Mod Benefit Drawback Is it a problem? Notes
Aftermarket exhaust
  • Reduce exhaust back pressure allowing better flow of exhaust gases
  • Stock exhaust restrictive
  • Stock exhaust rusts
  • Turbo spools up faster
  • More power, popular guess is approx 15 bhp, depending upon  several factors
  • Stainless steel exhaust guaranteed for life - normally!
  • Lighter
  • Looks better
  • Louder
  • May get exhaust rattles - aftermarket never fit as well
  • Awkward to fit over rear drive shaft area
  • Use of a ramp will help alignment and fitting
  • A free flowing exhaust will probably lean out the fuel/air mixture

Depends on which exhaust you fit...it might rattle, or be a bit too loud/drone

There is a limited choice for the 165 e.g. Scorpion, Mongoose, Aussie or specialist fabricator.

A 3" will fit and is quite a bit better than a 2"...

The Aussie exhaust is considered to be one of the best available and is 3", but it's steel

A custom 3" exhaust maybe the best choice, and is surprisingly affordable, ask these people for a quote, I can vouch for the service and workmanship

Gut Catalytic converter
  • Better exhaust gas flow
  • Improve turbo spool up time
  • More power - approx 5 bhp
  • If car is after 92 will fail MOT
  • Emissions will rise
  • Exhaust a little louder
  • Gases able to swirl around inside cat, thus preventing optimum gas flow


Access is awkward allow 3 hours to get this flaming thing out. Some of the nuts/bolts will probably strip...
Replace Catalytic converter with a downpipe
  • Better exhaust gas flow
  • Improved turbo spool up time
  • Less weight
  • More power approx 15bhp/15lbft
  • Reduce exhaust manifold temperatures
  • Will help to allow for later modifications e.g. boost pressure increases
  • Exhaust is not supported as securely as the Cat. Cat bolts onto turbo and block (twice)
  • Some aftermarket downpipes seem to be prone to cracking


No, but if you replace the turbo at some point, try and retain the turbo support bracket, if you don't you might start cracking manifolds and/or down pipes

Cat weighs 10.9kg, Aussie DP weighs 2.4kg

Select your DP carefully, stainless steel is more prone to cracking than steel

The Aussie DP is considered to be the best available and is 3" and steel

Debateable at what point a 3" DP is superior to a 2.5" DP, some say at ~350hp

Heat wrap exhaust under engine bay
  • Reduce engine bay temperatures
  • Faster exhaust gas flow
  • Improved power, (maybe)
  • Soaks up oil and smokes/smells if you have any leaks!
  • Traps water and may accelerate rusting (if you have a steel exhaust)


Port exhaust manifold
  • Improve the exhaust gas flow into the turbo
  • Improve output power
  • Need to take off the cat and turbo...
  • You'll probably shear a manifold stud


New manifold gasket comes in 2 halves and is ~60! Make sure you replace the manifold studs or you stand a good chance of shearing one of them on reassembly
Replace restrictive manifold with a tubular equal length manifold
  • Improve exhaust gas flow
  • Increase power output
  • Improve turbo spool time
  • Turbo will probably not sit in it's original location, oil and new water lines may therefore need to be installed
  • May require a custom downpipe as the turbo isn't sitting in it's original location
  • As turbo may not now be supported, stand a higher chance of cracking the manifold and/or downpipe

ish, depends upon the design of the manifold

A popular thought on the power increase is ~20bhp, but this would largely depend upon boost pressure, flow and other supporting mods