Macedo Using Wrong Spark Plugs
 
The following was discovered at while at Underground Racing for repairs - 

Those are not at all the correct plugs or even acceptable plugs to use in that application PERIOD. We have installed and use many of these Striker Heads from JM and they have worked perfect with NO tuning issues. For those of you who are wondering about using the plugs Kenny had installed in his STRIKER heads here is something to consider. Intake ports, combustion chambers, piston tops, and spark plugs are all designed together as a system to ensure good combustion. If one of the elements of the systems is changed, then the combustion system cannot function properly. In this case, installing a 3/4" reach plug in a combustion chamber designed to use a 1" plug leaves the spark plug electrode gap sitting in the spark plug hole, whereas the combustion chamber has been designed to have the spark plug electrodes protruding into the chamber. A hole is not a good place to initiate combustion, so the initial flame propagation (if the plug is able to light the mixture at all) will be sluggish. Sluggish burn rates will have the effect of retarding the combustion phasing relative to the piston motion, and increase the variability in combustion from cycle to cycle. Increased combustion variability will manifest itself in a vehicle as an engine that idles rough, perhaps has trouble starting, and doesn't make as much power as it would otherwise be capable of making. To summarize, a spark plug with shorter reach than the cylinder head is designed for will leave the spark plug gap in a hole, combustion quality will suffer greatly, and the engine will run poorly. The easiest solution here is to simply install the correct spark plug and reap the combustion benefits. Refer to the pictures to observe what I am talking about. I would *NOT* put the correct plugs in this car and try to drive it on it's present tune. Please see pictures below as one shows the 3/4 plug that is in Kenny's Striker Heads and the other pictures show the CORRECT plug that is supposed to be in Kenny's heads!