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An Exhausting Experience
Now that we have lots of fresh, clean air coming in, we need to get all that bad air out. Normally headers are the first line of defense, however in this case they prove to be of little advantage at the lower rpm's, especially with the super efficient mufflers we have chosen. The header's primary function is to scavenge spent exhaust from the cylinder, rather than just letting the air find it's own way out under pressure. By nature, headers are 'tuned' to create peak performance in a specific RPM range, dictated by their tubing diameter, length and tube configuration. This usually happens at between 3,000 to 4,000 RPMs. The unique Flowmaster muffler design can actually scavenge better at the lower RPM ranges, making an excellent compliment to the headers higher RPM characteristics. Flowmaster's new series 70 muffler is similar to their famous "Big Block" muffler, only not quite as deep in dimension, allowing for fitting in tighter areas.

Contrary to old beliefs, having too big of an exhaust tube can actually be detrimental to performance and efficiency gains. The flow effect of just the right exhaust tubing, can act like the difference between attempting to siphon gasoline with of a 1" hose versus a 5" hose.  The 1" hose will start the process easily and flow well, whereas the too big 5" hose will be very difficult to get the siphoning going at all. Only at ultra high RPM's or in Turbocharging applications will the exhaust want to "just get out of the tube as fast as it can," and ignore any benefits the smaller tubing can grant.

(Photo of MAC headers compared to stock manifolds): Note MAC's unique design of increasing the tubing size  as the runners collect together, creating an "expansion chamber-like" effect., thereby increasing the scavenging benefits. The MAC long tube Tri-Y header has a total of seven collector points, compared to the conventional header's mere two points. This further increases the scavenging effect even more, along with the ability to make more power. Mac Jr. from MAC industries tells us that a large, single high efficiency muffler and exhaust system may actually have the ability to produce more power than a dual system, however, under extremely loaded towing conditions, the single exhaust would become much hotter than duals.

(Photo of MAC headers assembled w/other headers and cast manifold): The MAC header system came complete with the O2 sensor and EGR emissions fittings ready to be hooked up. The patented True Fit® design eliminates the need for gaskets, which are prone to leak at the collector flanges. Mandrel bent runners insure 30% more flow and uniform cross sections of the tube's inner diameter. The fully aluminized and HTS coated tubes further reduces the effects of corrosion. Installation was fairly straight forward, however the install time would gone much quicker and easier had any kind of directions been included with our kit. MAC claims a 29 rear wheel horsepower increase with their headers.

(Photo of fabricated header divider laying down): In order to retain the low RPM scavenging benefits from the cross-over tube effect, yet still reap the benefits from a low restriction dual muffler system, we neatly custom fabricated a dual outlet divider that will be bolted onto the original header flange. Also, by having two Catalytic converters in parallel, would allow us the opportunity to free up even more artificial restriction. Notice the free flowing "D" shaped ports which efficiently split the large single tube back into two pipes with virtually no negative flow effects.

(Photo of fabricated header divider standing up): To fabricate this unique piece, Performance Unlimited cut out a heavy plate of steel and hand fitted the round tubes to the "D" port shapes. Then the precise fitting tubes were welded together with a space in between them to allow standard exhaust tubing and clamps to slide over them.

(Photo of headers clearing the sway bar bracket): The overall fit of the MAC headers were excellent, other than the passenger side sway bar mount needing to be modified to clear the tubing. Internal exhaust noises over the cast iron manifolds were slightly increased, with a powerful purring sound of the engine resonating through the thick individual header tubes. This condition was hardly noticeable in under all but full power situations, and the racy sound commanded authority to those looking on that this is no ordinary off-the-shelf rig.

(Photo of headers under the truck): The long Y-pipe was routed under the cross member (as OEM) making for an easy, yet more visually noticeable installation. The immediate increase in performance was noticed the first time the throttle was snapped, with the big 460 wanting to easily rev into the 6,000+ rpm range. Previously we could barely get the lumbering beast to strain into the 4,500 range! A slight loss in low-end acceleration was detected, but once it hit 4 grand... "see 'ya later!"

(Photo of headers connected to old exhaust system): This extravagant temporary exhaust system was concocted to compare the new headers against the rest of the exhaust system independently. Previously there already was an after market dual muffler and catalytic converter system installed in place of the original factory single configuration.

(Photo of Flowmaster compared to turbo muffler):
Note the larger size of the Flowmaster 70-series "Big-Block-II" muffler compared to a standard turbo style unit. The sizable case is needed to handle the higher flow and increased heat extracted from the cylinders, thereby improving power and increasing economy. The Flowmaster is a solid welded muffler with no seams to blowout or leak, and sports an aluminized coating to resist corrosion. Basically the Flowmaster is designed around performance, and the quieting conditions that result are a side benefit.

(Photo of Flowmaster cut-a-way with point to 'vacuum chamber' & to sound deadeners, not "baffles"): Inside, the Flowmaster has no internal packing material or sound deadening fillers. It's all done through absorbing the sound vibrations within the heavy steel case, which leaves the internal 'baffles' (pointed out) free to create a negative pressure zone (vacuum) to extract exhaust pulses from the engine, therefore acting much like the scavenging principle headers are based on. Note the small tubes going 'no where' in the upper right. These absorb high pitches, allowing only the much more difficult to hear 'bass' tones to exit the muffler, thereby reducing the sound without further restricting the exhaust flow itself.

(Photo of Exhaust tube bender in action): Here, Gary Mayer of West Side Auto is at work on the bender. Producing functional and form fitting hi-flow exhaust systems could be considered an art form in the hands of a qualified expert. Meticulous care was taken to reduce restrictions while making sure to clear obstacles as well as eliminate heat problems with underbody components. Our system took nearly 20 feet of tubing, 6 hangers and 16 clamps.

(Photo of close-up bend): Dan Johnson at Flowmaster recommended 2-1/4" tubing for maximum performance at mid-range speeds, however, we elected to go with the larger 2-1/2" size so we could make sharper corners to fit around the overdrive unit. In the end, we still have the same relative flow to that of the recommended 2-1/4" size. An incredibly more expensive mandrel bender could have done the job without reducing the diameter at the bends, however this procedure produced similar results in the end with much less cost. 

(Photo of tubing expander): All tubing joints were made to fit tight, and didn't leak even before the clamps were installed. The tubing Gary chose to use was .095" wall aluminized 2.5" O.D. Steel tubing (this stuff is the size driveshafts are made of!). The considerable heft of this nearly bulletproof material will really enhance the longevity of our custom system.   

(Photo of tubing extending out from the bender): Ray Zuelke from U.S Tire and Oil in Combined Locks, WI., the suppliers of our tubing,  tell us that, "the aluminizing process is the result of aluminum alloy being kilned into the metal during the drawing process, and the seam is then re-aluminized after welding. Since this process is not a coating, it will not flake off when bent in the machine. As a result, the entire metallic structure contains the alloy and therefore lasts longer and looks better all throughout the life of the product while in use." This also means that the inside of the pipe will be protected from corrosion as well as the outside.

(Photo of Muffler Heat  Shields, on installed and one in foreground): To further reduce underbody heat, Brian Moberly of Flowmaster provided us with some real slick aluminum heat shields for our monster mufflers, complete with clamps. Flowmaster claims up to 50% heat reduction and decreased interior noise levels with these little add-ons. Besides this reduction of radiant heat from the mufflers, the built-in shields on the Random converters reduced floorboard temperatures inside the cab by almost 90%, which increased the effectiveness of the air conditioning to almost blizzard proportions.

(Photo of heat wrap being applied to the exhaust tubing): In order to maintain maximum ground clearance we ran the exhaust perilously close to our revered Gear Vendors overdrive unit. To prevent premature failure due to unnecessary heat transfer, we wrapped the exhaust tube with DEI's header wrap insulation, thereby reducing radiant heat from the pipe in that section. The temperature was reduced more than half with the wrap in place.

(Photo of heat tape being applied to brake hose): Even though our custom bent pipes cleared all underbody obstacles, it was unavoidable to stay far enough away from everything. Rather than compromise the flow of the exhaust we opted to use DEI's thermal barrier tape, the same stuff we used on the Air Intake earlier on Project M-P-G. Any brake hoses and cables coming within five inches of the exhaust was wrapped to eliminate all potential problems under the worst conditions.   

(Photo of installed exhaust system- front half):  After 4 hours of painstaking labor, a proud step back to admire this work of art was deserved. Since no one obviously offered a complete bolt on exhaust kit for our one-of-a-kind customized Centurion, we particularly appreciated the benefits of a custom bent exhaust. 

(Photo of installed exhaust system- rear half):  By having the exhaust custom bent allowed us to work with the installer and place the tubing exactly where we wanted it, and how we wanted it. The inherently thicker tubing needed to withstand the forces while being bent will also mean a quiet, long lasting system.

(Photo of installed chrome tips):  Big 3-1/2" chrome tips exiting on either side of the truck gave the visual effect of performance while the authoritative yet quiet deep toned rumble of the Flowmasters when fired, completed the effect. These mufflers were selected due to their ease in which they handle high heat conditions over extended periods of time. The level of quietness we chose is un-characteristic of the typical Flowmaster by being nearly silent and un-noticeable while under full load at highway pulling speeds. This was a welcomed trait when driving 3,000 miles under heavy throttle while pulling a monstrous load.

(Photo of heat gun measuring exhaust): Flowmaster claims their muffler's advantage is that it not only reduces back pressure, but it actually scavenges exhaust, thereby producing even more power than with no muffler at all. The scavenging effect is backed up by temperature readings with an infrared heat gun made by Intercomp. External header temps averaged at 381 degrees while the further down the line the converters measured 194 degrees. Even further down the system the mufflers registered a sizzling 278 degrees. It's obvious the mufflers are doing there job, as well as reducing under hood temps as well.

(Photo of old O2 sensor compared to new one): Another fairly simple but typically overlooked modification would be the replacement of the Exhaust Gas Oxygen sensor on older vehicles. Fresh, new sensors respond much quicker and over a greater range of feedback than one that has aged over the years. This gives the computer faster, more accurate information and therefore the potential for increased cruise power and efficiency.

(Photo of installed O2 sensor): Care must be taken when installing the new sensor as to not get any grease or other contaminants on the probe itself, whereby it could damage the rare Earth materials used in the sensor, whereby false readings could result. Nothing other than a small dab of anti-seize compound is to be used on the self-sealing threads, as our new sensor already came with pre-applied.

Green and Clean
You normally don't think of Catalytic converters as being a "performance" piece, but in this day and age, pretty soon NASCAR will be running them, too. Like anything, there are performance converters that reduce restriction and improve flow over stock OEM units. Even though your vehicle may not need to be tested for emissions in your location, removing the catalytic converters from a vehicle originally equipped with them is a Federal offense anywhere in the United States, regardless. Therefore, keeping Uncle Sam happy as well as your rear  tires, can still be had with performance catalytic converters.

As for other emissions devices, such as the EGR (Exhaust Gas Re-circulation), they in many cases actually "help" in performance and fuel mileage by going into an "extreme lean" mode when in light cruise situations. This is where the computer realizes that performance is not the primary consideration and tries everything in it's power to run the motor as efficiently as possible. In many cases, once the driver demands any appreciable acceleration, the computer, for safety as well as performance reasons, immediately temporarily disables most emissions devices. Emissions are generally highest at idle, particularly during engine warm-up. As a matter of fact, the EGR, as opposed to the old wives tales, does not really "re-burn unburned fuel in the exhaust." The EGR is meant to introduce an inert gas to cool the combustion process (which is abnormally hot due to the leaner, efficient burn) in order to reduce emissions and Nitrous Oxide levels, which is blamed primarily for acid rain. Very little exhaust gas is needed to accomplish this, and when more throttle and power that is needed, the less exhaust gas is re-circulated, proving that removing good working emissions devices can most certainly reduce performance and economy.

(Photo inside of cat. converter comparison- standard performance): We made an initial visual inspection of several converters to narrow the field down to two of the best choices we would be testing on the flow bench. With a 100 watt light bulb placed on one end of the converter tube, we simply looked through the other side to see how much light passed, therefore giving a rough guess-timate on the internal restriction. This converter is a popular "high-performance" version.

(Photo inside of cat. converter comparison- high performance):
Even before we flow tested the converters we knew good things were about to happen. With the same light shining through this converter, it's obvious the Random Technologies unit was going to be much less restrictive even compared to the so-called "high-performance" version. Now we needed to confirm our theory.

(Photo of standard performance Cat being flow bench tested):
We had the opportunity to flow test several catalytic converters to "see" inside these mythical beasts. First we tested a typical after market high-performance converter, which flowed considerably better than a stock OEM unit.

(Photo of Random cat being flow bench tested):
Then we flowed the Random Technologies piece. Dave Emanuel at Random stated that their units out-flow most others, and they were right. The Random converter flowed so well, the SuperFlo 600 flow bench couldn't keep up at the typical 28 inch pressure standard, so we had to re-test at a lower 27 inch baseline. The airflow we used simulated approximately a 2,500 rpm engine at 60mph.

(Photo of muffler being flow bench tested):
George Forge at Motor Masters Racing also tested a typical performance turbo muffler for a "grins and giggles" comparison. We were surprised to find that the Random catalytic converter out flowed the muffler by almost 11 percent better, which proves that illegally removing this type of converter has no significant performance advantage over a standard performance exhaust. As our very impressed bench operator mentioned, "Flow bench numbers don't lie."