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Re: Axle ratio inpact
Of course, my '65 BB has M21 equivalent with 1st gear having 2.2 ratio and the '71 SB has M20 with its 2.5 first gear. The brute native torque profile of the 396 with it's 4.56 rear has absolutely no problema pulling out of the hole. But with earlier SB's too much gear reduction can make 'em sputter & grunt coming off the line.
This is another area that can be 'played' with. Instead of changing out rear ratios, folks can opt to tinker with the tranny (especially if it needs an overhaul to start with). You won't change the final drive gear (1:1), but you can easily get the effect of a taller rear coming out of the hole with a less agressive first gear (making M21 into M20 equivalent) AND this preserves integrity of the speedo gear.
On the other hand, it's possible to go the wrong way with a rear end. Fellow club member has '65 396 that's in full drag 'dress' for use at the strip. Factory original motor (one of the cars in the Noland Adams '65 owner survey) sits in the garage while a replacement 396 'lives' under the hood. This motor is built to the 'hilt' (roller rockers, ported heads, dry ice cooled fuel lines, full race electric fuel pump) and dynos at 640 HP altitude UNcorrected in Evergreen, CO (almost 7000 feet).
Owner had to 'struggle' to make car pull 3rd Flight for his Founders Award prerequisite. For completion of Founders, car has to be driven at least 500 miles in caravan on the National Road Tour. Member 'dreaded' the cross country drive in a drag strip optimized BB with 4.11 rear end, M21 tranny, and an engine that doesn't smooth out until you pull past 3500 RPM.
So, he pulled the 4.11 rear and tossed in a 3.36. Found it was 'too much' for the tricked out power plant and tall first gear. Car was prone to stalling -- not 'cool' in a polite group caravan.... So, the 3.36 has just been changed out for a 3.55. This seems to 'squeak' by. But, it will be 'truth time' in a few weeks when we set off for Sun Valley!
Of course, my '65 BB has M21 equivalent with 1st gear having 2.2 ratio and the '71 SB has M20 with its 2.5 first gear. The brute native torque profile of the 396 with it's 4.56 rear has absolutely no problema pulling out of the hole. But with earlier SB's too much gear reduction can make 'em sputter & grunt coming off the line.
This is another area that can be 'played' with. Instead of changing out rear ratios, folks can opt to tinker with the tranny (especially if it needs an overhaul to start with). You won't change the final drive gear (1:1), but you can easily get the effect of a taller rear coming out of the hole with a less agressive first gear (making M21 into M20 equivalent) AND this preserves integrity of the speedo gear.
On the other hand, it's possible to go the wrong way with a rear end. Fellow club member has '65 396 that's in full drag 'dress' for use at the strip. Factory original motor (one of the cars in the Noland Adams '65 owner survey) sits in the garage while a replacement 396 'lives' under the hood. This motor is built to the 'hilt' (roller rockers, ported heads, dry ice cooled fuel lines, full race electric fuel pump) and dynos at 640 HP altitude UNcorrected in Evergreen, CO (almost 7000 feet).
Owner had to 'struggle' to make car pull 3rd Flight for his Founders Award prerequisite. For completion of Founders, car has to be driven at least 500 miles in caravan on the National Road Tour. Member 'dreaded' the cross country drive in a drag strip optimized BB with 4.11 rear end, M21 tranny, and an engine that doesn't smooth out until you pull past 3500 RPM.
So, he pulled the 4.11 rear and tossed in a 3.36. Found it was 'too much' for the tricked out power plant and tall first gear. Car was prone to stalling -- not 'cool' in a polite group caravan.... So, the 3.36 has just been changed out for a 3.55. This seems to 'squeak' by. But, it will be 'truth time' in a few weeks when we set off for Sun Valley!
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