You will need a 4-2-1 design unless you want to bang/upgrade your crossmember. 99-00 si should be fine and have a muffler shop weld in another o2 bung. Ideally, If you have a 4-2-1, plug up the original o2 bung and get one welded in each of the "Y" spots (The "2" in 4-2-1). That is how the oem header is made. That is what I would have done if I could do it over. Pick up a b16 header off of here used, dont pay 300 for a new DC. Good luck

You will need a 4-2-1 design unless you want to bang/upgrade your crossmember. 99-00 si should be fine and have a muffler shop weld in another o2 bung. Ideally, If you have a 4-2-1, plug up the original o2 bung and get one welded in each of the "Y" spots (The "2" in 4-2-1). That is how the oem header is made. That is what I would have done if I could do it over. Pick up a b16 header off of here used, dont pay 300 for a new DC. Good luck

This is exactly the right way to do it. Let me give you a little more advice though, since I took my header into the muffler shop to get the 2 O2 bungs welded a week ago. I got the two bungs welded and the O2 sensor bungs are in the front (of the pipe), but pointing at an angle. Well, when I went to put it on, one of them was hitting the block, so I had to take it back to the shop. The guy put a bolt in the hole and welded a new bung sticking out the side of the header. This time I knew I'd be able to put it on and I was excited be able to drive my car again...wrong!! When I went to put it on, the other O2 was hitting the block! So, I had to take it back a third time (just today actually), and have him plug up that hole and weld a new bung for the other O2 to stick out the other side. I'm going to try puttin it on tomorrow and I'm pretty postive it'll go on just fine this time.

CLIFF NOTES: Get the O2 sensor bungs welded on the SIDES of the header!!!

Another option is to get the 99-00 Si header, and run one 02 in the location that already has the bung in it. Then, with the money you would have spent getting the header modified to work with 2 o2's, get an ECU chip for your PR3 (spoon, mugen, feel's, etc...) that deletes the secondary o2. I have been running it this way for 2000 miles or so with no side effects whatsoever. Driveability is exactly the same as when both o2s were located next to the block. The other benefit to this is that your car *should* feel stronger due to the optimized fuel and timing maps.

please show pics of the finished header

Another option is to get the 99-00 Si header, and run one 02 in the location that already has the bung in it. Then, with the money you would have spent getting the header modified to work with 2 o2's, get an ECU chip for your PR3 (spoon, mugen, feel's, etc...) that deletes the secondary o2. I have been running it this way for 2000 miles or so with no side effects whatsoever. Driveability is exactly the same as when both o2s were located next to the block. The other benefit to this is that your car *should* feel stronger due to the optimized fuel and timing maps.

HTH

-Todd