get a 3" at least if u want top end power..
not a bad figure for a carby setup..

i would have thought a 2.5inch would be best for the 1.2lt

Very nice output from an A12.

Exhaust diameter is primarily sized to the horsepower output, not the engine size per se.

2.5" is way to big for a naturally aspirated A12. You can do it, but it won't make your car go faster, but a little slower than a smaller pipe.

But for turbocharged 1.2 -- like this one -- making 71kw (96 hp) at the rear wheels... let's see that might be around 125 hp at the flywheel ... it would call for at least a 2.25 inch exhaust. And if engine 'should' make more power then a 2.5 pipe might be called for, which should be good for 150-200 flywheel hp. Reference: club wiki - Exhaust Piping.

Hay, well done mate, finally got the beast on a dyno. Exhaust wise I would go to 2.5in if you plan to keep that size motor in that car. If you are planning to get a bigger donk in the future go a 3in and save the hassel down the track.

As for what ddgonzal said about 2.5in being way too big on a 1.2L NA motor I dissagree and so does my time slip. I went from 19's to 18's down the quartermile by removing the stock pipes and fitting my own 2.5in system.

Granted its a PIG down low and sounds like a killer wet fart it revs much more freely and has a little more top end pull

Sorry I wasn't clear. I didn't mean that a 2.5" pipe was worse than the stock 1.5" pipe. I only meant that 2.5" is not optimum for a naturally aspirated A12. The 1.5" is too small for max HP if you rev (even a totally stocker engine) up high.

Do this: Dyno your stock A12 (or drag time it) with 2.5". Then, same hour, swap to full 2" system and see if it goes slower. I doubt it. I would expect it to be no slower, and run slightly better at lower RPM.

As ddgonzal said, on NA you could go to big, but for a turbo motor, the best exhaust is no exhaust. So taking into account regulations regarding noise, and that a turbo acts as a nice baffle, taking out that harsh engine note, you should try to go as large as possible. I currently run 63mm with the 4AGTE, but even a simple act such as placing a lambda sensor in the tailpiece drops the output by as much as 9hp, which should be a good indication why you must use the largest zorst possible.

EDIT: tappet, this is not a carby setup if memory serves me right...

AGAIN: yup, my brain still functions for a few minutes a day...


LAST ONE: I promise.... looking at this piccy, you should try to move your battery to the bin, and get the boost pipe shorter. Might score a few horses there...