Cylinder Head Compression

April 26, 2010 EngineHeads

The information below reflects the research conducted by Pontiac enthusiast/ author Pete McCarthy, much of which is from his book, Pontiac Musclecar Performance 1955-1977, as well as information gathered from many other Pontiac enthusiasts world-wide. Information about PMD heads is still being gathered. What is apparent is that while Pontiac had policies and specifications, both seemed to fluctuate as need be to build engines and place them in passenger cars.

 

Chamber size of heads is given as an approximate CC as is static compression. When examining any Pontiac head today it requires an open mind. All chamber sizes should not be assumed but cc’d to confirm the chamber size. I wish to point out that Pontiac manufactured heads with push-in studs and screw-in studs using guide plates. Most if not all performance heads used screw-in studs. Today machinists can easily improve on any stock iron Pontiac head with the inclusion of hardened seats, screw-in studs, longer valves, taller installed height for after market springs working with high lift camshafts.

 

Porting remains a viable means of improving flow for increased power. Most importantly, one must know the overall condition of the heads before attempting any performance modifications. Be sure to have them cleaned and magnufluxed by a competent machine shop.

 

If you have any information that may be useful in improving this head chart, please email me at: bboyle@boyleworks.com

 

Year

CID

Advertised HP

Head casting #

Valve Sizes intake/exhaust

Approx CC or static CR

1959

389

215-345 hp

531395

1.88/1.60

69

1960

389

215-345 hp

536109

1.88/1.60

69

389SD

348-363 hp

535461

1.92/1.60

69

1961

389

all

538177

1.88/1.60

69

421

all

538177

1.88/1.60

69

389SD

368/373 hp

540306

1.92/1.66

68

421SD

368/373 hp

540306

1.92/1.66

68

1962

389

all

538177

1.88/1.60

69

421

all

538177

1.88/1.60

69

389SD

385/405 hp

540306/544127

1.92/1.66;2.02/1.76

68

421SD

385/405 hp

540306/544127

1.92/1.66;2.02/1.76

68

1963

326

250 hP

543797

1.88/1.60

8.6 cr

326

260/280 hp

548232

1.88/1.60

10.25 cr

389

215/230/235 hp

543796

1.88/1.60

8.6 cr

389

267/283/303/313 hp

543797

1.88/1.60

10.25 cr

421

320 hp

543797

1.88/1.60

10.75 cr

421

353/370 hp

9770716

1.92/1.66

72

421SD

390/405/410 hp

544127/9771980

2.02/1.76

64

1964

326

250 hp

9773345 (845)

1.88/1.60

8.6 cr

326

280 hp

9773395

1.88/1.60

10.0 cr

389

215/230/235 hp

5437796

1.88/1.60

8.6 cr

389

267/283/303/306 hp

9773345/(845)

1.92/1.66

10.5 cr

421

320 hp

9773345/(834)

1.92/1.66

10.75 cr

389

325/330/348 hp

9770716

1.92/1.66

72

421

350/370 hp

9770716

1.96/1.66

68

1965

326

250 hp

62

1.88/1.60

8.6 cr

326

285 hp

22

1.88/1.60

10.5 cr.

389

256 hp

75

1.88/1.60

8.6 cr

389

290/325/333 hp

76

1.92/1.66

10.5 cr.

389

335/338/360 hp

77

1.92/1.66

10.5 cr

421

338 hp

76

1.92/1.66

10.75 cr.

421

356/376 hp

77

1.92/1.66

10.75 cr

1966

326

250 hp

94

1.88/1.60

8.6 cr

326

285 hp

95

1.88/1.60

10.5 cr

389

256 hp

91

1.92/1.66

8.6 cr

389

290/325/333 hp

92

1.92/1.66

10.5 cr

389

335/360 hp

93

1.92/1.66

10.5 cr 68cc

421

338/350 hp

92

1.92/1.66

10.75 cr 70 cc

421

356/376 hp

93

1.92/1.66

10.75 cr 68 cc

1967

326

250 HP

140

1.92/1.64

9.2 cr

326

285 HP

141

1.92/1.64

10.5 cr

400

255/260/265 HP

142

1.92/1.64

8.6 cr

400

290 HP

143/061

1.92/1.64

10.5 cr.

400

325/333 HP Big Car

143/061 (closed chamber)

1.92/1.64

10.5 cr

400

350 HP (GP)

670/9787671/187

2.11/1.77

72 cc

400

325/335/360 HP

670 (closed chamber)

2.11/1.77

72 cc

400

325/360 HP RA

670/97 (closed chamber)

2.11/1.77

72 cc

428

360/376HP

670/9787671 (closed)

2.11/1.77

72 cc

1968

350

265 HP

17

1.96/1.66

8.6 cr

350

320 HP

18

1.96/1.66

10.5 cr

400

265 HP

14

1.96/1.66

8.6 cr

400

290/340 HP Big Car

15/215

1.96/1.66

10.5 cr

400

350 HP (GP)

16/ 216/ 62

2.11/1.77

72-75 ccs

400

330 HP (FB)

16/ 216/ 62

2.11/1.77

72-75 ccs

400

335/350/360 HP

16/ 62

2.11/1.77

72-75 ccs

400

335/360 HP RA I

31/ (37)

2.11/1.77

72 cc

400

340 (FB) /366 (GTO)

R/96/ A (RA II) (rd port)

2.11/1.77

72 cc

428

375 HP

16/ 216

2.11/1.77

72 cc

428

390 HP

16/ 216

2.11/1.77

72 cc

1969

350

265 HP

47

1.96/1.66

8.6 cr

350

325 HP

48

2.11/1.77

10.5 cr.

400

265 HP

45

1.96/1.66

8.6 cr

400

290 HP

46

1.96/1.66

10 cr

400

340 HP (GP)

16/ 62

2.11/1.77

72 cc

400

330,335,350/ 366 HP

16/ 62/ 48 (MT)

2.11/1.77

72cc

400

345(FB) /370 (GTO)

722 (RA-IV)

2.11/1.77

71 cc

428

360 HP

16 (small-valve ) 46

1.96/1.66

10 cr

428

370 HP (GP)

62

2.11/1.77

72 cc

428

390 HP

16/ 62

2.11/1.77

72 cc

400

375 HP(RA-V)

44 Tunnel Port

2.11/1.77

67 cc

303

RA=V Tunnel Port

546184

2.11/1.77

56 cc

1970

350

255 HP

11

1.96/1.66

8.8 cr

400

265 HP

11

1.96/1.66

8.6 cr

400

290 HP

16 (small valve)

1.96/1.66

10 cr

400

330 HP Big Car

16

1.96/1.66

10 cr

400

330 HP

12 (MT)

2.11/1.77

72 cc

400

330 HP

13 (AT)

2.11/1.77

72 cc

400

345 HP(FB/RAIII)

12

2.11/1.77

72 cc

400

350 HP (GP)

13

2.11/1.77

72 cc

400

350 HP (GTO)

12 (MT)

2.11/1.77

72 cc

400

350 HP (GTO)

13 (AT)

2.11/1.77

72 cc

400

366 HP (GTO)

12 (RA III)

2.11/1.77

72 cc

400

370 HP (RA IV)

614 (Round Ports)

2.11/1.77

71 cc

455

360 HP Big Car

15

1.96/1.66

87 cc

455

360/370 HP (GTO/GP)

64

2.11/1.77

87 cc

1971

350

250 net HP

94

1.96/1.66

96 cc

400

265 net HP

99

1.96/1.66

98 cc

400

300 net HP

96

2.11/1.77

96 cc

455

280 net HP

98

1.96/1.66

114 cc

455

325 net HP

66

2.11/1.77

114 cc

455

335 net HP (455HO)

197(191) (Round Ports)

2.11/1.77

111 cc

1972

350

175 net HP

7H1

1.96/1.66

7.6 cr

400

200 net HP

7J2

1.96/1.77

8.4 cr

400

250 net HP

7K3

2.11/1.77

96 cc

455

200 net HP

7L4

2.11/1.77

114 cc

455

250 net HP

7M4

2.11/1.77

114 cc

455

250 net HP

7M5

2.11/1.77

114 cc

455

300 net HP(455HO)

7F6 (Round Ports)

2.11/1.77

111 cc

1973

350

150/175 net HP

46/4C

1.96/1.66

96 cc

400

170/185 net HP

46/4C

1.96/1.66

98 cc

400

200 net HP

4x/4C

2.11/1.66

98 cc

400

230 net HP (AT)

4X-7H screw-in studs likely

2.11/1.66

98 cc

455

215/250 net HP

4X-1H screw-in studs likely

2.11/1.66

114 cc

455

290 net HP (455SD)

16 (Round Ports)

2.11/1.77

111 cc

1974

350

155/170 net HP

46/4C

1.96/1.66

7.6 cr

350

200 net HP (GTO)

46 (screw-in studs)

1.96/1.66

7.6 cr

400

175/190 net HP

46/4C

1.96/1.66

8.1 cr

400

200 net HP

4X-4H/4C

1.96/1.66

99 cc

400

225 net HP (AT)

4X screw-in studs likely

2.11/1.66

98 cc

400

225 net HP (AT)

4C

2.11/1.66

98 cc

400

225 net HP (MT)

4X-3H screw-in studs

2.11/1.66

98 cc

455

215/250 het hp

4X-1H screw-in studs likely

2.11/1.66

114 cc

455

215/250 net hp

4C

2.11/1.66

114 cc

455

290 net HP (455SD)

16 (Round Ports)

2.11/1.77

111 cc

1975

350

ALL

5c/ 6X

2.11/1.66

7.6 cr

400

ALL

5c/ 6X

2.11/1.66

7.6 cr

455

AIR

6S

2.11/1.66

7.6 cr

350

HO non-air

6H

2.11/1.66

7.6 cr

1976

350

ALL

6X-4/ 6S

2.11/1.66

7.6 cr

400

ALL

6X-8/ 6S

2.11/1.66

7.6 cr

455

AIR

6S

2.11/1.66

7.6 cr

455

HO non-air

6H

2.11/1.66

7.6 cr

1977

301

ALL

1

1.72/1.50

8.2 cr

350

ALL

6X-4/ 6S

2.11/1.66

7.6 cr

400

180 hp

6X-8

2.11/1.66

7.6 cr

400

200 hp

6X-4

2.11/1.66

8.0 cr

1978

301

ALL

01-Feb

1.72/1.50

8.2 cr

350

ALL

6X-4/ 6S

2.11/1.66

7.6 cr

400

180 hp

6X-8

2.11/1.66

7.6 cr

400

220 hp

6X-4

2.11/1.66

8.1 cr

1979

301

ALL

1

1.72/1.50

8. 2 cr

400

220 hp (MT only)

6X-4

2.11/1.66

8.1 cr