ as offering “improved rider and
passenger thermal comfort due to
reduced heat absorption, increased
heat rejection and a redesigned
exhaust system. With a precision
cooling strategy [developed for the
Rushmores] based on the specific
demands of the motorcycle model,
using a targeted flow of either oil or
liquid coolant around the hottest areas
of the cylinder heads.
“A new knock sensor for each cylinder
enables more precise timing control.
The rear exhaust pipe is repositioned
and the exhaust catalyst is relocated to
move heat away from the passenger.
Idle speed is lowered from 1,000 rpm
to 850 rpm.” The new sensor is based
on reading acceleration to enable the
ECM to manage ignition timing rather
than the ion-sending knock detection
of the Twin Cam.
The mapped (command) based system
of the Twin Cam ECM has been

4

The number of valves per cylinder: 4-valve and, indeed, twin-plug heads
are far from “new-tech” where V-twin engines are concerned, with many
in the aftermarket offering conversions or alternate layouts with 2/4
thinking as far back as the 1980s, if not earlier.

7

All ‘Milwaukee-Eight’ powered models are fitted with an Assist and Slip
Clutch with improved hydraulic actuation that is said to reduce clutch
lever eff