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I have said it once and will say it again, biggest bore , then stroke it to the biggest diaplacment. NASCAR does it this way, IRL, Formula 1 they all do it this way. You don't see ANY NASCAR builders running a shorter stroke to get more out of it. They run the biggest bore the rules allow then stroke it to the maximum displacement allowed. When you are trying to squeeze every last HP and foot pound of TQ possible then that is how it is done end of story. I am not talking bracket engine builders or street builders (they should do the same as far as there budget or rules allows) but the guys being paid millions to get 5 more hp do it that way. If NASCAR said you could run a 4 inch stroke with the current bore (4.185)you would see them ALL running 4 inch stroke in a couple weeks, same with 4.5 stroke, bore to stroke ratio be danged they would run as big as possible. If Formula 1 said they could run a 2 inch stroke with the current bore they would all do it and very quickly, you would be shocked how fast they would get it done, they would trade some rod length for stroke also if that was needed.



The problem I have is with your example, not your answer.

There is almost never (I say almost because I admit, I don't know everything) a sanctioning body that stipulates engine geometry the way you have stated it. That is why I used Pro Stock as my example. The have a minimum weight, maximum displacement, 2x4's and gasoline. There are some newer, idiotic rules (like the 1090 minimum rule) but for the most part, that is Pro Stock. There is more than 1 way to get to 500 CID but the PS guys use the biggest bore and stroke for final displacement just as you said. But there is no minimum bore, max bore or stroke specs. In Top Fuel, they are 500 CID , but the bores (as far as I have seen) is a rather mundane 4.375 and is stroked to get displacement.

I do know in NASCRAP they don't have a minimum stroke, so they GENERALLY use the biggest bore (allowing for some overbore capabilities) and stroke for displacement.

As for the long debated R/S ratio thing. It gets old repeating but I will try one more time. When you are induction limited (and all the 4 V/cyl guys claim 2 V/cyl heads are intake limited) much more thought and care should be given to R/S ratios. Just the frictional losses dues to stroke length ( lets not forget about windage losses...in the 1960's Chrysler engineers KNEW that a hemi turing 8000 rpm's would hold 8 quarts of oil around the crank...with a 3.75 stroke!!!!) eats up a big percentage of what gains there are from increased strokes and high rod ratios (lower numerically). Induction limited packages should spend more time thinking about R/S ratios and less about torque under minimum calculated RPM (or observed). Just my humble opinion.

Just because you think it won't make it true. Horsepower is KING. To dispute this is stupid. C. Alston