My Plenum Project

An inside look at my project covering the plenum, Exhaust Manifolds, intakes, PVC valve's, & Map sensor locations.

A Little on the Plenum & Differences Between Early and Later Versions

The Mock Up

Directions for doing the swap

Plenum & Lower Intake Torque Sequence

Early & Later Vacuum Charts

Some Notes on my Plenum & Intake Research

Exhaust Manifolds & EGR System

PVC System

Fuel Rails

Map Sensor Locations

Some Related Links to 3.0 Litre Intakes on the Net

Other Misc. Links of interest

A Little on the Plenum & Differences Between Early and Later Versions

This above is a picture of the new plenum that is similar to the one I installed on my minivan.  I've been asked why a new plenum it looks just like your old one?  That's an easy one.  The early plenum used on the '87 and '88 3.0 V6 engines found in the Caravan, Voyager, Dynasty, and New Yorker are more restrictive & do a poor job in the airflow department in general.   The '89 and newer version was redesigned and gave better low end torque. Below you will find pictures of the two different designs with some comments so that the differences  the differences can be readily seen.  It has also been said that the plenum was redesigned to fit under the hood of the AA cars.

Pictures of the inside of the '87-'88 plenum.  Notice the long runner that goes down the center of the plenum.  I'm pretty sure this is not the greatest design when it comes to getting air to cylinders 5 & 6.  Removing casting ridges would be a challenge also.

Pictures of the inside of the newer style plenum.  A lot better design in the big picture.  The air does not have to run all the way across the plenum and then have to come all the way back across for cyl 5 & 6.

Above is the picture of the new valve cover that will be also going on.  The valve cover changeout  is required because on the '87 & '88 setup the PVC valve screwed into the valve cover.  On the '89 & newer setup the PVC Valve screws into the intake manifold & there is a nipple on the valve cover that the hose to it attaches too.  I wonder why Chrysler changed the direction of flow for the PVC system for the 3rd model year and later?  An update on '89.  I've seen both the old & new PVC setup while yarding for parts.

On the '89 & newer setup Chrysler went from the 52 mm to a 46 mm throttle body.  You can see a pic of all 3 of Chrysler's throttle bodies used on V6 engine's on Mark Sutyak's Site Here. Since I started out with the older setup I have the more desirable 52 mm throttle body already.  If you want to go extreme and do a throttle body upgrade you could have the opening for the tb on the plenum ported out and install a 58mm throttle body.  The 58mm Throttle body can be found on '98 and newer 3.8L V6 Town & Country Minivans.Boring a 52mm TB to 56mm is also an option for upgrade.  *Please note porting of the throat is required for use of any throttle body bigger than 52mm.  Epoxy reinforcement of the neck may also be required.


This picture should read '87-'88

'89 A529 Casting Lower Intake Manifold.

Anyone doing this swap from the older to the newer will discover that the hole for the charge temp sensor is missing.  It's boss is still there all you have to do is take it to a machine shop and have it drilled & threaded.  In the pictures above the one to the left is a later version that has had the charge/temp sensor location tapped & threaded and the one on the right is a plenum that has not been taped.  Also notice the location of the temp gauge sending unit moved also.  Wonder why Chrysler did that.  The stock wire will reach it with no issues.  There is plenty of extra.

The 4th picture is worth talking about a bit.  It is of a '89 lower intake.  What is so special about this one?  From what I have been able to figure it is a one year peice.  It is casting number A529.  '89 was the first year for the PVC valve in the lower intake and the last year for the old parallel fuel rail. Why have I assumed this?.  A few years ago I parted a '90 Caravan with 3.0LV6 and it did not have the provision to bolt the older style regulator up.  I really wish I would have kept ahold of it, but money talks.

I have done a little more research into lower's and to date I have found either myself or through others 4 different casting numbers.  I am sure there are more casting numbers out there I have not yet seen and would love to know about.

To date this is what I have:

Year Casting Number Comments
'87-'88 Casting #A516
'89 Casting #A529 PVC Valve & has stand off's for old style regulator
'90 Casting #A1  26 PVC Valve
'92 Casting #A912 PVC Valve
Unknown Casting #A910
Unknown Casting #A627

more to follow on this.....

The Mock Up



Above you can see a mock up of the new setup.  Notice the set of spacers between the plenum & lower intake.  These spacers were designed by Nitetrain & they turn one sharp turn into two smaller turns, with a straight area between them so that the air can accelerate before it hits the second. Pictures, directions to install, and ordering information can be obtained by clicking here.

The following is what Nitetrain posted to the Chrysler3LitreV6 mailing list:

"The spacers go between the upper and lower manifold.  They are made of heat insulating plastic.  This helps by stopping most of the heat in the lower intake from getting into the upper intake, resulting in a cooler intake charge.  Cooler air is denser air.  This results in more power.  They also help out by increasing the runner length by 1/2", resulting in more torque.  Also, Since the spacers are placed where the curve in the runners occurs, it helps increase airflow because it changes what is roughly a 60 degree angle(very tight),into two separate angles, one 90 degrees, and one roughly 30 degrees.  It is easier for the air to flow through the two separate angles, and since there is a straight area between them, the air has a chance to increase in velocity before it goes through the last angle.  I'm not going to go out on a limb and say that these are going to give a XX amount of HP and torque increase, as the results will vary.  They have been making these spacers for years for the Mustangs, and they sell for approximately $100.  I will say that there will be an increase in both torque and HP.  There are very solid scientific principals behind the design of phenolityc(sp?) spacers."

I will say now that I have ran a set for awhile that they do make a difference.  Especially up past the midrange.  Anyone interested in purchasing a set should drop an email to or visit

I'm figuring in the end that swapping the plenum on will be a 5 to 8 hp improvement,  I'm hoping for another 5 hp out of the spacers, and yet another 5 hp out of the throttle body for a net gain of 15 to 18 hp.  The 52 mm throttle body has been dynode by Angelo Taylor & showed a net gain of 6 to 7 hp with the later style plenum.  The info on the throttle body can be found at Gary Donovan's site Here.  The '89 & newer motors were rated at 141 hp where the '87 & 88 motors were rated at 136 hp so I am guessing the plenum is worth about 6 hp.  This is purely speculative at this time and has no scientific data, no dyno tests, etc.

Basic Directions for doing the swap from the older style to the newer style intake setup

Preparation for the plenum for install

1.)  Aquire a '89 or newer plenum & lower intake from the pick 'n' pull.  Also snag the front valve cover.  The one with
      the oil fill cap.  Go ahead and leave the fuel rail behind.  Chances are the rail is the newer style & the injectors are
      SMPI.  The older rail supposedly flows better & the fuel pressure regulator(FPR) is setup different allowing an easier
      after market FPR install.

Side note:  If your looking for a little more performance by adding fuel, a set of Turbo I injectors and a fuel pressure
                 regulator can be easily added while everything is apart. Make sure to hook up a pressure gauge and an
                 A/F gauge to fine tune everything.  It's been reported that 27psi is a nice base pressure to start with on this
                 setup. (Do not attempt this on SMPI injection equipped vehicles '92 & newer.  You can damage your
            computer.  24lb Ford Mustang injectors would be sufficient for most folks.)

2.)  Clean up plenum including gasket surfaces & the inside. You will find separating the plenum really helps to get the
      inside really cleaned out.  Trust me it's going to need it.  Something like soaking it down with carb cleaner will help
      dissolve the coating of oil & varnish on the inside.  (this will make working with the plenum a cleaner experience).  Too see pics
      of the plenum being seperated click here.

3.)  Have charge/temp sensor hole drilled & tapped. You could also have them tank it for you if you don't want to clean
      it up yourself.  (about $15-$20 at a machine shop for the tapping)

4.)  Port the intake & plenum to taste. (This step is totally optional and not required.)

5.)  Clean plenum again.  (You don't want any metal fragments to get into the motor.)

6.)  Decorate to taste.  (This is another optional step.)

List of other items that will need to be gathered & other preventative maintenance idea's.

1.)  Gather an intake gasket kit & new fuel injector O-rings from your local auto parts store.  I paid about $6 at
      Autozone for the intake gasket kit.

2.)  This would also be a good time to pick up a new thermostat, gasket, hose clamps and some antifreeze since you will
       have to drain the cooling system  It never hurts to do a good flush & fill.  This would also be a good time to upgrade to
       the 180^F thermostat.

3.)  Also during this procedure the water tube that runs between the heads will be accessible.  This would also be a good
       time  to replace all of the O-rings in that assembly.  Trust me it's a royal pain if you have to do it later.  Been there
       and done that.  The O-ring set is Felpro part #ES72872.

4.)  Gather any needed tools, rags, a roll of masking tape & a pen for marking hoses, and a bucket for catching the

Installation on vehicle.

These directions are going to take for granted that someone performing this swap is going to have a little experience and know how to do things such as draining coolant, depressurizing the fuel system, identifying components, etc.

  1.)  Drain the antifreeze.
  2.)  Remove the upper radiator hose & remove the thermostat housing cover.  Also remove the heater core hose from
        the lower intake.
  3.)  Remove all remaining hoses, electrical connectors, and vacuum lines.
  4.)  Remove the serpentine belt & alternator.  If you have the MAP sensor that is attached to the alternator bracket it's
        bracket will have to be removed also.
  5.)  Remove the throttle body & linkages and set them a side.
  6.)  Remove the plenum from the lower intake.
  7.)  Remove the bolts holding on the fuel rail and remove the fuel rail.  The rail may need a little persuading.  Replacing
        the injector o-rings might be a good idea while the fuel rail is out too.
  8.)  Remove the lower intake.  Held on by 8 nuts with lock washers below them.
  9.)  Clean all gasket surfaces on the heads, & prep them for new lower intake gaskets.
10.)  If you desire remove the water tube that runs between the heads & replace all of the O rings.  This is actually a very
        highly recommended thing to do.  It came to bite me in the butt.
11.)  Replace the front valve cover with the newer one.
12.)  Install new lower intake with new gaskets following the diagrams further down the page for tightening sequence.
        These should be tightened to 174 inch pounds.  If you wish you can do 13 before putting the intake on the motor.
13.)  Prep the fuel rail for installation.  Replace all of the O rings & install in intake remembering to replace all the bolts
        holding the rail on including the one by the fuel regulator.  Some people may discover the mount for the FPR is
        missing.  If it is you'll have to fabricate a mount for it.  Gas tank strapping might work well as long as it is rigid.
14.)  Install the plenum with new gaskets & tighten down following the diagrams further down the page.  The plenum
        should be tightened to 130 inch pounds.
15.)  Install new thermostat & replace housing cover. (This can be done prior to installation of the lower intake if wished.)
16.)  Reattach throttle body & all linkages.
17.)  Reattach alternator & restring serpentine belt.
18.)  Reattach all electrical connectors, vacuum lines, and fuel lines.  If you had the MAP sensor bracket on the alt
        bracket don't forget to install it also.
19.)  Reattach upper radiator hose.
20.)  Reattach air ducting & airbox to the throttle body or install a cone or cold air intake.
21.)  Refill & purge cooling system of all air.
22.)  Drive off in bliss.

Plenum & Lower Intake Torque Sequence

Plenum tightening sequence. Tighten to 130 inch pounds. 

Lower intake manifold tightening sequence. Tighten to 174 inch pounds. 

Early & Later Vacuum Charts

Vacuum routing diagram for the 1987 3.0 litre US models.

Click for a larger view
Vacuum Routing Diagram for a '92 Caravan/Voyager with 3.0 Engine.  See my notes towards the end of the page on Map Sensor Location Change.

Some Notes on my Plenum & Intake Research

To date there are  3 different versions of the plenums found on the 3.0 V6 engine.  The one from '87 & '88, one '89 and newer  that has no EGR mount, and '89 and newer where the EGR bolts to the plenum.  The '87 and '88 models the EGR bolted on to the back exhaust manifold.  See the pictures below in the Exhaust Manifold & EGR section for these differences.
This is a plenum from a '92 Acclaim.  You can see where 
The EGR attaches to the plenum.  The '87 & '88 have a 
flange that a tube connects there going  to the EGR
This is a plenum from a '90 Caravan and doesn't have the mount for the egr at all.

Exhaust Manifolds & EGR System

I've been asked a number of times what is the EGR system.  The EGR valve is part of the emissions system. EGR stands for exhaust gas recalculation (some people call it exhaust gas recovery). The object of this valve is to allow controlled amounts of exhaust gas to enter the intake manifold. This dilutes the intake mixture and lowers combustion temperatures. The lower temps reduces the NOx (nitrogen oxides) emissions.
Picture of an '88 2.25" output manifold with the EGR 
mounted to the manifold. 
This is a picture of a '90 manifold from a Caravan without the boss for either an EGR or the EGR Tube.  This is a 2.5" output manifold.


Another view of the '88 manifold w/EGR.

PVC System

I  mentioned earlier in this page about the flow of the PVC valve & it's locations.  Here are a few pics of these changes below.
Looking at the valve cover above you can see where The PVC Valve screws into the valve cover.  This is for '87-'88 setup. The intake manifold is where the PVC valve screws on to in '89 & newer setup's.  Notice the bolt I have sticking out of the location on the manifold pictured above.


Picture of newer valve cover with the nipple for the PVC hose. The PVC jet in the new style lowers runners

This is the 1987-1988 style lower intake. 
This is the 1989 and newer style lower

I mentioned earlier in this document about the PVC flow.  1987 & 1988 had the PVC valve in the front valve cover and the hose went to a nipple on the neck of the plenum to deliver gases back into the intake tract.  In 1989 they moved the PVC valve into the lower intake and added a runner along the bottom of the intake with a port at the bottom of each runner across from the fuel injector port.  Gases get sucked in and injected at the bottom of the runners instead of the neck of the plenum.  I'm geussing they did this for one major reason the redesign of the inside of the plenum.  In the old style there was the tube running the length of the plenum which gave time for the gases being recycled to be mixed into the airflow.  If they would have left the PVC alone with the new style plenum I'm geussing that they were worried about some cylinders getting a higher mixture than the others.  So injecting the mixture into each seperate intake runner makes sense to balance out the mixture of the gases being recycled.

Fuel Rails

Early style fuel rail. Later Style fuel rail

The 3.0 as used in Chrysler products came with 2 different versions of fuel rails through it's production life.  The older style used from '87 to '89 and the newer style introduced in the '90 model year.  The biggest distinguishing factor of the two rails is the fuel pressure regulator.  The earlier style regulator is bigger and has more after market choices while the newer style has a smaller regulator.

Map Sensor Locations

For my Last topic of this page.  Map sensor location.  If you looked closely to the vacuum diagrams above you may have noticed the change in location of the Map Sensor.  In Early 3.0 applications they placed the Map sensor up on the firewall & in some '89 and all later year applications they relocated it to a bracket in front of the alternator.  From what I understand they relocated the map sensor to address an issue with condensation building up in the vac line.  For anyone wishing to do the conversion the factory part number is:  4419451, Map Sensor Relocation Kit.


        In this picture you can see the location of the old map        In this picture you can see the relocated map sensor
         sensor in my '88 Caravan.                                                 in front of the alternator.

What do you do about getting the wiring to the new location.  That is easy.  Chrysler had a harness extension for the map sensor they used on some vehicles.  I found one on a '90 Caravan myself & have seen a few more in the yards on '89 & '90 vehicles.  This job took me about 30 minutes to complete & had a total pick 'n' pull price of $5.  Prices in other parts of the country may vary a bit.  All you need is the pigtail harness & the bracket.  The current map sensor bolts right up to the new bracket.  You won't get a performance gain out of this, but it helps clean up the engine compartment and gives less vac line to replace years later.

Some Related Links to 3.0 Litre Intakes on the Net

3.0L Port & Polish Tips

Adam Baumbach's Page on Spacer Installation

Nitetrains Extreme Porting Page

Other Misc. Links of interest

Modifying pressure regulators, extra injectors, etc.  From Gus's Web site.

Home Made Adjustable Fuel Regulator  (text only)

Dawes Devices - Maker of A/F Ratio Gauges

I will be adding more pictures & material to this page as I get new content.  So please check back once in a while.

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Visitors  Last Updated 11/01/2003