OK Olds guys whats the difference???

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TURNA

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Jul 24, 2009
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What the difference between 2A and 4A heads?

And are they interchangeable?

Will a 2A fit a 260, 307 and a 350 etc...?

Thanks
 

WanaBa442

G-Body Guru
Aug 5, 2017
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Some background here: OLds FAQ
2a have teeny valves, made for the 260.
4a were a 403 head, according to the above article. I cannot confirm, but I read it on the innerweb so it must be true.......
 
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TURNA

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Ah I actually ment 5A heads 2A vs 5A
 
Oct 14, 2008
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The 2A are very similar to the 7A heads, tiny ports near the top of the ports, 7A heads are in the middle. Basically the same craptastic chamber and awful exhaust port with a very recessed divider as the 5A heads. Even smaller 1.522"/1.3" valves and a 10cc smaller 55cc chamber to deliver a whopping 7.8 to 1 on the tiny 3.5" bore 260. The earlier #10 260 heads are a better choice, bigger ports, better exhaust port and 55cc chambers but still would need bigger valves and the bowls opened.
 
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TURNA

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So the 2A's are better than 5A's.......?
 
Oct 14, 2008
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fleming442

Captain Tenneal
Dec 26, 2013
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According to the Mondildo book, 2A are 57cc chambers with 1.522 intake and 1.3 exhaust valves whereas 5/5A (1969 casting # 397742) have 1.875/1.562 valves with a 68cc chamber and 5A casting (1980-85) 3317 has 1.75/1.5 with 67cc chambers.
 
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84 W40

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Dec 9, 2009
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fleming442

Captain Tenneal
Dec 26, 2013
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Overall, it depends on what you start with and where you want to be with compression. The best bet would be to mill the 5s, but I have no idea how much you can take off before compromising the water jackets....
 
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TURNA

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Jul 24, 2009
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Meh

i'll just get the Mondello Pro comps
 
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