I have SB 350 with aluminum heads. Choosing headers 1 3/4" OR 1 7/8 " ??
Thanks

 

you are not providing enough information.
this may help you decide
Primary Header Tube Length and Diameter Calculator

Wallace Racing-Drag Racing Pontiac powered Firebirds,Trans Ams and Dragstersheader_length.php

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Calculate Header Tube Length and Diameter - by Wallace Racing Home of Pontiac Powered Firebirds ... For a race engine, the peak hp RPM should be used.

 

As a general rule, match the header tube diameter to the head port diameter.
For street, tune for torque, generally a primary tube length of 36 inches, or longer.
For race, tune for horsepower, shorter primary tube length under 30 inches.

A 1-5/8 inch diameter by 32 inch equal length tubing with a 3 inch collector of about 20 inches long works well for the street. But then, we are subjected to the market availability.

 

Thanks the info and The Calculator was very helpful

 

You're welcome
And what did you come up with?