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Discussion Starter #1
Hey

Recently fitted a 2 1/2" muffler and 100cpi high flow cat to my TX5 Turbo and was going to finish up the system with a custom turbo back to cat (the piping from the turbo including the flex). This is my first turbo car so can anyone shine some light on this, i'm used to extractors on NA cars at this point in the exhaust. Any experiance with power gains, flow gains, noise that can be shared is appreciated.

Thanks -
 

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With most turbo cars overall, the section of pipe directly after the turbo is one of the most important to upgrade.

Sure a 2-1/2" exhaust and cat is a good thing to have, but without at least the same size turbine outlet and downpipe you won't get full benefit.
How much of a benefit depends on many things, but about 10hp would be good.
You'll get a bit more mellow sound and it'll be a bit louder due to the thin walled tube.

Now the problem is that getting an exhaust shop to make you an outlet will cost you a packet ~$300 (search the forum for Zebel housing to see what's involved)
If your handy and have some resources for plasma or LASER cutting and welding you can make one yourself for about $100.

The hardest part is that the first bend of the outlet needs to be very tight to miss the A/C compressor.
There's a couple of ways that you can get around that such as;
-pie cutting and tuncating a standard 2-1/2" mandrell bend "U"
-Or using a very tight radius 2-1/2" donut
-Or using a 2"NB x 90° SRBW cast steel pipe elbow (Weld-ell) and then a 2-1/2" x 45° mandrell bend.
Right now your thinking that the 2" pipe elbow would be a restriction, well not really since the turbine of the stock turbo only has an exducer diameter of 45mm.
 

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You want the proven results

From the turbo to the Cat = Nothing.

I got NO Gains from going bigger there.

The gain is - NOISE.

I originally had fromt factory dump -which unless your upgrading turbo will flow more then enough period. waste of money to change.

now you can only fit 3 bolt flange and 2.75 or 2.5inch pipe to it.
I ran 2.5inch - all the way - standard 2.5inch cat etc luckey semi baffle muffler.
Noise low over all

car pulled 165HP from wheels in 2000

In 05 - I fitted from 2.5inch bend under sum 3inch flex - half biscut cat - Now illegal but think well open pipe 95% 3inch mandrel and 3 hot dogs resonator.

175Hp and reall top end difference. Down side - 125DB and I had to see EPA - several years latter.

Now - no noise - NO top end pull.

It's a choice thing.

No real gains replacing the factory cast dump especially if you feeding a muffler.

Open pipe is the only way to gain.

I mean I new I gained - no other changes still tuned with unichip at the time 12psi and stock the rest.

once you go above 2.5inch in pipe Diameter you have to fit a very restrictive muffler to keep noise legal or at least make EPA in NSW. Even then if you feed one a 3inch pipe setup into muffler with mid to stock sized turbo It's very hard to keep it down.

IMO - you gain better with more even by keeping it 2.5inch from factory dump to the rear.


Plus unless you have Tuned ECU to get the most out of the top end gain of a open pipe setup. You proberly won't get the full potential.
 

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The moral of that story is, don't use half biscuit cats and hot dog resonators and expect your car to be quiet.

Thanks for the lesson in the obvious Rod.


In all honesty your opinions do not follow the experience of mosy owners who have fitted an upgraded outlet and downpipe.
Though most of their comments regarding this are highly subjective, no back to back dyno test results, but what do you expect?

So from what I gather from your experience is that further reducing the exhaust restriction gained you about 10hp (and probably a lot more in the midrange)
Sure, you poor choices of cat and so called mufflers caused you car to be illegal.

Now this may also be the case for Intercepted_TX5 what with his 100cpi cat.
But if his muffler has a decent amount of sound adsorbing material (unlike a hotdog resonator or cannon muffler) he should be a lot closer to legal DB limits even after upgrading the outlet and downpipe.
Or perhaps even 2 full size mufflers would be required (1 after the cat and 1 at the rear) but thats really not uncommon.

Plus, I'm sure he will get around to a turbo upgrade in time ;)
 

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once you go above 2.5inch in pipe Diameter you have to fit a very restrictive muffler to keep noise legal or at least make EPA in NSW. Even then if you feed one a 3inch pipe setup into muffler with mid to stock sized turbo It's very hard to keep it down.

IMO - you gain better with more even by keeping it 2.5inch from factory dump to the rear.


Plus unless you have Tuned ECU to get the most out of the top end gain of a open pipe setup. You proberly won't get the full potential.
I have 3" turbo back with no cat, no resonator, and a straight through magnaflow muffler. Before I put it on, the factory exhaust was broken right before the gas tank. The car got quieter when I put the exhaust on.

Also, the car definitely had more power. Quicker boost response, faster spool, and more top end. Without question. I think what it boils down to is that if you use nice shit, it makes more of a difference. If you use the pepboys special, hot dogs resonators, whatever the hell they are anyway, your upgrade will leave something to be desired.
 

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The dump pipe is the most restrictive thing with a standard rear housing turbo. If you can, get one of these dump pipes. Not sure if the guy is getting them made, but if he does, get one!

Going any bigger than 2.5" on the standard turbo setup is pointless in my opinion, unless you intend on upgrading the turbo down the track. 2.5" will outflow the stock turbo without any issues. A 2.5" crush bent system was enough for my old T25G setup to make 170kw atw, so it's got plenty of flow for the tiny stocker.

A front pipe in 2.5" from the dump to the cat wont cost much, even if it is made up with mandrel bends, as there is only 1 90degree bend in it.
 

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Trying to fit a 2.5"dump and keep your a/c is where things get interesting.
 

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Discussion Starter #8
Thanks for all the answers and advice everyone. I actually don't mind pissing off the AC all, it only reached 47c last summer..haha. I've heard of people removing the AC alltogeher is much involved in that? In response to upgrading my snail a bloke at work jut got me a WRX turbo which I highly doubt will fit. As i'm new to the F2T what are some suggestions in regards to turbo upgrades? I know of the VF range and thats all. Surely it's not just 'bolt on and go' I imagine ECU tweaks, injectors and a trans cooler is in order, not to mention a new cooler set up. Please advise :)

Thanks all
 

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Hi All,

CXan anyone give me a lead on a new or guaranteed good used TUBO for my 1985 TX5 TURBO car. I imagine a MAZDA unit would be exactly interchangeable for (at least) the same year.

Thank in advance.

Dan
 

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You might be struggling to find one of those.

Those cars were rare even when they were new. The good thing is that the VJ11 off the 2.2L AT/AV Telstar and GD 626 is a close fit and reasonably easy to come by compared with the VJ4/VJ5 from the earlier models.

The dump pipe though is a five bolt turbine housing flange and the engine pipe is a three bolt flange so you would need an exhaust shop to make an adapter
 
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