Last Update: September 13, 2003
Ok, it's happening late in the game, but it's time to get twin mufflers, pipes and tips under this car. Dual exhausts in theory provide for a freer breathing engine and reducing the back pressure would return some horsepower lost to the pipework. So, since I've got a 232 cu inch engine which is being force fed to flow volumes proportional to a 380 cu inch engine, it seems like a little more breathing space would be a good move.
I decided there was no reason to go and buy a fancy exhaust system from Borla for this car. For one thing it would have been fairly expensive (not that cost has been a deciding factor in any of these mods), and for another it seems pointless to worry about putting a performance exhaust designed for a souped up V8 on a V6. Additionally I'm not looking to make this car tremendously loud or obnoxious, which seems to be the primary goal of the muffler swappers. So, after all considerations, I bought a set of pipes and mufflers from a wrecked GT and an adapter from pacesetter. Total cost delivered to my local freght dock was about $250 combined and I got the pipes intact (not cut at the axle crossing. The new (used) pipes are shown below left.
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The first step is to get the old exhaust system off the car. Now, I could have just cut it off with a torch, but since I needed to unbolt the rear suspension to get the new pipes on, I just jacked the car up, unbolted the shock and upper control arm and lowered the rear differential enough to snake both the old and new pipes over the axle. The stock single exhaust is show below left after removal from the car. Pretty ugly.
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After the pipes are off, the Y in the existing system needs to be cut off behind the cats (above center). This is an unpleasant job without a lift. I did it on jack stands with a hack saw and it wasn't fun. Figuring out where to cut was tough to gauge, and since the pipes are curved where the adapter lines up, things are less than clean when you go to slide it over the ends. After a fair bit of pounding, judicous use of levers, ropes and pulleys, I managed to get everything pulled into the right place and clamped down (above right)
Now, this clamp arrangement is all well and good in theory. In practice it sucks and I had the pipes welded after exactly two days of driving the car when things started to shift around. My advice is therefore, go ahead and get everything ready under the car, and then take it to a muffler shop and say "weld here!"
Now, connecting the pipes is only half the task. New hangers are also required. I bought the Ford hangers from a GT. The part numbers required for my car are:
XR3Z5C263AA (1x Muffler Hanger)
XR3Z5A246AA (2x Tailpipe Hanger)
You'll also need the 1/4-20 mounting hardware and clip nuts. I got these at my local hardware store. Lastly the decision has to be made about the rear bumper. The GT's had cutouts in the rear bumper to pass the exhaust tips. There are several options at this point. (1) Buy a GT bumper cover (2) Make your own cutouts in the v6 cover (3) Lower the tips by about 1.25 inches to clear the stock bumper. I selected option (3) which meant I needed to make some kind of spacers for the tailpipe hangers. Working for an aircraft parts maker, I happened to have access to all kinds of aluminum stock. So I "aquired" two short 4 inch lengths of 1.25 inch square aluminum extrusion. Holes were drilled to match the tail pipe hangers, the parts were primed and painted black and presto, overkill spacers.
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With everything put together, the last step was to polish the somewhat tarnished stainless steel tailpipes. Stainless isn't the easiest thing in the world to polish, but a product called Luster Lace (available at www.lusterlace.com) is worth every penny. Before and after shots of a tip appear below.
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So, with everything done, here's a look at the install. The welded adapter is at left, an underbody overview in the center, and the pipes exiting the back of the car at right below.
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So, the obvious question is, did all this work pay off in horsepower? The answer is yes, but not by much. I think it's somewhere in the 3-5 pony range. Certainly nothing to write home about considering the more significant leaps that have come before.
Using the G-Tech Pro Competition I generated new dyno plots for the car with the new exhaust system. The plot below shows the power output with both the before and after the exhaust swap. The earlier curve is a little more eratic than the new one generated with the latest software updates from G-Tech.
Looking beyond the increase from this particular change, I also compared the new dynos against the theoretical performance curve generated in earlier steps. The new curves from the updated G-Tech software make this comparison much easier than before.
And lastly we have a plot comparing the current performance of the car against the stock profiles.
Another benefit of the better G-Tech software is that interpretation of the dynos has gotten crystal clear, and much to my chagrin, my earlier estimate of the horsepower peaks were in fact just shift spikes. The real power peaks appear to be about 213 SAE RWHP and 221 SAE RWTQ.
