Did Chevy change the exhaust manifold bolt pattern on small blocks? - Hot Rod Forum : Hotrodders Bulletin Board
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Old 05-12-2005, 04:39 PM
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Did Chevy change the exhaust manifold bolt pattern on small blocks?

I was told by a guy at work that Chevy changed the exhaust manifold bolt pattern for stock small blocks motors around 1982. He said they moved one bolt hole further back for some reason so earlier exhaust manifolds and later heads aren't interchangeable and there are 2 different styles of exhaust gaskets. Is there any truth to this??? Also, what year did they start the center bolt valve cover (wasn't it around 86 or 87) He said he had an 82 car with center bolt covers.

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Old 05-12-2005, 04:56 PM
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That applies to the 305 heads... (mostly) On the exhaust question...

Also late 86 saw some center bolt heads...

Last edited by Bumpstick; 05-12-2005 at 06:48 PM.
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Old 05-12-2005, 06:21 PM
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The 350 valve covers changed to center bolt in 1987.
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Old 05-12-2005, 10:32 PM
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actually bumpstick is right about saying "late 86." They made the change later into the model year, same with the 1 piece rear main seal change.
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Old 05-13-2005, 04:44 AM
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What about the 350 exhaust manifold, did they ever change the bolt pattern on them? My friends 82 truck must have had an engine swap at one point then if he claims it had center bolt valve covers.
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Old 05-13-2005, 06:20 AM
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Quote:
Originally Posted by STATUTORY GRAPE
What about the 350 exhaust manifold, did they ever change the bolt pattern on them? My friends 82 truck must have had an engine swap at one point then if he claims it had center bolt valve covers.
Yes they did, but I am not sure when.

I have a 91' GTA with stock heads. I also at one point had an 84' Firebird with a 350 that had early model heads (70's). The 91' had a stock exhaust system and the 84' had an Edelbrock TES system, so I swapped the two, since I was selling the 84' anyway.

When I went to install the stock 91' exhaust manifolds on the 84' (older heads), I soon learned that the rear hole on the passenger side would not match. The 91' exhaust manifold's rear most bolt hole was located further back. The 91' heads have both holes, but the older heads only had one that was closer the the exhaust port.

Long story short, I had no threaded hole to install the rear most bolt when installing the 91' exhaust manifolds on the older heads. My solution - I drilled a 3/8" hole straight through the exhaust manifold where the rear threaded hole was located on the older head. Then I used a piece of all-thread and lock nut turned around. The lock nut's rounded top turned around almost sealed the hole, since the manifold has a rounded surface. But it still leaked a tad and could be heard when idling.

I hope this answers your question, Ed www.edgesz28.com

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Old 05-13-2005, 07:30 AM
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This mismatch is why two of the stock exhaust gaskets have that extra bolt hole in the end.
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Old 05-13-2005, 05:34 PM
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So, does every head after '91 have two holes?
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