S&S Cycle Cylinder Heads for Harley-Davidson Twin Cam 88 Engines - Manual (Page 7)

G If the motorcycle is used exclusively on a drag strip where
engine temperatures vary, slightly richer jets may be
necessary for best performance. Larger jets/richer mixtures
will enable one to run a colder engine which is sometimes
desirable. This is best determined by experimentation.
G Carburetor jetting and spark plug color - While spark plug
color may be used to help determine carburetor jetting, S&S
recommends that our instructions be used as primary jetting
guide and that plug color indications be used only as
secondary aid. We have found that different brands of
gasoline, gasoline additives, engine heat (due to ignition
timing), and brands of plugs and heat range used distort
plug color drastically making plug reading difficult for the
average tuner. Also, new plugs usually require a road test of
10 miles or more to properly develop the color which means
that quarter mile tests may not be long enough and hence,
not always a good indication of carb jetting. It is best to use
recommended spark plug type and to consult the spark plug
manufacturer if you have questions.
Exhaust Systems
G
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.
G Muffler systems: Most stock and many aftermarket exhaust
systems are made exclusively for looks with little
consideration given to performance. A very good street
system consists of the stock header pipes with the crossover
tube and a set of low restriction mufflers. S&S
® slip-on
mufflers are designed to maximize the performance
potential of S&S cylinder heads. The benefit of S&S Slip-on
mufflers is two-fold: they replace the restrictive, power
robbing stock mufflers on an otherwise good set of header
pipes, and since they use the stock header pipes, there is no
concern over whether or not a complete new system will fit
properly. Low restriction mufflers and stock header pipes will
produce more power than than drag pipes in the midrange.
Since the midrange is where the vast majority of normal
driving occurs, it makes this system ideal for the street.
Gearing
G Gearing depends on the total weight of the machine and
rider, the size of the engine, cam, exhaust system and type of
riding to be done. 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.
G For those who wish to determine their final drive gear ratio
the formula is as follows:
Compression
G Generally speaking, while engines with higher compression
ratios make more horsepower and perform better, they also
tend to lose that performance edge faster, require more
maintenance, are harder to start, and require better
gasoline. As a rule, we recommend a compression ratio of
no greater than 11:1 for engines used in normal street
operation. A word of caution is in order. Before building an
engine that may be unsuitable for your application, carefully
consider your riding needs, riding style and overall
performance objectives.
7
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.