Which manifolds will fit
Drifting
Joined: Jul 2007
Posts: 1,889
Likes: 23
From: Kansas
Yes Sir: I just laid an 1963 300 H.P. 2.5 GM cast iron manifold against a C4 steel 2.5 exhaust and it is 2.5 inch longer ( lower ) where the head pipe bolts on. So You would have a lot closer bend, in the head pipe, also the flanges are different on the C4 and the 300 HP 1963. Have a great day. Gene
Le Mans Master
Joined: Aug 2003
Posts: 7,720
Likes: 12
From: Chattanooga TN
C4 manifolds will work from '84 to '91. There are some differences, but all are related to the AIR tubes. If you cut those off and weld up the holes like I did, than any will work. You really want 2 lefts if possible because the rights have another large tube for EGR instead of just the small AIR tubes. They show up on Ebay regularly, so you sholdn't have a big problem finding them. You really do want to get the flanges and a little bit of the pipe with them if you can to keep costs down.
Le Mans Master
Joined: Aug 2003
Posts: 7,720
Likes: 12
From: Chattanooga TN
The LT1 manifolds will fit but they are cast iron not steel tube. They are also bad to crack. The ones I am talikng about are from the 84 CFI cars and 85-91 L98 TPI cars. Not LT1, LT4, or ZR1 of course.
Safety Car
Joined: Jun 2004
Posts: 4,374
Likes: 223
From: Beecher Illinois
I've got a pair off a 78 L48.
These are pretty much identical to the 80 manifolds except they DON'T have the smog fitting holes. Sounds like you don't want the smog holes?
I'll even sandblast them and give em a coat of hi-temp cast blast paint.
$50 + shipping.
These are pretty much identical to the 80 manifolds except they DON'T have the smog fitting holes. Sounds like you don't want the smog holes?
I'll even sandblast them and give em a coat of hi-temp cast blast paint.
$50 + shipping.
Le Mans Master
Joined: Aug 2003
Posts: 7,720
Likes: 12
From: Chattanooga TN
You don't get the true 2 1/2" outlet with doing this like you would for C4 manifolds. If it isn't a big deal to you then that is OK, but the repop tubular manifolds are pricey for 80-82; you aren't going to save any money.
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Drifting
Joined: Jul 2007
Posts: 1,889
Likes: 23
From: Kansas
Yes Sir: Mr. Grumpy, I happen to have a set of 1986 C4 exhaust with the air tubes cut off and welded shut. They have the original galv. shielding still attached. Like I said before, they hang down another 2 1/2 inches. than the stock 2.5 did. Original cast iron manifold was a 2 inch. outlet. on the 1980 with the smog outlets. California engine was only a 305 with steel exhaust, is my understanding. I know that there are a lot of people on this forum that will know. I paid a 100.00 plus shipping. for the pair. I have decided to install the 2.5 inch. GM Orig. Cast iron 300 H.P. manifolds. I will take 50.00 Plus shipping. for them. Have a great day. Gene