Each bored out monstrosity required about 10 degrees more at lash duration to make up for the loss of real horspower as the engines got bigger. 1.5:1 rod ratios became coomon place, and to make up for it, Michigan had to make much more aggressive cam profiles. When hoods and wheels started dropping height in 1957, Pontiac started pushing the rod ratio friendshipin the widetrack cars, Ford USA did its worst in 1963 with the low slung Fairlane 200, then Australia with the Falcon 221 in line six, then USA again did its worst with the F100 300 cube six, the Ranchero 250, then Chev with the 400 Small block, and Chev 454's and Pontiacs 455 were pretty bad. Primarily the measured frictional horsepower loss goes up dramatically when you try to put a longer stroke and longer conrod in the 8.2" space below the head on a 5.0/302.īefore piston technolgy skyrocketed in the 50's and 60's, engine designers used to use 2.2:1 rod ratios in racing engines if they could, but no less than 1.75:1 in trucks and passenger cars. Ford did that with the Martel designed 351c, 351w, 400, just added an extra inch or so to the deck to drive the rod ratio close to 1.65 or more. Ford do that for the 5.4 /5.8 engines verses the 4.6 /5.0 Cammer engines. It would be, with a blank check book, normal to engineer a 331 engine with a 8.76" deck, and a 347 with a 9.1" deck engine to ensure the rod to stroke ratio is the same 1.7:1 as a 302. These are measured on dynos as frictional power and torque losses. If your going to build a 331 why not go a bit more and go 347 ?Due to diminishing returns from physical properties which distort the bore, create piston side thrust vector. Why a 331 and not a 347 ? Someone mentioned to me he was building a 331 stroker.
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