Page 16 - Combined_141_OCR

RACING FUELS
SPARK ADVANCE (Continued)
METHANOL
designed to make up for a displacement deficit by high RPM Methanol gives a bonus due to its “refrigeration” prop­
and superior “breathing,” but larger Detroit engines can erties ... a cooler, denser mixture enters the cylinders, con­
“fade” at extremely high RPM. Peak power can be developed sequently, a larger charge is taken into the engine on the
up to certain RPM ranges... once this range is exceeded, intake stroke. This mixture is so dense that only 6 parts of
additional spark advance is not beneficial. air to 1 part of alcohol (as compared to 12 parts of air to 1 of
An inexperienced drag racer will purposely set his engine gasoline) are required to produce efficient burning.
timing far beyond factory specs so his engine will wind up Just switching an engine from a diet of gasoline to alco­
very quickly when leaving the drag strip starting line. This hol will, with proper changes in jetting and spark advance,
is fine... he comes “out of the hole” strong, but starts to produce a 15 to 20% h.p. increase. For this reason, un­
fade three-quarters down the strip. Reason ... he set up his supercharged engines converted from gasoline to methanol
spark advance so excessively that an overabundance of will generally require a spari: plug heat range one step
spark lead causes detonation and a loss of horsepower be­ colder. Even more marked increases in power can be gained
fore he reaches the end of the strip. by raising the compression ratio ... reasons being:
There are trick ways to modify the distributor to supply 1) Under rich mixtures, alcohol has a higher anti-knock
a high advance for initial acceleration, yet “chop down” a value.
build-up of excessive advance near the end of the run. (Drag 2) Alcohol burns at a lower temperature than gasoline.
racers using supercharged engines often “lock” the mag­ There is a limit on compression ratio ... but some alcohol-
neto and run a constant advance, since any additional spark fed, non-supercharged engines can run as high as 16:1. pro­
advance at such high RPM would be ineffective.) viding combustion chamber geometry is “favorable” and the
When an engine is modified, optimum spark setting can­ engine can stand the increased mechanical stresses.
not be specified. Only by dynamometer runs or “trial and Remember:
error” settings can this setting be “pinpointed.” Drag race Jet size for alcohol-burning engines is over twice the
“spark settings” are usually different from oval track or road area for gasoline-burning engines. Jets should be flowed,
course spark adjustments. not drilled.
Different fuels, fuel blends, or supercharger drive ratios Alcohol has a slower flame speed than gasoline, conse­
have an influence on engine timing. Stock engines used for quently, more ignition advance is required.
racing purposes have various “states of tune”: If an engine is converted from gasoline to methanol and
no changes are made in compression ratio, a spark plug
a) Some top contenders run an extremely rich mixture one step colder will suffice ... however, if compression
with a warmer plug.., while others (who go just as ratio is raised considerably, you may have to go still
fast) believe in a leaner mixture using a cooler plug. colder.
b) Many employ special cams which have different Regular gap, projected nose, and “P” gaps can all be used
“breathing” characteristics at different RPM’s. in a methanol-burning engine, providing the compression
ratio is not too high. Extremely high compression will prob­
The compounding of various mixture settings, camshaft ably call for “R” gaps.
designs, and diverse spark advance positions are the major You may want to compare fuel characteristics to see just
reasons you can only put stock engines “in the ball park” on where gasoline and methanol stand in relation to each other:
spark plug heat range but cannot pinpoint heat range. Only
by trial runs and consistent competition can you arrive at a “REFRIGERATION” BTU ENERGY
precise heat range. PROPERTIES ANTI-KNOCK VALUE PER LB.
Methanol Methanol (rich) Gasoline
I
1 Ethanol Acetone Benzol
Isopropanol Benzol Isopropanol
Acetone Ethanol Acetone
- Benzol Isopropanol Ethanol
Gasoline Gasoline Methanol
DISTRIBUTOR MAINTENANCE
“NITRO”
Nitro-methane is extremely sensitive to combustion cham­
Prior to a race event, the distributor should be removed
from the engine and run on a distributor machine. The spark ber temperature and pressure, but combustion can be con­
trolled by the use of:
advance curve should be monitored ... proper dwell and
spring tension checked ... cam lobe spacing observed. The proper compression ratio suitable spark advance
distributor should be run in excess of “red line” race RPM spark plugs of proper heat range correct fuel/air ratio
to check for steady and reliable output. a) If 10 to 20% nitro is added to methanol, a range of “62”
Remember distributor speed in a 4-cycle engine is V2 to “60” is usually “in the ball park” (providing the engine
engine or crankshaft speed. is not supercharged or the engine is not 2-cycle).
Total spark advance is your distributor degrees doubled, b) If 30% nitro is used, a range of “60” to “57” is generally
plus the initial degrees you set the flywheel or damper with required.
your timing light. For example, if your maximum distributor c) A nitro-methanol mix in excess of 10% will almost surely
advance is 12°, you would double this figure to 24°... if you use a “54” series.
set the advance 12° at the flywheel with your timing light, Projected core nose plugs are not recommended for nitro­
your total spark advance would be 24 4- 12, or 36°. burning applications.
“Race” camshafts alter effective cylinder pressures at a Cold plugs, rich mixtures, and lower spark advance should
given engine speed, consequently, you may have to make be maintained when initially setting up an engine to run on
slight adjustments in the spark curve or initial settings to a nitro-methanol combination. Spark plug “readings,” engine
get the full benefit of the cam. symptoms, and general performance characteristics may
allow the hot rodder to increase the spark advance, set car­
buretion leaner, or go warmer in plug range, but such ad­
justments should be made carefully and cautiously.
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