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 configurations.

Air Induction

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 induction.

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 hood.

Air Filters

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 is maintained.

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.

Intake Manifolds

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 easier.

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.
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This page is maintained by Russell W. Knize and was last updated 02/16/99. Comments? Questions? Email minimopar@myrealbox.com.

Copyright © 1996-2003 Russ W. Knize