Technical Bulletin 119901, dated 11/99, revised 02/01

General Motors 3.8 liter Supercharged V6 engines

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Supercharged engines are much harder on spark plugs than normally-aspirated engines - particularly late model street engines delivered with wide spark plug gaps to initially help control exhaust emissions. Supercharging an engine raises the cylinder pressures, and for this reason, itís critical the correct spark plug heat range is maintained, the spark plugs are gapped appropriately (not necessarily the factory recommended gap) and the spark plugs are replaced regularly.

Spark plug manufacturers and tuners suggest reducing the factory recommended spark plug gaps on supercharged engines because using a too wide gap can result in misfires, loss of power, poor fuel economy, premature spark plug failure, uncontrolled exhaust emissions and possible engine damage. If you use your supercharged street engine for commuting, keep in mind the spark plug gaps progressively erode and widen with everyday use.

Supercharged race engines use special racing spark plugs which are constantly replaced. Heat range and gaps are carefully selected so as not to overstrain the ignition system and the spark plugsí ability to provide an efficient spark to ensure the engine produces maximum horsepower.

Magnecor KV85 and R-100 Race Wires are primarily designed for race engines requiring EMI suppression, but unlike other "performance" wires, Magnecor wires can also be used on any street engine. If fitted correctly, Magnecor Race Wires will not reduce spark current like factory carbon conductor wires, therefore a spark plug problem not immediately apparent with current-reducing carbon wires will quickly become noticeable with Magnecor wires conducting full current to the spark plugs. If you fit a set of Magnecor Race Wires and notice a miss or hesitation not previously apparent, you may have a spark plug related problem. Usually, sparks are arcing (inside a wireís spark plug connector/boot) from microscopic cracks in the spark plugís porcelain to the spark plugís metal base.

Both Magnecor and specialist performance tuners have discovered that many recent US stock vehicles are delivered to consumers with spark plug gaps set overly wide, presumably to improve exhaust emissions . Unfortunately for consumers, by nature of the design, overly wide spark plug gaps erode even quicker with everyday use, resulting in premature spark plug failure ó  which either appears as a loss of power, when used with factory carbon conductor wires, or an engine miss with wires designed for a race engine.

Supercharged engines are particularly prone to this problem, more so with high mileage engines, and if spark plugs are not replaced and properly gapped at regular intervals, or immediately after a problem become obvious, heat damage to a wireís spark plug boot can result from boosted combustion gas passing through cracks which develop in a spark plug's porcelain body inside the boot. Usually, the first spark plug to fail will noticeably affect engine performance. 

Another problem area is wiring looms into which the spark plug wires are fitted. Depending on the engine, some wires will touch either or both the engine and other wires in some spots. Because an ignition spark always takes the easiest path to ground, a failing spark plug (or with a wide eroded gap) can cause the spark traveling in a wire to find it easier to induce itself into an adjacent wire (cross-fire) or to ground on the engine. On any engine, itís never a good idea to allow spark plug wires to touch each other, or rest against metal parts of the engine.

Itís important to remember that, even though your vehicle is manufactured by a large automobile manufacturer for the mass market, it contains a very high performance supercharged engine which requires regular preventative maintenance and additional care to overcome the problems associated with using such an engine in a street vehicle. Even more care will be required if the superchargerís drive ratio is changed, as this method used to boost horsepower places an even greater strain on spark plugs not designed for racing.


Unless you have already done so, always replace the spark plugs before fitting Magnecor Race Wires. Use a smaller plug gap. If necessary, seek advice as to the best gap for your engine. Replace your spark plugs regularly ó more often if you have changed the supercharger's drive ratio. Ensure all spark plug wires are separated, with at least a 1/8" (4mm) gap between each wire, to avoid cross-firing when a spark plug is about to fail ó you may need extra wire separators. 

If the spark plugs are relatively new, and an engine misfire is apparent, examine each spark plug very carefully for microscopic cracks that develop in the porcelain. Below are enlarged photographs of what to look for ó although it will be a lot more difficult to see the microscopic cracks on an actual spark plug.


The 2 photographs below show spark plugs from a GM supercharged 3.8 liter V6 engine which was misfiring badly. The cause was diagnosed as "faulty" spark plug wires. The wires were replaced without first inspecting the spark plugs, and a few miles later, the engine was again misfiring. The misfiring problem was finally solved by installing new spark plugs. 

Highlighted are microscopic cracks that developed in the porcelain upper body of both spark plugs. Although both spark plugs shown are from the same engine, just one spark plug in this condition will cause any engine to misfire at certain times (usually under load) because the spark will track inside the spark plug boot from the cracks to the spark plug's metal body. The gap on the left plug measured 53 thousands of an inch (1.35mm), and the right plug measured 61 thousands of an inch (1.54mm).The spark plug on the right also shows some combustion gas leakage.

A close-up of the porcelain section of the spark plug on the left is shown in another photograph below.



Please understand ignition wires are nothing other than conductors of spark energy, and while it is possible bad installation and failing or improperly gapped spark plugs can eventually damage ignition wires, the wires themselves cannot damage the spark plugs. Although fitting carbon conductor wires can seemingly postpone a spark plug problem, these wires will not miraculously cure the problem for very long, and the engine will lose power.

Magnecorís warranty DOES NOT cover ignition component failure problems caused by a poor choice of spark plug gaps and/or heat range, lack of separation between wires or allowing spark plugs to deteriorate to a condition where damage to a wireís spark plug boot could eventually occur. If you don't want to use spark plugs with smaller gaps, do not separate the spark plug wires and are not prepared to replace the spark plugs regularly, we cannot warranty wires damaged for reasons beyond our control.

Magnecor provides the above information for your benefit, to ensure your vehicle's ignition system functions as efficiently as possible and to save you future aggravation and unnecessary repair costs. We are happy to help you further, so please contact us or our dealers/distributors if you have any questions.

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