(JP 5508898) CHR...Cool - SHR...45
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After several years of development Model Technics entered the glowplug market in 1994 with the FirePower range of plugs. These plugs knocked the UK market for six, taking more than 50% of the market within six months of launch.
Later the MaxFlash range with enhanced throttlability came next in 1996.
CHR = COMPARATIVE HEAT RATING - This denotes how `hot the plug is within 'the Fire Power range but it does not directly relate to any other range.
SHR = STANDARD HEAT RATING - This denotes how hot the plug is on the `Standard Heat Rating scale. Any plug can be rated on this scale and it allows plugs to be compared from different ranges. The scale runs from 0 to 100 :-
0 = Excessively Cold 100 = Excessively Hot
DEFINITION OF HOT AND COLD - If an engine is adjusted to run well on plug A: And when plug B is substituted it is noted the needle valve must be leaned to get equally good running: Then plug A is said to be `hotter than plug B. Plug B is `colder' because the element needs the extra heat, generated by the leaner mixture, to reach the optimum operating temperature in the required time.
CORRECT SELECTION OF HEAT RATING can give up to 2000 rpm power increase and improved throttling. Too cold a plug will cause loss of power and or poor throttling.
TOO HOT A PLUG will also cause loss of power and or poor throttling but, additionally, it can cause pre-ignition, overheating and detonation leading to FAILURE OF THE PLUG and DAMAGE TO THE ENGINE.
When a needle valve is leaned, the leaner mixture heats the plug element faster and advances the ignition. Maximum power is achieved when the ignition timing is optimised. If the plug is too hot, then, although the timing can be optimised the mixture is still too rich for absolute maximum power. But, if the needle is further leaned, then the ignition becomes too advanced and again loses power.
With the MODEL TECHNICS RANGE it is possible to fit a colder plug so that when the needle is leaned to give optimum timing, it also gives optimum mixture AT THE SAME TIME and thereby gives ABSOLUTE MAXIMUM POWER with extremely good throttling.
SELECTION OF THE CORRECT PLUG can only be made by testing and in most cases the plug that produces the highest rpm is the best choice.
Other parameters to look for are:- lowest reliable idle speed; cleanest pick-up from idle having allowed time for the engine to cool; strongest mid-range pick-up and an uncritical main needle setting.
HIGHLY TUNED RACING ENGINES will probably require an F2, F3 or F4. HIGH PERFORMANCE CONTEST ENGINES F3, F4 or F5. HIGH POWER SPORTS ENGINES F4, F5 or F6 and REGULAR SPORTS ENGINES F5, F6 or F7. But there are many exceptions to these suggestions, so don't be afraid to experiment - though be careful to avoid detonation when trying hotter plugs by setting the needle a little on the rich side.
Two important factors that influence the choice of plug: If the NITROMETHANE content is increased significantly a colder plug will be needed if the COMPRESSION RATIO is reduced a substantially a hotter plug will be needed.
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