Ported GM Bow Tie AFR 180 CNC
Lift (Inches) Intake Flow (cfm) Exhaust Flow (cfm) Intake Flow (cfm) Exhaust Flow (cfm)
0.200 116 107 140 112
0.300 169 143 201 152
0.400 212 166 244 190
0.500 239 169 260 208
0.550 225 172 262 214
0.600 228 174 263 219
Head Gasket Thickness vs. Compression Ratio
Although bore size affects compression ratio, Fel-Pro reports that a general formula for calculating how head gasket thickness affects compression ratio is as follows. For every 0.005-inch thickness increase/decrease, gasket volume changes by about 1 cc, which translates to slightly less than 1/8 (0.125) of a point of compression ratio. We did the exact math on our 327 V-8 and came up with these figures:
 
Gasket Thickness Compression Notes
(inches) Ratio  
0.015 10.68:1 Steel shim previously on 327
0.020 10.61:1  
0.030 10.31:1  
0.040 10.03:1 Fel-Pro gasket used on this test
0.050 9.76:1  
 

Dyno Test

 
 

Bow Tie

 

AFR 180 CNC

 
RPM HP Torque HP Torque
3,000 194.5 340.4 194.6 329.5
3,100 198.8 336.9 194.9 329.8
3,200 205.3 336.9 201.0 329.9
3,300 214.1 340.8 209.7 333.7
3,400 223.1 344.6 217.7 336.3
3,500 230.5 345.9 225.0 337.6
3,600 236.3 344.7 230.6 336.4
3,700 242.0 343.5 237.0 336.5
3,800 246.8 341.1 244.4 337.8
3,900 252.5 340.0 251.8 339.2
4,000 260.9 342.6 260.3 341.8
4,100 270.4 346.4 270.8 346.9
4,200 280.0 350.1 282.5 353.2
4,300 288.8 352.7 293.4 358.3
4,400 296.6 354.1 303.4 362.2
4,500 304.5 355.4 312.5 364.8
4,600 312.5 356.7 321.7 367.2
4,700 320.4 358.1 331.0 369.8
4,800 328.5 359.4 340.5 372.6
4,900 335.4 359.5 348.8 373.9
5,000 341.1 358.3 356.0 374.0
5,100 345.6 355.9 363.2 374.1
5,200 350.0 353.5 369.1 372.8
5,300 355.6 352.3 375.0 371.6
5,400 361.1 351.2 382.2 371.7
5,500 367.8 351.3 389.3 371.8
5,600 373.3 350.1 396.5 371.9
5,700 377.3 347.7 402.3 370.7
5,800 381.3 345.3 406.7 368.3
5,900 383.8 341.6 412.4 367.1
6,000 387.5 339.2 416.7 364.7
6,100 392.6 338.0 420.8 362.3
6,200 397.6 336.8 424.9 359.9
6,300 399.8 333.3 430.3 358.8
6,400 401.7 329.6 435.8 357.6
6,500 401.9 324.8 439.6 355.2
6,600 400.3 318.5 442.0 351.7
6,700 394.2 313.6 442.5 346.8
6,800 385.6 308.1 442.8 342.0
6,900 380.8 304.4 439.6 334.6
7,000 374.4 300.1 438.9 333.3
SOURCE
Air Flow Research
10490 Ilex Avenue, Dept. MMFF
Pacoima
CA  91331
Westech Performance Group
11098 Venture Dr., Unit C
Mira Loma
CA  91752
9-09/-685-4767
www.westechperformance.com
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