While our Gen-3 Coyote boasts the latest go-fast technology to help us exceed the performance of a GT500 on the dragstrip, this 2018 Mustang GT also comes with 90,000 miles on the clock. The higher mileage kept our purchase price reasonable, but it also introduced some risk. To be fair, certain components — such as the 10R80 transmission — can decide early in their lifespan that the boosted life isn’t for them, as we discovered with our Pony Wars GT years ago.
Since the last track date, Project Magneto has been exhibiting some unusual behavior. The dyno session didn’t go smoothly, and although we suspected something might be wrong, we couldn’t pinpoint the issue. A week after the track session, the S550 was transported to North Carolina, where both it and I, the author, now reside. Upon arrival on the East Coast, I scheduled an appointment with Pro Dyno in Fort Mill, South Carolina to put the boosted GT on the dyno for diagnostics and potentially some tuning.
During the dyno session, we attempted to make pulls using sixth gear, but encountered slipping. We contacted Suncoast Performance in Fort Walton, Florida for a fresh 10R80 transmission. The stock transmission was removed and shipped to Suncoast, where it received fresh Raybestos clutches, a proprietary valve body, and pump. When the transmission arrived in South Carolina, it included a Suncoast billet flexplate and a modified stock converter (details on this will be covered in a subsequent transmission build article).
Pro Dyno got started by installing the Suncoast billet flexplate and adding 7 quarts of trans fluid to the converter. Three clicks ensured the converter was seated on the input shaft of the 10R80. The converter uses studs (not bolts) to connect to the flexplate. A trans jack was used to raise the trans into place and bolt to the block and crossmember.
Charlotte, We Have A Problem
Upon pulling the stock transmission, it became apparent there was another issue: the factory converters were starting to fail. About half of the drivers-side cat had vaporized. There was no telling whether the addition of the supercharger and subsequent tuning had done the damage, or if the mileage got the best of it. At this point, we decided that our CARB-legal testing had run its course and it was time to get serious. If we were going to beat a GT500, we were going to have to turn it up a notch.
We contacted Kooks, renowned for crafting some of the finest fitting 304-stainless steel headers and exhaust systems for Mustangs. With their extensive experience in the Super Snake program and ensuring catalytic converters withstand high horsepower, Kooks suggested 1-⅞-inch headers paired with a special High Output (HO) GREEN cat connection pipe and a 3-inch cat-back exhaust system. This setup maintains a consistent 3-inch diameter throughout the exhaust system for our 2018 Mustang GT.
The headers boast a 3-inch collector featuring a velocity spike designed to enhance exhaust scavenging, while the 1-⅞-inch primaries are mandrel-bent to maintain volume and optimize flow. These primaries mate to laser-cut ⅜-inch-thick flanges for a secure seal. Kooks meticulously digitizes all designs to ensure precision, resulting in each pipe exiting the jig meeting exact specifications—a testament to their ISO certification.
For the connection pipe, I opted for an X-pipe configuration along with GREEN catalytic converters. The X-pipe configuration typically imparts a higher and crisper exhaust note at wide-open throttle, a sound I personally favor. Additionally, in theory, it offers slight performance benefits (perhaps around 0.5 horsepower, though the actual gain may vary). The GREEN catalytic converters are EPA-verified and incorporate a higher concentration of precious metals, enhancing their ability to cleanse exhaust emissions compared to conventional aftermarket catalytic converters.
“The High Output (HO) catalytic converters feature a stainless steel 4.5-inch body with 300 CPSI. The larger cat body, coupled with a lower cell count compared to our traditional GREEN cats, enables these converters to withstand over 1,000 wheel horsepower on naturally aspirated (NA) or forced induction (FI) builds,” explains Sales & Marketing Manager Becky Sliney. “While we continue to collaborate with different partners on testing, any issues encountered with our catalytic converters typically stem from overheating, exhaust pressure, or a combination of both factors.”
With a good tune, we’ve seen the HO cats withstand up to 1,100 wheel horsepower thus far with no problems. Becky Sliny, Sales And Marketing Manager, Kooks
“Our traditional GREEN cats feature a 4-inch body with 400 CPSI, offering high flow compared to most OE cats — typically between 2-3 times better flow. However, the smaller body and higher cell count limit these cats to 750 wheel horsepower,” Sliney elaborates. “Nevertheless, they remain suitable for boosted applications within that power range. Additionally, all of our GREEN cats, including the High Output (HO) variants, adhere to EPA standards. With a proper tune, they should not encounter issues with check engine lights (CEL) or inspection.”
Unlike the factory exhaust, which narrows down to 2.5 inches, the Kooks catback system maintains a consistent 3-inch diameter throughout for optimal performance. It’s worth noting that exhaust piping is ideally largest just before exiting for maximum efficiency, rather than decreasing in size. The oval mufflers (Part Number MUF-018) feature a single entrance and exit, often referred to as a turbo-style muffler. These mufflers utilize a perforated core and proprietary Kooks packing material. The straight-through design is engineered to enhance exhaust flow while effectively minimizing exhaust drone. Opting for the matte black tip option, which complements Magneto’s color palette perfectly, aligns with my preference for subdued finishes over chrome or polished accents.
The factory exhaust necks down to 2.5-inches using this reducer pipe (left) before it enters the mufflers, which is not ideal for flow or exhaust velocity. The Kooks system (right) is 3-inches all the way through.
Not only does Kooks manufacture the necessary parts, but they also have them readily available — a rarity in a world plagued by endless back orders and unfulfilled promises. Yes, they actually maintain stock of their products, and the turnaround time for items being manufactured isn’t too shabby, either. After all, you can’t build a car solely on hopes and dreams, ladies and gentlemen. Without Kooks’ stock of exhaust components, the 2018 Mustang GT would have been left stranded at Pro Dyno for months on end.
Fixin’ To Get Fixed
To commence the installation of the exhaust system, Head Technician Paul Conner began by removing the motor mounts, utilizing screw jacks to support the engine. This approach provided optimal access for removing the factory exhaust manifolds. Once the top nut was removed from the topside, the remainder — including the actual manifolds — was taken out from the bottom of the engine bay. The Kooks headers were also installed from the bottom. The headers came with a top-quality set of steel gaskets, which we placed between the cylinder head and the thick Kooks flanges. The OEM studs and nuts were discarded and replaced with bolts supplied by Kooks. Additionally, O2 sensor extensions were necessary to complete the header installation, and fortunately, they were included in the kit.
The passenger side presents a challenge with the A/C lines which are a little tough to work around. At times, it required patience and one turn at a time with an open-ended wrench. Paul tightened the front bolts from the top, similar to removal of the stock manifolds.
Moving rearward, the connection pipes with the GREEN cats bolted up to the ball and socket flange on the header collectors. For those unfamiliar with header installations, this type of connection is much more convenient and straightforward compared to dealing with slip-fit connections. It’s advisable to keep everything loosely fitted until the exhaust is fully installed and adjusted to your preference. Lifting the X-pipe into place was a two-person task; it clamped to the connection pipes and hung in front of the axle center section using hangers. The final piece of the puzzle was the axle-back portion, comprising the mufflers and exhaust tips. The mufflers slid into the hangers, and clamps were used before and after them. These slip-fit sections with clamps allowed for adjustments to ensure the exhaust tips were centered in the rear valance. Regardless of the vehicle or exhaust brand, achieving this alignment is always a delicate process. Once everything was adjusted to Paul’s satisfaction, all connections were tightened securely.
The transmission and exhaust installation was completed in less than 8 hours in total. However, I reckon your average DIY’er might stretch it out into a weekend affair, what with all the cursing, tool throwing, trips to purchase missing tools, and misreading directions after a few too many beers. Surprisingly, the most painful part of the install was the bill for the transmission fluid. The 10R80 transmission requires a concoction of unicorn dust and chupacabra blood — quite the costly blend.
Although I adore my 2018 Mustang GT, my biggest complaint revolves around its sound. Evidently, Ford shared this sentiment, as evidenced by the engineers’ decision to create a tube for piping engine sounds into the cabin. During Mustang Week, multiple people approached me to inquire whether the GT had undergone modifications — aside from the lowering springs and wheels, of course — bearing in mind it was generating over 550 rear-wheel horsepower with a VMP supercharger at the time. If the GT were to rival a GT500, which doesn’t elicit such sound complaints, we needed to take action. However, I also didn’t want to sacrifice my hearing or sanity during drives to Darlington, Myrtle Beach, or local cruise-ins.
The Kooks exhaust system struck a pleasant balance between the stock setup and something overly loud. The Mustang’s sound transformed from stock to what I’d describe as “healthy.” Upon cold-start, you immediately notice a significant departure from the stock system. It awakens with a deep exhale and a lower tone, serving as a reminder to the owner that their Mustang is no longer stock. After a minute or so, it settles into a quieter rhythm. Off-idle acceleration produces a moderate level of sound, noticeable but unlikely to disturb the neighbors. With a moderate throttle input, the exhaust truly comes alive, though for the most part, conversations inside the cabin can be conducted at normal volume during stop-and-go driving around town. The same holds true on the highway, where talking to passengers remains effortless.
The exhaust does exhibit the typical aftermarket drone at very low RPM on the highway, but this was easily mitigated by — quite simply — adhering to the speed limit. I found this most noticeable when the 10R80 shifted into 10th gear at around 45-50 mph. However, by 65-70 mph, the drone had disappeared. In my experience, there are certain frequencies that simply can’t be tuned out of a muffler. I’ve encountered this exact issue with every brand I’ve tried, though some are notably worse than others, reaching the point of being unbearable. Kooks falls on the better end of the spectrum in this regard.
Below are the sound measurements in decibels, obtained using a Tadeto Digital Sound Level Meter purchased from Amazon. We had initially hoped to conduct a sound comparison with the stock system, but unfortunately, circumstances prevented that opportunity. We’ll update the story, as well as our social media platforms, once we gather some numbers with a bolt-on S550 in our possession.
Around town, the exhaust system averaged 70 dBs. For comparison, this is just below my typical radio volume setting (72-75 dBs) and significantly lower than conversational volume (81-85 dBs). At part throttle and 3,500 rpm, it peaked at 85 dBs. The idle sound measurements were taken after the car had warmed up.
SOUND LEVEL
- DBs at idle outside car: 68-83
- DBs at idle inside car: 53-62
- DBs around town inside car: 63-85 (avg @70)
Bull Run on the Rollers
After breaking in the transmission with 500 carefully-driven miles, it was time to unleash the full potential of this pony. Pro Dyno’s owner and calibrator, Dan DeSio, meticulously put our 2018 Mustang GT through its paces while closely monitoring the diagnostics. We initiated the process with a safe base tune on the first pull, featuring approximately 16-17 degrees of timing at the top.
Unfortunately, it seemed that once again, I had stumbled upon another supplier of subpar pump gas. The engine was pulling 4 degrees, and it struggled to reach 595 horsepower. Granted, this figure was an improvement over the 557 horsepower it generated before leaving California, but it was only 16 horsepower more than my baseline at Pro Dyno with a compromised transmission and malfunctioning catalytic converter.
Here is our baseline from a few months ago with the broken cat and slipping transmission. No bueno!
What came next, I didn’t expect. After trying a few different things with the tune to isolate that it was, in fact, a fuel quality issue, Dan grabbed a can of Boostane he had on the shelf and poured it into the tank. He fired up the VMP-boosted Coyote one more time, and it screamed to just shy of 7,500 rpm. Welp, our knock issue was gone – 666.55 horsepower at 7,410 rpm and 541.55 lb-ft of torque, according to Pro Dyno’s Dynojet. Now we’re “cookin’!” With a healthy transmission, Kooks long-tubes and exhaust, and Pro Dyno’s tuning, we picked up 87 horsepower and 27 lb-ft of torque at peak.
What’s really crazy is this car is just a pulley change away from 700 rwhp with a stock engine. I spoke to Justin Starkey at VMP about the results, who informed me that they just made 780 rwhp with a similar combo after switching to E85 and dropping only one pulley size. The Gen-3 Coyote is truly a stout platform.
We were quite pleased with the final dyno results of our 2018 Mustang GT with a VMP Loki Level 1 supercharger kit as well as the newly added Kooks headers and exhaust on 93 octane pump gas with a bottle of Boostane.
And there you have it, Project Magneto is back in action and nearly ready for the track, with even more power on tap and sounding better than ever. Speaking of sound, make sure you tune in to our social media channels for exclusive content on our 2018 Mustang GT, such as sound clips of the exhaust and installation tricks. In the next installment of Project Magneto, we’ll see how these modifications perform at the track and whether we’ve met our goal of beating a GT500 at a fraction of the cost.
