Advantages of 3 inch vs. 2.5 inch?

[amp9211]

I was just wondering how adventagous using a 3 inch turbo back exhaust is instead of a 2.5 inch exhaust. I want to upgrade my exhaust, but am trying to cut costs to get other stuff done to it. I know it would save me some money by doing a 2.5 inch, but is it worth it??? Also, since I want to do this, is there anything else I should go ahead and get done with the exhaust while I'm down there?

Thanks!

 

[ProjectTalon130]

I also wanted to do a bigger (3") piping from the turbo back in SS, but a friend of mine said he knows a guy that did it with his DSM and he regretted it from going 2.5" to 3" b/c he got nasty lag low end and didn't kick in until very high on the RPM's, anyone notice this or can put some truth/light on the subject? would this only happen with a stock turbo/manifold?

 

[vertGST]

with no restriction the turob should spool faster not slower. i simply unbolted my downpipe and the turbo spooled fast as shti and i got boost spike like hell.

Brendon

 

[deusxmachina]

2.5" mandrel is plenty for around 400hp. If you're going to make more than that, get 3". If you're going to make less than that, then take your pick. One thing of note, however, is 3" downpipes can be a tight fit. A 2.5" downpipe and 3" catback is often the best of both worlds.

And there are different grades of stainless just as there are different grades of aluminized. The old HKS muffler was stainless and rusted out in a couple years. Meanwhile, the non-ss 3" cheapo pressbent exhaust on my first Talon is still just fine in the snowbelt after five years or so.

 

[doug]

Originally posted by deusxmachina
2.5" mandrel is plenty for around 400hp. If you're going to make more than that, get 3". If you're going to make less than that, then take your pick. One thing of note, however, is 3" downpipes can be a tight fit. A 2.5" downpipe and 3" catback is often the best of both worlds.

Werd.

Originally posted by vertGST
i know doug is gonna jump in this thread sooner or later

Bite me.

 

[ozzeran]

You guys do know mustangs run about 500hp with 2.5 inch exhausts? Doesn't matter if you have a turbo or not. 2.5 is plenty. 3 inch is just stupid on cars under 500hp. It's kind of a ricer mentality to have a bigger exhaust pipe.

 

[a_scobel]

Hmmm another monkey wrench...will a 3" exhaust always be deeper (sound-wise) than a 2.5" exhaust, given the same amount of power??? Or is there pretty much no difference??

 

[kraka]

You guys do know mustangs run about 500hp with 2.5 inch exhausts? Doesn't matter if you have a turbo or not. 2.5 is plenty. 3 inch is just stupid on cars under 500hp. It's kind of a ricer mentality to have a bigger exhaust pipe.

Are you sure you know what you're talking about?? There is a huge difference between v8 mustangs and 4 cyl. DSM's...3" exhausts are not ricer and are most definitely not stupid on cars under 500hp...There is no way you will get anywhere near the 500hp range on a DSM without a 3"...well, unless you just unbolt the whole thing completely and run without any of the pipes...but to help out amps question, go with the 3" catback/2.5" downpipe combo to stay safe and run well. I still think you should just get a full 3" turbo-back but at the first stages in modding, it is definitely not needed...
-Btw, if you don't have a big budget then why are you planning on paying a guy to intall the exhaust?..thats going to cost you an additional $45+ anyway...Just do it yourself; that way you saved money and you become more familiar with your car

 

[out there]

get a 2.5" press-bent exhaust and dyno, then use a 3" mandrel bent and dyno again, i'm quite sure that you will see a big difference (assuming everything is the same on the car for both runs)
your idea isn't very sound. turbos need as little restriction as possible to work the best, so the best exhaust is a pipe the size of the exhaust housing exiting the engine bay(hence the reason that most drag cars have big pipes on the side of the engine bay)
also using your logic, a v8 with 2.5 pipes (keyword: pipes) is roughly equivalent to a 4cyl with a 3.5" pipe, because the total area of the exhaust of two 2.5" pipes is about 9.8in-squared.
using fuzzy math, a v8 producing 500hp is two 4cyl's producing 250hp, each with a 2.5" pipe. so a turbo 4cyl making 250hp (a little than what your car is making now) would want a 2.5" exhaust, you are accurate there. however, to go beyond that area, you need to have the ability to flow more air, and the next step is generally 3", which is good for 500-600 depending on who you talk to.
i may have missed something, but i believe my point is made

 

[mntalon_05]

the guy building my car is makin me a 2.5" exhaust and said on a lightly modded car the EGT sometimes doesnt get hot enough to get the o2 sensors out of warm up mode when using a 3" exhaust and that you need some kind of air correction computer like an AFC to lean out the mixture enough to heat it up. Any truth to that? the guy has a lot of building knowledge, but his son does most of the tuning and reccomended that people going with smaller turbos shouldn't go with anything larger than 2.5". I'm going with a 16g so I'm going with his 2.5" turboback now cuz I'm gettin it done for cheap, but may upgrade next summer if I find that it's constricting too much, I'm on a pretty tight budget just getting the car finished right now.

 

[ozzeran]

get a 2.5" press-bent exhaust and dyno, then use a 3" mandrel bent and dyno again, i'm quite sure that you will see a big difference (assuming everything is the same on the car for both runs)
your idea isn't very sound. turbos need as little restriction as possible to work the best, so the best exhaust is a pipe the size of the exhaust housing exiting the engine bay(hence the reason that most drag cars have big pipes on the side of the engine bay)
also using your logic, a v8 with 2.5 pipes (keyword: pipes) is roughly equivalent to a 4cyl with a 3.5" pipe, because the total area of the exhaust of two 2.5" pipes is about 9.8in-squared.
using fuzzy math, a v8 producing 500hp is two 4cyl's producing 250hp, each with a 2.5" pipe. so a turbo 4cyl making 250hp (a little than what your car is making now) would want a 2.5" exhaust, you are accurate there. however, to go beyond that area, you need to have the ability to flow more air, and the next step is generally 3", which is good for 500-600 depending on who you talk to.
i may have missed something, but i believe my point is made

Ok yes turbos need little restriction but what kind of loss in torque are we taking about on 3 inch exhausts? I mean down low just city driving. You don't want to struggle to move. If 3 inches on our cars don't do that then yeah i guess it's fine.

 

[dmak]

i want to know y no one would run 3"dp and 2.5 or 2.75 exhaust ??

What i heard from others are, gas will cool down whent it exit the engine/turbo.
So after the dp, the same gas would take up less space.....would means dont need as big as an exhaust.

everyone understand this right?...I just don't know what's the point of 2.5dp and 3" cat-back.

 

[90TSIAWDTALON]

amp started this thread more than a year ago, im pretty sure he now has the exhaust of his choice, be it 2.5 or 3 inch.