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400 heads

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Old May 31, 2018 | 01:13 AM
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black & blue 78/9's Avatar
black & blue 78/9
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400 heads

Hello all.
My local jy recently brought in an April 72 galaxy500 with a 400. So here is my question. Would the heads from the 72 400 have better comp ratio than the heads on my 79bronco 351m or better than the heads on my 79 400 f150?

I thought I would ask here first but if I need to I will post in the 335 engine section. Thanks for the help.
 
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Old May 31, 2018 | 09:28 AM
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I don't think the compression ratio will be different, however the later model heads are restricted in the exhaust. The floor is raised.
 
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Old May 31, 2018 | 09:33 AM
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Aaron-71
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Originally Posted by black & blue 78/9
Hello all.
My local jy recently brought in an April 72 galaxy500 with a 400. So here is my question. Would the heads from the 72 400 have better comp ratio than the heads on my 79bronco 351m or better than the heads on my 79 400 f150?

I thought I would ask here first but if I need to I will post in the 335 engine section. Thanks for the help.
Here is a great reference website. Take a read, but read all of it. You might be surprised that bumping compression at the heads doesn't mean a whole lot unless you also address the cam and pistons too - the article touches on this.

351M/400 Performance Build Up
 
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Old May 31, 2018 | 09:34 AM
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What I've read says the 400 was 9.5:1 until 1973 when it went to 8:1. However, I don't know what they did to change the ratio. Was it dish pistons, or larger combustion chamber? I also read that combustion chambers ran from roughly 74cc to 80cc. It might be worth it to pull those heads and measure the volume.
 
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Old May 31, 2018 | 10:04 AM
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Aaron-71
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Originally Posted by ranger140892
What I've read says the 400 was 9.5:1 until 1973 when it went to 8:1. However, I don't know what they did to change the ratio. Was it dish pistons, or larger combustion chamber? I also read that combustion chambers ran from roughly 74cc to 80cc. It might be worth it to pull those heads and measure the volume.
I believe the maximum the compression ever ran in these old motors was 9.1:1. 9.5:1 seems a bit high because that's the tilting point when you start having issues with pre-detonation / pinging.
 
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