This modification marks the third overall, and second in performance, for Project C700, a 2015 Corvette Stingray Z51 equipped with the eight-speed, paddle-shifted automatic transmission. The car currently only has a few hundred miles on it, and is truly in showroom condition.
To this point, we have been beyond pleased with the performance, drivability, sound, and handling of the Stingray. However, we can never seem to leave well enough alone, and as such we have officially started down a path that will hopefully allow us to fulfill the goal of this build, and prove worthy of its name … producing 700 hp.
The exhaust system chosen for this installation comes from Billy Boat, which we selected for a number of reasons. To start with, Billy Boat has a long-standing reputation for building some of the highest quality, best-performing, and best-sounding exhaust systems for high-end sports cars.
For our application, we opted for their C7 Long Tube Tri-Y Header (PN: FCOR-0655), C7 3-inch X-Pipe with Hi-Flo Cats (PN: FCOR-0635), and C7 FUSION Bi-Modal Exhaust System with Quad 4-inch Double wall round tips (PN: FCOR-0665).
We had the opportunity to speak with Mike Boat who filled us in a bit more on what went into designing such a system. Boat explains, “Our muffler system is all constructed from 3-inch tubing with 3-inch butterfly valves, compared to the factory 2.5-inch parts. Our Tri-Y design you see here was developed in our NASCAR Truck Series vehicle, and that technology has directly translated to the parts you can purchase for your own vehicle. Our system is very user-friendly and comes to you as a true bolt-on upgrade, no cutting or welding required.”
We opted for the catted X-Pipes for a number reasons. To begin with, we know that even a high-flowing cat will help to muffle our exhaust slightly, which we don’t mind considering this car will be driven on a regular basis on public roads.
Secondly, while they do not function to the same level as the factory units, they do cut down on some the noxious gases which results in a cleaner exhaust both environmentally and for odor. Lastly, some states may not have smog requirements, but do require some sort of catalytic converter to be in place, compared to an “off-road only” pipe which is simply an unobstructed X-pipe.
Some of you may be wondering what would posses us to replace the exhaust system on a nearly brand-new C7 Stingray. Well, the simple answer is that they sound awesome, and provide more power, especially when combined with an air intake system as our car is currently equipped with – think more air in, more air out.
They can also provide some weight savings compared to the stamped steel or cast iron exhaust manifolds that are typically fitted from the factory. Most importantly however, we mentioned earlier we have some big plans for Project C700, and these headers will allow us to move a significantly increased volume of exhaust gases that our LT1 will produce.
After double-checking we had all necessary parts and tools, we drove the car onto our BendPak XPR-10ALP lift, and allowed the car to cool down in order to perform the install comfortably. During this time we disconnected the battery, covered the fenders with protective cloths, and unboxed our Billy Boat exhaust system.
Once the exhaust was cool, we lifted the car up and started by removing both the center skid plate, and the valence of the rear bumper.
After these were clear of the vehicle we removed the factory mid-pipe and mufflers, but not before disconnecting the electrical connections for the bi-modal exhaust option.
Our next step involved unbolting the bottom halves of the exhaust manifolds and pulling them free of the car before lowering it back down. We also removed the electrical tray which enabled us to move the components around individually.
Then we removed the coolant overflow tank and the intermittent steering shaft for easier removal and installation of the headers. As we learned in a previous C7 header install, you’ll want to remove the manifold heat shields first to make the following steps easier.
Next, we loosened the factory bolts holding the exhaust manifolds on, and removed the manifold gaskets, placing them on top of the engine on their appropriate side.
After sliding the headers in place we reinstalled the gaskets and tightened down our headers for a proper seal. From here, we reinstalled the other factory components: steering shaft, engine oil dipstick, plugs and plug wires, coolant tank, and the electronics tray.
At this time we moved our work to the ground, where we transferred the AMF modules over from the factory exhaust system to the Billy Boat exhaust. The rear modules are there for the NPP adjustable exhaust options, whereas the forward module works in conjunction with the cylinder deactivation mode.
We also utilized our factory O2 sensors here, reinstalling them into the pre-cat or “upstream” bungs located in the collector portions of the headers. We knew that our tuner would be turning off the “down stream” O2 sensors, so we simply sealed these bungs with the appropriate plugs and unplugged the O2 sensors from the harness downstream.
From here we simply installed the factory hanger onto our new X-pipe, bolted it to the headers, and bolted the muffler assemblies into place to complete the installation. After checking all the clearances and hardware for tightness, we reinstalled the center skid plate, connected the battery, and put the car back on the ground.
Once we were sure we had collected our tools and everyone was free of the engine compartment, we hopped in and fired it up. Do not be alarmed by any smoke emitting from the tailpipes, as there can be mandrel oil that has to burn off inside a new exhaust – though our system appeared to be squeaky clean and did not smoke.
With the installation complete, we headed down the street a few blocks to Cunningham Motorsports (CMS) to do a bit of tuning. For our install here, we turned to EFILive to supply the software and do a little remapping on Project C700.
We had the opportunity to speak with Donna Blackmore at EFILive, who was happy to explain, “EFILive’s FlashScan system includes two programs, one to monitor and data log ECM/PCM and TCM operations, and one to read, modify and reflash and ECM/PCM/TCM operating systems and calibration files.”
Blackmore continued, “In addition to its extensive tuning capabilities, FlashScan offers a unique interaction between the monitoring/data logging and tuning programs. This allows a tuner to quickly identify, and modify the specific cells within a calibration file that caused a specific condition identified in a review of logged data. FlashScan also offers custom operating systems that extend the capabilities of select ECMs and PCMs.”
Bark With A Bite
Upon driving Project C700 into our shop for this installation, it was completely stock with the exception of a K&N air intake system. With this sole modification, the car was producing 412.2 hp and 390.1 lb-ft. Between the seamless Billy Boat exhaust system and the work done by the guys at CMS with the EFILive software, our LT1 is really starting to put down some serious power.
After doing a few passes on our DynoJet in-ground dynamometer, we were extremely happy to see that our Stingray produced a tear-jerking, 438.7 hp and 452.9 lb-ft of torque at the rear wheels. To put this into perspective, that is a horsepower increase of over six percent and a torque increase of 16 percent when compared to running the K&N air intake alone.
As you can see on the dyno chart, our exhaust and tuning install added 26.5 hp and 62.8 lb-ft of torque. While this is quite a sizable gain, we were really happy to see how the power under the curve has transformed in comparison to the factory graphs.
The horsepower curve has shifted to the left about 750 rpm and now breaks into the 300+ rwhp area just after 3,500 rpm compared do about 4,250 rpm before. While our LT1 is now putting down some serious rear wheel horsepower at its peak, we are extremely excited to see the transformation present under the curve. As you can see the in dyno chart, our C7 now produces more than 350 lb-ft of torque at the rear wheels from around 2,500 rpm to over 6,000 rpm. This is a very important factor as it shows the amount of power on tap within the RPM range that we will typically be using the car.
In other words, peak numbers are great but the engine only runs in that window for a very short time within each gear selection, if at all. Having a high and broad power curve is what really makes a car quick in many aspects of motorsports, and generally more pleasant to drive.
Driving Impressions and Performance
After completing the K&N air intake system install, we took the C7 for a drive. We definitely felt a difference when the 6.2-liter V8 began pulling through the revs in the taller gears, thus spending some increased time in the higher RPM range. The motor seemed to breathe better and act a bit less starved for air. More importantly, we believed that the intake would really show its true colors once paired with a high-performance exhaust system – we like it when we’re right.
We designed these systems to produce an aggressive yet deep, mellow tone. – Mike Boat, Billy Boat Exhaust
Aside from the noticeable gain in horsepower, the throttle is crisp and clean, with zero lag, as if your foot were connected to the throttle body. This just goes to show what a solid, knowledgable tuner like CMS can do when armed with a laptop.
As we have said before, all of the mundaneness and factory “Consumer Reports-friendly” fluff has been stripped away. What remains is the C7 that Zora Arkus-Duntov and Harley Earl would really be proud of. The shifts are firm, purposeful, and to top it all off, this exhaust system sounds just plain mean.
Overall we are extremely satisfied on all fronts with both the complete exhaust system and tuning software. The quality of craftsmanship of the exhaust looks great on our Corvette and you can really tell that Billy Boat goes the extra mile when it comes to things like material selection, welding, and manufacturing, and the final cleaning and inspection before sending their products off to the customer. Likewise, EFI’s program enabled Ryne Cunningham to quickly and effortlessly get Project C700 running just right, to put down some impressive power.
If we had to do this install over again, we honestly wouldn’t change a thing. We are certainly enjoying the increase in horsepower and the new exhaust notes. Most importantly, we know that this hardware will become evermore crucial in the coming months as we continue to push America’s sports car towards that 700 hp goal, while enjoying some high-performance driving!