extra holes in Big block intake - Impala Tech
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post #1 of 6 (permalink) Old 08-19-2019, 04:07 PM Thread Starter
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extra holes in Big block intake

I have a 427x aluminum edelbrock intake on a 454 block that I did not build, not sure what heads are on it. It runs good but appears to have 4 extra bolt holes that aren't used in the intake, 2 on each head. I've read online that the extra bolt holes were used on some heads and not on others, etc.

I'm just curious why they are there on some manifolds/heads. There must be a reason that I'm not aware of.

Also will it cause any problems later if they are mis-matched as mine appear to be?
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post #2 of 6 (permalink) Old 08-19-2019, 11:07 PM
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Not aware of this issue. Need to see a photo.

Big Dave
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post #3 of 6 (permalink) Old 08-20-2019, 07:44 AM
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I think he is talking about the attached pic. I had the same issue on my 496 with Dart heads. Four extra, unused spots in the intake bolt pattern and no matching threaded holes in the heads. Was not an issue.
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1968 Impala SS
496 Stroker
T56 Conversion
3.73 Posi-Trac
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post #4 of 6 (permalink) Old 08-20-2019, 11:29 AM Thread Starter
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Yep, that's exactly it. I have read that it might be rectangle/oval mismatch. But I don't know if that's correct. I've also seen pictures that indicate if you have a slightly different gasket, there is a leak path from the intake to atmosphere that can cause a vac leak. In some cases people would remove the manifold and plug the holes from the bottom with epoxy and sand them smooth to seal on the gasket.

below is mine. You can see the 2 extra holes on the right side.

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post #5 of 6 (permalink) Old 08-20-2019, 12:14 PM
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Not anything to do with head to intake mismatch I don't think. My Edelbrock Airgap intake was for rectangular port heads, which matched the heads perfectly and I still have the extra holes. Just speculating, but I think it might have to do with a head / intake engine generation mismatch.

Had I dropped that intake onto the cast iron Gen IV 396 heads I had previously, there would have been threaded holes to match. That intake onto more modern aluminum heads with raised exhaust ports? Extra holes. Probably better to have them and not need them than need them and not have them.

1968 Impala SS
496 Stroker
T56 Conversion
3.73 Posi-Trac
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post #6 of 6 (permalink) Old 08-20-2019, 03:04 PM Thread Starter
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That makes sense. I'm not sure what heads I have on my engine. I need to find out. The block itself is just an old 4 bolt main 454 truck block around the late 70's I think. The heads might be a different vintage.
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