Compression Calculator

Simply fill in the form below to calculate your compression ratio

Bore: (diameter)
Stroke:
Cylinder Head Volume:
Effective Dome Volume:
Use (-) for Dome and (+) for Dish.
Deck Clearance:
Compressed Gasket Thickness:
Number of Cylinders:
Compression Ratio :  
Total Displacement (in.3) :  
Total Displacement cc's :  
 

The cc for the piston is entered as a positive number on a -cc Dish or Flat top piston and a negative number on a dome piston. This seems very confusing but it is because even though it is a -cc on the piston, those same cc's are gained in cylinder volume. Hence the positive number in the calculator. Same goes for a dome where it is positive cc's on the piston but a reduction in cylinder volume. Hence the - (negative) number in the calculator.


Popular Block and Bore Sizes Compression Chart

Pontiac Cu.In. Chart
326 Block Stroke
Bore 3.75 4.00 4.21 4.25 4.50
Stock 3.720 326 348   370  
+.030 3.750 331 353   376  
+.040 3.760 333 355   378  
+.060 3.780 337 359   382  
 
350 Block Stroke
Bore 3.75 4.00 4.21 4.25 4.50
Stock 3.875 354 377   401  
+.030 3.905 359 383   407  
+.040 3.915 361 385   409  
+.060 3.935 365 389   413  
 
389 Block Stroke
Bore 3.75 4.00 4.21 4.25 4.50
Stock 4.062 389 415   441 467
+.030 4.092 395 421   447 473
+.040 4.102 396 423   449 476
+.060 4.122 400 427   454 480
 
400 Block Stroke
Bore 3.75 4.00 4.21 4.25 4.50
Stock 4.120 400 427 449 453 480
+.030 4.150 406 433 456 460 487
+.035 4.155 407 434 457 461 488
+.040 4.160 408 435 458 462 489
+.060 4.180 412 439 462 467 494
+.065 4.185 413 440 463 468 495
 
421 Block Stroke
Bore 3.75 4.00 4.21 4.25 4.50
Stock 4.093   421 443 447 474
+.030 4.123   427 450 454 481
+.035 4.128   428 451 455 482
+.040 4.133   429 452 456 483
+.060 4.153   433 456 461 488
+.065 4.158   435 457 462 489
 
428 Block Stroke
Bore 3.75 4.00 4.21 4.25 4.50
Stock 4.120   427 449 453 480
+.030 4.150   433 456 460 487
+.035 4.155   434 457 461 488
+.040 4.160   435 458 462 489
+.060 4.180   439 462 467 494
+.065 4.185   440 463 468 495
 
455 Block Stroke
Bore 3.75 4.00 4.21 4.25 4.50
Stock 4.151     456 460 487
+.030 4.181     462 467 494
+.035 4.186     464 468 495
+.040 4.191     465 469 497
+.060 4.211     469 474 501
+.065 4.216     470 475 503
 

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