WHY ARE FACTORY
EXHAUSTS SO
RESTRICTIVE?“Legislation!” says Barney from
Legendex Exhausts. “The
Original Equipment
manufacturers need to meet a
very high emission and sound
standard. Plus, they are trying
to do this on a very tight budget- every cent counts for them.
Lucky for us 4WDers, the
aftermarket legislation is very
different. The cheapest way to
make an exhaust quiet is to
make lots of baffles inside the
muffler box with no packing,
and to reduce the pipe size. The
secret to a high-flow
performance off-road exhaust
is in the design. OE
manufacturers don’t offer an
off-road warranty, so they don’t
have to go the extra mile with
things like extra under-vehicle
clearance, lower EGTs, stronger
hangers etc. This costs too
much when the goal is to make
a 4WD as cheap as possible –
not as off-road capable as
possible.”
CHOOSING THE
RIGHT EXHAUST
“When it comes to exhausts,
size is of massive importance,”Barney continues. “If you
want to do your 4WD a
favour, get the right sized
exhaust, not the biggest.
Each motor has different
requirements. Some, like
3.0L Patrols, have boost
spike issues so 3inch
directly off the turbo is a
big no-no. Others like the
VDJ LandCruisers love a
3inch exhaust, but their
turbo outlet is only
1.75inch, so how you get
them from 1.75in at the
turbo to 3inch is very
important. A smooth
increase in diameter has
way better flow dynamics
than a sudden step which
produces gas turbulence.
We test multiple setups.
Take my 3L HiLux for example;
we tested nearly 10 different
setups. I wanted to know how a
2.25inch v a 2.5inch v a 3inch
pipe size worked off the turbo.
We changed positions of the cat,
then tested a 100 cell cat v 200 v
standard, etc.”TURBO BACK V
CAT-BACK
A turbo-back exhaust generally
includes a larger dump pipe
(the immediate first section ofexhaust from the turbo),
and all new piping, cat and
muffler(s) whilst a ‘cat back’
exhaust is merely larger piping
from the rear of the catalytic
converter to the end of the
exhaust. Is there any real gain
or does it just sound a bit
tougher?
“A cat-back system will
produce more power than
stock,” says Barney. “That’s
because replacing the stock
muffler (which is very
restrictive) and the larger pipe
size will still produce better
flow, but it won’t beat a turbo
back system. For example we
offer two systems for the 1KZ
Hilux, but only because the
stock dump pipe can be
extremely difficult to remove.
Where possible turbo-back
systems are the best choice.”DPF SYSTEMS &
EXHAUSTS
Brought in as an emissions
system to ensure vehicles
meet emissions standards, the
upshot of DPFs is that as ofright now, modification options
are limited if you want to stick
to the letter of the law. And
that’s not even to mention the
fact that we’re already hearing
about DPFs failing. So the big
question is what can you do
about it?
“I knew this question was
coming!” says Barney. “That
DPFF – diesel particulate
freakin’ filter. If you delete it
you could be facing huge fines
of $10,000 to $100,000 – yeah,
that much. If you keep it, you
could be doing a lot of harm to
your engine in the long run. So,
back to the question about what
to do? You can fit a DPF-back
exhaust ASAP as they lower the
EGTs and overall pressure – do
this NOW. From a power gains
point of view, a DPF-back
exhaust and a good tune will
give you 15-24% all day long,
depending on what 4WD you
have. I’m working on a
high-flow legal DPF
replacement exhaust. Testing
has already begun and the
results are excellent.”Performance tuning doesn’t have to be exhausting
The first^ step^ to^ getting^
your^ vehicle^ running^ better^
is to^ fit^ a^ bigger^ exhaust^ –^
but^ why,^ and^ how?^