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Ol' Ron · 07-28-2010, 08:51 AM

The biggest problem with the long stroke is piston speed. As the valve opens it shouls reach max lift at about 70 degs after TDC. This is when the piston is reaching max speed. the valve begins to close at around 135 degs and the piston begins to slow down. At very high RPM's the piston runs away from the intake charge, effectively de-stroking the engine. I di believe a pop-up piston will breath better. There are a coupla things you can do to do this without spending allote of money. Using a 3 3/4 strole piston on a 4" crank, then recessing the piston .125 into the head. Now remove the lip created by the transfer area. This can give aprox 9:1 in a 276 engine. After you build a few dozen engines, you'll learn allote.
Good luck.
PS Just remember, ALL the power the engine makes has to come through those ports.

07-28-2010, 08:51 AM	#43
Ol' Ron Senior Member Join Date: May 2010 Location: Chester Vt Posts: 8,860	Re: Boring a flathead The biggest problem with the long stroke is piston speed. As the valve opens it shouls reach max lift at about 70 degs after TDC. This is when the piston is reaching max speed. the valve begins to close at around 135 degs and the piston begins to slow down. At very high RPM's the piston runs away from the intake charge, effectively de-stroking the engine. I di believe a pop-up piston will breath better. There are a coupla things you can do to do this without spending allote of money. Using a 3 3/4 strole piston on a 4" crank, then recessing the piston .125 into the head. Now remove the lip created by the transfer area. This can give aprox 9:1 in a 276 engine. After you build a few dozen engines, you'll learn allote. Good luck. PS Just remember, ALL the power the engine makes has to come through those ports.