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| Username | Post: Exhaust manifold bolt patterns?? | |
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dogan Member Posts 28 |
05-07-12 05:24 PM - Post#2223550
I am replacing my current broken 350 with another. The new one is a 73-75 vintage. The problem is the exhaust manifold bolt pattern. The manifolds I had have a bolt pattern about 3/16 closer from end bolt to end bolt than the holes in the head. The head number 3827185 fits a 350 but I wasn't aware that exhaust manifolds had different bolt hole variances. Such as being a wee bit farther apart. Am I doing something wrong or do small block manifolds differ from year to year? Hope I'm not too confusing in my message. Don |
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N8sToolz Very Senior Member Posts 2314 
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05-07-12 06:31 PM - Post#2223583
The manifolds have shrunk, there is a tool to expand them to fit, but might just be time to buy new ones. You can also drill the holes larger too.
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Donolie "2nd Year" Gold Supporting Member Posts 150 
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05-08-12 03:04 AM - Post#2223666
I used a portapower to spread a manifold, but it split a little on the drivers side front. After the one manifold split, I tried makeing the holes egg shaped... this worked for me the best. -Don |
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Vaughn "11th Year" Gold Supporting Member Posts 13637 |
05-09-12 05:20 PM - Post#2224269
There are places to get NEW cast iron exhaust manifolds, the new manifolds are more ruggedly constructed to eliminate cracking problems common with original GM manifolds (especially on the BBC). http://www.1aauto.com/1A/ExhaustManifolds/C hevy/C1... |
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N8sToolz Very Senior Member Posts 2314
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05-10-12 09:42 PM - Post#2224686
There are places to get NEW cast iron exhaust manifolds, the new manifolds are more ruggedly constructed to eliminate cracking problems common with original GM manifolds (especially on the BBC). http://www.1aauto.com/1A/ExhaustManifolds/C hevy/C1... My Ex GF used to work there. Their office is about 30 mins away from here.
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raceman6135 Senior Member Posts 884 
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05-11-12 01:54 PM - Post#2224894
In approximately 1983, the cylinder head exhaust manifold bolt spacing did change. The early heads generally only have one bolt hole at the very end of the exhaust manifold flange, but the later heads often have two. See the image below:  The head casting number you provided seems to indicate it would be an early head, but I'm not sure what exhaust manifold you are trying to use. While it is not unusual for small block Chevrolet exhaust manifolds to warp a bit, I've never had them become mismatched by 3/16" -- that seems like an awful lot to only be a warping issue. |
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64ss409 Senior Member Posts 607 |
05-12-12 09:51 PM - Post#2225308
Here is what the manifold spreader tool looks like. I have a pair of them. http://www.summitracing.com/parts/WMR-W80663
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someotherguy Moderator Posts 23559 
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05-13-12 05:10 AM - Post#2225359
Those spreaders are real handy, haven't ever needed to use more than one at a time so I just own one. You can get it locally in the Lisle brand part #13000 if you're lucky enough to have someone nearby that carries Lisle tools.  Richard
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