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MRT H-pipe and Cat-back
Product Review - December 2005

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After making such major changes to our '99 GT project car, we decided it was time to replace the stock Mustang catback exhaust system. We enlisted the help of Mustang Racing Technologies (MRT) to test their custom built stainless steel exhaust setup. At the time, our Vortech Supercharger was putting out 412 horsepower at the rear wheels. The exhaust gases were flowing through stock headers, a Prochamber off-road Hpipe, and the stock cat-back. We knew there were some restrictions in the exhaust, but what we were about to uncover, were exciting results we never expected to happen! Read on....

We decided to ditch our rusty Prochamber as well, and ordered a replacement MRT unit in stainless steel to compliment the stainless cat-back. There's not many exhaust manufacturers that offer stainless steel on both the H-pipe and the cat-back setup so it was refreshing to find MRT's catalog. The mufflers themselves are aluminized, not stainless, but that was expected. You can see the difference in the new vs. the old in the photos below.

We ordered the following items from MRT's website:
MRT Stainless H-PIPE 99-04 Without Cats - $415.00
MAXFLOW-V-1103 - MRT V-Force 304SS CatBack W/Brushed Tips - $499.95
MRT stainless offroad hpipe MRT catback w/Vforce mufflers

We decided to perform the installation in a standard garage to simulate the average backyard mechanic, and show that it could be done without a professional shop's assistance. If you're not able to crawl under your car for several hours, or don't have the proper tools, we recommend a performance shop. MRT actually performs installations in their Northville Michigan location if you're in their neighborhood.

Removal of the factory catback requires cutting off the exhaust pipes with a saw. From the factory, the exhaust is installed as one welded unit before the axle assembly is bolted up. This means you can't get the entire catback off the car in one piece without dropping the axle, or cutting the pipe (unless you have a lift). We chose to cut the pipe for obvious reasons. If you want to save your old system, be sure to cut it on a straight section of pipe for easier welding later on. Cutting in a bend will make it difficult to put a sleeve on it later.

After we had backed the car up on ramps, we used jackstands at the front to get the front and rear high enough to work under the car. Be sure to take the proper safety measures to have the car stable. You'll be doing lots of tugging and pushing on the exhaust. We unbolted the flanges at the H-pipe and Catback connection, popped the rubber exhaust grommets off the hangers, and then sawwed the pipes just aft of the mufflers. The whole piece falls down enough to get your hacksaw in there for easy cutting. Wiggle the curved piping over the axle and out of the car.

The H-pipe removal is not difficult. Unplug the 4 O2 sensors first. The 4 header bolts will require several different socket extensions including a swivel extension. We used a 15mm deep socket and the various extensions to unbolt the H-pipe from the headers. These are usually stuck pretty tight due to the extreme heat and rust, so you may need to spray WD-40 on them and soak for a few minutes before they'll come loose. Once you get those off, you can remove the entire H-pipe.

You will need to transfer the O2 sensors from the old pipe onto the new one. Carefully remove the 4 sensors and re-install on the new pipe. If you're using an offroad pipe, you need MIL eliminators to prevent a check engine light from occuring. We separately placed each piece of the Hpipe under the car and lightly bolted up to the headers to hold them in place. Notice the different flange types in these photos.

The driver's side flange is a ball-and-socket style while the passenger side is a gasket flange. Make sure the gasket is installed before you mount it up. The driver side has no gasket. The new MRT H-pipe comes in two sections, left and right. It joins at the center "H" crossover with one side sliding into the other. We pressed the 2 sections together at the crossover pipe. It will take some banging with a rubber mallet to fully seat the 2 sections together. (Be aware that if you're doing this after Midnight, you'll likely have a few angry neighbors.) If you assemble the two halves before installation, you may not be able to get the pipe in place with only the clearance of jackstands. You need some wiggle room so assemble it after you get under the car to be safe (unless you have access to a lift)

If you're doing this alone, use your knees or body to hold the H-pipe up close to the floor pan where it will need to go. Then tighten the 15mm nuts at the flanges by hand as tight as you can get them. You may need a long ratchet handle or breaker bar to get them tight enough. If you're not familiar with the ideal placement, then you might want to save the final tightening until you have completed the catback as well. The pipe should not be touching the floor plan or other items. Give it some clearance and run the pipes parallel to the driveshaft. Plug in your O2 sensors that are mounted on the black shelf to prevent them from touching the hot pipes later.

Like some other exhaust brands, the MRT catback comes in several sections as seen above. This allows fine tuning of the parts to ensure a perfect fit. It also requires a little extra installation time to get them all lined up properly so block yourself out some time to get it right. The first step is the short extensions that lead to the mufflers. Bolt those with the supplied bolts to the back of the Hpipe flanges as seen below. Leave loose so you can maneuver them into place later. Attach the V-force mufflers to the extensions using the supplied U-bolts. Again, only snug the nuts so as to adjust later.

The axle loop is the next piece, and the most challenging to get in the car while doing a garage installation. In order to get the loop over the axle, you may need to jack the body of the car slightly to increase the gap from the axle. Even with the body raised, we fumbled with the pipe for 15 minutes trying to figure out how it would go over the axle. The concrete flooring was our biggest obstacle, and having a lift would have solved it. But eventually we found that there was only one way that it goes over. From the back of the car, the pipe goes over the axle to the front. There was one particular way to position the pipe so that it would drop over that axle. So believe me, keep trying until you get it. It can be done. Bolt up your axle loop to the muffler backsides with the provided U-bolts, and hang the pipe on the stock hangers.

With those pieces in place, you need to position your tailpipe extension. First put the mounting rods on the tips and tighten the Hex head bolts. Use the wide clamp to attach them to the axle loop pipe. With everything loosely in place, it's just a matter of going back to the beginning and tightening all the bolts. As you start with the muffler extensions at the hpipe connection, align the pipes in a manner that doesn't conflict with the driveshaft or other components. Then tighten your muffler clamps down. Be sure to turn the U-bolts up out of the way so they don't drag over speedbumps and roadkill. You'll want the mufflers to be as straight and flat as possible to prevent them from hanging down.

When tightening the axle loop down, try to watch your tailpipes for an alignment that aims at the exhaust cutouts in the bumper. The pipe should make a perfect line for the cutout. If, after tightening the bolts, you find that it doesn't line up, you can either adjust those bolts again, or go back to the extensions before the muffler and adjust those bolts to move the whole section around. Eventually, you'll have them all lined up and ready to do the tailpipes.

fully installed mufflers
The tailpipes are tricky because of the tight tolerance with the bumper cutouts. There's nothing worse than seeing a car with a dangling tailpipe or a blackened bumper, so dig out your best patience hat and get this one right. You'll need to use both the small hex head bolt on the rod, and the large clamp at the back to adjust it properly.

As I mentioned in the first paragraph, we did discover some amazing dyno results with the exhaust system in place. Our Vortech supercharged GT had long since surpassed the air flow capabilities of the stock catback exhaust system. Our previous best dyno results were 414 horsepower (graph says 423 because of a spike) and 405 torque SAE corrected. The new numbers you ask? How about 460 horsepower and 421 lb/ft of torque! Now we're not going to exaggerate and say all 46 horses gained were due to the exhaust because it wasn't. The only other changes from one dyno session to the next was the cooler air temps (although the SAE correction factor still adjusts for this accordingly to simulate equal conditions), and we moved the rev limiter from 6000 to 6500. When we saw that the RPMs were continuing to climb at 6000, Dan at Pro-Dyno performed his magic and moved the limiter to 6500 and found gobs more power there, partly in thanks to the higher flowing catback. We also iced the intercooler on all dyno runs to simulate a track pass.

If you look at the graph below, you can see that the gap between the old run and the new runs drastically increases over 4500. We believe that to be the result of the exhaust getting the gases out of the car quicker when it needs it most. There's no doubt the exhaust helped the power range tremendously. You can certainly feel it in the ole butt-o-meter as well!

As for the sound of the new combination... this monster is L.O.U.D.! If you want a quiet system, you don't want this setup. We previously had a Prochamber off-road H and Flowmaster mufflers. That combo was loud, but when you stomp on the pedal now, you can hear all 460 ponies screaming to fight their way out of that engine. We stressed to MRT that we were looking for a chambered sound similar to the Flowmaster that didn't have a raspy tone. The V-force mufflers exhibit exactly that concept. We love the new sound and the new intimidation factor that comes with it!

We also found some other goodies to purchase on the MRT website including these matching Charcoal running pony floor mats, and a yellow MRT shift knob that matched the Chrome Yellow paint. There's more to MRT than exhaust so feel free to browse their website HERE.
MRT Charcoal floor mats MRT yellow shift knob

Written by: Steve Shrader, YMR

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