I picked up a set of Hedman Headers P/N 68270 (1 5/8") and when I measured the ID (inside diameter)on the tubes they came out at 1.505 inches. When they advertise 1 5/8 shouldn't that be the inside diameter? The unit I measured them with is a very accurate id micrometer good to 1 ten thousandths of an inch. Is this what you get when you don't pay the big bucks?

What's up Guy? Advertised 1 5/8" headers are the outside measurment not the inside. Even if you were looking for an inside measurment you can't trust what you measure (good tools or not) as things change when pipes get bent... You would have to cut through a straight section of tube to get a good inside measurment. Way too much going on at the flanges...

Hi Dennis,

Thanks for the reply. I would have thought the inside was the critical path, oh well! I understand what you are saying on getting a good measurement as I have been in the measurement business for 30 odd years. I did take quite a few measuremnts and that was an average with a standard deviation you wouldn't believe.Hope to run into you sometime at Vics!
Later,

Guy

A while ago there was some discussion on this dimension being affected by the manufacturer's gauge choice. Some headers are 14 gauge, further reducing that inside dimension.

Tubing is sized by o.d. instead of i.d. If you bought some trick stainless u-bends to make your own exhaust it would be the same way.

Jody