Early or Late 4-2-1 exhaust manifold

[kmoses]

I have purchased an early 4-2-1 exhaust manifold (it was on a 1600) to go on my '79 2000. Will this one flow as well as the one used on the FI 2000?

[azruss]

I had to modify mine as the 2000 head have a port that needed to be blocked. went to a machine shop and they make a flat plate and notched the manifold to have it hold in place when i bolted it down.

[joelittel]

I thought earlier cars had the 4-1 manifold and later models had the 4-2-1?

[bobplyler]

My 79 came with a 4-2-1.

[kmoses]

This 4-2-1 has no emission holes to plug. I was reading that the early 4-2-1 exhaust manifold may have smaller ports and not flow as well as the ones that came on the Fuel Injected Spiders, I'm just trying to verify this before installing it. I will be bolting it to a 1800 head along with a single plane intake and Weber 32ADFA. I know that a 34ADF or 32/36DFEV is the way to go, but the 32ADFA only cost me $25 + cost of rebuilding (replaced every gasket, O-ring and diaphragm).

[Nanonevol]

A '79 4-2-1 I have has ports just a hair under 1 1/2" diameter.

[azruss]

The 4-2-1 I installed on my 79 2L was off a 71.

[kmoses]

My ports are close to 1 1/2" also. It looks like I am good to go! thanks for the info.

[Nanonevol]

Correction! The 2 exit ports on my '79 4-2-1 measure 1.25", a bit more than "a hair" less than 1.5" as I reported earlier.
The 4 ports at the head are oval and measure 1.25" x 1.5". I'd like to hear what others measure to put some closure to this issue - so much misinformation out there (as everywhere).
Also found:
'79 4-2-1, 1.25" x 2 = Area of 2.46 sq in.
'77 4-1, 1.56" = Area of 1.91 sq in.

[narfire]

Perhaps trying an exhaust gasket from a 79 and place it over the manifold from the 71. Any difference?

[kmoses]

Took measurements at work today with dial calipers. The measurement of under 1.5" taken with a tape measure was wrong.
The ports that mate with the head are 1.620" x 1.380". I can't get to the outlet ports yet due to the nuts being rusted to the studs, but I should be able to post the outlet sizes Monday night. Also the casting number for this manifold is 4151276.

[kmoses]

Outlet ports on the 4-2 are 1.475" and 1.500" I.D. for the two ports.

[Nanonevol]

Now I'm a little jealous but I'll live with the improvement. My '79 4-2 out ports are much closer to 1.25" . That would pretty much squash and reverse the "earlier have less flow" you've heard. Anyone else want to add to the knowledge base?

[Nanonevol]

Reviving this thread to see if any one has input. A search of this site shows most of the opinion that early 4-2-1 manifolds are larger while some making the logical (but incorrect?) assumption that a manifold from a 2 liter would be larger. I'm going to say that any are an improvement but the difference could be significant. See photo above of my 1.25" opening manifold which I believe is from a '79 2L. An improvement on the 4-1 but not extreme. Earlier ones are said to measure 1.5" or more.
I'm not about to go looking for an early one and another downpipe and worrying about routing and all that again but for someone about to undertake this...

[RRoller123]

Correction! The 2 exit ports on my '79 4-2-1 measure 1.25", a bit more than "a hair" less than 1.5" as I reported earlier.
The 4 ports at the head are oval and measure 1.25" x 1.5". I'd like to hear what others measure to put some closure to this issue - so much misinformation out there (as everywhere).
Also found:
'79 4-2-1, 1.25" x 2 = Area of 2.46 sq in.
'77 4-1, 1.56" = Area of 1.91 sq in.

The 4 manifold inlet ports at the Head on an '81 manifold that I have, are oblong slightly, and measure ~1.45" x ~1.50". There is considerable carbon buildup so the measurements are approximate.

The 2 ports at the 6-bolt outlet interface are circular (also with considerable carbon buildup) and measure ~1.45"

Pete