[autoxmike]

I have a 408 CI Clevor that my brother built circa 1993. Here is some interesting Cleveland head data from my archives. Hopefully it will be easy to read when I paste it into this message:

Cleveland Head FYI
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Production cast iron Cleveland style heads have several different combustion chamber, valve, and port sizes. Closed chamber refers to the smaller volume heads and the 4V refers to the heads with larger ports and valves that originally came on cars with 4V carbs. There are also aftermarket SVO aluminum heads (C302, Yates) which bolt onto Cleveland blocks but have non-stock intake and exhaust port locations, requiring special manifolds.

Chamber Int/Exh Intake Exhaust Notes Casting
Volume Valve Dia Port Port Numbers
CC's inches inches inches


Boss 302W
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1969 61.3-64.3 2.23/1.71 1.75x2.50 1.74x2.00 2,3,8
1970 57.0-60.0 2.19/1.71 1.75x2.50 1.74x2.00 2,3,8

Boss 351C
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1971 66.1 2.19/1.71 1.75x2.50 1.74x2.00 2,8 D1ZE-B

351C 4V
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70-71 62.8 2.19/1.71 1.75x2.50 1.74x2.00 1,8 DOAE-H,R
71 CJ 75.4 2.19/1.17 1.75x2.50 1.74x2.00 1,9 D1ZE-DA
72 HO 75.4 2.19/1.71 1.75x2.50 1.74x2.00 2,9,10 D2ZE-A
72-74 76.2 2.19/1.71 1.75x2.50 1.74x2.00 1,4,9 D1ZE-GA

351C 2V
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70-74 US 76.2 2.04/1.65 1.40x2.02 1.38x1.84 1,5 DOAE-E,J; DOAZ-A,B,D; D1ZE-CB; D1AE

351M/400
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75-82 78.4 2.04/1.65 1.40x2.02 1.38x1.84 1,7 D5AE-AA; D5AZ
71-74 78.4 2.04/1.65 1.40x2.02 1.38x1.84 1,7 D1AE-A; D3AE-G2B

Aussie 2V
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Aussie 2V 62.0 2.04/1.65 6,8
Aussie 2V 78 2.04/1.65 9,11



Notes:
1. Non-adjustable, cap screw with 5/16 inch bolt, pedestal rockers, non-hardened pushrods, multi-groove valves
2. Adjustable, 7/16 inch screw-in studs, guideplates, hardened pushrods, single groove valves
3. has intake manifold water thermostat passages to match 302W block
4. open-type combustion chamber and induction hardened exhaust valve seats, otherwise same as early 4V
5. Nearly identical to 351M/400 heads, oval exhaust ports
6. used on Australian 302C and 351C, fits US 2V intake and exhaust manifolds, rumored to have a slightly larger (10%) intake port, combustion chamber shape may be different that U.S. 4V closed chamber so pop-up pistons meant for 4V heads may not fit with clearancing
7. May have an additional EGR passage, otherwise nearly identical to US 351C 2V, oval exhaust ports
8. Closed chamber
9. Open chamber
10. open-type combustion chambers otherwise same as 71 Boss 351
11. Used on later Pantera 351C's which were sourced from Australia (probably originally meant for Australian truck applications), heads appear to be the same as U.S. 2V open chamber items.



Miscellaneous:
There are two major differences between the open chamber 2V and closed chamber 4V heads. First is the ports. The 4V heads have good intake ports and horrible exhaust ports. The 2V intakes flow almost as much, with considerably higher velocity, and have much better exhausts. The flow balance across the ports dramatically affects the engine's camshaft requirements.



The second difference is the combustion chamber shape. The open chamber head burns well, has low emissions, and is reasonably resistant to detonation at low (under 10:1) compression ratios. The closed chamber (also known as quench chambers) heads are more sensitive to octane, but the shorter flame path helps reduce required spark lead and makes more power. The fuel and timing requirements for open and closed chamber heads are much different. David Vizard claims open chamber heads respond well to multiple spark ignitions (e.g. MSD 6), requiring less ignition lead.