Because of the length issue, We stayed with the stock plug for long time. The problem was that when we boosted high we were cooking the plug and our engines due to them only being available as cold as the 6 heat range. The Iridium plug is the closest available length to the stock size TT plug. The Iridium plug does completely protrude through the head. In our testing the Iridium that is slightly shorter fires better and has more available proper heat ranges than the Platinum that is the exact correct length. From my experience having the proper heat range for the power level is much more important than having the exact correct length.