Weak links in Gen4 Exhaust. Is the Y pipe?

[mynameisdaniel]

I thought xforce gave you an option for a cat if you ordered thru best mufflers, just that the cost for the cat was high for that option. Does it matter where you fit the cat in your system or is it best placed on the dump pipe?

PM me if you want to have a look at mine, I'm out Modbury way though.

The cat needs to be hot to work effectively which is why it's usually in the dump pipe

[dr20t]

3" v band dump, 38mm ewg plumbed back with about 1.5 ft of 40mm tubing, no cat, no resonators, 3" all the way through to twin 2.5" y pipe, to twin tcp quad tip mufflers.

Stop it...

[Shaheenis]

Yes I could actually go the Xforce option but from memory when I spoke to Chris from BM he said the cat was weld in and I want to do it all myself so bolt-on FTW. Xforce do actually do a dump option with 'pre-cat' for an extra $25 which is purely for looks so when you have the real cat installed it looks like you have two = standard but seriously, I think that is a bit over the top but good they have the option! Now I just need to decide between TCP and inVIdia dump, the main difference being one is full open bellmouth (TCP) and one has a splitter. I don't actually think the splitter does a lot when you have an open bellmouth as there is heaps of room for the pressure/gas to escape/diffuse. I am planning to upgrade to a VF52 and note their wastegate opens sideways unlike the VF46. Something to think about.

TCP


Invidia


PHAT

[alexeiwoody]

Yes I could actually go the Xforce option but from memory when I spoke to Chris from BM he said the cat was weld in and I want to do it all myself so bolt-on FTW. Xforce do actually do a dump option with 'pre-cat' for an extra $25 which is purely for looks so when you have the real cat installed it looks like you have two = standard but seriously, I think that is a bit over the top but good they have the option! Now I just need to decide between TCP and inVIdia dump, the main difference being one is full open bellmouth (TCP) and one has a splitter. I don't actually think the splitter does a lot when you have an open bellmouth as there is heaps of room for the pressure/gas to escape/diffuse. I am planning to upgrade to a VF52 and note their wastegate opens sideways unlike the VF46. Something to think about.

TCP


Invidia


PHAT

Have invidia started making dumps for aussie right hand drives now?

x force will flow best...depends what you'd like to get out of the system later on. If you're sure you won't want to get more power or go e85 down the track - go the most budget friendly option, won't be noticing any performance gains between any brand

Splitter might get you 5kw up top on a VF52...or it might make you nothing depending on your tune. You won't feel it either way. Ask them all for a discount

[shav]

Im considering the invidia myself as it's designed to suit auto boxes for my07 with no mods, I heard there some modification required with the xforce versions. Something to do with having to extend the pipe to get around the gearbox.

Flow will most probably be same, but I'd rather have a no fuss bolt on option than having to have a hack job done on a new part to make it fit.

[bigBADbenny]

http://www.prospeedracing.com.au/produc ... y-BL5.html

http://www.prospeedracing.com.au/produc ... MATIC.html

[JSarge]

Hi mate, I've just recently gone through this exact exercise so thought I'd share my experience. I ended up going for the Garage 88 dump pipe as a few have already recommended. I mated it up to an xforce centre/y pipe and bolted straight up to the sti quads . There is a noticeable increase in low to mid range power untuned, and the sound is perfect in my opinion (with the exception of minor resonance at low speed).

I did plenty of research on this forum and obviously everyone raves about the phat dump pipes, so I ordered one. It is a quality product but the issue I had is there is no updated information about the dump pipe that is currently being sold. This is quite evident from a few posters in this thread suggesting that the dump pipe still comes with the 3 inch bolt on adapter. This is no longer the case (as I found out after receiving the product). The dump pipe now has a welded on reducer only (3 inch to 2.25 inch) to suit the standard subaru donut flex joint and standard rear exhaust. It is perfect for bolting up to the standard rear section but less than ideal if you are planning on upgrading the mid pipe due to the unnecessary contraction at the join.

Also, be careful with calculations on pipe diameters with the y pipe split. Two 1.5 inch pipes aren't the equivalent of one 3 inch pipe as you need to use the pipe area rather than the diameter They're actually closer to a 2.1 inch pipe equivalent which is almost exactly half the area of a 3 inch pipe.

As you said it's definitely a good idea to taper the pipe when there's a reduction in the exhaust size, and the Garage 88 dump pipe does this well with it's 2.25 inch reducer. The problem is that when you have the 3 inch centre pipe you then have a very abrupt expansion from 2.25 inch to 3 inch which is actually worse for air flow than an abrupt contraction the other way.

If I had my time again i'd go for an xforce dump and mid, or a TCP dump and mid as I think the open bell mouth is the go with the vf46 and would prefer no restriction at the flex join. In saying that I'm happy with the G88 dump for now as I'm not planning on upgrading the turbo (yet ). If I was though I'd have to look at cutting up the dump to remove the restriction at the join, which is extra $$$. I think you're on the money with your thought on the vf52 and the side opening wastegate. It would probably benefit more from an exhaust splitter like in the invidia dump pipe.

Cheers, Joel

[dazzz168]

Are liberty mid pipes 2.25" and y pipe made of two single 1.5" pipes?

[Kekotic]

Are liberty mid pipes 2.25" and y pipe made of two single 1.5" pipes?

The Y-pipe is 1.75 I think.

[dazzz168]

Are liberty mid pipes 2.25" and y pipe made of two single 1.5" pipes?

The Y-pipe is 1.75 I think.

Yeah, my stock Forester mid pipe is 2.5" and 1.75" Y split, so I thought the liberty ones were the same. Seems to make no performance difference at my power levels if I run a 3" to 2.5" mid or my stock mid, but there's a big difference in sound levels (without a mid muffler in place of resonator on 3").

[alexeiwoody]

Hi mate, I've just recently gone through this exact exercise so thought I'd share my experience. I ended up going for the Garage 88 dump pipe as a few have already recommended. I mated it up to an xforce centre/y pipe and bolted straight up to the sti quads . There is a noticeable increase in low to mid range power untuned, and the sound is perfect in my opinion (with the exception of minor resonance at low speed).

I did plenty of research on this forum and obviously everyone raves about the phat dump pipes, so I ordered one. It is a quality product but the issue I had is there is no updated information about the dump pipe that is currently being sold. This is quite evident from a few posters in this thread suggesting that the dump pipe still comes with the 3 inch bolt on adapter. This is no longer the case (as I found out after receiving the product). The dump pipe now has a welded on reducer only (3 inch to 2.25 inch) to suit the standard subaru donut flex joint and standard rear exhaust. It is perfect for bolting up to the standard rear section but less than ideal if you are planning on upgrading the mid pipe due to the unnecessary contraction at the join.

Also, be careful with calculations on pipe diameters with the y pipe split. Two 1.5 inch pipes aren't the equivalent of one 3 inch pipe as you need to use the pipe area rather than the diameter They're actually closer to a 2.1 inch pipe equivalent which is almost exactly half the area of a 3 inch pipe.

As you said it's definitely a good idea to taper the pipe when there's a reduction in the exhaust size, and the Garage 88 dump pipe does this well with it's 2.25 inch reducer. The problem is that when you have the 3 inch centre pipe you then have a very abrupt expansion from 2.25 inch to 3 inch which is actually worse for air flow than an abrupt contraction the other way.

If I had my time again i'd go for an xforce dump and mid, or a TCP dump and mid as I think the open bell mouth is the go with the vf46 and would prefer no restriction at the flex join. In saying that I'm happy with the G88 dump for now as I'm not planning on upgrading the turbo (yet ). If I was though I'd have to look at cutting up the dump to remove the restriction at the join, which is extra $$$. I think you're on the money with your thought on the vf52 and the side opening wastegate. It would probably benefit more from an exhaust splitter like in the invidia dump pipe.

Cheers, Joel

Thanks for sharing mate What's the problem at the flex joint?

And thanks Ben That was some fun times Poida gt had with invidia...

[Shaheenis]

I agree with most of what you say JSarge but not sure on your point about a smaller diameter opening into a larger diameter is worse, I don't think this is the case. With you current setup you will have a 5-10mm blunt edge where your aftermarket meets your muffs. People go to great lengths to port extractors, up-pipes and turbs to remove ~1-2mm of obstruction from welds etc and even though the impact of this reduces towards the rear of the vehicle, still something deserving of rectification IMHO. Personally I recon this negates any possible benefits from a larger diameter mid&Y and hence why I am opting for dump with smooth transition to stock. I am torn between the TCP and iNVIDA and I agree there is probably ~5% difference between all reputable brands but looking at the money you spend and the quality (even if some of it is cosmetic) it is pretty apparent to me that TCP and iNividia win the quality battle at $799 full stainless, very clean mouth and welds. You might save $100 on a MS Xforce once you include decent CAT. Cheers for all the feedback.

[alexeiwoody]

I'm a little puzzled at all these questions and talk of budget while we discuss new retail prices.

There are a tonne of excellent dps for sale second hand on this forum and others....

As an example...
http://www.rexnet.com.au/forum/index.ph ... try2503522 I'm sure you could make this fit even if an exhaust shop want $100 to modify...

Or this for a definite fit and second best flowing dump on the market after x force.

www.rexnet.com.au/forum/index.php?/topi ... try2504556

[JSarge]

I agree with most of what you say JSarge but not sure on your point about a smaller diameter opening into a larger diameter is worse, I don't think this is the case. With you current setup you will have a 5-10mm blunt edge where your aftermarket meets your muffs. People go to great lengths to port extractors, up-pipes and turbs to remove ~1-2mm of obstruction from welds etc and even though the impact of this reduces towards the rear of the vehicle, still something deserving of rectification IMHO. Personally I recon this negates any possible benefits from a larger diameter mid&Y and hence why I am opting for dump with smooth transition to stock. I am torn between the TCP and iNVIDA and I agree there is probably ~5% difference between all reputable brands but looking at the money you spend and the quality (even if some of it is cosmetic) it is pretty apparent to me that TCP and iNividia win the quality battle at $799 full stainless, very clean mouth and welds. You might save $100 on a MS Xforce once you include decent CAT. Cheers for all the feedback.

Yeah actually I just checked and you're right about the smaller to larger diameter losses when talking about small changes (ie 2.25>3 in). It only goes the other way when there are very large differences in areas, althought the losses are very similar either way I had to check my text books this morning!

You're right about the blunt edge where the mufflers bolt up, it's very ugly and has high losses. It would be great if there was some kind of insert you could put in the exhaust just before the join to smooth the flow out into the muffler. It would make a huge difference.

Thanks for sharing mate What's the problem at the flex joint?

There's no real problem with it, It's just not ideal for a 3 inch mid section as it reduces to 2.25 inch at the join and is an unnessesary restriction. It's perfect if you're bolting it up to the standard rear section though.

[dazzz168]

There's the TurboXS one on Ebay for real cheap! But not sure if they will fit the Auto Libs ok.

http://www.ebay.com.au/itm/Subaru-2008- ... 7772929%26