Upgrading The Intake
[ Air Induction | Air
Filters | Throttle Body | Manifolds
This page describes the available options for upgrading the intake system
on 2.2L and 2.5L engines. You should read the Turbocharger
Concepts page if you are not familiar with Chrysler's various turbo
In this section, air induction refers to the method for getting the air
to the air filter. The most important issues with air induction is
temperature and restriction. Which issue is the most important depends
on the type of engine you have. If you have a Turbo I engine, then
the biggest concern is temperature. If you have an intercooled engine
(Turbo II, III, and IV), then you are less concerned with temperature and
can concentrate more on restriction. The details are discussed below.
Non-intercooled engines have the disadvantage that they cannot get rid
of the heat in the air that the turbo creates when it compresses it.
Because of this, you need to be concerned with the temperature of the air
entering the turbo. The air under the hood of a car is usually much
hotter than the air outside because most of it has passed through the radiator
and because of all the hot components under the hood. The stock induction
setup pulls cool air in from behind the front facia through the power module
(or SMEC). This air also cools the components in the module, but
it adds very little heat. The disadvantage of this system is that
the module and ductwork acts as a restriction. Since we are more
concerned about temperature and because this restriction is not really
a problem while driving (ram-air effect) with a K&N drop-in filter,
the stock induction system is actually best left alone. If you really
don't like having this restriction, you can get creative and figure out
a way to install an open element air filter (round or cone type) in a spot
where cool air is available. You then have to run smooth ductwork
from the filter to the throttle body (pull-through) or turbocharger (blow-through).
I don't recommend cutting holes in the airbox. This completely defeats
the idea of pulling in cool air, and it could also lead to drawing water
in the engine.
Intercooled engines have the advantage of the intercooler. The
drop in temperature of the air by the intercooler is usually greater than
the increase in temperature from drawing in the hotter under-hood air.
This, of course, depends greatly on the efficiency of your intercooler
setup since the stock Turbo II setup is rather inefficient (see the Intercooler
Upgrades page). If you have an efficient intercooler on a blow-through
engine, then your best bet is to install an open element filter right on
the turbo inlet. If you don't like the swooshing sound that the turbo
makes with this setup, then put the filter on the end of the stock turbo
inlet duct. If you have a pull-through intake setup, then you can
put the open element filter on the end of the rubber stock throttle body
inlet duct. For most mild performance applications, the stock induction
setup provides sufficient flow, plus you get the advantage of cool air
Another issue that is often not addressed is emissions. Some states
do not allow open element filters and most do not allow modification to
or removal of the crankcase vent recirculation that connects to the airbox.
If you live in such a state, keep your stock induction parts.
You will need them to pass emissions tests where they inspect under the
The answer to the air filter question can be given in two letters: "K"
and "N". :) K&N air filters use an oiled cotton element
suspended by a metal mesh. This design makes for an almost invisible
filter, as far as restriction is concerned. As far as filtering,
the K&N element actually filters better than most paper filters and
actually filters better, the dirtier it gets (to a point, of course).
For a real run down on their filters, see the K&N
Engineering home page.
For most street performance applications, the best filter configuration
is to simply get the K&N drop-in replacement, which goes right in the
air box. The part number for this varies, so just go to your local
auto parts store and have them look up your car to order one. With
this filter installed, the restriction of the stock induction system is
greatly reduced, yet the benefit of cool air induction and emissions handling
If you are going to go with an open element design, then the sky is
the limit. K&N offers a wide variety of shapes and sizes that
will clamp onto any size ductwork you install. If you are going to
mount the filter right on the turbo inlet, use K&N part number RU-0840,
which is a round straight (cylinder) element that measures 4 1/2" in diameter
and 5" long with a 2 7/16" ID and 5/8" long centered mounting flange.
This filter will fit any Mini-Mopar vehicle. Some body styles may
have more room and can fit a larger filter. If it will fit, there
is the RU-1000 filter that has the same size, but offset, mounting flange
and has a 5 1/2" diameter element that is 6" long.
Throttle Body Options
Another way to increase airflow is to increase the throttle body size.
A popular choice is to switch to the 52mm or 56mm throttle bodies (stock
is 46mm), which come from Chrysler's V6 engines (3.0 and 3.3), on blow-through
engines. They bolt right on to either the one piece or two piece
intake manifolds, but the inlet on the manifold has to be ported out to
take advantage of the larger bore. Basically, if you are porting
your intake, then go with a larger throttle body and port-match to it.
If you have an early Turbo I with the pull-through setup, you can achieve
a gain in flow by switching to LRE's
"Big Throat" 46mm throttle body (stock is 43mm). Since the throttle
body is connected to the turbocharger with a rubber hose, no porting is
necessary. Again, if you are going to port your early Turbo I intake
manifold, then you should consider upgrading the throttle body. If
you are also going to retrofit the early Turbo I manifold for intercooling,
then you can also switch to the blow-through style throttle body, but some
fabrication will be necessary to connect it to the turbocharger.
There are three intake manifold designs available for turbo engines.
These include the early Turbo I short runner manifold (often called the
"log"), the early Turbo II tuned long runner intake manifold (called the
"two piece"), and the later Turbo I, II, and IV tuned long runner manifold
(called the "one piece"). Each is described in detail below.
The most common way to upgrade the intake manifold is to either port the
one you have, or switch to the long runner style if you have an early Turbo
I engine. The better the porting, port-matching, and polishing job,
the better the manifold will flow. It should be noted that each intake
manifold requires a differently designed fuel rail.
The "Log" Intake Manifold
This intake manifold was used on all 1984 through 1987 Turbo I engines.
It was designed specifically for the pull-through intake setup and is untuned
with short runners. I believe it is called the "log" because it looks
like an aluminum log connected to the back of the head. The primary
disadvantage with this manifold is that it makes installing an intercooler
nearly impossible. The inlet to the manifold points straight down,
so that it can be connected directly to the turbo, who's outlet points
straight up. To intercool this setup, the intake manifold has to
be removed and modified by a machine shop so that the inlet points forward.
The turbo housing also has to be rotated to point forward. Another
problem is that the manifold does not isolate the fuel rail from the exhaust
manifold and turbo. Although there is a heat shield there, it is
not effective enough to prevent fuel inside the rail from boiling.
This boiling causes erratic hot engine startups. The untuned nature
of this manifold seems to limit its flow capabilities, even when ported.
Maximum boost levels of about 18psi have been reported. Beyond 18psi
or so, there is no major increase in performance. Also, as boost
pressure increases from 7psi, the air distribution to each cylinder becomes
more uneven with more air reach cylinders #3 and #4 than #1 and #2.
An advantage is that the short runners make porting this manifold much
The "Two Piece" Intake Manifold
This intake was only used on 1987 Turbo II engines and on the 1986 Shelby
GLHS engine. It features a tuned, long runner design and was the
first to implement the blow-through intake setup. The main purpose
of this manifold was to make intercooling possible. Since the runners
can be removed from the upper section, it is possible to port this manifold
without cutting and welding. Since the bulk of the intake manifold
lies between the fuel rail and the exhaust manifold and turbo, it does
not suffer from the fuel rail boiling effect. However, it's design
makes removing the fuel rail very difficult. Although it is usually
possible to get it out, you may need to remove the valve cover or upper
manifold section to do it. This manifold is still listed in the Mopar
Performance catalog (P4529100). This is probably one of the more
popular choices for top-end performance because of the easier porting.
Whether it performs better or worse than the one piece manifold is a subject
of much debate. In stock form, the manifold halves don't match each
other well and the two piece may not perform as well as the one piece until
the two halves are at least port-matched.
The "One Piece" Intake Manifold
This intake manifold was used on all turbocharged engines after 1987 (except
for the Turbo III) because all turbocharged engines used the blow-through
intake setup. The only difference between the one piece Turbo I manifold
and the one piece Turbo II and IV manifolds is the air charge temperature
sensor and the color. The Turbo I manifold did not have the spot
for the sensor drilled and tapped because the 1988 and later Turbo I engines
did not feature this sensor. Also, the Turbo II and IV manifolds
were painted black, while the Turbo I was unpainted (silver). The
main disadvantage of this manifold is that it cannot be disassembled.
To port this manifold, it must be cut in half and then rewelded.
The main advantage is that these manifolds are very common in the Turbo
I form. A Turbo I manifold can be fitted for an air charge temperature
sensor by drilling a hole in same location (top center, facing forward)
and tapping it with a 5/8" pipe tap.
One problem with switching from the short runner "log" manifold to one
of the long runner manifolds is the exhaust manifold and turbo wastegate
actuator clearances. The early Turbo I engines featured a different
exhaust manifold that has to be modified to clear the #3 intake runner.
The flange that mounts to the turbo must be ground out. Also, the
bracket holding the wastegate actuator comes in contact with the #4 runner.
The bracket has to be ground down and a notch in the runner has to be carefully
ground out. Also, the turbocharger compressor housing has to be rotated
so that the outlet points forward.
This page is maintained by Russell W. Knize and was last updated 02/16/99.
Comments? Questions? Email
Copyright © 1996-2003 Russ W. Knize