S&S Cycle Sidewinder 3 5⁄8 Big Bore Cylinders for Harley-Davidson Sportster Models—1986–2003 - Manual (Page 18)

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carburetion
• All S&S® test engines are run using S&S carburetors. S&S Super E and G carburetors are recommended for most applications with the Super G
being used more often on larger displacement, freer breathing engines with higher compression ratios. Typically, engines equipped with S&S heads
require the same or slightly leaner jetting than those engines fitted with stock heads. Consult the carburetor jetting instructions for specific jetting
recommendations.
• If another type carburetor is used, it must be made to run rich enough to operate properly and to prevent engine damage. If you have a problem
with another carburetor, S&S cannot help you and recommends you call the carb manufacturer with any questions you may have.
• 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.
• 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 proven spark
plug combinations and to consult the spark plug manufacturer if you have questions. If one desires to become more proficient at plug reading,
Champion Racing Division has a very informative booklet which may be helpful. For details, write:
Champion Spark Plug Co.
PO Box 910
Toledo, OH 43601
• Cams and exhaust systems can make some engines difficult to carburate. We have found that certain cams and exhaust systems will cause poor
performance at a specific RPM, and attempts to correct jetting for that specific level usually destroys carburetion over the balance of the range. A
combination of cam overlap, reversion, and back pressure, or even lack of back pressure can cause mixture dilution at certain engine RPMs. This
dilution will cause engine roughness or misfiring when engine is held in this range.
Exhaust Systems
• Drag pipes—While drag pipes can be used with good results to establish performance guidelines on pre-1984 engines, they are generally not
recommended for 1984 and up big twin engines in street applications. Big twin engines are easier to carburate with muffled systems.
• Muffler systems—Most stock and many aftermarket exhaust systems are too restrictive and made exclusively for looks with little consideration
given to performance. A very good, economical street system consists of the stock header pipes with the crossover tube and a set of low restriction
mufflers. S&S offers a line of slip-on mufflers that create performance economically. This combination will typically produce 10 hp more 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
• Gearing depends on the total weight of the machine and rider’s, the size of the engine, cams, 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.
• For those who wish to determine their final drive gear ratio, refer to the formula shown below:
compression
• Generally speaking, 1984 and later engines with the proper camshaft selection can operate using higher compression ratios with fewer problems
than their earlier counterparts. Keep in mind, though, that while engines with higher compression ratios make more horsepower and perform
better, they also tend to lose that performance edge faster, require more maintenance and start harder. As a rule, we prefer to limit the compression
ratio to no greater than about 10 to 1 for engine combinations used in normal street operation. A word of caution is in order. Before building an
engine you may regret later on, carefully consider your riding needs, riding style and overall performance objectives.
(Clutch Sprocket*) X (Rear Wheel Sprocket*)
(Motor Sprocket*) X (Transmission Sprocket*)
Ratio =
Ratio is engine revolutions per one (1) rear wheel revolution.
*number of teeth on each sprocket