All Ivan Korda wanted to do at Memphis International Raceway was set a new personal best quarter mile time. Unfortunately, his 2015 Mustang GT did not want to cooperate. On a cold November day at a Test n’ Tune event, Ivan heard a menacing sound emit from the rear end on his third pass, and he was towed off track by the safety crew.
What Ivan likes most about drag racing is the feeling of acceleration in the first 60-feet. He bought the Mustang GT because he knew it would be able to run 10-second passes and still be a fun car to drive. Within a week of ownership, he knew the car was capable of nine-second passes, and a new goal formed.
Ivan is a lifelong automotive enthusiast. He has interned at Master Engine Tuner Magazine and built a 2004 SVT Cobra Mustang with 550 horsepower, focused on all-around performance before he made a move to the S550 platform.
“My car started out as bare bones build to test the OE components’ limits,” Ivan said of his 2015 Mustang. He added that within his first year of ownership he had done a few upgrades such as a Roush TVS supercharger, Sai Li return style fuel system, ID1000 injectors, JMS Wheels with Mickey Thompson ET Street tires, and BMR Drag Springs. With a full leather interior, heated and cooled seats, along with navigation and stereo unit Ivan accomplished his personal best: 9.8 seconds at 140 mph.
On the first pass during the Test ‘n Tune, Ivan noticed some traction issues and lost 2 miles per hour on his second pass. The loss in speed and traction led Ivan to believe the problem was with the track prep and he attempted a third run. “As soon as I felt the weight transfer to the rear of the car I heard this sound like a metal spoon caught in a garbage disposal,” he said.
“When the rear differential broke, I decided it was time to upgrade some of the weak links. I didn’t want the car to leave me stranded again,” said Ivan.
Out with the Old, In with the New
Ivan got a complete Ford Performance Super 8.8-inch IRS Differential to replace the damaged OE unit, and he upgraded many of the stock components to ensure the new differential would be consistent and eliminate traction issues.
Ivan’s car has an automatic transmission, which is ideal for drag racing applications as well as daily driving. The automatic transmission helps get those ET’s down by reducing shift times while it offers ease of use for daily driving. Mustangs equipped with an automatic transmission come stock with a cast aluminum differential housing which is not the strongest, particularly in drag racing situations. The stock configuration also comes with 3.15 gears.
The new setup includes a stronger iron housing with an aluminum cover, Traction-Lok differential and 3.55:1 gear set, however, because it was not made for automatics, it requires a Ford Performance Automatic 8.8-inch IRS Pinion Flange Kit to work.
Due to the factory gearing on the stock S550 6r80 automatic transmission, Ivan went with a 3:55 gear because its a “tall gear.” Tall gears are typically thought to be anything less than 3.31, and short gears are thought to be anything higher than 3.73 with 3.55 being the middle ground.
“Anything taller would have serious traction issues off the line with the positive displacement blower since the boost comes on instantly,” Ivan said.
With a forced induction setup, the goal should be to remain in boost for as long as possible and a tall gear is a great way to do that.
When it comes to the quarter-mile, most enthusiasts with automatics go with a 3.15 or 3.55 gear as it provides an ideal shift point. The tall gears also allow for a high(er) top speed. Going with 3.73s or 4.10s typically cut down how fast the Mustang moves. Shorter gearing allows for quicker acceleration with a strong low- and mid-range power band, but ultimately cuts down on the top end.
A Stronger Driveline
One of the significant features of the S550 is that it comes with independent rear suspension (IRS). IRS setups allow both wheels to function and move independently of the other which allows for greater control and handling.
In IRS setups, there are two half shafts, one going from the driver side rear wheel to the differential housing and one going from the passenger side to the differential housing. If driving down the road and the wheels hit a bump or a section of uneven pavement, the S550 Mustang feels more planted than previous generation Mustangs as each side of the car is affected and responds independently of the other side.
When it comes to drag racing, to perform at the top of its class the S550 needs some IRS upgrades, like replacing the half shafts. The half shafts are a weak point in the system and can fail, especially when launched at the track on a sticky tire.
GForce Engineering makes a set of axles that serve as a direct replacement for the factory half-shafts. Named the “Outlaw 1500+hp Axel,” the half shafts are made from a billet high alloy aerospace material similar to 300m but with other various properties that make it stronger.
The Outlaw 1500+hp axles feature billet one-piece 34 spline inner and 32 spline outer stub ends. The CV joints are severe duty with CNC billet centers all using Aerospace electrically bonded e-coating to resist corrosion. Additionally, the axles also offer a significant reduction in wheel hop during hard launches.
To further aid in the transfer of power to the ground, Ivan upgraded the OE driveshaft to a GForce Engineering 3.5-inch Aluminum Driveshaft.
The GForce driveshaft has been designed with a tightly fitted splined assembly that lets the shaft plunge in-and-out but also gives the shaft the ability to spin vibration free and with strength. The splined area comes with a boot to protect it from dust and other road debris. It also comes with a solid core, heavy-duty U-joints in front and rear.
The driveshaft offered by GForce is approximately 17 lbs total and gets approximately 7 pounds of weight reduction from the removal of the CV joint and rubber couplers. It can take up to 900hp and speeds up to around 160 mph without vibrations.
Keeping it Together with BMR Suspension
Vibrations are sent throughout the rear end of the Mustang due to the spinning driveshaft and differential shaking within the cradle; thus IRS is prone to wheel hop. Wheel hop is where the rear wheels hop, or sort of jump, but very quickly and violently, almost as if the rear end is going to fall out of the car. It only occurs during quick acceleration off the line as the wheels are trying to put the power down.
As the wheels start to move forward on acceleration, the toe angle changes and grip is lost. As the Mustang loses grip, the wheels spin and acceleration is drastically reduced which causes the wheels to go back to their original toe angle. The tires regain grip, and then the process continually repeats itself until speeds are adjusted. The wheel hop is the quick back and forth between accelerating and spinning of the wheels which are caused by the change in toe angle.
To eliminate wheel hop, Ivan used a Knuckle To Toe Link Bearing from Ford Performance and other bushings from BMR Suspension, BMR vertical links, toe links, and subframe bracing.
The Knuckle To Toe Link Bearing from Ford Performance replaces the original rubber toe link bushing in the rear knuckle of the S550 Mustang with a high-performance, production style bearing. The assembly comes with two bearings that work to improve the handling performance, particularly during those power down situations, and removes any suspension compliance with minimal impact on the ride quality.
From the factory, the S550 uses rubber IRS bushings that have air pockets and are made from soft rubber. The rubber bushings produce excessive lower control arm movement during normal and aggressive driving. BMR suspension offers a Lower Control Arm Spherical Bushing Kit that goes in place of the OE rubber bushing, nearly eliminating lower control arm movement by linking the rear portion of the lower control arm to the cradle. This not only reduces wheel hop but increases handling stability.
BMR’s bushings are internally fluted, which allows grease to coat the inner sleeve evenly. These flutes also direct grease to the outer edge of the bushing, keeping the thrust surface lubricated. This efficient lubrication ensures quiet, reliable operation over the life of the bushings.
Toe links are considered one of the main issues in wheel hop and are one of the most direct ways to address it. The stamped steel factory toe links are non-adjustable while BMR offers on-car adjustable toe rods made from heavy-duty 1 1/4-inch DOM steel tubing. TIG-welded chrome-moly tube adapters with a heavy-duty center adjuster make on-car adjustments straightforward and straightforward so even while under hard acceleration off the line, the toe angle remains as close as possible to where it was while sitting still.
Stock upper control arms with soft rubber bushings deflect under load and absorb power instead of transferring it to the tires. The factory arms also don’t allow for proper camber correction on lowered vehicles. BMR’s Delrin, non-adjustable camber control arms for Mustangs are CNC-machined from 6061-T6 billet aluminum.
The factory S550 vertical links are stamped steel with soft rubber bushings that deflect under load and absorb power instead of transferring it to the tires. The BMR Vertical link design provides a robust control arm that significantly improves performance with zero deflection as the rear wheels stay firmly planted and deliver power to the pavement without massive increases in weight.
Another significant part of the S550’s wheel hop comes from the subframe’s movement during off the line acceleration. To address this directly, many Mustang aftermarket parts companies have released subframe braces that stiffen the subframe up, eliminating any movement. To address this, Ivan used BMR’s Differential Hardware Kit and Cradle Lockout Kit to improve off the line acceleration, hard braking, and spirited driving, while not adding much weight at all.
Down the Line with a Smooth Ride
With the increased rigidity of the IRS, Ivan went with a set of Viking Performance Crusader Double Adjustable Rear Shocks.
He selected these shocks so he could easily transition between on-and-off track use without going through a complicated setup process. The 22-position rebound adjustment and 19-position compression are the options he needed and wanted for his set up.
After Ivan had installed the rear differential, driveline upgrades, and suspension components on the Boosted Coyote, the car needed to get an alignment.
On his way to the shop Ivan noticed the car was eating coolant, and further testing prompted him to replace the head gaskets. The machine shop that performed some work left metal shavings in the oil passages for the cylinder heads. Unaware the metal within had starved the top end of motor oil, Ivan heard a terrible noise when he tried to start the car as the metal was pushed throughout the engine.
Stay tuned for more details and Ivans next project on the Boosted Coyote.