Gearing change
Bosscar9er
11-18-2008, 12:04 PM
Looking to lower my rear end gears for improved acceleration for low cost. I have a 71 Buick 455 engine with a Turbo 400 auto and 3:42 gears. I was thinking of 3:91 gears which was an option for non-A/C cars like mine. But maybe a bit too low and not practical. I may settle for 3:73. Anyone have any experience with a big block with a Turbo 400 transmission and the lower gears? Whats the 3:91 gears like to drive? The car is not a daily driver and used mainly for show. Any suggestions?
MrPbody
11-18-2008, 03:00 PM
Boss,
I think you would be much happier if you stay with the 3.42. Due to the tremendous low-end torque the Buick 455 generates, it's MUCH better suited to the "taller" gears. The 455 Pontiac is similar in power output in stock form. Adding too low a gear makes the engine rev "too" quickly, not effectively "spreading" the torque out. They rev much too quickly and as a result, tend to turn rod bearings. The Buick won't turn a bearing as easily, but due to the thin casting, the block will flex and break the crank.
We have a Buick customer with a 625 HP 455 in his '78 Regal. The car goes 6.70s (1/8 mile) and 10.40s (1/4 mile). It revs to 6,100 RPM. He runs a 3.90 gear in that, and it's a pure "race" car (zero street miles, "lives" on a trailer). His engine sports a .600 " lift solid flat tappet cam, well-ported heads, Eagle rods, Ross pistons, and even has one of those lifter bore "braces". The latter may or may not help. Can't say, but it makes him FEEL better that it's in there!
We've learned to listen to Smokey (Yunik, RIP). He was talking about the Pontiac, but it applies to your Buick as well. "Don't REV it up, GEAR it up!"
I always found the Buick "interesting". The weight of the engine is nothing short of amazing. How one can get that many cubes into a package that weighs less than 600 lbs. IS amazing. The low-end torque is it's "long suit". Unfortunately, the same issue that makes it cool, makes it very weak, as well. Not unlike the Pontiac, the BLOCK is the weakest link. The heads aren't quite as well designed for flow as the Pontiac. The crankshaft is quite tough except the thrust face, which I believe is due to the flex in the block more than anything else.
Jim
I think you would be much happier if you stay with the 3.42. Due to the tremendous low-end torque the Buick 455 generates, it's MUCH better suited to the "taller" gears. The 455 Pontiac is similar in power output in stock form. Adding too low a gear makes the engine rev "too" quickly, not effectively "spreading" the torque out. They rev much too quickly and as a result, tend to turn rod bearings. The Buick won't turn a bearing as easily, but due to the thin casting, the block will flex and break the crank.
We have a Buick customer with a 625 HP 455 in his '78 Regal. The car goes 6.70s (1/8 mile) and 10.40s (1/4 mile). It revs to 6,100 RPM. He runs a 3.90 gear in that, and it's a pure "race" car (zero street miles, "lives" on a trailer). His engine sports a .600 " lift solid flat tappet cam, well-ported heads, Eagle rods, Ross pistons, and even has one of those lifter bore "braces". The latter may or may not help. Can't say, but it makes him FEEL better that it's in there!
We've learned to listen to Smokey (Yunik, RIP). He was talking about the Pontiac, but it applies to your Buick as well. "Don't REV it up, GEAR it up!"
I always found the Buick "interesting". The weight of the engine is nothing short of amazing. How one can get that many cubes into a package that weighs less than 600 lbs. IS amazing. The low-end torque is it's "long suit". Unfortunately, the same issue that makes it cool, makes it very weak, as well. Not unlike the Pontiac, the BLOCK is the weakest link. The heads aren't quite as well designed for flow as the Pontiac. The crankshaft is quite tough except the thrust face, which I believe is due to the flex in the block more than anything else.
Jim
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