With the introduction of the C6 Z06 in 2006, the factory “Dual Mode” exhaust system gave Corvette owners the best of both worlds – a nice, even sexy tone for cruising around town, and a deep, wide-open sound (and a bit more power from less restriction) that you could use on the racetrack. Base Corvettes got the option (RPO code NPP) in 2008, and in 2009 the ZR1 debuted with the Dual Mode exhaust as a standard feature.
Of course, this presents a challenge for those who might want to fit a lighter, better-breathing aftermarket exhaust. Do you ditch the factory Dual Mode system, and live with a louder exhaust all the time? Or do you keep the stock pipes and hope they aren’t a performance bottleneck?
Well, it’s not necessarily an either/or proposition – our friends over at Billy Boat Performance Exhaust offer their Fusion cat-back exhaust systems to give you the best of both worlds for exhaust performance.
We installed a system on a 2011 Z06 Corvette complete with LS9 supercharged engine at Cunningham Motorsports, and were quite pleased with the power and sound boost we received in the process. Follow along to learn about Billy Boat’s Fusion systems, the installation process on the complete exhaust system from headers to tips, what kind of power gains we saw, and what it sounded like on our car on the dyno.
The 1-7/8-inch header tubes we used on our supercharged engine are designed to enhance exhaust flow and provide a horsepower and torque boost.
“Our real niche in the industry has been our development of the bi-modal Fusion mufflers. We’ve taken what the factory has done with the bi-modal systems and taken it up a notch or two in terms of performance and sound. Ours is a mild-to-wild, Jekyll and Hyde system that sounds mean and loud in the open position and then tone it down with the secondary passage in the muffler to get it where it’s nice and streetable, doesn’t drone, and just has a nice tone,” says Billy Boat.
In The Front
The first order of business for our installation was to get the factory exhaust manifolds out of the way so that we could get our beautiful new Billy Boat 1-7/8-inch long-tube headers [PN FCOR-0455, MSRP $1,305] and X-pipe into place.
Billy Boat’s long-tube header system has been developed specifically for the C6 Corvette, and the tubes are mandrel-bent from T-304 stainless steel and welded to 3/8-inch thick flanges at the cylinder head mating surface. One item that was important during the research and development phase for this header system was the need to keep the headers tubes equal-length, as this permits the exhaust flow to continue uninterrupted as each firing pulse enters the collector at a different time.
Collector design has been optimized to provide improved scavenging as each cylinder fires.
The tubes run into a 3-inch-diameter, 4-into-1 collector that has the tubes paired according to firing sequence to promote scavenging efficiency. As you will see from our dyno results later, this setup has proven to increase horsepower and torque throughout the entire RPM range.
We’ve taken what the factory has done with the bi-modal systems and taken it up a notch or two. – Billy Boat, Billy Boat Performance Exhaust
The headers are a true bolt-on installation (although it sure helps to have a lift) and are delivered with all of the necessary hardware for installation. They carry a limited lifetime warranty, as do all of B&B’s products.
“304 stainless is just a superior material. It’s better for corrosion and durability, and once a customer buys one of these systems, he’s never going to buy another system again,” Boat explains.
The 3-inch catalyst-equipped X-pipe [PN FCOR-0433, MSRP $987.00] is hand-fabricated from the same T-304 stainless steel as the header system from CNC mandrel-bent tubing to provide unencumbered flow through the 3-inch path from the collector through the exhaust tip.
The use of the X-style crossover allows the exhaust pulses to merge and provide balanced scavenging of the flow, in addition to enhancing the exhaust’s sound as it passes through the pipes. Billy Boat uses 200-cell high-flow metal catalysts at the front of the pipe, just beyond the collector connection.
“Each of the pieces are interchangeable with the factory parts. A lot of customers start with the cat-back, then replace the X-pipe, and finish the system off later with the long-tube headers. The long-tube header takes the place of the factory short-tube manifold and the factory catalyst section, and will mate up with the factory crossover pipe if a customer wants to do that. It gives the customer a lot more flexibility,” Boat says.
Left - 200-cell catalytic converters are used to keep the emissions man happy and your Corvette green and mean in the process. Right - Notice how the crossover section is moved further aft on the Billy Boat system - this enhances the sound and flow.
The Fusion Technology
Billy Boat’s Fusion exhaust systems are bi-modal, which means that it has two modes that the exhaust flow can travel through. Essentially, there are two separate passages through the muffler, and each muffler has dual outlets, with one side equipped with a butterfly valve that allows that side to be turned off. This regulates which side of the muffler is operative at any particular time.
This valve is present on both muffler cans and provides a switch between the “quiet” and “loud” flow paths based on throttle position.
One side of the muffler is the quiet side, and the opposing side is the loud side – simple, right? It sure is. In order to dampen the sound on the quiet side of the muffler and make long drives to the beach and mountains more tolerable, Billy Boat uses a variety of proprietary methods to control the sound including reflection, cancellation, and chambering technologies. When the valve is closed at lower throttle pressure, all of the exhaust runs through the quiet side of the muffler, which provides a sweet-but-not-overpowering exhaust note and, most importantly, no drone effect inside the car.
When you drop the hammer, the valve opens up and all of the flow passes through the loud side, where there are no controls, no compromises, and no excuses – you get 3-inch-diameter tubing straight through the muffler, uncorking all of the sound and power your ‘Vette engine is capable of producing.
Removal of the stock system is a time-consuming process best done on a lift. The factory mid-pipe is removed first before the rest of the components are removed step-by-step. It's a tight fit under there!
“The open side is a straight-through passage so that the exhaust is basically unrestricted. On the quiet side, there are a lot of different things going on inside the muffler to achieve the tone and the desired level of sound,” says Boat.
Our Fusion system is constructed of T-304 stainless steel and features four 4-inch, round double-wall tips for a sweet look from behind.
The complete Fusion axle-back exhaust system we installed [Part Number FCOR-0466, MSRP $2,133.00] is hand-fabricated from T304 stainless steel from 3-inch CNC-mandrel-bent tubing.
As a direct-fit replacement system, no cutting or other modifications are necessary, and the system makes use of the factory mounting locations and includes all of the hardware you’ll need to snug it into place. The valve operates in one of two ways – using the factory ECU-driven controller on Z06/ZR1 and 2008 NPP-equipped C6 models, but owners of older and non-Z06/ZR1 machines will have to install one of Billy Boat’s stand-alone retrofit kits to control the valve for the bi-modal system.
The Retrofit Kit
Corvette owners without the factory exhaust valve controller have an option – Billy Boat spent months developing a standalone retrofit kit to control the Fusion exhaust system’s bi-modal technology. It is shipped complete with all necessary wiring, a remote switch to open and close the valve, the vacuum line, vacuum switch, and accumulator necessary for installation. The engine provides the vacuum source, and installation is straightforward to allow you to take advantage of the Fusion system’s two-for-one sound.
Pipes Into Place
While this install can be completed in the home garage, Boat recommends that it be done on a lift unless the owner is quite proficient with mechanical repairs. Removal of the factory pipes takes some time, as there isn’t a ton of room to work underneath the car, and the ability to get it way up in the air is most helpful when it’s time to get the new headers into position. Here’s a brief overview of the process, but as always, it helps to have a shop manual for your particular model on hand before starting the process.
Tools You’ll Need:
Mechanic’s Hand Tools
Four Tall Jackstands
Exhaust Removal Pliers (available on Amazon)
WD-40 Or Similar Lubricant
One BFH, Dead-blow Preferred
Once you have the car up in the air safely, the first thing to do in order to simplify the process (especially if your Corvette has seen winter road salt) is to get underneath and soak all of the connection points in WD40, or Liquid Wrench, or something similar to give the rust a chance to loosen up. Do the same with a squirt of loose-juice on each manifold bolt – trust us, you’ll be happy you did this as the install progresses.
While the bolts are soaking, you can begin by disconnecting the battery and removing the spark plugs, as you’ll want them out of the way for purposes of removing the headers. By this point your exhaust connections should be thoroughly soaked through and ready for removal, as getting the plugs out will take some time to accomplish.
Left - Spark plug removal comes first - if you can find a friend with small hands this portion of the install will move more quickly. Left Middle - Move to the rear of the car, and drop the rear sway bar and then loosen all the cradle nuts from the studs, but not all the way. This will help gain the needed room to drop out the axle tubes. Right Middle - Remove the factory mufflers - here's where the exhaust removal pliers will come in handy. Don't forget to disconnect the vacuum line to the exhaust valve before pulling the canisters up and over the rearend. Right - Now you've got plenty of room, but don't worry - this will get filled back up with your new Billy Boat catback.
First up is the mid-pipe – get that out is important as it will allow you to get the axle-back system removed. There are two ball-and-socket connections in the rear of the car, hangers in the center of the car, and two band clamps in the front of the car that attach to the manifold downpipes. Remove the mid-pipe and set it on the ground out of the way.
In order to get the muffler cans out of the car, it’s necessary to remove the nuts holding the rear sway bar into place, as the bar sits underneath the cans and won’t allow them to sneak out if it’s in the way. There are two bolts and two nuts here – the nuts are the same ones that hold in the lower control arm while the bolts hold in the top half of the bushing bracket. Also, back off the four rear cradle nuts on the studs, leaving a few threads at the bottom. This will help gain more access to the floor so that the mufflers can tilt out.
Left - Remove the heavy stock catalysts from the car from underneath. Look how massive these things are, and then think about how much flow you'll be gaining with the new catalysts! Right - Here's where 'small-hand-guy' will be an advantage again. Pull the mounting nuts from the stock manifolds, then move to the bottom side to drop them out of the car.
Once you’ve got the sway bar out of the way and the cradle loosened up, you’ll be able to release the rubber hangers and pull the monstrous stock exhaust cans out from under the rear of the car by snaking the flow tubes up and over the rearend assembly.
Next up is the removal of the stock exhaust manifolds from the cylinder heads. First you’ll need to get the catalytic converter pipes out of the way, then move topside to get at each of the exhaust manifold nuts. Pull the manifolds out from the bottom of the car – though some prefer from the top – then prepare yourself for reassembly.
Left - Sneak your new headers into place from underneath the car. It's a tight fit, but the headers hug the block and transmission. Middle - Move to the top side and get them mounted into place. Don't forget the gaskets! Right - Here's where you can see just how tight these things fit.
Now the fun begins – with the stock parts out of the way, it’s time to get your new parts into their new home. The headers go in the same way the catalytic converters came out – from underneath. Swap the oxygen sensors into the bottom of the new headers and make sure to use a bit of anti-seize on the threads. Take care to not touch the bulb of the sensor with your fingers, or get any anti-seize on it, or you’ll be hatin’ life a bit later on when the sensor fails. Snake them into their new home, get the gaskets put into place, and tighten up the hardware. It’s not nearly as quick and simple as we make it sound, but take care during the process and think about how awesome your machine is going to sound when you’re all finished, and it’ll be over before you know it.
All pieces hung into place and ready for dyno time!
Once you’ve got the headers in place, move to the back of the car and get the new muffler cans hung up under the bumper, then connect the vacuum hoses to the flow control valves, and follow with the X-pipe. Adjust the exhaust so everything looks spiffy from behind the car, and it’s time to enjoy your new badass Billy Boat exhaust system.
Before And After
Before we started the project, our ZR1 turned the dyno roller to 550.7 horsepower and 514.9 foot-pounds of torque. In the interest of doing a back-to-back test, we set it back on the roller when we were finished with the exhaust installation, and came up with 556.6 horsepower and 528.7 foot-pounds of torque, but we weren’t finished as we knew that there was more power locked up in the tune thanks to the added flow.
Click on the graph to enlarge it – you can see how the Billy Boat headers and exhaust system tuned up our ZR1 from start to finish.
The car was placed in the able hands of Ryne Cunningham of Cunningham Motorsports for a quick tuneup on the PCM to take full advantage of our new exhaust’s greatly-improved flow. When he was finished tickling on the laptop keys, finals numbers came to 578.0 horsepower and 528.3 foot-pounds of torque.
That’s a peak-to-peak gain of 27.3 horsepower and 8.4 foot-pounds of torque. Most notably, there are no dips in performance throughout the RPM range – the Billy Boat parts exceed the stock pieces in every aspect of power production.
And now, what you’ve all been waiting for – the sound. Check out the video!