66 exhaust manifolds

[mark 66]

I'm looking for the casting # for 327 2 1/2 inch ramhorn exhaust manifolds for my 1966. Can anyone help me out? If so thanks. Also looking to buy these manifolds.

 

[impala]

NCRS Spec Guide states:

3846559 (left) and 3747042 (right) for 300 & 350 HP 327


3872765 (left) and 3872778 (right) for 300 & 350 HP 327 with K19 Air Injection Reactor.

Eugene

 

[JohnZ]

The 559 and 042 are 2" outlet manifolds. The '65 2-1/2" outlet manifolds are 3846563 (LH) and 3797942 (RH) - were also used on SHP 64's.

 

[mcditalia]

I'm curious, I found this thread after searching the data base regarding the different size ram manifolds (2.5" vs 2"). If the L79 was rated at 350hp for 65, 66, and 67, wouldn't a 65 L79 with a 2.5" exhaust manifold make more power than an identical 66 L79 with the smaller 2" manifolds?

Also read that 2.5" manifolds should have no date codes, while 2" manifolds have them, is this correct?

 

[youwish2bme]

To be honest I just did this swap from 2" to 2 1/2" and really did not notice a seat of the pants improvement. It's a good chunk of change once you include the price of the exhaust manifolds and the pipes.... I probably could have spent the money better on a set of aluminium heads instead and made a real improvement in HP...Dave..

 

[mcditalia]

Thanks Dave,

I found a pair of correct for 66 - 2" manifolds on e-bay that I'm interested in.

I just can't figure out how a 2" manifold equipped motor would make the same hp ratings as an identical motor with larger 2.5" manifolds? There's got to be some hp loss, maybe small, as you mentioned with no noticeable seat of the pants feeling.

 

[Ron Miller]

Thanks Dave,

I found a pair of correct for 66 - 2" manifolds on e-bay that I'm interested in.

I just can't figure out how a 2" manifold equipped motor would make the same hp ratings as an identical motor with larger 2.5" manifolds? There's got to be some hp loss, maybe small, as you mentioned with no noticeable seat of the pants feeling.

Only the manifold is 2" in a '66 with 2 1/2" exhaust system, on a 2 1/2" small block exhaust system, the pipes go to 2 1/2" diameter at the manifold. So, there's really not a great deal more restriction v.s. a complete 2 1/2" exhaust system, the manifolds being the only difference. And, at most rpm's, I suspect you'd be challenged to feel the difference.

 

[mcditalia]

Help please,


Since I don't have Chevrolet by the Numbers, how do I decipher date codes on 2" manifolds, front and back? Any takers on this item?
http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&category=33632&item=7949212930&rd=1

 

[Ron Miller]

Help please,


Since I don't have Chevrolet by the Numbers, how do I decipher date codes on 2" manifolds, front and back? Any takers on this item?
http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&category=33632&item=7949212930&rd=1

Some manifolds may not carry a casting date. Those that do use the same date codes as used for engine blocks, except without the calendar year reference. The first two digits represent the month (01 thru 12), and the last two represent the date of the month (01 thru 31).

The two shown in your E-bay reference should be the correct castings for a '66 300 or 350 hp car without the A.I.R. system.

This is the info I have from an old edition of the NCRS spec guide, hope it helps.

 

[Donny Brass]

Thanks Dave,

I found a pair of correct for 66 - 2" manifolds on e-bay that I'm interested in.

I just can't figure out how a 2" manifold equipped motor would make the same hp ratings as an identical motor with larger 2.5" manifolds? There's got to be some hp loss, maybe small, as you mentioned with no noticeable seat of the pants feeling.

My L-79 ran 13.84 @ 101 though the 2" manifolds, shifting at 6200.........

I think the sidepipes are more of a restriction than the manifolds.......

 

[mcditalia]

Well, I ended up getting the manifolds, now I have to see about replacing the studs. I hear lots of heat does the trick with the "Double nut trick". Hope I don't break anything.

13.84 huh? that's pretty impressive.