The Header on the left of the picture is my everyday port-side use header. I have a matching starboard-side Header that I run on the boat.

The Header on the right of the picture is the port-side Header I put on for tuning. It has an O2 bung welded into it. I do not have a match for it. The primary tubes on this header are 1 1/2" longer than the primaries on my starboard header.

My question is, Am I hurting the motor by running a mismatched set of headers. Also would this effect my 02 readings.

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I don't think effect the 02 readings, and not all headers have the same length tubes anyway, probably never see a difference...just would change the torque curve slightly I would think

More importantly, Make sure the primary ID is the same and the collectors are identical ID and length.

Yeah even on the same header each tube is a little different in length. On manifolds I think the differnce between cylinders is even more.

Yes on both accounts.

I'm more picky than the next guy when it comes to exhaust tuning, and if I had your system I'd be fine with that.

Only the more expensive headers are true equal length...marine ones very doubtful

Thank you for the replies guys