Induction Modifications
The first place most people start when
trying to increase the performance of modern EFI engines is with the induction
system. Improvements to the induction system allow the engine to breathe better
by decreasing restrictions to air flow, which results in increased performance.
The induction system on most EFI engines consists of a pickup snorkel, an air
box that houses the filter, an airflow meter and the throttle body. Any or all
of these components may be restricting the flow of air to the engine. However,
in order to assess the effectiveness of the standard induction system and to
identify the greatest sources of restriction it is a good idea to measure the
flow performance of the standard system.
Measuring restrictions to flow in the
standard induction system can easily be done by determining the pressure drop
across each major component. To do this a home made fluid manometer can be used
to measure the pressure losses at each stage of the induction system, allowing
the systems losses to be quantitatively analyzed. The results of this test on
my 205 GTI can be seen below.
As is typical of Peugeot the standard
induction system flows very well with only 3.5 KPa of
restriction. The main restriction to flow occurs at the inlet snorkel, which
draws air in through an oval orifice behind the front grill. The standard foam
air filter also flows quite well with only 1.1 Kpa of
pressure drop. It is important to note that on later models such as the 206,
306, 405 or 406 the plastic air box itself may be a restriction to flow.
Despite the fact that there was not much
improvement to be made on the original induction system I decided to look at
the variety of after market options available. The most common modifications to
‘improve’ air flow are replacement elements and induction kits. Replacement
elements are a direct swap for the existing filter and work on the premise that
the existing filter is a restriction to flow. Induction kits usually substitute
the air box for a conical pod filter and come with the associated ducting and
heat shields to direct cool air into the engine. The pod filter eliminates all
flow restrictions associated with the intake snorkel and air box as its draws
air from a 360 degree opening. The ‘Piper Cross’ induction
kit and pod filter can be seen in the pictures below.
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However the main draw back with this type
of induction kit, particularly on the 205, is the filters exposure to hot air
from the engine bay and exhaust manifold. The cooler the air being fed into the
engine the greater its density, resulting in more oxygen being drawn in per
stroke. Therefore in order to gain the maximum performance from any induction
system it must be free flowing and provide the engine with cool air. The Piper
Cross induction system utilises the standard piping
to direct cool air towards the filter, as well being supplied with a heat
shield to deflect the heat radiating of the exhaust manifold. I have also
wrapped the exhaust manifold in a thermal wrap to limit as much of the heat
dissipation from the manifold as possible, though this is still not ideal.
The benefit I found with the kit fitted
was increased fuel economy, as well as a slight increase in mid-range pickup.
Oh, and of course the obligatory street cred that
comes with the purposeful looking pod filter. Another common characteristic of
these kits is a throaty induction note such as that heard on the black 206 GTi at Decca, though on my 205 nothing can be heard over
the interior rattles and squeaks. An approximate price guide for some of the
air filters available is listed below.
|
Model |
Sparco: Induction Kit |
Piper X – Induction Kit |
K&N – 57i Induction Kit |
K&N – Panel Filter |
|
205 GTi |
$145 |
$160 |
$195 |
$97 |
|
206 GTi |
$375 |
$195 |
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$72 |
|
306 GTi6 |
$200 |
$195 |
$210 |
$97 |
**Note: Prices are based on
Leon Saliba