club.liberty.asn.au

Hi All,

Been doing a lot of research and still can't definitively confirm some details about my MY04 liberty GT Auto (VF38 twinscroll). I'm looking to fabricate my own up-pipe and downpipe.

1. Does my model liberty have a cat in the up-pipe?
If so, is it worth fabricating a new cat-less up-pipe? Does it have to retain the two separate pipes leading to the turbo?
If there is no cat in the up-pipe, it looks like there would be no real benefit enlarging the two parallel up-pipe sections as they would restrict at the turbo inlet flange holes anyway. Has anyone done this or used a single larger pipe?

2. From looking at other suppliers downpipes for the MY04 liberty, they look pretty straight forward except for directly after the turbo, where the flange is larger and will reduce to 3". I have seen some "home made" types that just use two pipes - 1 larger full diameter pipe with a smaller diameter pipe cut in half and welded together to form the larger opening. Others use two completely separate pipes that connect up a little bit further down. Any benefit of one over the other?

My car is stock except for a Kido tune. I would be getting it re-tuned post install of both pipes (or just the dump pipe if there is no benefit of the up-pipe).

Cheers guys!
Dave

No cats in the uppipe for these cars. Better off just keeping the stock uppipe, won't make any noticeable difference and having the two runners will make it quite a complicated one to make up. You lose the twinscroll benefits if you somehow made a single runner uppipe.

Could also just decat the stock downpipe. Mine makes the same power with a decat as others have got with fancy, rather expensive downpipes.

Twin scroll turbos are a slightly different animal to regular single scroll turbos as they try to make better use of the exhaust pulses to reduce spool times. That's why you have two seperate pipes and inlets to the turbo. Bigger isn't always better and, basically, using a single larger pipe would reduce the exhaust velocity which is what drives the turbine. Personally, I don't think there's too much to be gained from changing the design of the header/up-pipe if you are keeping the VF38. The most effective thing you could do is try to maintain the heat in the system which will increase the gas expansion rate and improve the gas velocity by wrapping or ceramic coating the pipes. You could also look at the joins and try to smooth out the transitions between headers, up-pipe and, turbo to reduce any turbulence.

On the exhaust side the two restrictions in the downpipe is the wastegate exhaust and the cat. In Aus if you completely remove the cat you risk huge fines but if you have a MIG/TIG welder you can modify the OEM pipe to perform well as an aftermarket one by replacing the standard cat with a 100 or 200 cell high flow one.

The problem with the waste gate is when it opens the exhaust gas has to do two 90 degree turns to enter the stock exhaust system and this will create turbulence in the system and reduce the efficiency. What most dump pipes attempt to do is smoothly combine the two. With the VF38 you need a plate that protrudes into the turbo exhaust flange to seperate the wastegate from the turbine exit. On the STi turbos this is done in the casting but not on the VF38/TD04. You can then weld in a path to smoothly introduce the wastegate gasses into the turbine gasses.

Im selling my dump pipe (used for a month) for auto vf38

andy_mac wrote:No cats in the uppipe for these cars. Better off just keeping the stock uppipe, won't make any noticeable difference and having the two runners will make it quite a complicated one to make up. You lose the twinscroll benefits if you somehow made a single runner uppipe.

Could also just decat the stock downpipe. Mine makes the same power with a decat as others have got with fancy, rather expensive downpipes.

I do believe this - but would like to add my 2c on why this may be the case (for the sake of anyone reading this and thinking they may as well just remove the cat in their dump pipe instead of changing to a more efficient dump pipe altogether).

The cat in the stock dump pipe will absolutely increase post turbo back pressure. This back pressure is detrimental to turbo efficiency (heat, spool, losses etc). By removing the cat, you have removed a huge restriction.

The vf38 is such a tiny turbo, that reducing the back pressure / restriction caused by the cat, effectively takes the turbine wheel to its limit of efficiency. The restriction has now become the turbine wheel / p15 twin scroll housing itself, and no matter what you do post turbo to improve efficiency, it won't make a difference to turbo performace.

This why comparing a decatted stock dump to a full dump pipe, you won't see a great improvement in performance.

However - (and this is an important point). Whilst you make not see any power gains from a dump pipe, the knock threshold is absolutely improved with a dump pipe, as is wastegate efficiency and thus your boost curve. The stock dump pipe effectively blocks the flow of exhaust exiting the wastegate. Think about the work required in doing so.

Mick

Do the dump only.
you wont regret it!