I am looking at the headers off a 90 Vette and the tubes are
1-1/2" diameter. They are welded on the inside which reduces
the diameter to about 1-1/4" or less on some. If I reweld them
on the outside and grind the weld out from the inside is a 1-1/2"
tube large enough or will it restrict flow too much?

I see that most headers are 1-5/8" or 1-3/4" diameter.
Is 1-1/2 too small?

 

1 1/2" is certainly small, but the rewards are in flow. A 1 1/2" header will maintain volocity and scavaging better than manifolds with rough casts and 90° turns.


This would get more answers on the exhaust board.

 

Ok, heres my situation. I have a Jaguar with a 350 TPI in it.
It now has a pair of cast iron ram horns on it. Because of room
restrictions I have to stay with a center dump manifold.
WIll the Vette header flow better than the ram horns?

 

Possibly, although I think that a custom setup would be better suit your needs with the space restriction. Some block hugger headers may be what you want to look at. And the smaller size does have a better scavenging effect than larger tubes.

 

Yea, I contacted sanderson headers but they didn't have any
huggers that would work. The place I bought my swap kit from
sells a set but they are major $$$$$.