You don't always need short strokes to rev high RPM! I've built many 292 Chevy's that turn 10,500 RPM at the starting line and were shifted at 9500-9700 RPM. They have over 4" of stroke! It just depends on how much $$$ you want to throw at it. The main premise for what Navarro did with his destroked engine was several reasons: First, in an inline 6, everyone here is familiar with harmonics im sure. With its 120 degree firing making different harmonic levels as RPM goes up, the shorter the stroke the less severe and destructive the harmonics are. Second, the shorter the stroke, the more rigid the crankshaft becomes, because it has more main to rod journal overlap making it flex less. Many modern BMW German Touring car racing 6 cylinder engines race at or beyond 9000 RPM for the same length of time many of our Nascar races last. Their strokes are also around 3", plus having fully counterweighted cranks helps also. He also was trying to make the cubic inch limit for the class to be legal for competition, and there probably weren't many engine combinations at that time that would have allowed him to devise the combo he chose. As someone has also stated, the blocks were very strong, so that coupled with the equally rigid and strong crankshaft made a good foundation for him to build upon.
Last edited by CNC-Dude; 10/15/08 06:13 PM.
