FV-QR
The old CIS cars came in a few different forms. Let's look at the differences...
GX engine code- used on 85-87 Jetta, Golf (85hp)
smaller valves in head
single (toilet bowl) downpipe
no knock sensing system (vacuum timing advnace)
single wire oxs
8.5:1 compression
HT/RD engine code- used on 85-87 GLI and GTI 8v (100 or 102hp)
bigger valves
dual downpipe manifold
knock sensor, more radical timing advance
more advanced computer (CIS-E with DPR for more dynamic fuel control, though some GX engines came with this)
10:1 compression
(* the HT engine was use din 85, and the RD was used in 86-87. On the HT there is a wire on the ECU that connects to another pin on the ECU... supposedly if you cut it the timing map changes to match the RD code and you gain 2hp...)
A head and downpipe swap will get you much more power off the bat. But the compression won't change... the compression is low to prevent ping. if you had more you'd need the knock sensor system to compensate for increased ping/knock.
There was also another engine, the MZ. It was in Canada only. They were identical to the GX 9small valves and all) but they deleted the oxygen sensor and computer (it was pure mechanical CIS). THis engine made 90hp.
In short... there are several computers (knock control, oxygen, and ignition controller which really isn't a computer but still...). The GX shouldn't have a knock system, and the oxygen sensor computer is what controls fuel. Only some GX engines had CS-E (the majority of GX engines had a completely different computer that won't swap with the GLI one). The ones that DID have CIS-E, I guess you could swap them and it might provide a theoretical advantage but I don't see much...
Modified by VDub2625 at 1:59 PM 3-20-2010