Dual Mode Muffler
All of us like the heavy power sound from a good running Jeep engine and the factory grocery getter sound does not get it.
I have tried MANY exhaust setups on mine: glass pack, Flow 40, Delta flow 40, and straight pipe, with my full 2.5 inch exhaust system from the engine back, route for the power-house sound and, for a while, it sounded good.
The only problem is, after a while the sound tends to drone from the back glass, and the constant loud exhaust, becomes a detriment to conversation on long highway hauls. There had to be a better way.
Off to the Summit catalog, which of course I keep in the “Library”. What do I find, but a muffler called the Warlock in all sizes and inlet selections. The interesting thing about it is that it has three ports. Inlet, outlet (Which is offset) and a bolt-in removable plug for straight through exhaust (Read Sound) flow.
Now, getting under the Grand to remove and install, this plug, is not in the cards for every day driving. What if I could get this port to open from the inside of the cab while driving, or better yet, if I want to get it automatic for power, but quieter for normal driving.
There are a number of electric cutouts on the market, but they use stepper motors for a controlled opening amount. I wanted automatic open and close, and these systems will not stand continuous signal. They cannot open and close via the use of a micro switch, which would be more difficult to install anyway. They are also VERY PRICY.
Back in the late 80’s General Motors used a vacuum actuated heat riser valve just outside of the right hand exhaust port on many of the small block V-8’s. This valve was spring open and vacuum closed. If I could use this valve for an automatic bypass, I would be in business.
I bought one of these valves (part number below), although you can find them on, for example a mid 80’s Suburban in the junkyard. I connected it to the intake manifold of the Grand with a 10 foot hose and off for a drive. Within about one second of start up, the valve closes. Cruising speed vacuum is around 10-16” vacuum. Start to accelerate and the vacuum drops fast to 0. If the intake manifold vacuum drops at or below 5”, the valve begins to open and is fully open at around 2.5”. This will work!!!
One call to Summit Racing for one 2.5” Warlock (BIG-50522flt) center inlet and center outlet muffler and a 2.5” “Y” pipe (SUM-G4821) and a short piece of 2.5” pipe and we are off.
This is the plug that comes with the muffler to block off the center through flow passage. Originally, you need to unbolt and remove this for unrestricted exhaust flow. It will now be discarded.
[FONT="]Here is the heat riser valve (Oreilly auto part number Murry #150) used to create the automatic bypass effect. Spring open and vacuum closed. Begins to open around 5” vacuum. It is not a sealed closed valve, in the closed position, but enough to do the job.[/FONT]
[FONT="]The Y pipe that comes from the Summit, come with extra flange adapters, You will need a short length of 2.5” exhaust pipe and weld one of these flanges on to it and the pipe modified to return to the Y pipe. This is the standard muffler outlet to the tail pipe.
[/FONT]Here it is being mocked up prior to welding to get the proper angle. I wanted to be able to remove the system, if maintenance were required. Note the second flange adapter mocked up on the straight part of the Y pipe. The heat riser valve has a tapered end that will seal directly into the muffler outlet. Make sure that ther
e are no burrs in the outlet pipe and there will be no leak after you tighten the three bolts. You do need a gasket for between the y pipe to heat riser valve and the muffler outlet to the y pipe. These come with the Y pipe.
Here is a picture of the valve in the closed position. This occurs at full vacuum down to 5”, where it begins to open.
[FONT="]Here, the valve open with no vacuum
[/FONT]Close up of the installed vacuum valve installed and bolted together. No gasket is needed as the tapered seat goes to the muffler. Just make sure the inlet hole has no burrs and it will seal. You need a gasket between the valve and the y pipe and some small grinding of the holes for alignment may be necessary. I used 3/8” bolts and lock washers.
Here is the final installation. Note, I have heard that the Warlock is prone to rusting. I sanded off the original paint and repainted it and the installation, less the valve with the best high heat paint I could find. The original paint came off WAAAYYY too easy, so I would really recommend this extra step.
Final Installation
older pic before I got the rear adjustable arms and welded the exhaust instead of the clamps.
Make sure the vacuum valve is pointed in the up position to avoid damage.
Just bolt, clamp or weld the system into the exhaust pipes as you would a normal muffler and hook up a vacuum line to any port on the intake manifold and you are in business. The Grand now has over 10,000 miles on this set up and it works perfectly. Reasonably quiet for normal driving, but “aggressive” straight through exhaust when you get on it
BUT, I needed an exhaust now. Had the cash in hand and wanted to try somethnig differant. Whats the fun of running a flowmaster40 like the other 100,000 XJs? I just like to experiment and try new stuff when it comes to my truck. If it doesnt work out....i'll go with a more simple muffler. but this will be a fun project
