club.liberty.asn.au

A lot gets mentioned about down pipes but I can't find detail on UP pipe to turbo VF46.

Can some one please clarify: Does the 07-09 post facelift GTB EJ255 have an UPpipe CAT?

Does the 07-09 post facelift GTB EJ255 STI version have an UPpipe CAT?

If no CAT in STI, could it be a worthwhile simple mod?

I'm thinking before any costly exhaust mods, to change the UP-pipe from the header to the turbo.

Thanks,

People rarely change the up pipe, headers etc on Subarus as it can causes the car to loose the boxer sound that we all know and love. I think that's why you can't find much info on them.

Thanks and I do agree with the headers but the up pipe is a well known mod for improvement.
I'm trying to determine if the STI up pipe is different to the basic GT-B?

Also I believe the 06 and before had a CAT in the up pipe but not sure about post face so asking the question. I can't quite see under the heat shields.

A catted up-pipe seems unlikely. Surely you would see a bulge in the up-pipe to account for a cat - even with heat shields in place. The up-pipe space is pretty tight, so a catted up-pipe would be an even harder fit.

Ages ago I bought a stock WRX exhaust manifold & up-pipe set from the wreckers when I had plans for porting them and putting them on my Forester. No cat in the stock pre-turbo stuff from that collection.

Also the first O2 sensor is I believe in the UP pipe and called the Pre-Cat lambda sensor.

After some initial searching on the web, there is quite a bit of info from the USA. There was a Youtube clip on replacing the UP pipe which I believe was on a 05-06 Liberty.
What was interesting is they replaced the stock catted up pipe with a STI non-Cat up pipe which was what got me wondering. It could be the 2.0L was different to the 2.5L.

It is also interesting Some of the Brands like Invidia, AVO, Cobb, etc sell 2" up pipes.

It makes sense if more gas can enter the turbo quicker it could spool up faster.

Watch out for American stuff. I believe that California has quite strict emissions requirements, so "more cats" to meet that requirement in the yank market is not unusual.

Regarding:

It is also interesting Some of the Brands like Invidia, AVO, Cobb, etc sell 2" up pipes. It makes sense if more gas can enter the turbo quicker it could spool up faster.

Note my comments from the other thread:

Keep your wits about you when considering any aftermarket larger-diameter up-pipes.

The whole point of a turbo system is for the exhaust gasses to be funnelled into a very tight nozzle within the turbine housing where they can impart maximum velocity in the turbine wheel. The tightening begins earlier - noting that the cross sectional area of the up-pipe is not double the cross-sectional area of each exhaust bank's merged output.

If you swap out a factory up-pipe for a name-brand aftermarket large diameter up-pipe (but otherwise keep a stock-ish sized turbo etc.) you'll just have this large diameter, lower-velocity exhaust hitting the flange of the turbine housing and having a sharp 90 degree edge as the point of reduction to go into the turbine housing.

A larger diameter pipe will flow the same fluid/gas at a lower velocity. See for example your garden hose with no fitting on the end versus a restricting nozzle that lets you squirt water 20 metres at much higher velocity. Which hose configuration could spin a waterwheel faster do you reckon? Same principles apply for turbos. Look at the snail shell shape of a turbine housing - designed to focus the gas through the smallest orifice in the whole exhaust system (disregarding the wastegate) at maximum velocity to impart energy on the turbine wheel.

Larger diameter up-pipes might have their place for Subi owners running massive turbos, but for a street car running a street-style turbo I recommend much more research before getting out the credit card on "bigger is better" principles.

Also, aftermarket up-pipes seem to leave it to the user to figure out heat shielding, with most solutions being sub-optimal compared to the factory dual-layer stamped steel heat shield in my opinion.

Good points Yowie. Smaller dia, higher velocity.

So how does the extra volume on the exit improve with a bell mouth exit and 3" dump pipe?

Good points Yowie. Smaller dia, higher velocity.

So how does the extra volume on the exit improve with a bell mouth exit and 3" dump pipe?

The pressure difference between the gas in front of the turbine and the gas after the turbine is important. Low pressure post-turbine means pressure before the turbine will do more work on the turbine blades.

A bellmouth dump pipe (and ideally a 3" exhaust & low-restriction mufflers after that) allows lower pressure after the turbine than a stock dump pipe & exhaust system does.

In a turbo-back application I have never found compelling any arguments around "keep the gas velocity up" (whether via heat wrapping or narrow pipes or whatever). I'm open to learn if sensible information comes to hand. To be clear, heat management is a good thing, I just don't think one of the material reasons is making post-turbo gas faster.

It can be a thing for race cars, where maintaining heat in the exhaust post turbo is said to be beneficial for both egbp/flow and heat management.
I’ve never seen actual testing with this approach on a street car…

The uppipe diameter effect can be seen on the differences between eg oem lgt and jdm sti twinscroll uppipes, the former being smaller diameter than the sti, because the entire exhaust & turbo system is designed for early spool, not top end power potential.


I’d say for a stockish postfl stock single scroll setup, the stock uppipe is just fine, unlike the USA catted uppipes where the cat may fail due to afr/egt/tune issues, or might be regarded as restrictive to flow.

If you go to aftermarket headers and uppipe you may have options for the uppipe, the bigger option being for extreme power applications and not necessarily desirable for lower powered applications, likely to hurt spool etc.

Not touching the uppie....thanks for feedback.
Noticed that JDM one that was for sale from Canada for STI turbo conversion.

Are there two Cats after the Turbo in the post face lift Auto's? Can we do with one?

You could but it’s even more defectable, it’s the common aftermarket approach for a catted dump.

You can have a second cat fabricated into the exhaust if you wish.

At which point you’d need a tune to suit.