only9k

Swapped Factory Duals with a Single Vibrant Streetpower 2.5 Inch Muffler welded just before the factory Y pipe location last year. Did not notice any smells then. (could be wrong)

Now every time I smell of exhaust/internal engine gas smell if I do the following: (with the windows down. Nothing with the windows up)

1. WOT in high gear + low rpm (3rd, 4rth, 5th, 6th)
2. WOT or 75% WOT (even for a second +), or goto redline in (1st, 2nd, 3rd)

Failed Solutions

1)Gas Cap (thinking maybe it was blowby pressure leaking)
2) Swap the Catalytic with 100k mile one thinking maybe it was cat causing restriction (esp since car died at lights after strong smash, fine after starting again)
3) 10k mile OEM almost brand new Oxygen Sensor thinking it was bad o2 sensor running rich.
4) Swapped OEM Exhaust Studs, with ARP since one stripped off while tightening exhaust manifold
5) New OEM Exhaust Manifold Gasket .Thinking maybe gasket was bad.
6) Checked around exhaust manifold for obvious leak signs, black soot. Found nothing
7) OEM PCV Valve + Rubber Gasket.


Potential Explanation

1) The muffler being 2.5 inch inlet/outlet is causing the exhaust to get backed up --> where engine isnt breathing well, and its going into crankcase.
2) The muffler being 2.5 inch inlet/outlet is causing the exhaust to get backed up --> Leaking from exhaust manifold without leaving soot.
3) Blowby is leaking from valve cover rubber seal because the pressure is too strong (potentially from exhaust)
4) The engine has ridiculous flow requirements, where a 2.5 inch single straight through muffler isn't enough (even though some people run them on 400hp). (need a bigger muffler, a 3inch?)


For what its worth, another s2k runs it on his car, and hasn't complained.

Chuck S

Grasping at straws here and assuming you've eliminated all the gasket for leaks:

Where does the exhaust exit? There's a low pressure area at the back of all cars (unless extremely streamlined) and exhaust gas can be sucked back in to the car from that area. Running a station wagon with the rear window down is a prime example of this. Something similar could be happening in your case depending on where the exhaust tip is.

-- Chuck

only9k

The muffler exits on the rear right. A part of me thinks its the muffler causing me these issues, but then there are mufflers for sale (2.25 inch/2.5 inch) that don't seem to be causing this issues for others.

I could get a 3 inch muffler, but I don't want to spend the money only to have it not fix the problem.

I think I will try to like plug my exhaust with a cloth or something and see where the smell comes from, I assume it would behave similar to WOT going through a small pipe with my temporary rag/restriction.

jyeung528

not sure if you're saying you smell exhaust fumes and/or fuel.

Chuck S

The header outlet is under under 60mm as I recall. 2.5" exhaust is larger at 63.5mm.

-- Chuck