Plus and minus of up/down pipes on 02 wrx

[02wrxdemon]

Im thinkin about upgrading i know people here have done these upgrades
any positive or negitive feedback on these mods!!! Im currious as to how this will affect the cel

Thanks
Rich

[Dean]

Done correctly, it will have no effect on CEL. Most every bug eye in the grooup has both at this point. I personally like the divorced waste gate pipe on the down pipe, and up-pipe doesn't appear to make much difference as long as it doesn't have a cat. A couple have just gutted up-pipes as I recall, and even that works well.

[Kevin M]

Pretty much any catless FLEX uppipe will be fine. Subaru Specialists has frequent specials on theirs, $315 installed I believe.

Downpipes are an excellent mod as well. What diameter is your catback? If it isn't 3", I would plan on buying a complete turboback and selling the Magnaflow when you get it installed. I'm not sold that divorced wastegates are better than a good bellmouth- Vishnu's Signature Series turboback exhaust, with a divorced wastegate, actually tends to make slightly less power the the standard Aussie bellmouth one.

I would also highly recommend making the trip down to Nate at subaru Specialists for an Ecutek reflash, especially since you're running a cold air intake. Those are notorious for wreaking havoc with A/F ratios on a stock ECU, and many actually lose power.

A WRX with uppipe, turboback, and reflash makes around 50 extra whp on Nate's dyno. Well worth looking into.

[Dean]

I'm not sure the Vishnu is a great divorced wastegate design.

As you can see from the picture, is makes some pretty hrd turns, and then rams back into the main imediately before a reducer... Not good flow IMHO...

The BPM like I have is much cleaner, and merges much more smoothly. I assume the head end of the Vishnu has a splitter that fits into the turbo body like the BPM, but haven't seen the head end on it. Also, as far as I can tell, Vishnu doesn't sell the bellmouth any more, so perhaps they changed their minds on which was better since you were there Kevin.

Vishnu:


BPM: More BPM Pics


I'm not sure I'd reccomend Vishnu stuff anyway at this point, just from a customer service perspective.

Bell mouths are good, but I would suggest one that extends the split beyond the first bend like the Cobb if yo uget one. Shorter than that, and I'm not conviced they are much better than stock.

[Kevin M]

The BPM design is probably better than Vishnu's. I doubt they stopped selling the standard exhaust, unless the exchange rate got so out of hand it's almost as expensive as the Signature. A bellmouth design like Nate's proprietary one is probably as good as a good DW pipe though, especially when you have the cat in the downpipe.

Also, Vishnu doesn't recommend their stand-alone downpipe (or any other like it) because of the taper at the end. They will always recommend you buy a complete turboback unit (even one that isn't theirs) before buying a downpipe that works with stock components.

[Dean]

You will find that we bicker quite a bit here, but overall we have good info. Kevin and I often push each others buttons...

Kevin, I only saw the divorced on the web site, and the kits all included it I beleive.

I say a resounding no to Cat in the downpipe! Put it in the Mid pipe. it will likely require an extension on the second O2 sensor, but big deal.

I haven't see Nate's Bellmouth, but unless the bell extends past the first bend like the Cobb, I'm not convinced.

Cobb:


Oh, almost forgot. A good fitting non-flex up-pipe is as good if not better than a flex one IMHO. Everything involved is bolted to the engine, there is no need for flex, it just puts more load on the other flanges, like the heads to headers. I have a flex, but that was an emergency,, and I haven't had a good reason to change.

[Kevin M]

Yeah we tend to focus on the 2% of things we disagree on, rather than the 98% we do agree with each other on.The downpipe you posted isn't the Signature Series downpipe. It's actually made by the company in Australia that makes the standard bellmouth exhaust. Here's the standard bellmouth exhaust. I'd like to see some sort of tech, or even a reasonable explanation, as to why it's actually better to put the cat in the midpipe. I do know that it functions very poorly in that location, as it's very difficult to get it up to light-off temp. Having it 6-8 inches away from the turbo, where exhaust flow whould be fairly smooth, shouldn't make a huge difference, especially when you have a bellmouth.

I can't go into details about Nate's downpipe magic, but I can explain it in person sometime.

[Dean]

Originally Posted by BAN SUVS

as to why it's actually better to put the cat in the midpipe. I do know that it functions very poorly in that location, as it's very difficult to get it up to light-off temp. Having it 6-8 inches away from the turbo, where exhaust flow whould be fairly smooth, shouldn't make a huge difference, especially when you have a bellmouth.

Huh? A ton of NA cars have much lower ETs, and have no problems with Cats under the car.

I can't think of a single good reason to put it that close to the turbo exit generating back pressure. The only ungood reason was becasue the stupid STX rules were written so poorly originally, you had to.

[Kevin M]

Originally Posted by Dean

Huh? A ton of NA cars have much lower ETs, and have no problems with Cats under the car.

I can't think of a single good reason to put it that close to the turbo exit generating back pressure. The only ungood reason was becasue the stupid STX rules were written so poorly originally, you had to.

How does it create more backpressure by being closer to the turbo? Shouldn't the pressure drop be the same across the cat regardless of where it is? Or does the extra volume and additional exhaust cooling before it gets to the midpipe make some weird thermodynamic change that I don't know about?

[Dean]

Originally Posted by BAN SUVS

How does it create more backpressure by being closer to the turbo? Shouldn't the pressure drop be the same across the cat regardless of where it is? Or does the extra volume and additional exhaust cooling before it gets to the midpipe make some weird thermodynamic change that I don't know about?

Both... Pressure is a function of volume and temperature! PV=NrT Flash Demo

A quick example would be to compare how long an engine will continue to idle with a blocking plate after the turbo vs. after the stock muffler. Neither will be long, but the differential will be relatively huge.

[Kevin M]

pv=nrt doesn't apply to exhaust systems because it's not a closed system.

Your examples are pretty reasonable though. I may end up with a midpipe cat yet.

[AtomicLabMonkey]

I don't know how close these things are you're talking about, but two separate obstructions (pressure drops) in pipe/duct flow can have an effect on each other if they're in close proximity, producing a greater total pressure drop than if they were far away from each other.

[Dean]

Originally Posted by BAN SUVS

pv=nrt doesn't apply to exhaust systems because it's not a closed system.

Your examples are pretty reasonable though. I may end up with a midpipe cat yet.

PV=Nrt appies to partial pressures as well, there are just more variables you have to throw in. I'm to lazy to go look it up, but at minimum you have to account for flow in and out.

If there is more volume and lower average temperatures before a restriction, it has a lower overall impact to the flow of the system, especially in a variable flow system like an exhaust. The volume tends to smooth out the peaks.

[Kevin M]

Originally Posted by Dean

The volume tends to smooth out the peaks.

Okay, that makes tons of sense.

[02wrxdemon]

Easy Fellas..No fightin or should i say bitchin concentrate all that negitivity towards a evo

[Kevin M]

We like the Evo.
















It's the SRT4 we hope to see burninated.

[Kevin M]

Anyways, about your question... yes, an uppipe and full turboback are great WRX mods. Definitely do it if you can.