GamblerZ

I will have to replace most of the exhaust system on my 1UZ as the previous owner began to hack it up (presumably to install cut-outs). For the time being I have clamped sleeves so that the exhaust gases won't settle underneath the car at idle. Unfortunately, he also removed the mufflers BEFORE their flange so I have no way to recreate the intricate bends at the differential. But that is not my question...

As I am looking at the distinct possibility of installing an entirely new catback exhaust, has anyone replaced their catalytic converters yet? If memory serves, the standard life expectancy for a cat is only around 100k miles. This car has 135k miles and I feel pretty sure that the cats are probably gutted. Those who have, did you replace them with hi-flow cats (HFCs) or just a more standard version? Did you notice any noticeable change (ie. drone, resonance, metallic sound) in the sound?

Also, I frequently read here that the center resonator has been referred to as a "mid-cat". If that is indeed the case, there is a chance the exhaust shop may NOT remove this in favor of a single collector (perhaps 4") Y-pipe back into duals. Is removing the mid-cat not an issue like the primaries would be? Or, does the mid-cat act more as a resonator?

Constructive input would be appreciated. Thanks.

Ali SC3

iTrader: (10)

it looks like a mid cat, but it is just a resonator more or less, the primaries do all the work.
high flow units will get the job done when the primaries give out, and you can just install one unit like you said where the center resonator is and use a collector, and then a Y split out back.
this will also allow you to install headers up front and still be smog compliant.
you could get new primaries, but they are part specific and I would guess they are really expensive, and since you are starting from scratch it sounds like, you wouldn't want the stock cat size anyways.
3" would be enough for n/a. 4" makes me think you have some forced induction plans in the future, good luck!

GamblerZ

I was thinking perhaps the 2.25"~2.50" into a 4" back into a 2.25"~2.50". However, I thought the cat had to be much closer to the exhaust manifold in order to reach temperature to perform correctly?

Meanwhile, I would certainly like to install headers, but I don't imagine they are readily available for the 1UZ.

And yes, there are forced induction plans in this car's future...just not right away. I want to get everything else squared away and running 100% BEFORE moving into any kind of performance mods.