Well, that didn’t take long. After completing the latest upgrades to Project SC650 — including new Weld wheels with optional beadlock rears wrapped in Mickey Thompson tires, a full TBM braking setup to reduce weight and accommodate said wheels, and a pair of heavy-duty axles to handle the increased traction — we knew it was time to upgrade the suspension. To complement these improvements, we turned to BMR Suspension and Viking Performance to ensure our Performance Pack stays planted during its first outing, avoiding the hop, skip, and jump behavior often seen in the independent rear suspension S550 and S650 chassis.

Well, you could say things are getting pretty serious with our S650. This is not the sight we thought we’d see so early on, but here we are — gearing up to install the new suspension from BMR Suspension and Viking Performance. Let’s rock and roll!

Challenges Of An Independent Rear Suspension

Up to this point, our upgrades have focused on improving traction and shedding weight, a simple yet effective recipe for success. However, suspension is a critical factor in a car’s ability to launch hard and consistently down the track. For us, owning the latest generations of Mustangs meant battling the challenges of drag racing with an independent rear suspension.

Before you start thinking about a live axle swap for your 2015-and-newer Mustang, hold off — we discovered with our 2020 Shelby GT500 that a properly set up IRS can handle track duties just fine. To delve into the multi-faceted benefits of suspension upgrades, we spoke with Connor Capar from BMR Suspension to learn why our latest changes were worth the investment.

An EcoSystem Of Its Own

Much like the fuel system or drivetrain, suspension operates as its own ecosystem, with each component playing a distinct role to ensure optimal performance. When these parts work harmoniously, they create a winning formula — one that’s not only felt in the car’s handling but also measurable in the trophy slips we collect after each successful pass. We decided on the entire suspension revolving around BMR and Viking Products starting with our pesky rearend. 

One thing we’ve consistently noticed on previous builds is the excessive deflection and wallet-scary wheel hop in the IRS rearend. The inconsistencies at launch were our primary challenge. “Our Aluminum Rear Cradle Bushing Kit (P/N: BK048), Billet Aluminum Differential Bushing Kit (P/N: BK050), Rear Bearing Kit (P/N: CBK774), and Rear Strut Mount Kit (P/N: SM762) are all designed to increase chassis rigidity, maximize control, eliminate deflection, and drastically reduce wheel hop,” said Capar.

To further understand each part’s role in addressing our issues, Capar explains, “BMR’s Aluminum Rear Cradle Bushing Kit eliminates rear cradle movement and significantly increases the rigidity of your Mustang’s chassis to provide maximum control and consistency. The Billet Aluminum Differential Bushing Kit drastically reduces wheel hop by eliminating differential bushing deflection. The Rear Bearing Kit replaces the factory lower control arm bushings to eliminate rear lower control arm bushing deflection — further minimizing wheel hop and increasing rear stability on the track.”

We’re always looking to enhance chassis rigidity, and for this build, we opted for BMR’s rear strut mount kit. This kit connects the suspension in the trunk, offering a stronger mounting point at the wheel well for improved structural integrity.

While the S650 chassis is far more rigid than what we saw in our Fox Mustang days, Capar explained that the Rear Strut Mount Kit still brings improvements by increasing the rigidity of the S650 Mustang’s rear strut mounts and enhancing chassis stiffness.

Back To The Front

With the rear cradle finished, we shifted focus back to the front with a K-member replacement — a modification we’ve relied on for decades. After all, it’s the quintessential weight reduction upgrade for drag racing a Mustang. However, shaving weight was just the tip of the iceberg for this BMR product. 

Capar explains, “The BMR K-member (PN: KM761) is designed specifically for drag racing your S650. The KM761 is significantly lighter than the OE K-member and engine mounts while still offering a substantial increase in front-end structural rigidity.”

While this all sounded fantastic and aligned with what we’ve come to expect, BMR actually takes it a step further. “BMR’s design lowers the engine to provide additional clearance under the hood and is compatible with both factory and aftermarket steering racks,” Capar added.

Looking at the factory K-member compared to the aftermarket BMR Suspsension unit, the difference in strength is immediately clear. While taking it off was straightforward, removing the rack felt more like an Olympic rowing workout!

Aligning With Our Goals

The first step in our suspension upgrade was ensuring our S650 Mustang could stay planted while making passes down the dragstrip. The next step was to ensure it could do so in as straight a line as possible. To achieve this, we focused on correcting any OE components that could affect alignment. Capar gave us the product list consisting of Adjustable Camber Links, Rear Camber Adjustment Lockout Kit, Rear Toe Rods, and Spherical Vertical Links 

“Adjustable Camber Links (PN: UCA763) are perfect for owners of lowered Mustangs looking to correct the negative camber that results from lowering,” Capar explained. “They feature Delrin bushings to eliminate control arm bushing deflection and chrome-moly rod ends for on-car adjustments, ensuring repeatability on the line.” Knowing that this aspect was handled before lowering the car gave us great peace of mind.

Although it’s a bit hard to spot in this crowded area, the Adjustable Camber Links play a crucial role in lowering the car while maintaining optimal camber. Keeping the rear tires properly aligned ensures we get the biggest contact patch to the ground.

“The Rear Camber Adjustment Lockout Kit (PN: WAK761) is an excellent solution for locking out camber adjustments with the factory eccentric bolt when using an adjustable upper control arm,” Capar explains. “It ensures that your Mustang’s alignment stays locked in place when using an adjustable upper control arm.

“Rear Toe Rods (PN: TR005) are designed to dramatically reduce toe rod flex on your S650 and eliminate eccentric bolt slippage,” Capar said. We found that the rear toe rods include lockout plates, which Capar explained eliminate the factory eccentric adjustment bolts, thereby minimizing toe change and deflection which should help us put the power down on hard launches, naturally aspirated or otherwise.

These BMR heavy-duty rear toe rods reduce flex and eliminate eccentric bolt slippage, offering increased stability. We’re excited to see how they’ll help us put the power down on hard launches, whether we’re running with or without forced induction.

Our final step was the BMR Spherical Vertical Links (PN: TCA045), which Capar explains “are designed to eliminate deflection and wheel alignment changes, thanks to their 6061 billet aluminum and spherical bearing construction. This eliminates vertical link flex and bushing deflection.” We were also concerned about noise, vibration, and harshness — since we may or may not have told some close family members that this car wasn’t going to be nearly as drag-oriented (A lie we use far too frequently!) — we still wanted it to be enjoyable on the street. Capar assured us that we need not worry about NVH with the Spherical Vertical Links.

Rolling Pin Of Doom

With the chassis still in the air, we decided to adhere to NHRA rules and add a touch of safety with a driveshaft loop. Hypothetically speaking, I’d rather take a Mike Tyson punch than be slapped in the kidneys by a metal driveshaft spinning at 7,500 rpm after puncturing the floorboard of our brand-new S650 Mustang. To address this, BMR offers an inexpensive and easy-to-install driveshaft safety loop.

Balanced or not, a driveshaft failure at the track is no joke. Thankfully, BMR Suspension has us covered with this ultra-easy-to-install driveshaft loop, keeping us safe and compliant with track regulations.

“BMR’s Driveshaft Safety Loop (PN: DSL017) is designed to contain your Mustang’s driveshaft, preventing it from tearing through the floor in the event of a failure,” Capar explains. “By simply attaching to the factory transmission crossmember, the DSL017 is an affordable yet efficient way to protect your Mustang and comply with NHRA rules.” Sounds simple, and it was. A few quick bolts, and we were up to spec on driveshaft safety.

Invading The S650 Struts And Shocks

Our final step in ensuring everything worked in unison for our suspension was installing new shocks and struts. As luck would have it, our Performance Pack Mustang threw us a curveball once again with its MagneRide-equipped suspension. No worries, though — Viking Performance had a drop-in solution ready for us. 

The front suspension installation went smoothly, with no surprises along the way. However, it wasn’t until we tackled the rear suspension that we uncovered a hidden “Easter egg” Ford left for Performance Pack owners.

“A double-adjustable shock or coilover is an absolute must for dialing in any drag-raced vehicle,” states Mike Proulx at Viking. “For the horsepower level and performance goals we used the AK valving up front. This valving has a very wide rebound tuning range so it can easily adapt to various racing surfaces preps for controlling how fast the front rises for weight transfer.” The Crusader Series all-aluminum double adjustable front coilover struts (PN: J325AK-225P) we selected with AK valving offers a soft setting similar to the AD valving (designed for maximum front weight transfer at lower settings), while tightening up like the AP valving (ideal for high HP radial cars) at higher settings. We also added the sway bar mount option (P/N: 7976-201).

“In the rear we used our AM valving which has excellent control of the Ford’s IRS suspension to promote nice smooth transition when loading the rear tire and maintaining traction throughout the run,” Proulx continued. “The Crusader series shocks are our max-effort, race-only shocks, so you do have to turn the setting down when you are done racing. However, this valving will yield a pretty decent ride quality for street duty when going from track to track.” We paired them with the rear drag shocks (PN: B378AM) with BMR’s Drag Springs (PN SP088), this combination ensures the perfect balance of adjustability, performance, and compatibility to optimize our Mustang’s setup for the dragstrip at any power level.

The front coilover struts offer the advanced adjustability and performance that our factory suspension couldn’t handle. Engineered by Viking for race cars and weekend warriors (a slight upsell on our Mustang’s capabilities), these double-adjustable coilovers allow us to fine-tune both rebound and compression for track prep — or the lack thereof in California. The lightweight aluminum design reduces weight while featuring precision-machined pistons and stainless steel bearing mounts for the force control needed in drag racing.

We continued with Viking Performance for the Crusader rear shocks, too. With over 418 adjustment combinations, we can fine-tune the suspension for track-specific conditions. The progressive rebound valving and precision engineering offer superior force control, while the user-friendly design means we can adjust them trackside without special tools — something we’ll definitely appreciate as we dial in our setup. 

After completing the installation, we obtained a set of Mag Ride bypass sensors and used an Opus diagnostic tool to zero out the sensors.

Chassis Is All Done

Now that our chassis is well-sorted and ready to be fine-tuned for different track surfaces, it’s time to turn our attention to other areas of our S650 Mustang, including what’s under the hood! I don’t know about you, but I can’t wait to share this ProCharger install. Stay tuned to see how our boost-maker of choice comes together to make even more power and take our Mustang’s overall performance to the next level!

Nothing says “I love working on cars” quite like Seth’s facial expression.