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Street Race Truck More... The Toolbox

Choosing a Flexplate for a Small Block Chevy

7/7/2016

Whether you’re racing or building a street vehicle Speedway Motors offers several flexplates to choose from for your small-block Chevy engine. Both SFI rated for the track and non-rated for street applications. There are four main factors to consider when purchasing a flexplate.

  • The crank style: One or two piece rear main seal. Older style blocks ('55-'85) used a two-piece seal, '86 and up blocks used a one-piece seal
  • The torque converter bolt pattern: large 11 1/2-inch or small 10 3/4-inch
  • Ring gear tooth count: 153 or 168
  • Internal or external engine balance
Internal vs External Balance

Almost all small-block Chevys are internally balanced. The harmonic balancer and flexplate/flywheel are what you would call “neutral” balanced, meaning they are balanced like a car rim, with no other parts attached to them. They do not need to be balanced together, just balanced alone. The only small blocks that are externally balanced from the factory are 400 small blocks, because there is not enough room on the crank throws to neutrally balance them, so they offset the missing weight with the harmonic balancer and the flexplate/flywheel.

Bolt Pattern and Tooth Count

The key to choosing the correct bolt pattern and tooth count is measuring the torque converter you are using. A 153 tooth flexplate will be paired with a torque converter that has a 10 3/4-inch bolt circle. A 168 tooth flexplate uses a 11 1/2-inch bolt circle. Some aftermarket flexplates are drilled with both patterns to accept large and small diameter torque converters. You can also note that a 153 tooth flexplate always uses the straight bolt pattern starter, and the 168 tooth flexplate uses a angle bolt pattern starter.

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