Upgrading Exhaust, need real answers

[97TSIAWD]

Okay, well currently the car has a Buschur 2.5" dp, and a Greddy 60mm cat back with test pipe. I know the Greddy is kinda small. The turbo is a small16g turbo, and the car amazingly has run a fast time with this setup, look to the left. Anyways, I'm planning on upgrading the exhaust because I think I might be able to get a few more hp, and maybe a whole tenth at the track. I have read and seen that possibly upgrading to a 3" mandrel bent catback would give me the hp and tenth that I am looking for. Now exhausts are always tricky to get right, especially with a turbo car. My father who races the TTAs with me, insists I don't need a full turbo back 3", that the 3" dp isn't really going to help and in reality will either net no gains or even harm the performance. My question is what should I do, based on real world knowledge of flow and so forth. I will probably be upgrading to a Evo3 b16g eventually, since I want a bigger turbo and it is still a daily driver, this seems to be the best and would yield me an 11 second timeslip hopefully. Anyways, considering that Iam probably going with that turbo later on, should I upgrade to a 3" catback since I can see the benefits now with the small16g and then upgrade to a full 3" when I get the Evo3, or upgrade the whole turboback now because I won't lose any potential from the car? Thank you for you help guys.

 

[Lunch_Box]

My understanding is that turbo cars don't like back pressure so a free flowing exhaust would be better.

 

[97GS-TSpyder]

less backpressure means less bottom end also, and dont forget to adjust tuning if your going to do it

i had the 3" and gained a tenth on just a downpipe open dump. N1 downpipe, i swear by apexi. I love em. But its up to you, it cant hurt to free it up believe me.

 

[Quasimondo]

Maybe your father is thinking with a n/a frame of mind, even though he has a TTA, because what he says would apply to n/a cars, where if the exhast is too large, the escape velocity of the exhaust won't be enough to produce a scavenging effict that helps draw in fresh air during the intake & exhaust overlap.

With that said, such a principle wouldn't apply to forced induction engines and the general rule of thumb is the more flow, the better. You'll get a bump in the top end, especially if when you switch to a B16G (I recommend the Evo III 16G instead) and you use a 7cm exhaust housing on the turbo, along with a full 3" system.

The only thing that might suffer is your spoolup, but with a turbo like the 16G, any increased lag won't be noticable.

 

[91 white tsi]

What O2 housing are you using? If stock i think a 2.5 or 3 inch O2 would deff bump you into the 11s. it would do lil good to run 3 inch on a stock O2 and i think with 2.5 and an aftermarket O2 you would notice major gains. I am currently getting a full 3 inch including O2 for my talon. It is a custom job but i cant find any shops around me that manderal bend so i hav eto go with press bend :thumbdown but with labor and parts including high flow cat and a cut out in the DP its going to cost me 450$ or less so if you did something like that but got madral you might be better off

 

[97TSIAWD]

I am running a ported stock O2 housing currently. If I would upgrade to a Evo3 16g I was planning on probably going with the Evo O2 housing as well as I heard that the dp will twist slightly if you don't use the Evo housing, I think it was on RRE site that I read upgrading the O2 is a good idea. Not sure that if I upgraded the exhaust before the turbo that I would do the O2 also, I think that is more of an upgrade to compliment the turbo upgrade. Quasi, I'm not sure where my father is coming from on this one. He has been racing for many years, 70's and his original car was 69' GTO running 11's. Now we have had the TTAs for many years and we have cutouts on the cars but never use them since my father thought the 3" on the cars was perfect. Funny story once at the track the catback popped off at the cutout, bolt broke or something and the car ran the fastest it ever had. I thought that would prove to him about free flowing exhausts. Anyways, so you think that a 3" catback for now until the new Evo3 turbo would be beneficial? Then upgrade to the dp later with turbo/o2 housign? I could go for the complete exhaust, but as stated it looks like you guys are saying I will lose a little low end but gain a little up top, would this also be true for the small16g that I am running now, until I upgrade the turbo later of course. Thanks guys, I think this thread could be real helpfull to others also as long as we keep giving good info and not just opinion (although opinions in exhausts brands are always welcome, I agree that the N1 is a great system, my brother has one on his turbo spyder)

 

[91 white tsi]

im not to sure what you were saying about the O2 complementing the turbo not the exhaust. From what i understand it will help you spool faster with a better flowing O2 and with a restrictive O2 how can exhaust help. The exhaust has to pass thru the O2 before getting to the Down pipe so if it isnt free flowing then your free flowing exhaust wont be as benifical. its kinda going from a 2inch exhaust (the O2) to the Dp whatever size you have. so why not make it all the same and gain spool time from what ive read. that should help your bottom end since you hit boost sooner and help flow the exhaust better on the top. correct me if im wrong but thats the sense im making of it

 

[97TSIAWD]

im not to sure what you were saying about the O2 complementing the turbo not the exhaust. From what i understand it will help you spool faster with a better flowing O2 and with a restrictive O2 how can exhaust help. The exhaust has to pass thru the O2 before getting to the Down pipe so if it isnt free flowing then your free flowing exhaust wont be as benifical. its kinda going from a 2inch exhaust (the O2) to the Dp whatever size you have. so why not make it all the same and gain spool time from what ive read. that should help your bottom end since you hit boost sooner and help flow the exhaust better on the top. correct me if im wrong but thats the sense im making of it

This is what I was referring to from RREs site.

If you already have a 2.5" DP with a slotted flange, it is _possible_ to bolt it up to an EVO O2 housing. Usually it will stress the flex section too much so it should be considered a temporary solution only. We include a larger flange and also the larger inlet and DP gaskets with the O2 housing to make things easier for you.

So I would like to either get the o2 housing once I upgrade to the other turbo, or add it in addition with a 3" dp. Instead of just buying it an adding it to my current dp. I can see how a better flowing o2 housing will help, but I don't think the gains are going to be so extreme that it is necessary to put on on immediately, because mine is already ported, although the price for one is no exactly steep so I could see getting one sooner then later.

 

[97TSIAWD]

So I did some more research and it seems like I might be able to build my own exhaust, mandrel 3" and have my uncle weld it. I was wondering everyone's thoughts on this muffler from slowboy http://www.slowboyracing.com/more.php?id=1465&, it's a 109 dollars and is 3". Here is a picture of it, I actually like this design better than the mellon shooters like the N1 although I like that system over all. Let me know what you guys think, I'm going to search the internet and look up some specs on it, although it seems like a 3" in muffler is a 3" muffler there shouldn't be too much difference between brands.

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[Shadowfax]

So I did some more research and it seems like I might be able to build my own exhaust, mandrel 3" and have my uncle weld it. I was wondering everyone's thoughts on this muffler from slowboy

I am putting 3" O2 back on my 14B, running a Magnaflow single 3" in, dual 2.5" out - I have a thread called "definative 1st gen FWD exhaust thread" I listed the part numbers there. I think building your own exhaust is a better idea

Now on to what size and why...

Spoold U's 98 GS-T runs 106mph traps on 93 pump on a 14B- with a stock 2nd gen O2 and 3" downpipe/catback, with stock 450's and a 190lph. I know you're 8mph, but you've got a good bit more flow. The point is that for a lightly modded 14B car, that's hauling.

I see a lot of guys say 2.5" exhaust is all you need, but I've never known one car making 300HP+ that didn't NEED dual 2.5" or a 3" (basically same flow). Mustangs, LS1's etc, all run dual 2.5's or a 3" (98 ls1 SS and WS6) - and they are all in the 300's for HP (you know what I mean).

Most of the exhaust shops I've dealt with said 250-400/450ish WHP can run 3" worth of flow and be in okay shape. You start heading up past 450WHP and you'd gain from 3.5" worth of flow. A lot of the 450-550WHP big block cars I've dealt with run dual 3" which is a bit more flow that 3.5" (20% increase in pipe diameter = 100% flow increase- IE- 2.5X1.20=3" and 3X1.20=3.6" basic rule of thumb - which is general, not flawless)...

long and short is that regardless of the size of your motor (displacement) the airflow is the key, and if your turbo is pulling in enough air to make XXX power, then you need exhaust sized for that power.

 

[97TSIAWD]

Yeah, as I said I really like the way that muffler looks, hopefully it has a nice tone to it as well. As for the exhaust, yeah I decided that I might try to build one since it isn't that hard and I should get if I use the right bends the same kind of flow as a bought full exhaust. It seems that the general consensus is saying 3" all the way, as it will not hurt performance but improve it over the 2.5". That sounds great, and I'll be looking at upgrading shortly. Now I need to go buy the parts, either piping to make the exhaust or a built one, haven't decided completely yet.

 

[me612]

Just wanted to chime in about your EVO O2 statement. The downpipe fitment deals with the O2 Housing, not the turbo. The EVO O2 housing is angeled slightly differently, which causes a problem with the downpipe. Whether it is a EVO O2 housing on a regular 16g, or Evo 16g, doesn't matter. To avoid the downpipe issue, just stick with your 2g housing, or go with a mandrel bent aftermarket one.

And about your exhaust system, just get a full 3" system. Don't worry about the backpressure issue. For our vehicles, you want freeflowing exhaust. So I agree that a 3" system will benefit you over a 2 1/2.

 

[97TSIAWD]

Just wanted to chime in about your EVO O2 statement. The downpipe fitment deals with the O2 Housing, not the turbo. The EVO O2 housing is angeled slightly differently, which causes a problem with the downpipe. Whether it is a EVO O2 housing on a regular 16g, or Evo 16g, doesn't matter. To avoid the downpipe issue, just stick with your 2g housing, or go with a mandrel bent aftermarket one.

And about your exhaust system, just get a full 3" system. Don't worry about the backpressure issue. For our vehicles, you want freeflowing exhaust. So I agree that a 3" system will benefit you over a 2 1/2.

Yeah, that is what I was reading from RRE site. The thing I was saying was, I wouldn't get the o2 housing because mine is ported and unless I went full 3" dp and all, which it looks like I'm doing now. Instead I was saying that I would possibly go the Evo O2 housing was if I would get an Eb16g, if it would benefit that turbo at all, but it seems that a ported 2g is almost just as good.

 

[knappstaman]

backpressure??? BAH!

backpressure is the worst thing possible for turbocharged cars. Go with the 3 inch DP and exhaust, with a straight through muffler design, this would yield you with the most power gains. For the muffler id prefer magnaflow over any due to their Stainless steel straight through design. Over on the cougar boards theres always talk of backpressure and the negative effects on larger exhaust for N/A Applications, its true for an N/A car larger exhaust can hurt performance, but taht isntdue to backpressure, but other factors such as scavaging and velocity which we wont talk about now. With todays modern cars(fuel injected)... backpressure is not needed, and is a thing of the past unlike carbuerated cars or 2 strokes.

What do you think is the main cause of backpressure in a turbocharged car? A turbocharger. To some of you guys who are either noobs or dont know, yes, a turbo is the greatest cause of backpressure on your car. Just look at it this way, you have an exhaust manifold coming off of your head, and within 5 inches of the manifold, the exhast gas is flowing into the turbocharger compressor which merges the 4 exhaust ports down into opening the size of a few Millimeters. This is how they work, they compress the exhaust to then intern basically compress the incoming air connected by a shaft, so yes go with a 3" i think you will see a better gain getting the exhaust out with larger tubing. Besides the way i look at it, with a turbocharged car 3" should be the minimum size piping.

Thanks for reading all this info, if you actually did

 

[Bostedquest]

What O2 housing are you using? If stock i think a 2.5 or 3 inch O2 would deff bump you into the 11s. it would do lil good to run 3 inch on a stock O2 and i think with 2.5 and an aftermarket O2 you would notice major gains. I am currently getting a full 3 inch including O2 for my talon. It is a custom job but i cant find any shops around me that manderal bend so i hav eto go with press bend :thumbdown but with labor and parts including high flow cat and a cut out in the DP its going to cost me 450$ or less so if you did something like that but got madral you might be better off

look on ebay and buy the bends there...
I get all my stuff through vertexnow... good prices, all 304 stainless, all mandrel bent. I did a 2.5" transition to 3" DP and a full 3" back for like 120 in tubing and bends for a car. Not including muffler or resonator...

 

[91 white tsi]

Yeah thats what im doing except i cant find a shop to madrel bend around here but i got a 3 inch high flow cat the magnaflow 3 inch in 2.5 dual out and 3inch cut out and full 3 inch piping plus 2 o2 bungs 15 3inch flanges and the O2 flange for a custom 3inch O2 and i have spent $248.63 shipped to my house. just waiting on some shop to bend & weld it

 

[97TSIAWD]

A few more questions. How necessary is a flex section? It will cost more to put one on the exhaust, and I was wondering how important it was. Also, what are your views on instead of upgrading the O2 housing, I go with an eliminator kit? Do I gain anything from that, or should I stick with the 2g ported o2? Also, I found a Magnaflow muffler, similar to the one I posted already, the 3"in and out. Are all the magnaflow mufflers the same, that one is listed at 109 at slowboy and I found one for 90 on another site. Not sure if they are all universal or if one would be better then the other. I'll try to get part numbers so I can put those up for comparisson. Thanks guys.

 

[mntalon_05]

without a flex section your downpipe will crack in no time, I'll give it 3 weeks

 

[97TSIAWD]

without a flex section your downpipe will crack in no time, I'll give it 3 weeks

Flex it is.