Advice on exhaust setup, 2.5 or 3?

[jumpfroggy]

I have a 95 TSI stock, looking to go 16g/T28. It's going to be a fun daily driver with good spool and good pull in the midrange. Car will never see a track (unless it can learn to swim, no tracks on island), just looking to learn how to wrench, tune (going DSMlink probably), and get ready for probably a GSX in the distant future.

The stock exhaust was pulled off (as in, someone lowered the car until a speed bump helped remove the exhaust... forcefully) and has been replaced with a locally-made "2.5" catback exhaust with a 5zigen straight-through. It was crush bent, so the bends (especially the one going over the rear axle) narrow down quite a bit.

I'm planning my upgrades and have a chance to get an exhaust setup now. I've gotten some advice that for <=300 hp, 2.5 is sufficient. I have the opportunity of getting an old RSR 2.5 catback, and I was thinking of adding in a 2.5 downpipe/cat elminator (like in http://www.dsmtuners.com/forums/showthread.php?t=217631&highlight=ebay+downpipe ... I know, ebay). I want quiet but hopefully without choking performance when I upgrade. Power is not the ultimate goal, although I'd like to have more . More important is streetability and fun.

Just checking on advice from others. Here's some things I'm wondering, I'll just type them all out and let others pick and choose...

-I've heard good things about RSR. Any opinions?
-Everyone says go 3" for performance. If I know I'm not going to upgrade too far, would 2.5" be sufficient?
-I assume FWD and AWD use different downpipes (looked at RRE's photos, one bends more).
-Would a 2.5 downpipe be a good increase over the stocker? Last I looked, the stock seemed kinda small (can't tell under all that heat shielding, etc).
-Would a real 2.5 mandrel be noticeably better than the 2.5 crush bent?
-Any thoughts on an RSR Muffler vs. the 5zigen?

I apologize for the length of all this. I try to read as much as I can without asking questions (to see if I can't answer them on my own) so I end up with lots of unanswered bits, and it's all coming out at once. Any thoughts and opinions appreciated.

Summary: I want to get a 16g eventually and tune a bit. Will a 2.5 downpipe, no cat, and RSR 2.5 catback be quiet and flow well?

 

[500hpgsx]

do the mandrel bend not the crush for flow reasons ive herad aolt of good things about the rsr not alot on the zigen

 

[SBstar]

You seem pretty set on "quiet" so I suggest the 2.5". My Buschur mandrel bent 2.5" was by no means loud so I think that would be best for you. On a turbo car (forgive me if YOu already know) the whole backpressure=torque thing (which is debateable on all cars anyways) doesn't apply so in essence the larger the exhaust the better the flow (although you can run into things like boost creep). The mandrel bent tubing will flow much better then the pressbent. Now will you notice the difference? I"m not sure I haven't run both. I would guess the difference on the butt dyno would be minimal but I'm sure the car won't complain. If you don't plan on going further then a 16g the 2.5" should be fine, I would suggest porting the turbo for fear of boost creep (for some reason 16G's seem to be notorious for it with larger exhausts). Either way it is a great improvement over the stock exhaust. happy boosting
Edit: holy run on sentence...

 

[brute]

I have a 2.5" downpipe into a 3" high flow cat and 3" back from there. If you want quiet, just get as big as you want. I suggest the 2.5/3 combo like I have. The high flow cats have been dyno proven by some local guys to not decrease horsepower or torque even the slightest. I have a cat and a muffler on it, and it's not loud at all (unless you get up into the 4k and above range). Like SBstar said, the bigger you go, it doesn't matter. Go as big as you want. But like I said, I suggest the 2.5" downpipe - 3" catback solution.

 

[somdturbo]

Go big or go home. 3" all the way.

 

[brute]

Go big or go home. 3" all the way.

WTF Yea, and while you're at it, get some 26" wheels, a 5.0L, 4 turbos, and they all must be GT42r's or bigger.

This is a fine saying to live by in snowboarding, but not DSM's.

 

[SBstar]

I have a 2.5" downpipe into a 3" high flow cat and 3" back from there. If you want quiet, just get as big as you want. I suggest the 2.5/3 combo like I have. The high flow cats have been dyno proven by some local guys to not decrease horsepower or torque even the slightest. I have a cat and a muffler on it, and it's not loud at all (unless you get up into the 4k and above range). Like SBstar said, the bigger you go, it doesn't matter. Go as big as you want. But like I said, I suggest the 2.5" downpipe - 3" catback solution.

Compared to a full 3" (if you know) is it relatively quiet setup like this? I haven't compared them so I wouldn't know. I know the 3" I had on my first car was loud and the 2.5" on the one I have now was very quiet by comparison. Combining the two might be the happy medium. And like I said on a turbo car the bigger exhausts do not make you lose hp or torque at all, its all due to the turbo, I believe there is a good writeup either in the faq or the newbie tech section that explains it all.

 

[PieEyedPiper]

Compared to a full 3" (if you know) is it relatively quiet setup like this? I haven't compared them so I wouldn't know. I know the 3" I had on my first car was loud and the 2.5" on the one I have now was very quiet by comparison. Combining the two might be the happy medium. And like I said on a turbo car the bigger exhausts do not make you lose hp or torque at all, its all due to the turbo, I believe there is a good writeup either in the faq or the newbie tech section that explains it all.

http://dsmtuners.com/forums/showthread.php?t=168578

 

[jumpfroggy]

I know for my car if I want straight out performance I should go with a full 3" with a straight through muffler, or a 2.5 to 3 like brute said. But I know I'm not going to tune the car very much. I live on an island, all the speed limits are slow, there's always traffic, always cops, and they just shut down the only track on the island . So now I'm just concentrating on learning how to tune with some mild upgrades, and when I get my next car I'll go all out.

My main concern is how much of a match/mismatch a full 2.5 is with a 16g. Sounds like I could do it without too much of a hit.

If you don't plan on going further then a 16g the 2.5" should be fine

That's what I'm wondering.

Compared to a full 3" (if you know) is it [the 2.5 to 3 combo] relatively quiet setup like this?

Yeah, I wonder that now. Actually, with my current exhaust it has quiet a bit of very low note (no fart/burp sound, just low rumble) and at wide open it sounds... big. I just don't want it to get too much louder. The first DSM I drove was a 1G AWD full 3" with no cat and one of those coffee can mufflers. Shook the houses nearby, and you could hear it blocks away at open throttle. Fun, but not thanks, I have to live with my neighbors.

 

[SBstar]

Thanks PieEyedPiper! The 2.5" will fit perfectly with the 16G, would it hurt at all to go bigger? Nope not at all. Like I said earlier you seem worried about the noise so I would suggest going just 2.5", you don't seem like you need the fastest car on the planet and I think it would be plenty for you. Like I said wide open the 2.5" I had wasn't loud or obnoxious, the 3" definately was like you've said.

 

[kenamond]

As several have already said, decreasing exhaust restrictions doesn't hurt performance. Any increase in exhaust flow will help the turbine spool up faster and help with flow at higher RPM. Since you want street performance, the faster the spool, the faster the torque from boost. 2.5" would be fine, but you can find 3" for almost the same price - but it may be louder if you care. And the muffler is going to have the biggest impact on how loud you are.

Creep will probably be a problem with an E316G, so you may want to read up on that. If you want to do your upgrades incrementally, and you get the exhaust+turbo first, you'll probably struggle with creep. The solutions to creep are to either do a really good port job on your turbine housing, mani, and O2 housing, put an external gate on it, or run ~20psi boost.

If you choose the last option of running 20psi boost (the E316G will probably stop creeping around there - sort of a "live with it" creep fix), you'll also need supporting fuel mods and some form of control. If you're not going DSMLink right away to control larger injectors, FP, FPR, etc., then you'll still be stuck.

If you choose to port, you may still see some creep, depending on the quality of the port job, so that's risky, and can only be fixed by dropping the turbo for a second port job or reverting to one of the other options.

If you choose the external gate, you'll either need a compatible mani or a different O2 housing (depending where you want to put the gate) and a DP that can re-incorporate the dumped exhaust.

You might not have creep with a 2.5" exhaust, though. But if you do, what's your gameplan?

The FP B28 might be a better turbo if you're aiming for 300hp, considering the potential problems of the E316G and the streetability of the B28. But if you don't pick up that GSX and you catch the fever, the 16G will take you farther (not a bunch) in hp.

And that's my novel.

 

[SBstar]

Just a suggestion guys...read the actual posts above yours. Other then that you gave some good information Kenamond. The EvoIII 16G's do have the boost creep problems, however, they wouldn't be such a popular turbo if it was really all that bad. Most reputable shops that sell the turbo and do portwork for you will know of the problem, when and if you buy the 16G make sure you have them port it for you. But considering A. you didn't want the noise I would consider 3" out, and B. saying you didn't really want a speed demon, running 20psi would be out as well.

 

[jumpfroggy]

I think I'm going to go with 2.5, since it seems like it'll fit my needs (no further than a 16g/t28, on the quiet side).

I haven't thought much about boost creep, since it didn't seem to be as much a problem on the 2.5 exhausts. I would probably try a T28 with full 2.5 exhaust, and if I hit creep I'd try porting. If I still needed more, then I was thinking of going with an external wastegate on the O2 housing. That way I'd replace the stock O2 and get the wastegate, 2 birds with one stone.

And actually, I'm considering DSMlink as my first mod. Sounds crazy, I know, but I really have this fascination with measuring what I do to my car every bit along the way. Also, I figure that's one thing I can take with me to my next car (already have a replacement ECU), so it's better than buying a logger + afc and then turning around to sell it later. I don't like how the AFC messes with timing, I'd rather be able to tune it myself.

I was trying not to dump everything in this thread, but I might as well now. Here's my tentative list.

Have these:
free mods
cone air filter
autometer boost gauge
1g bov (not installed)

Planned:
EGT gauge
MBC
BigT28
DSMlink
Walbro 190
2.5 exhaust

Long term (may never get to these, except the injectors):
bigger injectors (550? 660?)
UICP/LICP
o2 housing
intercooler (supra or ebay FMIC)

Do you think boost creep would be a problem with a 2.5 exhaust, stock O2 housing? How about a ported 2g o2 housing?

 

[SBstar]

It seems like hit and miss with the 2.5" exhausts, sometimes it does sometimes it doesn't. If your buying the turbo new, like I said before, it never hurts to just have the shop port it for you. I would think the cost would be worth it considering how much of a pain it would be to find out its creeping and having to take it off and find someone to do it or have to buy the tools to do it yourself. DSMLink is a great first mod. I love it personally. I would never suggest starting to turn up boost or anything until you have something to log with, and dsmlink is just about the best piggyback setup you can buy. Make sure you check your ecu to see if it is eprom. Yes, I know all 95's were supposed to be eprom but you can never be sure until you check. The gauges are good. The walbro 190 I would suggest as your third or fourth mod (cone filter in there somewhere), along with rewiring it http://www.raktron.com/fuel/rewire1.html yes the link is from a Spyder but the same principles and process apply. The rest of your mods seem pretty good and thought out and compliment each other nicely. I'm not extremely familiar with the T-28 but with the 16G go all out and get the 660's if and when you do get injectors, you have the means to tune for them don't forget