Refitting 2 1/2 inch manifolds on a 66

[BlackVette66]

I have a 66 with the 327/350 horse vette with 2 inch exhaust manifolds. I want to go to 2 1/2 inch. Has anyone done this?
Where did you get your parts from. My alternater is driver side
mounted and I'd like to keep it over there.

 

[JohnZ]

'65 L-75 (300hp), L-76 (365hp) and L-79 (350hp) used the 2-1/2" exhaust manifolds (last year for them), and with A/C, the alternator was mounted on the driver's side. LH manifold was casting #3846563, RH was casting #3797942.

 

[00fxd]

Hey John; A couple questions about the 2 1/2" outlet exhaust manifolds. What is the cast #3797901? I thought that was the left side with the alt bracket but you mention #3846563 is. Also, if I'm running a later eng with the alt mounted to head, I should be able to use 2 right manifolds [3797942]? Are there any right side alt mount 2 1/2's?
Are the casting #'s the same as the oem part #'s? With GM sometimes they are and sometimes they aren't.
Thanks, Frank.

 

[BlackVette66]

RH manifold

My RH(passenger side) has no mounting holes I'd like to keep it
looking the same, does RH casting #3797942 have mounting
holes, if it does did they make one without mounting holes.
My car has no A/C, or powersteering.

 

[JohnZ]

#3797901 was used on the LH side on '62 and '63 300hp and 340hp engines (pass.-side generator on '62, pass.-side alternator on '63).

Pass.-side alternator mount 2-1/2" manifolds are casting #3797902 (were used on '65 300/350/365/375hp engines without A/C). Casting numbers are rarely the same as the GM part number, as the same basic casting was usually machined into several different final configurations, each of which had its own GM part number. The casting #3797902 RH manifold was GM P/N 3814970, but the part number doesn't appear on castings, and it was discontinued over 20 years ago.

Paragon carries a reproduction of this RH 2-1/2" manifold, identical to the original casting #3797902, as their #802, for $210.00. They also have the LH manifold, identical to casting #3846563, their #1827, for $225.00. Both have the original casting numbers on them.

 

[00fxd]

John, so I have this correct, is the 3797901 a 2 1/2" with alt/gen mount for the L/drivers side? In your post you mention the 901 on L/pass side, did you mean L/driver side? I see a couple of 3797901's on ebay with the alt/gen mount for L/driver side.
So the 3797902 is the 2 1/2" with alt/gen mount on the r/pass side?
The 3797942 has no mount and will work on either side?
And the 3846563 has an a/c compessor mount?
It makes sense to me now why the casting # isn't necessarily the part#. Thanks for your time, Frank.

 

[JohnZ]

The 901 is for the driver's side, and has the mounting ear. The 902 is for the passenger side and has the mounting ear. The 942 has no mounting ear, and was originally used on the driver's side on fuelies (has choke tube hole for F.I.). The 563 was used on the driver's side and has an alternator mounting ear (A/C compressors were always on the passenger side).

 

[00fxd]

Thanks John. I think I've got it now.

 

[Jack44]

You might check ZIP Products too...

 

[youwish2bme]

Or even Paragon..They claim to have the largest inventory out there OEM and other...