A quick simulation of a B8(BP) 1.8 SOHC - I'll use B8 because our B6 is an 8 valve carb engine -.
Posted figures are
The 1.8 L (1,839 cc) B8 (sometimes "BP") SOHC
103 hp (77 kW), 111 lb-ft (U.S./Canadian market)
106 PS (78 kW) at 5,300 rpm, 151 N·m (111 lb·ft) at 4,000 rpm (European markets)
Pipe simulated is simple 4 into 1
Single Primary Pipe Specs --- for 112.536 CID from 3300 to 5800 RPM
Diameter= 1.186 to
1.311 Length=
32.9 to 35.5 inches long
Diameter=
2.496 Tuned Lengths=
20.2"
Changing pipe diameters
Changing Primary pipe diameters
Yellow - 1.3" (pipe above)
Red ---- 1.0"
Green - 1.6"
You can match torque curves from legend boxes on the right.
Changing pipe lengths
Changing Primary pipe lengths
Yellow - 33" (pipe above)
Red ---- 23"
Green - 43" - has more torque by dies very quickly after peek HP
These simulators aren't great, hence why I don't use them any more, but you'll get an idea of changes.