and about how much hp increase after decat??

Unlikely although it will help.

D6C (non-cat) = 10.4:1 compression
DFW (cat) = 9.4:1 compression (I believe)

A de-cat will likely free up the motor somewhat but how much depends on the condition it is in. The more collapsed/blocked up the internal structure of the cat is, the bigger the gain.

RFY is 10.4 + cat.

i meant the 2.0 mi16 not the 1.9

Ah good point. I've never even seen a 2.0 Mi16 so I'm always thinking 1.9

Would the ignition/fuel mapping be any different between the cat and non-cat models?

i think it's a hardware issue but not software, it's a box that filters carbon monoxide and within the time it becomes somewhat blocked so the air flow become slower which slows the acceleration so taking off the cat box would free the airflow making the engine breath more freely which will give more horse power so i was asking if any one has tried this before on a mi16 2.0

^yeah, I was just wondering if due to the better breathing, the non-cat 1.9 engines may have more aggressive ignition/fueling profiles. These may have also been changed to reduce emissions in the 2.0?

the cat is 101k miles old on my 2.0 and hasn't slowed it down at all, 2 separate RR's gave a reading of 160 bhp.

though the heads are the same the bottom ends behave a little differently, the 1.9 is a long stroke whereas the 2.0 is square.


I would imagine PeterT could tell you what the difference is in the ignition tables from D6C to the DFW, though I'm not sure if he has experience of the RFY unless you got the early 306 S16 there (rather than the later RFS engined 6 speed variant known as the gti6 here)?