My Jeep ZJ Modifications:
My Custom Exhaust
No exhaust system manufacturer could supply me with a system that could meet my specifications. So, I had to go with a custom fabricated exhaust.
I chose to do a complete system, so that I could remove as much restriction after the stock exhaust manifolds as possible.
The catalytic converter is a big restriction. Replacing it with one high flow cat would be an improvement. But, replacing the stock cat with two high flow cats, would cut that restriction down to less than 1/2 of the stock setup.
Increasing the pipe size is another great way to reduce exhaust restriction. The stock pipe that crossed under the vehicle on V8's is very small. Off of each exhaust manifold, I wanted the pipe size to be 2.5". The bends (wherever possible) are made with mandrel bent sections. Mandrel bends retain the same cross-sectional area throughout the entire bend, unlike most pipe bending machines used in exhaust shops. Mandrel machines are very expensive, and that is why the price for that product is so high. Each exhaust bank has it's own high flow cat, which are also 2.5" in/out. Up to the muffler the system is dual exhaust.
At the muffler, the two 2.5" pipes enter, and only one 3" tailpipe exists the vehicle. The tailpipe is entirely done with mandrel bends. The muffler I chose to use is a Dynomax Ultra-Flo. It is entirely made from stainless, and carries a lifetime warranty.
Because of the space limitations when increasing the pipe size off the manifolds, an oil filter relocation kit was necessary. It's also nicer to not have to deal with spilling oil all over my starter now.
Performance:
Prior to installing the exhaust, in bone stock form, my ZJ ran 16.2 @ 83.6 mph in the quartermile. It would also "best" around 19-19.5 mpg on the highway.
After installing the exhaust and a 180 deg thermostat, on the very same launch (identical 60' time) the ZJ did 15.9 @ 85.5 mph. The mileage also increased to a best of 21.5 mpg on the highway. (this is in New England, where we don't have many flat highways) So my exhaust was good for an increase of 11hp (average hp through quarter) and also good for a 13% increase in fuel mileage. It also increased the low-end power, as noted by the 3 tenth improvement in E/T.
The work was done in Connecticut, at Carr's Radiator and Exhaust, located in Rockville. He will do other ZJ's with the same set-up if so wanted.
How to install a fog switch (and override headlight "on")
Foglight relay (located near battery, in a protective box) must be jumped out. The foglight relay is the first one from the left, as you stand in front of the vehicle, looking at the battery.
You need to remove the wires for one of the terminals on the relay
. (This is indicated by the white arrow) The wires you need to remove are for the headlight on signal. Normally the headlights need to be on, this is the power for the primary switch on the relay. You can override this by removing the headlight wire from the relay box, then be sure to tape it up properly to avoid any short-circuiting. You can see in the pic, there is no female terminal. It is taped up and tucked under the base of the relay socket.The headlight terminal is the one on the left (as you look down from in front of the vehicle) with the foglight relay removed. Once you have removed the headlight "input" then you must give the primary switch a power source. This can be accomplished by sing a small jumper wire across two of the terminals of the relay.
(This is indicated by the blue line, jumping across the two terminals of the relay. The terminals of the relay have been indicated with black lines) You can solder them if you like. NOTE: be sure you can still plug the relay into the socket. I used the power supply for the secondary of the relay (the power that will be sent out to the foglights when the switch is turned on. This is a battery power lead, which has power at all times.All that is now needed is to add a second foglight switch separate from the headlight position. I used a small micro toggle switch, instead of a larger normal sized toggle.
(You can see in the pic it's mounted next to the headlight switch) I positioned mine next to the headlight switch above the switch for the EVSII alarm. Originally I was looking for a pushbutton toggle similar to the EVSII switch which also doubles as an indicating light. To wire the switch, all you need to do is splice into the wire on the headlight switch that grounds the foglight relay. This wire is colored brown/ with thin orange stripe. You can double check to make sure you have the proper wire by checking the color against those on the fog relay. I also further verified by using a thin sewing needle to pierce the wire's insulation and check for continuity using a multimeter.
Once you spliced into the wire, you then go through a switch and then to a good dash ground. If you don't ever care to use the stock fog position on the headlight switch, you could just cut the wire and send through a switch to ground. I however wanted to retain the use of the headlight switch fog position also, so I paralleled the toggle switch with the headlight switch. I experimented with a lighted toggle, and if you want to use one, it will work. Also, the foglight indicating light will work if you have the headlights on and the fog "override" toggle on. With just the fogs on, though, I have no indicating lights. I may add a small LED, but I have not yet.
Now you can successfully turn on your fogs without having your headlights on.
Hella Fog/Driving Light Install
(on factory fog light equipped 93-95 ZJ's)To install Hella 500 series driving lights, I utilized all the factory foglight mounting and wiring. The only thing necessary was to add some stainless nuts to act like spacers to make up the difference in width of the light mounting bases.
I zoomed in a bit, but you can see the nuts on each side, just making up the difference in width.
I used the stock fog wiring, removed from the old factory lights, so that I could retain the wiring connectors without having to splice any wiring. You will need a different wire grommet though I modified the existing one to fit securely in the Hella case.
Air Intake Modification
Of course, as we all know, the ZJ air intake system looks as if a summer intern for CC had designed it. Opening up the exhaust, and easing the airflow into the motor is the most cost-effective mods. You can free up horsepower that is just being lost. The easier exhaust can flow out of the motor, the less "pumping" the motor has to do to remove the spent gases of combustion. One big benefit, is a noticeable increase in fuel mileage. The same is true on the intake side. The easier you can make air flow into the motor, the more efficient it will be.
To that end, I modified the stock throttlebody end of the air intake plumbing. I wanted to try this, because as I see it, it is the biggest restriction of the entire plumbing. At one point the air is all "funneled" down to a 1"x 3" area.
Here's all I did.
Removed the TB section of air intake, cut along the plastic welding, then added epoxy putty to raise the two pieces further apart. Added a small piece to the area, which the TB stud goes through, to support it when tightened down. A longer stud is needed, and I used on off an older carburetor with some nylock nuts tightened down real well (don't want nuts getting sucked down into the TB!) All you need to do then is just modify the corrugated hose end so it can slide over the piece.
Pretty simple, took a couple hours. The epoxy putty can be found at most auto stores right at the counters. Here are some pics; you can clearly see how the piece is now "fatter" looking. I wanted to make it even taller, it is only about 0.75 - 1" taller. But this almost doubles the cross-sectional area of the restriction.
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