I recently installed a 15g on my 92 940 turbo sedan, and realize I need to upgrade the exhaust to take full advantage of the bigger turbo. I have been doing quite a bit of searching and lurking but I would like some thoughts on my idea. [I've read 3" downpipe, to hollowed [or no cat], then a simple bent 3" side discharge exit pipe...is the "ultimate setup"... this setup is on my sons 740 and its WAAAY to loud for me..

My 15g has the conical flange with the stock 2 1/4" (?) downpipe. I've read plenty of argument over 2.5" system vs. the 3" system. So, here's my thoughts..

Run the stock short elbow from the turbo, leaving it long enough to access the bolts on the flange and keep the stock 02 sensor. From there, run 2.5" pipe to a 2.5" core size converter.. out 2.5" , then up over axle, to a 2.5" full core sized turbo muffler out the back. I like the deep tone of a turbo muffler... straight thru is too loud for my old ears.. **LOL**

My plan for the car is 15g, @15 lbs boost, fleabay inter cooler. MBC valve, larger injectors [my son (liquid x), is going to custom burn a chip to get this all to work together..] ... and this design exhaust. [Maybe 3" is too big for this level of build?]

I'm not after a total hot rod, but a nice tractable daily driver.

The local custom muffler shop says 2.5' pipe will work great, but 3" will be crushing it too bad... I really don't have the cash to go all out with cutting and welding up sections of mandrel bent pipe..

I've also read something about a 3" down pipe to a 3" cat.. then out to 2.5" pipe, over axle to 2.5" turbo.. then out... The reasoning is having the big pipe up front and the smaller stuff to bend over and out the back easier.. thoughts?

Thanks in advance,
Mike

 

First off, what you propose are relatively mild mods. There is no need to alter the stock ecu chip. LH2.4 is VERY adaptable. I've run 72# injectors, 25 psi, 3" amm, water/meth injection, hot turbo cam, NPR i/c.......all on a stock ecu.
If you plan on going with crushed pipe rather than mandrel bent, go as big as you can. It's amazing how much restriction there is in crush pipe. Remember, a turbo needs NO back pressure so every impediment saps hp. I'd go with a 3" dp myself. If you need to neck it down at the cat, so be it. A 3" mandrel bent exhaust turbo to tail is ideal, but not all can do it at once. Better to at least do the dp. Later, dp to muffler and then to rear bumper. If your muffler man can't run a single 3" crush bent pipe to the rear, shop around for someone else.
I did a 3" turbo to tail myself on my 760 in a weekend.





It sounds to me like you want to have fun with the car...you will be disappointed eventually paying good money for an inferior exhaust. With turbos...bigger is better.