Thornton exhaust manifold (403)
 

Anyone use these?

Trying to decide whether to use these or fight with long tube headers

Any info either way is appreciated

I had to look up what they were, seems to be someones effort to make a RA exhaust manifold for an olds 350/403.

I did find a review from some people that owned them, that felt they were less than optimum as cast;
https://www.tapatalk.com/groups/real...lds-t5837.html

If you really want to wring all the power out of a combo, headers are a necessity. If you just want to connect the engine to the exhaust system with less than optimum scavenging, then cast iron is going to be less headaches than headers.

Installing headers is of course more labor intensive than cast iron, less noise with cast iron. Cast iron is probably fine for 95% of the people that drive their cars on the street primarily.

If it were me, I'd probably just lift up the air cleaner and shove a 400/455 under it................:D