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#1
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I need to know the size of the combustion chambers for these two heads. I know that the compression ratio is lower for the 340 from 1971 and up, but is it because of the heads or the pistons? Or both?
Thank You |
#2
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Ok, here is the info I have on 340 heads, I hope that it is accurate, but if not, I'm sure someone can correct it. Here goes:
68-71 Cast.# 2531894, 63cc 70T/A Cast.# 3418915, 65cc 72 Cast.# 3418915, 65cc 73 Cast.# 3671587, 65cc ok, that one has me stumped. I dunno if my book is wrong or the T/A heads may have just had radically different machining on the same casting as the 72 heads. I'm not that familiar with T/A heads to be honest. Anyone else? ~Elwenil~ ~.\|/.~ |
#3
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I don't know about the "X" or "J" heads specifically, but I recently cc'd a set of 273 commando heads. They were 65 cc's. I thought they would go closer to 60 flat. With this in mind, I would be surprised if the open chambered heads were under 70 cc's.
The chamber on the T/A heads should be the same as the "X" or "J" heads. The only difference should be the intake pushrod location and the offset intake rocker. |
#4
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My x heads are 63 cc. The change in compression ration was in the shorter pistons. the 10.4-1 pistons stick out of the block at tdc, I think mine were out .014 or so. The lower compressi0on engines also had the cast crank.
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#5
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What ever you do you actually need to do the cc'ing of your heads. The book will tell you what it is supposed to be but it is typically WAY off in stock form. I just did a set of 015 cop heads from 1980 and the spec on them is supposed to be 68-72 cc. The machine shop told me these things measured out at 80cc!! Checkum.
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#6
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Every single head I have measured has been way over the factory ratings, but I haven't kept book about them. Latest measurement was stock '83 318 heads that were 68cc. The '68-71 heads I prepared for the engine had a 'deep' valve job done, and after I modified the chambers they were 73cc. These heads on a stock 318 short block would give about 7.5:1 CR, a little on the lower side. That is, if you have a blower.
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