Question on Exhaust with TURBO

[Redmofo]

I plan to order an exhaust this summer and a turbo kit in the winter. I was wondering if PPl with turbos are using 2.5" or 3" piping in their exhaust. I dont want to get 2.5 and creat too much pressure and then need 3". Thanks

[Topik]

my current setup is 3 inch turbo back until the muffler where it downsizes to 2.5 inch

[Redmofo]

THx
Has anyone ever used 2.5" on a turbo set up?

[Blackcoog]

I have a 3" setup here. I didn't have any troubles running it on my Cougar before my supercharger kit.

[20COUG00]

If your going to spend the money get a 3" all the way, 2.5 will be cheaper and easier but will cut you a few losses.

[SpookSVT]

Seeing how the turbine operates on a pressure differential, I'd go ahead with the 3", especially if the WG is recirculated. This will keep pressure lower downstream of the turbine.

[justa2pt5L]

I have a 2.5" SS setup and I plan on using it with the stage 3 from joey, but my WG wont be recirculated. I think I'll be fine and I plan on testing it out on the dyno by dropping the exhaust for a run or two. Depending on what your goals are and if you want to hear the wastegate or not will determine what size exhaust you need to run. If you're going all out with a built up motor, stage 3 turbo, and you dont want to hear the WG, then buy 3". If you are going with just a stock motor and a stage 1 kit, then 2.5" will work.

If you can wait to buy the exhaust till you buy the turbo, I'll have the stage 3 tested out with a 2.5" setup before it gets cold!

[Blackcoog]

With any FI you never want any back pressure and since the difference from getting a 3" over a 2.5" is almost nil always go with a 3" over a 2.5" for an FI setup. That isn't to say a 2.5" won't work but if you have a choice go bigger.

[justa2pt5L]

With that being said, I have to state that I bought the 2.5" before the turbo was offered. I was talking to Craig at KKO and he said the 2.5" will be fine with what I had for plans at the time, so I bought it. Well a few months later I met Joey along with my newly developed, never ending expense!

Yes, if I was to do it all over again, I would've bought the 3". But now I'll test out the 2.5" and if it decreases flow/hp, then I'll sell it.

[Blackcoog]

That will be really interesting to see the results. Make sure to post them up.

[Redmofo]

I was figuring 3" was the way to go but was curios if anyone had tryed 2.5 Def will need to see the the dyno wen u do it.

[foxslayer]

There is a thread over on CEG about exhaust size and all that with turbos. I have 3" down pipe that converts to 2.5" at the mufler too, but i have a WG that dumps the the atmosphere. A few other guys on CEG said that it shouldnt be a problem. We will see, but i will take a few losses in the hp/tq area, in order not to have to squeeze 3" exhaust all the way back. I already bottom out too much.

[gamiller]

I'm currently using a 2.25" SS Borla dual-exit exhaust. If I find it's a problem, I'll post here - and in the for sale forum!

[warmonger]

I have a 2.5" SS setup and I plan on using it with the stage 3 from joey, but my WG wont be recirculated. I think I'll be fine and I plan on testing it out on the dyno by dropping the exhaust for a run or two. Depending on what your goals are and if you want to hear the wastegate or not will determine what size exhaust you need to run. If you're going all out with a built up motor, stage 3 turbo, and you dont want to hear the WG, then buy 3". If you are going with just a stock motor and a stage 1 kit, then 2.5" will work.

If you can wait to buy the exhaust till you buy the turbo, I'll have the stage 3 tested out with a 2.5" setup before it gets cold!

You'll be fine.

the cross sectional area of the 2.5" pipe with 1/16" walls is about 4.43in^2
the cross section of a 30mm wastegate dumping a 1.5" tube is about 1.77in^2 totaling about 6.2in^2 total, not to mention the pressure for the wastegate dumping to atmosphere is lower than wastegate dumping to a pipe that already has pressure in it such as a 3" pipe.

A 3" pipe with 1/16" walls has a cross section of about 6.5in^2
Therefore 6.5" versus 6.2" with a higher pressure differential means IMO that I'll take the 2.5" with dump pipe any day over the sealed 3".
However, a 3" with a dump pipe will obviously flow even more with the same or lower pressure differential. :cool:
So unless you get a good price for your exhaust it is not worth it by this simple beer math used here.