Just real quick to settle something.

2.4 liter 4cyl 5k max RPM 135hp stock

5psi off a T3 turbo off a turbocoupe

Say it adds 50hp. Would 2inch exhaust be dangerously restrictive? Or would it just not be giving full potential to the setup.

 

135Hp + 50Hp = 185Hp

Running 2" on a 185Hp engine is like running dual 2" on a 370Hp engine. Sounds pretty restrictive.

 

Well hell it puts a monkey wrench in things. Back to the drawing board!

 

Many small displacement cars use 2" (or smaller) right from the factory. And thats with cats and restrictive mufflers. So you can defiantly say it's not dangerously restrictive.

IMO if you aren't installing a cat and use a turbo type muffler you'll be just fine. And although a 3" system may help you a tiny bit... I'd bet your money/time would be best spent elsewhere and just run the 2". I'd bet you'd gain more power running 2" and upping your boost a pound or two. Buy an intercooler, Better yet, buy and alcohol injection kit with the left over dough and run 10lbs. You'll forget all about that 2" exhaust.

 

Well here's the reason I wanted to do 2inch.

My muffler rattles now and needs replaced. Dynomax sells a muffler and tail pipe I can get at cost but it's only 2inch. So I guess I could and just fab a tail pipe, it will just suck going back and forth to the exhaust shop and I can't afford too much down time with this thing.

But I might have to take a week off work!

 

My dd is a 2.5L turbo and it started with the factory 2" exhaust on it. The backpressure at the turbine outlet was incredible at just the factory boost setting, it has been quite a while but I want to say double the boost pressure. Went to a 2.5" with no cat and a dynomax muffler and took off the Mitsu and put on a .60/.63 Garrett and a real improvement. Then I made a custom swingvalve and 3" exhaust and no measurable back pressure at 14 lbs but now have a creep issue with the stock internal gate. I would save the money and replace the 2" from the turbo back with at least 2.5", I think you will see a significant improvement. When I rebuilt the engine all 4 of the inconel exhaust valves had to be replaced because they were bent I believe this was due to the incredible heat this thing must have been dealing with using that tiny ass exhaust....kind of like a factory boost controller.

 

Alright. I think what the plan is now it cut the exhaust right after header hookup and right before tailpipe. Make an exhaust that is 2.5. So the exhaust will go, header, 2inch exh , connect to 2.5 piping and muffler, then back to 2inch tailpipe. This will be N/A, once I get all the turbo stuff hack off the 2inch and make a new tail pipe and down pipe.

 

I did a rear turbo setup on a car recently, and I learned alot about figuring sizes of pipes for distances and flow needs.
Depending how long you exhaust is total, say its only 5', with a turn down before the axle, you could get away with 2".(with no muffler)
But with a muffler, i would go to 2,25"
But say its 8' total lenght, from downpipe, to tailpipe tip, you would want to stick to atleast 2.25"
2.25" dosent sound like its much bigger, but it really is plenty.
Usually anytihng after the turbo the bigger the better dpending on lengtht, and anything before needs to be smaller, but really calculated.