I did a bit of searching, and never saw this spec. Does anyone know what the diameter of the factory stock 240Z exhaust pipes were?

This is no guarantee but when I bought my car in 1985 the exhaust system (including the stock manifold) looked really old so I have no reason to think that a previous owner replaced more than just the muffler (if that). I have 160,000+ miles on my 240SX with the original muffler and the 240Z didn't have that many miles when I bought it.

I still have that system. I just measured the outside diameter of the pipe just before the muffler and get a whopping 1 5/8". Obviously the original specs would be in metric so, perhaps 40mm?

When I bought my '73 it had 1 3/4'' piping . I doubt that it was origional but it appeared to be OEM . Gary:classic:

OK, that helps. So when I get my new exhaust built with 2 1/4", even if I don't get mandrel bent it looks like I'll still be at least equal to stock.

Arne,

I just had my '77 280Z's exhaust replaced with a custom welded 2.25" exhaust and it utitlizes a Magnaflow muffler and sounds really good considering it still has the stock exhaust manifold.

I have a new NOS Nissan exhaust for a 280Z and I just measured it:

1.75"

OK, that helps. So when I get my new exhaust built with 2 1/4", even if I don't get mandrel bent it looks like I'll still be at least equal to stock.

O' yeah the 2 1/4 is really just right for your L-24 or a L-28 for any street driven Z , according to the people in the ''know '' the I have talked with. Mandrel bent is best thou no doubt. Gary

I measured my exhaust pipe OD off an original unused NOS set hanging on my garage wall for my '72.

So for a 240Z, it appears to be 1 5/8". Thanks to all!

The outside diameter of mine is 1.75 inches as well with old fashioned bends no mandrel used on this one. This answers some of the clearance issues the guys are having getting the larger pipe under these cars.