These pages are devoted to the 1991 3000GT VR4
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 Removal of Stock Exhaust
Weight Specifications: Original Active Exhaust from the Cat Back = 47 lbs
Borla Cat Back System not including clamps                                  = 28 lbs
Original Down Pipe including Main Cat and Left Bank Pre Cat        = 28 lbs
Savings in weight for Borla Cat Back System over Active Exhaust = 19 lbs

Original Active Exhaust System Including
Main Cat and Left Bank Pre Cat

 
 

 I began the modification on 11/20/98. This modification will take a little while only because of
additional work done during the change over. We always proclaim, do this and do that as long as you have
it apart, when we refer to the 60k tune up. Well, we are installing an exhaust system that probably will be
with the car for the rest of it's life, so we will never have access to what is behind it unless we take it back
out just to get behind it and we hesitate to do this. The question is, why don't we do it while it is apart?
At least the things that we wouldn't normally do such as cleaning and painting and undercoating and in
general bringing the car back to near new again. Treating rusted parts with rust converter and putting a coat
of paint on them will save a lot of problems later and preserve their present condition and greatly improve
your pride in your car and it's resale. Just consider this senario. It has been a few months since your exhaust
modification and you here a rattle under the car. Come to find out one of the sheilds above the exhaust
has rusted out and has to be replaced. When would you rather have done this????
  Before I start the photos, if you have storage at home with limited tools and still wish to do the cleanup,
go to your favorite muffler shop and ask them to work with you on this. Have them remove the
whole system from the Catalytic Converter back and also loosen the nuts on the exhaust manifolds and
then replace them just snugging them up. Bring along a small box to keep all the hangers and bolts they
remove and a blanket to bring home the old exhaust if you wish to keep it. When you take the car home, just
take it easy because it will be a lot louder but not that loud if you don't gun it. Keep the RPM's low. Then
you can proceed with the rest from where I am starting, skipping over the places you already have done.
Here is a list of the equipment you need to accomplish an "at home" exhaust modification.

 Tools Needed when you have the muffler shop remove the exhaust from the Cat Back and loosen the
Exhaust Manifold Nuts

1/2" Drive Ratchet and deep well #18 Metric or 3/4" socket and 1/4"
Drive Ratchet and small metric socket set both with extensions
Electric Drill Motor     Wire Cup Brush       2" Putty Knife   Small Wire Brush      Large Wire Brush
Regular Screw Driver,,  Set of 3 Ton Jack Stands,,,       3 Ton Hydraulic Roller Jack with 18 inch lift
Safety Goggles or Glasses

 Extra tools needed for complete job in addition to above

(Possibly if nuts frozen, mine were)
Air Compressor with air chisel (cold chisel with hammer is Ok,  but a lot more work)
1/2 inch drive X 18 inch Torque wrench or Breaker Bar and large 3/4" or #18 Metric Box Wrench
Channel Locks
 Cleaning products needed: Castrol Concentrated Degreaser, spray bottle for concentrate, a large drain pan,
cleaning brushes

If you are also doing a cleanup
Other Products: Couple cans of Undercoating, Couple cans of Black Spray Enamel,
Spray can of Rust Converter
 

The Place we have to start is to jack the car up all the way around or on one side (preferably drivers side).
Here is mine jacked up to 17 inches clearance to undercarriage
 

Shown below is where we want to start. The back side of the Catalytic Converter, hence the Cat Back System.
We want to start there while we still have the rigidity of the down pipe connected to the exhaust manifolds.
Using a #18 Metric or a 3/4 Standard Box wrench (they are very close in size) remove the bolts on the
flange connecting the Converter to the back end of the system. The flange is shown here to the left side of the
photo in front and to the side of the transfer box. Before you start removal of anything go around to all
the nuts for the complete system change out and apply WD40 or a similar type penetrating oil
 

Mine was rusted and frozen so I had to take the air chisel to it to break it loose. Using the air chisel or a
cold chisel cut into the nut at an angle toward a counterclockwise direction so as to force the nut to turn in
that direction and break it free while increasing it's outside diameter on one side. Once it breaks free a pair
of channel locks will remove it. Here is a photo of the direction of the air chisel Notice it is on a flat below
the center of the stud. Once you cut into it a little you can angle it a little more
 

Here is a photo of the nut after it broke free
 

Here is a photo of both nuts removed. Notice they are not cut all the way through, so the studs on the Cat
are still in good shape and the only thing I have to get is two new nuts
 

Once Both nuts are removed using the cold chisel or the air chisel, wedge it between the two halves of the
flange to separate them Here is a photo of the flange, separated

Next remove the exhaust manifold nuts starting with the front or from the drivers fender the left side
of the engine. Here is a photo of that area. In this photo you can also see the oxygen sensor sticking
out from the manifold further up with the brass sleeve around it. To the left, the alternator can be seen.
Take note of their locations for future reference. These can be removed using a #18 Metric or a 3/4"
Deep Well Socket with an extension and a breaker bar or an 18" torque wrench. Make sure you have
prepared them prior with WD40 or a similar type penetrating lubricant and add more. Don't force them
too much as you don't want to break them off. If they do not break free with a substantial amount of
force, don't get over zealous and put your all into it with a breaker bar or a cheater or using your legs
Breaking them off will mean going back to the muffler shop or trying to drill the studs out and replace them
and at this angle it would be a lot of work Take your time with this as our only objective is to get them
off without damaging the studs. These are not usually as rusted as the ones further back because
they are close to the engine and experience more heat and less moisture. Applying tightening pressure
sometimes helps to loosen them up from the rust bond. Just remember we are not trying to actually
tighten the bolts more, just stress the nut to break free the bond. This is neither felt or seen, it just
happens on a molecular level (don't want to get to technical here)
The other one can't be seen here but is accessible on a straight in approach just as this one is using an
8 inch extension. You might be able to get away with a standard socket and not a deep well. It
depends on how the socket is made and it's depth and inner clearance
 

Once you have removed the bolts on the front side, move to the back side. All the while you are
working on these, keep applying penetrating oil to the back or right side exhaust manifold nuts.
Below is a photo of this area
 

Once these are removed, leave the one in that can be seen here (next to the bushing near the top of the
photo you can see the tip of it) at a point where it can be taken off by hand near the end of the threads
and move to the hanger bracket shown below
 

Enlarge the photo if you need to but the hanger bracket can be seen on the right side attaching to the
bracket coming out from the exhaust pipe. Use a # 12mm socket and 1/4 drive ratchet. Once the
bolt is removed the weight of the pipe will be hanging on the tailpipe side of the Catalytic Converter
and the nut you left in earlier. Now remove the nut you left on earlier while supporting the unit, bringing
the front of it below the air dam and slide it towards the front of the car to remove it from the
studs on the other end.
Here is the exhaust  (referred to as the down pipe) and Cat out of the car. On the left side the first
part with a flange on either end is called the pre cat. It has a ceramic type platinum coated honeycomb in it.
At the far right is the main Catalytic Converter. In the center is just a flanged connector pipe.
The part it connects to on the engine also has a honeycomb in it and is your rear pre cat. When they talk
about getting a new down pipe it goes from the first pre cat all the way back to the Catalytic Converter.
The rear connection might be tuned so the exhaust actually directs towards the front of the car and ties
in at a Y in the pipe and then mixes with the front half exhaust and heads out to the main cat. The
purpose of this would be to equalize back pressure and have the length for the two exhaust ports the
same theoretical length creating the same theoretical back pressure for each bank of the engine
therefore balancing the exhaust and giving you a more balanced engine. The same is true for
tuned port headers and the reason they do twists and turns. In these cars I am not sure if this is
accomplished as they do not call it a tuned header but rather a "down pipe" of increased size and
therefore less restriction. Shying away from the terminology of a tuned port header and seeing the
fact it does not originate at the exhaust ports of the engine and therefore balancing each cylinder
with the whole system I am not quite sure of the reasoning behind the turn to the front of the engine
and also not sure if all models do this. For this reason and the lack of my knowledge in their line of
thinking, I opted to not go with the down pipe as of yet and will alter this page when I can come up
with concrete evidence of it's benefits. Guys, educate me,,
 

 Ok Now that we have the Cat forward removed you might be asking yourself why I told you to remove
the cat forward. For obvious reasons it is to clean up the area and also to clean up the stock exhaust or
anything else you might wish to do that might remain a mystery to me. If one could read between the
lines you might think of something
The purpose might be to gut your cats which might be beneficial to added horsepower, but you should not do this, :-)
Now we can move on to removing the original cat back. We want to move to the rear of the car first for this.
First remove the drivers side rear wheel. Looking in from the drivers wheel well you will see your
Active Exhaust hook up pictured below.
 

Using a #12 open end wrench loosen the nut on the cable retainer bracket and slide it up out of the
bracket, then pulling on the cable to turn the valve, slide the cable under the retainer tab you see below
and then using a screw driver pry the cable end up and out out of the round slot. The photo below shows
the cable removed and a little better view of what the end looks like.
 

Once this is removed you are ready to start removing the hanger bolts for the exhaust system. It is not
that heavy, but the assistance of a 6 foot piece of 1/2 conduit or similar will aid in the removal.
Shown in the photo below thread it through the car's shipping anchors This will hold the exhaust up till removal.
I used a 10 foot length of ½" conduit and just left one side sticking way out rather than cutting it
 

Starting on the passenger side remove the two #12 X 1½ bolts supporting the exhaust tips shown below
 

Next moving across the back of the car remove the #12 X 1¾  bolt back from the passenger side tips
shown on the left below and the one just upstream of the active exhaust valve shown on the right below
 

Now move over to drivers side muffler bracket and remove the two #12 X 1½ bolts shown below on
the left and next from the wheel well remove the one shown below on the right.
 

At this point you want to move over to under the car just in front of the rear drivers wheel and
remove the #12 bolts from the hanger bracket towards the rear of the car shown on the left below and then
remove the ground strap and both bolts from the front most hanger shown on the right below. You now
should have only the front most hanger bracket and the piece of pipe in the back supporting the exhaust.
Lifting up on the front side of the exhaust, remove the last bolt on the drivers side of the bracket on the
right and allow the bracket to swing out of the way. Pull the exhaust towards the front of the car
and it should drop off the pipe to the ground. You are done removing the exhaust. This part takes
about twenty minutes and is a lot faster than removing the Cat Forward
 

 At this point you are ready to install the new exhaust if you are not doing extended cleanup. There is one
thing left to do do it you want a professional job and that is to push the cable for the active exhaust up inside
the car. Remove the rubber grommet and when the cable has been slid up inside, use a caulk or some
other sealing compound and replace the grommet sealing it off from leaks. If you wish to disconnect the
active exhaust motor and cable, you must remove the rear and drivers side panel inside the trunk along with
the tool tray on that side to gain access. Leaving it alone will make the system think it is functioning ok if
you happen to hit the switch to activate it. The switch should however remain in the off position and not
used unless you can figure out another mod for it to accomplish.
 

 Going on to the Installation of the Borla

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Photos and text Copyright John C. Adams  Use prohibited without authorization.
For questions send e-mail.   Last Update 03/04/99