1) Buying
a bolt-on, jig made exhaust – We constantly have people coming in to
the shop who have tried to save money by buying a bolt on ready-made exhaust
for their car only to find they don’t fit well and usually sound terrible. They
will ask us to fix the problems but most times we can’t cut and weld them
because the metal is so thin the welder blows holes in it. Even if we could fix
them, the extra cost means they have spent more than they would have if they
had bought a custom built system from us, in the first place. These bolt-on
systems are usually made in China and look pretty and shiny on the shelf, but
are very poor quality, and are sometimes no cheaper than our custom made
systems. With a custom system, we build it on YOUR car, so it fits perfect and
we tailor the sound to suit YOU by using a combination of quality mufflers and
designs that achieve the sound and look YOU want.
2) Going
‘too loud’ with a performance exhaust – A common mistake is choosing a
system based on the sound level from outside the car. DRONE is something that
seems to get worse the longer you put up with it. This is another problem with
bolt on systems as, for example, a Commodore sedan with a manual transmission
will have a different exhaust to an auto, or a Wagon/Ute etc. For example,
using a system that is too loud, on an automatic wagon will create a harmonic
drone inside the car, which will frustrate even the most tolerant person.
3) Choosing
mild steel over stainless steel because it’s cheaper – If you plan to
keep your car for longer than 3 years, and you don’t drive it every day for
long distances, a stainless steel system will be more economical because you
won’t replace it again. As condensation builds up in the exhaust, a mild steel
system will corrode unless it is used often, for prolonged periods of time.
Stainless steel however, will not rust/corrode due to this condensation.
4) Wanting
a mandrel bent exhaust on a street car – The average street car spends
most of its time between 1000rpm and 3000rpm, with the odd squirt from a set of
traffic lights spinning to maybe 5000 or 6000rpm. With a well-designed press
bent system, horsepower losses are practically immeasurable, and
certainly don’t warrant the extra expense of a mandrel system. If you
were constantly at 4000 to 6500rpm a mandrel system would certainly be
recommended.
5) OVER
EXHAUSTING – This is the most annoying trend at the moment. When
combustion happens in your engine, your exhaust gasses are extremely hot and
expanded, as they travel down the exhaust they cool and therefore shrink.
Having a 3” diameter pipe from the front to the back of your
car doesn't make sense. The gasses actually slow down, causing drone.
Over exhausting will cause a loss of torque under 3000 RPM (where most of the
work is done). At 4000 to 6000rpm on the dyno it will be fine, but in real
world conditions when you need bottom end torque, it will cost you as well as a
loss of economy!
This is
more noticeable on, for example a V8 commodore, with the standard 2 1/4” front
pipes and cat converters still in place, where a 3” dual cat back
system has been fitted. Think of reticulation or fluid flow, you always go from
a big pipe to small pipe to gain pressure and fluid speed; the fundamentals are
exactly the same when it comes to exhaust flow.
In
summary, every car is different and every owner is different, one
size doesn't fit all!
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