exhaust manifold difference?
 

I have the correct 64 drivers side exhaust manifold for dual exhaust but I have a passenger side which numbers come out to be a 66 with the heat riser valve. Are the 64 and 66 manifolds the same except for part numbers? Will the 66 bolt up and work?

The 64 heat riser “weight” is different from the 65 and newer style.

Below is a NOS 64 RH exhaust manifold (first 4 pics).
Last pic is a pair of 65 manifolds.

Same bolt pattern on all of them.

Chris.

Hello Chris. I see your 64 manifold does not have the little anti rattle spring but the 65 does. Did they not use that spring in 64?? I don't know. "Bill"!

I'm not too worried about the heat riser, I'm probably going to make sure it stays open. I'm more worried about flow and if it is basically the same if I go with the 64 on one side and 66 on the other.

Thank you for all the help and pictures!

Mr. Ryder,

I purchased the NOS 64 manifold as shown. I’m sure it had the anti rattle spring at one time.

I have an NOS Spring and my MPC shows 63-67 All exc. T/6 #521580.

Chris.

As always, Chris, many thanks!!!! "Bill"!

If you were to put a '64 and a '66 manifold side by side you wouldn't be able to see any difference in the manifolds themselves, the manifold castings are pretty much identical. The overall design didn't change for quite a few years. Dual exhaust and single exhaust applications both used the same manifolds.

You're good.

Thank you! Were the down pipes 2 1/2" from the manifolds in 64?

I remember 2-1/4" but that was a long time ago with a lot of header swaps after those days.

Tom V.

For '64 GTO

Head pipes were 2.25"

Mufflers were 2.25" inlet and 2.00" outlet

Tailpipes were 2.00"

Same exhaust for auto and manual trans

'65 was different.