ix21@sdccs6.UUCP (David Whiteman) (05/10/84)
I am going to get my Datsun 310-GX 1980 tuned up. The owners manual lists as replacements standard, hot, and cold spark plugs. Standard plugs are for normal driving, hot for short range and cold for long range driving. My question is how short is short range driving. I drive about 10 miles to school, and that is the most I drive at one time. Should I put hot or standard spark plugs. I also live in Southern California where not even the winters are cold, if that matters. The manual listed BP5ES-11 for standard, BP4ES-11 for hot, and BP6ES-11 and BP7ES-11 for cold. Also what is a resistor built-in spark plug?
wookie@alice.UUCP (Keith Bauer White Tiger Racing) (05/14/84)
As you already pointed out the heat range of the spark plug is selected by the type of driving you do; hotter plugs for colder driving and vice-versa. If a plug is too cold for the application it will tend to carbon foul because of combustion products condensing on the tip. Sufficient heat is required to keep the plug clean. If the plug is too hot for the application it will not only stay clean but start burning away! This will lead to greatly shortened plug life and possibly (probably with todays gas!) detonation beacuse of the red hot (or hotter) plug tip. The trick is to read the plugs. If after one of your typical runs you have black sooty looking plugs a higher heat range is indicated. If you have absolutely clean white plug tips possibly with little melted looking splotches then the plug is too hot. I suspect for what you are doing and where you are the standard plugs are fine. By the way there are extended temperature range plugs available. In the AC Delco line this is the type with the S suffix ie a 45S is the extended range 45. This is usually accomplished by using a much longer reach on the plug thus putting the business end of the plug much deeper into the cylinder. This allows the incoming cool fuel-air mixture to cool the plugs on the intake stroke and thus a hotter plug can be used for the same application thus giving better slow speed operation while allowing highway driving as well. A resistor plug has a resistor built into the ceramic tower to aid in noise suppresion and to help build up a hotter spark. (We are dealing with a nice inductance, capacitance and resistance circuit here but I don't want to get technical! Another type of plug is the auxiliary gap plug which actually has a gap built into the core. This gap is larger than the gap at the plug tip and thus allows the voltage to build up to a higher value before the plug fires. Since the voltage must be able to jump across the wider gap inside the plug it is guaranteed to jump at the tip. This helps in engines which tend to oil or carbon foul plugs. The carbon provides a leakage path and the spark is either very weak or doesn't occur at all. All this isn't nearly as critical in the average car as it is in the racing area! TTo have a plug last on the track they are very very cold plugs and so they foul terribly when the engine is just puttering around and so you get that characteristic rough running idle under 2000RPM. By the way, your plugs should have a nice even tan color if they are running in the right range and if your engine burns some oil expect to find alot of tan colored deposits on the plugs. If you have nice gooey black deposits then you are probably burning a ton of oil (that's assuming anything is burning at all in that cylinder!) Sorry this is so long winded! Keith Bauer White Tiger Racing