10- Tuning Guidelines
Ignition timing and carburetor jetting are responsibilities
of the customer. If not thoroughly familiar with these
procedures, contact a professional mechanic.
A- Exhaust Systems
Muffled exhaust systems.
If you have an existing 2-into-2 system that uses slip-
on style mufflers, whether it is an OEM or an
aftermarket system, we recommend the new S&S slip-
on mufflers. S&S
®
dyno tests achieve almost 8 more
horsepower and 5 ft. lbs. of torque on a stock Harley-
Davidson
®
Twin Cam 88
®
engine using stock header
pipes and S&S slip-on mufflers, and S&S Super
Sidewinder
®
engines
have
produced
1-1.1
horsepower per cubic inch using stock style exhaust
and S&S slip-on mufflers. These mufflers will allow
your engine produce more horsepower and torque
than straight-through drag pipes in street and
highway driving, and work equally well on both stock
and large displacement engines.
Drag pipes
While drag pipes can be used with good results to
achieve top end horsepower, they are generally not
recommended for street applications. Carburetor
adjustment and jetting is generally easier for engines
with muffled exhaust systems.
B- Gearing
Gearing depends on the total weight of the machine
and rider, the size of the engine, cam, exhaust system
and type of riding. Most high performance engines,
and particularly those with larger displacements, are
capable of pulling more gear. We suggest you break
the engine in with stock gearing to minimize the load
on the engine. After the engine is broken in, you will
have a better feel of its potential and can change
gearing accordingly.
The following formula will determine final drive gear
ratio:
Engine Revolutions Per One Revolution of Rear Wheel=
(Clutch Sprocket*) x (Rear Wheel Sprocket*)
(Motor Sprocket*) x (Transmission Sprocket*)
*Number of teeth on each sprocket
11. Engine Specifications & Torque Values
14
Displacement
Bore
Stroke
Compression Ratio
111”
4
1
⁄
8
”
4
1
⁄
8
”
9.77:1
Cylinder Heads
Specification
Valve guide in head (tight)
.0015”-.003”
Valve seat in head (tight)
.005”-.0075”
Valves
Specification
Service
(Fit in guide.)
Wear Limit
Intake
.0012”-.0015”
.0025”
Exhaust
.0018”-.0023”
.0035”
Seat Width
.040”-.062”
Stem Protrusion
2.045”-2.060”
2.080”
Rocker Arms
Specification Service
Wear Limit
Shaft fit in bushing (loose)
.0007”-.0018” .0035”
Bushing fit in rocker arm (tight) .002”-.004”
Hydraulic Lifters
Specification
Service
Wear Limit
Lifter fit in guide (loose) .0006”-.0017”
.003”
Pistons
Specification
Service
Wear Limit
Fit in cylinder
.002”-.0025”
.005”
End gaps:
.017”-.025”
.028”
Top two compression
Oil control rails
.016”-.035”
.050”
Crankcase
Specification
Service
Wear Limit
Timkin
®
race in case (tight) .001”-.003”
less than .0025”
Pinion race in case (tight)
.001”-.003”
less than .0025”
Connecting Rods
Specification
Service
Wear Limit
Crankpin bearing
.001”-.0012”
.002”
Running clearance
Piston pin fitment in rod
.0005”-.001”
.002”
Connecting rod side-play
.015”-.035”
.040”
Flywheels
Specification
Service
Wear Limit
Runout (shaft at flywheel) .0005”-.001”
.003”
End play
.001”-.005”
exceeds .005”
