[rstolz]

I'd go 2" on the 1.6 non-turbo. I run 2.5" on my Audi 1.8T, more than that and you can really start to feel the low end loss.

I have the DC Sports system on my V, which is a 2" with canister muffler. nice setup, no real low end loss, definite bonus on the high end. It was cheap, looks nice, and works. There is a bit of drone, but nothing too bad unless you're running the A/C and cruising at 80mph. VersaSpeed also offers a silencer that fits into the exhaust tip, and really quiets the system down. You lose some benefit from the open exhaust, but you get a much quieter ride and nice deep tone.

There is a serious restriction on the header. At the collector, where the 4 goes into 1, the pipe diameter is severely choked, before opening back up for the flange. So any gain you get from opening the exhaust is going to be tempered by the restrictive header.

 

[rstolz]

I think any header that fits the 1.8 also fits the 1.6... could be wrong there though.

 

[rstolz]

yea it's only a few ponies, but with 120 stock for the 1.8, and less for the 1.6, a 5% gain is just 6, which is generally in-line for a small displacement NA engine.

It won't make a rip roaring difference, but it will help smooth out the flow and influence the torque curve.

Header design affects torque more than HP; and not only how much, but when. pipe length and collector design (diameter, geometry, length) affect when the torque peak occurs.

OBX and DC 4-1 units have very short pipes and collectors, pushing the torque gains higher in the RPM range. Stretch out the collector and you can push the torque curve lower, while still seeing improved top end.