Exhaust manifold ID - Pontiac GTO Forum
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post #1 of 3 (permalink) Old 03-23-2018, 10:04 PM Thread Starter
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Exhaust manifold ID

I'm changing the exhaust system on a 70 RA III I just purchased. Was surprised to find that both manifold flanges were three bolt rather than the standard two bolt/three bolt setup. The casting numbers confirm they are 70 RA III manifolds. I want to change back to the original 2 1/4 pipes rather than the 2 1/2 inch system now on it. Can I use these manifolds and flanges for a 2 1/4 inch system,and does anyone know what the the dual three bolt flange setup is all about? Thanks in advance!
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post #2 of 3 (permalink) Old 03-23-2018, 11:45 PM
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Welcome to the forum. You have me puzzled on rhe cadrings. What casting number are your RA exhaust manifolds? Original drivers side '70 RA III manifolds are slightly different than previous '69 RAIII GTO versions due to the '70 drivers side manifold also having to fit with manual trans Z-bar in the 2nd Gen F-body chassis, that's why the new casting number. I have excellent original versions of each year's manifolds & an original '70 RAIII drivers side manifold should have 2 bolt bosses.

Original '70 RA & '71-72 455 HO head pipes were 2 1/4" diam. Have had these flawlessly recreated in aluminized steel using the correct card machine dimensions. Also have have recreated the '70-72 RA head pipes with a 2 1/2" mandrel bent section coming down from the manifold.

The Classics brand which was avail in the 90's & 00's from Ames, PY, and from Year One were only avail in 2 1/4" outlet version & can be identified by the CM instead of GM cast near the ex manifold casting number.
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post #3 of 3 (permalink) Old 03-24-2018, 05:27 PM Thread Starter
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Ex manifold I D

Thanks for the great response. The casting numbers I was relying on we're from the seller. I got under the car and found the drivers side number - 977?646. 9777646 is from a 67 Ram air, and I read that this year alone used a three bolt flange on the driver side. Now all I need to determine is if the flaired pipe end on the 2 1/4 inch system I bought will work on these manifolds ( currently have an old 2 1/2 Dynomax on it) The 2 1/4 flanges I got for the new system do line up with the manifold holes, so I'm hopeful the new stuff will work. Thanks again for the guidance.
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