ABF into mk2 Exhuast bore/system

[WYATT]

Alrite im going to be fitting my ABF into my mk2 golf , the exhuast is seeming bit hard if i run the mk3 mani/downpipe , then where the cat should go if i get a decat pipe then slot teh lambda in there i cant seem to fine any decats with the Inner Diameter of 2.5 inchs , thats what the end of the downpipe is showing , and i'd like to run the rest of the system striaght trhough and just use a jetex bax box , i've seen that on jetex you can buy just univerail parts of tubing/bends and all that so this is how i'd make the rest of the system ,


Im pretty sure the downpipe came up at 2.5ID but that was very earlyer this morning before work , if i made the rest of the system 2.5 is that alrite or would 2.25 be arlite , the ABF will go in stock then when i get the money i'll be putting cams/aftermarket manifold and a few others things , so if i get the system sorted now while i can for the higher BHP aimed for at a later date ,


Cheers Joe

[Diamond Hell]

Keep the 2.5" diameter for as long as possible in the system.  As the exhaust gases cool they condense and take up less space, which means you can run the rear end of the system as is at the moment - contrary to barry-wisdom where the back box is the largest diameter pipe on the car. 

Just make sure you have the lamdba in the system and keep it as close to the OEM location as possible - too far back and it won't warm up fast enough, too close and you may burn it out.

The biggest gain will be from putting a tubular manifold on the back of the engine to get those gasses away as fast as possible.