This is for the TJ...

How much difference could I expect to ghet from changing my system from a 2.5" cat back to high flow cat and 3"?

I was going to get the same system just without the extractors on the TS that i just bought but thought it may be a better idea to just swap the TJ one to the TS and get the better system for the TJ as that is what I wish I had got to start with but just want to make sure it is worth my while...

I am seriously considering going turbo at some point so figure that the 3" will be best for this but not sure how much difference it will make now

Any thoughts would be really helpful

You will prob find most shops wont do a 3" onto a stock car.. i did my exhaust a week before we pulled the engine out for rebuild and had to spend 40mins to convince liverpool exhaust to put a 3" exhaust on my car. they wouldnt as it would be stupid unless engine mods to suit.. they finally came around once they had plenty of finer details..:)

On a stockish motor I dont think it will make much difference, it wont hurt but wont give you much. The gain that you would see would be from the cat.

It won't do much if improve performance at all.

If your sure you want to turbo later on, keep the stock exhaust until you do turbo it and get it all done then. Otherwise you'll be throwing money away, the stock exhaust is a very good performer.

You simply don't have the gas that necessitates a 3" exhaust at the mo.

3" vs what i had before saved me appprox 1L/100km but... there is no real way to prove that as one week i could have had less inflated tyres etc....

i say dont go 3" purely cos of the fact that it's going to be dam loud, i have 2 mufflers and 2 resonators and it's still loud and drones so bad that you cant talk to the passengers :badgrin:

Cool guys thanks!
I will just stick with what I have for new I think - not only good advice but reasoning to back it up as well...

If I have to upgrade later I will just cut my losses and have some spare parts :)

It already sounds awesome with the 2.5 and probably would send me deaf with a 3" anyway!

Cool guys thanks!
I will just stick with what I have for new I think - not only good advice but reasoning to back it up as well...

If I have to upgrade later I will just cut my losses and have some spare parts :)

It already sounds awesome with the 2.5 and probably would send me deaf with a 3" anyway!
Good decision. I put a hi flow cat and cat back system on before i did the cam work and noticed no difference other than a little better sound. even the drags showed the same time. The stock system, even the cat is a good flowing system.

All following information was told to me by an exhaust mechanic (I think its BS)

Upgrading to a 3" will kill the low-down power on a Magna. The back pressure in the system won't be enough with just a standard engine. If the engine was turbo-charged, or was going to be, then 3" is pretty good. Otherwise, no useable acceleration. The Hi-Flow CAT won't increase performance at all, unless your current CAT is screwed.

he right about the low down power, big pipes encourage big revs.
when i fitted the 2.5" pipe to my Golf (2.8 V6) it moved peak power up around 6000rpm from 5500rpm. Its a little doughy below 2000rpm, but wakes up at around 3500rpm. Im not sure the 3.5 could rev hard enough to utilise a 3" pipe. if you could rev to around 7000rpm (redline) then a 3" pipe would be great.