providing the 3.5 is a good design id stick with it,im running 360+rwkw with a custom 3.5 dump(seperate runners at the top)and its great down low and up the top,4inch is good for over 400+rwkw

cheers lee

Ok guys. Im confused and need help

Buf-Phoon, who was at the same power level as I am now, recently replaced his APS system which is a proven performer with a custom 4" dump, cat and intermediate etc and picked up over 30rwkw.

This contradicts whats been said here.

So whats right and whats not? Exhaust mods is one of the 1st performance mods that T owners do so I just want to set the record straight as this is what forums are for.

I'd be looking at your intake system first as your exhaust ( APS is it ? ) must be able to flow more.

18psi is rather high for 325... mines around 300 on 12psi with stock dump but revised intake/ic

I mentioned in my opening thread that Ive just updated my I/C which includes intake mods and want to fix up what might be a potentially restricted exhaust before I find out the hard (and costly) way during the retune.

My exhaust isnt an APS. I mentioned APS for Buf-Phoon's experience with exhausts where he went from an APS to a custom 4" system and picked up over 30rwkw from that mod alone. Against an APS system that's definitely saying something.

My exhaust is a 3.5" dump, 3.5" metal cat, 3.5" intermediate and then it splits into 2 3" pipes up and over the diff to quad tips.

325rwkw/18psi is rather high and that's what Im trying to cure. My car has never been a dyno queen however it does perform quite well against higher powered cars on private roads.

Ah ok, thought you were still using the stocker rubber hoses and crossover section

Even though Ive updated the intake, I still retain the crossover section cause Ive heard that its been tested a few of times by different people and its not a restriction.

your exhaust is fine, just maybe check your cat, and make sure you have not melted it at the entry,

other then that, it is better then a APS one, the car that made 30kw's more, must have had a melted cat, which was limiting its power, because I would expect about that improvement from going from stock, to yours or a 4inch one, if your cat is in good condition, the exhaust will not restrict you,

my exhaust is like a APS exhaust (which has not got a full dump) you can still make good power from it, but I see mine fall off compared to a exhaust like yours over 5200rpm,

David

Hi David.

Sticking with the 3.5" dump looks like the way to go. I will look at the cat but do you think while Im there I should increase the intermediate pipe (between the cat and diff) to 4" or Im not gonna get any gain from this? I definitely dont want to lose bottom end torque.

Arthur

Just remove the cat all together.... do it arthur... problem is now all fixed

pete

I wouldnt do the intermediate... updgrading the dump and cat will always make more peak power, right up until you have no exhaust at all you get maximum. Its not just a flow issue, but also a heat and pressure phenominon. the bigger the difference in heat and pressure from in front of the turbine to the back (dump) the more efficient it is...

low end torque is differnt story, some say you get less with bigger dump, but I havent seen any proof of this yet - not to say its not true, just havent seen proof personally...