mrbeaubo

Hey folks, I need a bit of help here.

I need a header gasket for my new OBX Sidemount headers (big rectangular ports). My heads are aluminum angle plugged heads with round ports. The car is in the shop to get painted, so I can't measure the round port size but that's not really the question. I know the rectangular ports on the OBX will cover the round ports on the head, so should I match up the gasket to the heads (round smaller) or the headers (rectangular larger)?

DRIVESHAFT

Buy gaskets to match the headers.

JimT

If the head port is smaller than the header port, I would match the header gaskets to the head port size. This way you eliminate any possibility of an exhaust leak due to the mismatch between the two.

mrbeaubo

I would assume this wouldn't cause issues as exhaust is flowing OUT therefore not a huge deal that it's smaller than the header port, right?

JimT

It is not the inside diameter of the gasket but the outside area of the gasket. I've got the same headers as you and tried to use the provided gaskets. After a few weeks I noticed exhaust leaks.
I removed the headers, and found that although the large gasket fit the headers perfectly, they extended over the outside rim/edge of my smaller head ports.
Place the provided gasket on the heads and verify that the larger header port opening doesn't extend over the head port facing.
The correct head gasket fits the head port, does not interfere with exhaust flow, and insures the headers make contact with the entire facing of the heads.
I hope this makes sense!