True 3" Downpipe/Full exhaust available?

[Cap1]

I've been searching for a true full 3" exhaust from the o2 back... and I've yet to find one. Almost all of them have a 2.5" section before the flex pipe. I've always been told your exhaust is only as big as the smallest section.. so I don't get why they call them 3" when it's actually a 2.5". Anyone have a TRUE 3" downpipe thats 3" from the o2 housing back? If so, where did you get it?

Thanks -Cap

 

[Bender]

Order an ebay special, cut off the tip, and weld on a 3 inch flange, and a couple inches of 3" stainless piping. Check local exhaust shops for the 3" piping, or have them do the welding for you if you cant weld.

 

[deflator]

Buy a 3" muffler and maybe a resonator and get an exhaust shop to make the rest. I bought a Megan N-1 muffler for $90 and a bullet muffler to use as a resonator for $45, and the shop welded it up for $150. Looks great, perfect fit, sounds nice quiet and deep, and was only $300 total.

 

[S_Ranger]

So the muffler shop can make the downpipe?

 

[deflator]

So the muffler shop can make the downpipe?

Sure, I went to a shop I know and trust, and they made me a downpipe, 2.5" to the flex section, 3" after that.

 

[S_Ranger]

^
What's the purpose of the flex? And how much did they charge you?

 

[deflator]

^
What's the purpose of the flex? And how much did they charge you?

Its so the downpipe doesn't snap when you hit bumps. They charged me $120 to weld it up and like $30 for the pipe sections they used. I provided a muffler and resonator.

 

[chaclark83]

my megan came three inch all the way.

 

[mhuffman]

i dont think youll notice the short section of 2.5". itll act as a throttling valve in thermodynamic terms and they're might be a little pressure loss but i bet it isnt noticeable.

 

[pboglio]

I've been searching for a true full 3" exhaust from the o2 back... and I've yet to find one. Almost all of them have a 2.5" section before the flex pipe. I've always been told your exhaust is only as big as the smallest section.. so I don't get why they call them 3" when it's actually a 2.5". Anyone have a TRUE 3" downpipe thats 3" from the o2 housing back? If so, where did you get it?

Thanks -Cap

Megan has one that is 2.75" at the flange then expands immediately to 3" all the way thru.
Unless you need 3" at the 02 housing, this as good as it gets.

 

[Mr Peepers]

The o2 housing outlet is ~2.5" anyway. With a 3" DP flange connecting to the o2 housing it will have a step, hurting flow more than helping. Most will have 2.5"-3" in a smooth transition which is exactly what you want(should want).

I don't see an aftermarket o2 housing, that would change the story a bit. If the o2 outlet was 3" then by all means go with an immediate 3" DP.

http://www.tercelreference.com/tercel_info/turbo_exhaust_theory/turbo_exhaust_theory.html

Directly from the article:
"There's more to it, though-- if a larger bellmouth is excessively large right at the turbine discharge (a large step diameter increase), there will be an unrecoverable dump loss that will contribute to backpressure. This is why a gradual increase in diameter, like the conical diffuser mentioned earlier, is desirable at the turbine discharge."

 

[deflator]

i dont think youll notice the short section of 2.5". itll act as a throttling valve in thermodynamic terms and they're might be a little pressure loss but i bet it isnt noticeable.

From the info I received, I came to a similar conclusion. I was told that the exhaust gases are hot enough in the first 24" or so that you can get away with 2.5". I went with that since I bought a 2.5" Megan O2 housing.

 

[S_Ranger]

Is sound pretty good?

 

[mhuffman]

I also have the megan 3" downpipe. It has a pretty smooth transition from 2.5" to 3" at the o2 housing. It's a very nice part.

 

[Mr Peepers]

Is sound pretty good?

I'm assuming you were talking about the DP that the shop made for deflator.

A 2.5" to 3" mandrel bent downpipe will sound the same no matter who makes it. Pipe is pipe. Just make sure the transitions are smooth and that there is a flex section. The flex section is there because the exhaust system moves when the engine revs or is under load, it keeps the exhaust system from seeing this torque, especially the manifold(cracking).

 

[mhuffman]

I also have the megan 3" downpipe. It has a pretty smooth transition from 2.5" to 3" at the o2 housing. It's a very nice part.

 

[Cap1]

I have an SLS o2 housing... parts list updated

 

[Cs4g63]

Its so the downpipe doesn't snap when you hit bumps.

I thought for sure the purpose of the flex section on the downpipe was to allow for movement due to the movement of the engine.

 

[gsxAWDdsm692]

If your only running the turbo you got (EVO III) then you should be fine. That extra half inch from the O2 housing to the flex section isn't going to give you nothing noticeable. For a bigger turbo then yea you should try and find a bigger downpipe.

 

[Cs4g63]

If you want a downpipe with nothing but 3 inch pipe than check this one out. It eliminates the o2 housing and is 3 inch with no neckdowns.
http://www.forcepower.ca/
Click on the products section and it will take you right to it.

 

[andy4g63]

Yes there is a true 3" downpipe.I have it on my car.It is 3" from the O2 housing.Of course you must have O2 housng that will mach the downpipe,at least the flange,because is for 3" pipe,not 2.5".It is gonna misalign with O2 housing/ the holes on the flange will not mach with 2.5" flange/.You need either evo3 O2,or something similar/in size/.If you are ready with that you can call VRS exhaust/the web site is the same/,and order yours.Because they don't make it standard,the downpipe will come in two pieces,so you have to weld flange on top and that 90* piece to the flex section.I know if you can't weld is gonna cost you few more dollars,but is definitelly worth it.

 

[mhuffman]

I thought for sure the purpose of the flex section on the downpipe was to allow for movement due to the movement of the engine.

I'm sure it helps with both, but if the car is any good the suspension absorbs most of the bumps and the rubber exhaust hangers do the rest. i imagine the flex joint is there mainly for the engine movement part of things.

 

[deflator]

I'm sure it helps with both, but if the car is any good the suspension absorbs most of the bumps and the rubber exhaust hangers do the rest. i imagine the flex joint is there mainly for the engine movement part of things.

Well, wherever movement comes from, its there to prevent the downpipe from snapping. Not something you want to go without.

 

[TSiAWD666]

VRS Exhaust told me that if you ask them to keep their downpipe a full 3" they will make it that way, as their downpipes can be made to order. If you paypal you would need to put this in the notes of your purcahse.

I personally went through the trouble of asking them this. I then proceeded to forget and leave it that part out of my order details and am now having a shop cut that 2.5" neckdown out hehe. doh!

 

[hallperson]

on my gsx i run a hahn racecraft 3 inch o2 housing and 3 inch downpipe piad like 450 for it it is true 3 inch