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JWL · 12-01-2019, 08:33 AM

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Adding compression has nothing to do with exposing the weakness of the 21A connecting rod. The 21A rod will fail at high RPM, on the exhaust stroke, at the pin end, just below the pin bushing. New 21A rods will usually withstand 3 drag strip runs at 6800 RPM in the lights when used with maximum lightened pistons and pins. However, if anything, ANYTHING, happens in the driveline and the engine buzzes to 7000 RPM, for only one second, they will do serious damage to the engine.

As OlRon says, the best first step for improving your Flathead is to bump up the compression ratio. Adding compression or displacement are the only methods for improving power and efficiency at nearly all RPM levels.

12-01-2019, 08:33 AM	#6
JWL Member Emeritus Join Date: May 2010 Location: Fitzgerald, Georgia Posts: 2,204	Re: Flathead domed pistons and 21A rods Sponsored Links (Register now to hide all advertisements) Adding compression has nothing to do with exposing the weakness of the 21A connecting rod. The 21A rod will fail at high RPM, on the exhaust stroke, at the pin end, just below the pin bushing. New 21A rods will usually withstand 3 drag strip runs at 6800 RPM in the lights when used with maximum lightened pistons and pins. However, if anything, ANYTHING, happens in the driveline and the engine buzzes to 7000 RPM, for only one second, they will do serious damage to the engine. As OlRon says, the best first step for improving your Flathead is to bump up the compression ratio. Adding compression or displacement are the only methods for improving power and efficiency at nearly all RPM levels.