would say that a good exhaust system couldn't make your engine produce
more power as a straight piece of pipe can make your engine work properly,
but a system that is unsuitable will cripple it. A well-designed system
is made to reduce noise without losing power. The exhaust manifold is
the most important part of the exhaust system, but it will only work
properly if the system it is connected to is of a good design, e.g.
unrestricted and of the same diameter as the exhaust manifold chosen.
If it is not, it will reduce the efficiency of the manifold. In some
cases we may recommend a system of a larger diameter.
manifold is one of the most important parts that control the output
of an engine. You can spend endless amounts of money on tuning your
engine internally, but if the exhaust manifold's design does not complement
it, your engine may not produce the power you expect. It may move the
torque band into a different place, causing all sorts of problems. For
example if the manifold you have chosen to fit on your engine is designed
to give an all round mild improvement over the standard item, it would
be useless to fit it to a full race engine, which would
be strangled and as the engine begins to come on cam at quite high
rpm, the exhaust gases would be totally restricted & probably generate
nothing like the power expected. If your engine has been designed to
produce large amounts of torque at low rpm for a particular type of
motor sport, e.g. National Hotrods or grasstrack racing, if you were
to fit a full race exhaust manifold it would not help the engine at
lower revs to produce its full potential, since the manifold is more
suited to higher rpm.
done extensive testing with both Vauxhall and Duratec engines, spending
hundreds of hours testing manifold designs on the dynamometer &
just by changing the diameter of manifold pipes as little as a 1/16",
or its length by only ½", you can get quite dramatic changes
in the characteristics of an engine. If the manifold you have chosen
to use is badly made, or of the wrong design, the problems you will
experience will increase as you tune your engine further as time goes
by. This is because when the engine is only mildly tuned, although the
exhaust manifold is still important with mild cams fitted, the manifold
is called upon less to help with the charge of fuel rich air being drawn
in to the engine on the overlap. Overlap is when the exhaust cam is
about to close and the inlet cam is just opening, but as the engine
is tuned further the amount of overlap is usually increased. As this
happens the manifold then becomes more important because it is used
more and more to help with the incoming air fuel charge which the
engine needs to generate power. If its design does not match the characteristics
for which the engine has been designed, the manifold could be at its
most efficient at the wrong rpm and have past its optimum when the cams
begin to start working. Or maybe the complete opposite, the exhaust
manifold may not be at its best until the cams have past the working
case of a fuel injection engine, if the manifold you choose to run is
not to the same spec that it was originally programmed on and is totally
different in its design, not only could it stop your engine from producing
the power, it is likely to change the fuel requirements of your engine.
So it could even it by under or over fuelling unless it is reprogrammed
Frequently asked questions about exhaust manifolds:
I really need a manifold that long?
Answer: If that is what the engine spec has been designed & tested
on then yes.
have an exhaust manifold a mate of mine says is the best he (or
she) has ever seen and it works on his engine, so it will work on
mine won't it?
Answer: It may be the best manifold ever but until it is tested
on the dynamometer in a back to back test we cannot know and even
if it is better your engine will almost certainly require re-jetting
or re-mapping to suit.
man who is making the exhaust manifold for me says he cannot make
it fit unless he makes one of more of the pipes shorter than the
others, will it matter?
Answer: About the worst thing you can do on any exhaust manifold
is to make the pipes uneven. What your exhaust manufacturer usually
means is if you want the pipes that accurate then the job has been
if you decide to ignore any of the above don't come running to us saying
that your engine doesn't produce the power we promised. Since we only
know what power your engine should produce when it has been built carefully
with the correctly matched and accurately made exhaust manifold and
good quality exhaust system.
There are two basic types of exhaust manifolds the 4>1 and 4>2>1.
The 4>1 manifold is traditionally used on an out & out racing
engine. This is because they work well at higher RPM but they are not
very good at low of mid range RPM. The 4>2>1 manifold normally
works better in the lower & mid range RPM areas but is not as good
at higher RPM. We have developed a range of exhaust manifolds combining
the best characteristics of both these types of manifolds, which involves
using unusual length primary & secondary pipes. We would recommend
a custom made exhaust box be made for your car, since the box specifications
will depend on your requirements as regard to use & noise limitations.