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Unless you have a built, big cube motor, the 1 7/8 are too big, and will rob torque.
Even a 500rwhp 346 would be best served with a 1 3/4" header.
Remember, headers aren't about flow, their purpose is to scavenge, or help suck the air out of the cylinders. If the tube dia is too large, it reduces the scavenging effect, and defeats the purpose.
Seems so few people understand this, and only think bigger is better.
Got the word from Chris @ ECS... He said even with HIGH boost, they still run the 3/4 to get the air out with the 346. He said even if I was to upgrade the motor to a 383, which is the most cid I would most likely go... He said I should still stick with the 3/4.