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What compression piston do I need?

The below topics will help you answer the question above:

  1. Calculate Block Height
  2. Calculate Connecting Rod Length
  3. Calculate Stroke Length
Compression Height

Before selecting a piston, the desired compression height must be known. As shown, compression height is the distance between the centerline of the pin bore and the top of the piston. To determine the compression, three things about the engine must first be known: block height, connecting rod length and crankshaft stroke length.

Deck Height

1. Calculate Block Height Top↑

Deck height is measured from the crankshaft centerline to the deck (cylinder head mounting surface) of the block.

Stock Chevrolet V-8 Block Heights

Displacement Cubic InchesLitersDeck Height (inches)
3024.99.025
3055.09.025
3275.49.025
3505.79.025
350(LT5)5.79.025
350(LS1)5.79.240
364(LQ4)6.09.240
3836.39.025
4006.69.025
3966.59.800
4026.69.800
4277.09.800
4547.49.800
5028.29.800

Stock Ford V-8 Block Heights

Displacement Cubic InchesLitersDeck Height (inches)
2894.78.206
3025.08.206
302(Boss)5.08.201-8.210
302(SVO)5.08.201-8.210
351 W ('69-'70)5.89.480
351 W ('71-'965.89.503
351 (SVO 9.2)5.89.206
351C (Boss)5.89.206
351M5.810.297
429 STD ('68-'70)7.010.300
429 STD ('70 1/2-'71)7.010.310
429 CJ/SCJ ('72-'73)7.010.322
429 Boss (S)7.010.300
429 Boss (T)7.010.300
4607.510.322
281 (modular)4.68.937
331 (modular)5.410.079
Rod Length

2. Calculating Connecting Rod Length Top↑

Connecting rod length is measured between the centers of the "big end" (journal end - rotating) and the "little end" (piston pin end - reciprocating).

Stock Chevrolet V-8 Connecting Rod Lengths

Displacement Cubic InchesLitersBig End Dia. (inches)Rod Length (inches)
3024.92.10005.7000
3055.02.10005.7000
3275.42.10005.7000
3505.72.10005.7000
350(LT5)5.72.10005.7400
350(LS1)5.72.25006.0980
3836.32.10006.0000
4006.62.10005.5650
3966.52.20006.1350
4026.62.20006.1350
4277.02.20006.1350
4547.42.20006.1350
5028.22.20006.1350

Stock Ford V-8 Connecting Rod Lengths

Displacement Cubic InchesLitersBig End Dia. (inches)Rod Length (inches)
2894.72.12325.1550
3025.02.12325.0900
302(Boss)5.02.12265.1500
302(SVO)5.02.12265.1500
351 W ('69-'70)5.82.31105.9560
351 W ('71-'965.82.31105.9560
351 (SVO 9.2)5.82.31105.7800
351C (Boss)5.82.31105.7800
351M5.82.31076.5800
429 STD ('68-'70)7.02.5006.6050
429 STD ('70 1/2-'71)7.02.5006.6050
429 CJ/SCJ ('72-'73)7.02.5006.6050
429 Boss (S)7.02.5006.5490
429 Boss (T)7.02.5006.6050
4607.52.5006.6050
281 (modular)4.62.08635.9331
331 (modular)5.42.08636.6575
Stroke Length

3. Calculate Stroke Length Top↑

Stroke length is twice the distance from the centerline of the crankshaft main bearing journals to the centerline of the connecting rod journals. It is also the distance the piston moves up and down in the cylinder.

Stock Chevrolet V-8 Bore & Stroke

Displacement Cubic InchesLitersBore (inches)Stroke (inches)
3024.94.0003.000
3055.03.7403.480
3275.44.0003.250
3505.74.0003.480
350(LT5)5.73.8983.661
350(LS1)5.73.8983.622
364(LQ4)6.04.0003.622
3836.34.0003.800
4006.64.1253.750
3966.54.0943.766
4026.64.1253.766
4277.04.2503.766
4547.44.2504.000
5028.24.4704.000

Stock Ford V-8 Bore & Stroke

Displacement Cubic InchesLitersBore (inches)Stroke (inches)
2894.74.0002.870
3025.04.0003.000
302(Boss)5.04.0003.000
302(SVO)5.04.0003.000
351 W ('69-'70)5.84.0003.500
351 W ('71-'965.84.0003.500
351 (SVO 9.2)5.84.0003.500
351C (Boss)5.84.0003.500
351M5.84.0003.500
429 STD ('68-'70)7.04.3603.590
429 STD ('70 1/2-'71)7.04.3603.590
429 CJ/SCJ ('72-'73)7.04.3603.590
429 Boss (S)7.04.3603.590
429 Boss (T)7.04.3603.590
4607.54.3603.850
281 (modular)4.63.5523.543
331 (modular)5.43.5524.165

How Compression Height Is Calculated:

Compression height = block height - rod length - (0.5 X stroke)
 
 Example:block height = 11.685"
  rod length = 7.500"
  stroke = 5.500"
 
Compression height = block height - rod length - (0.5 X stroke)
Compression height = 11.685 - 7.500 - (0.5 X 5.500)
Compression height = 1.435"