We recently had a Corsa VXR in for mapping and rolling road set up. The car was previously fitted with (by another company) a Full 3″ Turbo Back Exhaust System and uprated intercooler – which should be ideal for performance.
Our K06 turbo, an 80mm air flow meter and some higher flow injectors were added into the mix (the engine had previously been strengthened with forged pistons and steel rods)…….
Imagine our surprise when no matter what we did software wise we could achieve more than 266bhp, when around 300bhp was the aim with the components we had.
So When is a 3″ Exhaust NOT a 3″ Exhaust??…..
When it looks like this:
Restrictive Centre Section
You can see from the restriction caused by the baffles that narrow the bore of the exhaust through the centre pipe, that the bore size is greatly reduced. This obviously reduces flow, increases exhaust back pressure and hampers performance massively.
In fact when the car went from a Stage 1 Remap, to having this particular exhaust fitted the customer did report he thought that the car felt slower!
Not only was there a problem in the centre section, but the tail pipes had the same problem:
Restrictive Tail Pipe
Needless to say once we had found the restriction we switched the cat back section for one of our Courtenay Piper developed 3″ systems, which does not feature restrictive internal baffles and finished off the mapping, successfully achieving 306bhp, gaining over 45bhp mid range, 40bhp peak to peak and 50 lbs ft torque mid range!
Corsa VXR with K06 Turbo Before and After removing a poor flowing 3″ exhaust