S650 Convertible 810HP Build - Looking for Technical Feedback

[Vidley]

I'm moving forward with an 810HP Whipple build on my S650 Premium Convertible. Most of the heavy lifting is already accounted for:

• Whipple 3.0L Stage 2 System
• Ford Performance Half Shafts
• Full Suspension/Lowering Kit

I'm specifically looking for advice or "gotchas" regarding the frame and chassis bracing for this power level on the convertible platform. My current plan is:

1. BMR 2-Point Subframe Brace
2. J&M Full-Length Jacking Rails
3. VMP High-Clearance Strut Tower Brace (to clear the Whipple while keeping the factory K-brace)

I’ve verified the factory cowl-to-tower (K-brace) is in place, but I want to hear from anyone who has run this setup. Any clearance issues with the 10-speed lines or convertible-specific bracing?

If you’ve done this build or something similar, I’d appreciate your perspective on the chassis setup or anything else I might be overlooking before it hits the shop.

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[MustangMitch69]

Plan on supercharging my GT convertible too.

Phase 1 (done): Steeda G-Trac K-Brace + Jacking Rails + Billet Vertical Links + IRS Bushing Support + IRS subframe alignment kit

Here is the breakdown of the Steeda hardware I went with and the reasoning behind it:

IRS Subframe Alignment Kit & Bushing Support: We all know the factory rubber IRS bushings allow way too much deflection under load. Because I plan on running a staggered setup with massive 305mm tires in the rear, I needed the subframe dead-squared to the chassis and perfectly locked down. This combination completely eliminates the wheel hop and prevents the rear end from actively steering itself under heavy torque.

Billet Vertical Links: This was the final piece of the rear-end puzzle. Swapping out the flexing factory links for rigid billet keeps the rear knuckles firmly in place, ensuring those wide rear tires stay perfectly planted to the pavement during a hard launch or heavy braking.

G-Trac K-Brace: The convertible chassis naturally has a bit more flex without a fixed metal roof. Bolting in the K-Brace ties the lower control arm mounts together, which drastically stiffens the K-member. It makes the front end feel significantly tighter, flatter, and more responsive on turn-in.

Jacking Rails: Pure quality of life. The S650 convertible is a heavy car, and having these installed makes throwing it on a lift or jack stands effortless without constantly worrying about crushing the factory pinch welds.

Getting the foundation sorted first has completely transformed how the car puts power to the ground. It feels incredibly planted and predictable now.

Phase 2 (summer 2026): Boundary Billet Oil Pump + Crankshaft Sprocket + Ford Performance Engine Oil Cooler

Phase 3 (spring 2027): G-Force Outlaw Axles + Michelin Pilot Sport 4S Tires + Staggered wheels (20x9.5 & 20x11)

Phase 4 (summer 2027): Whipple Stage 1 + Whipple dual IC pump kit w/ HD Race Heat Exchanger + Ford Performance Air/Oil Separator kit + Reische 170° Performance Thermostat

 

[Ninjak]

@MustangMitch69 :I would also advise "Steeda stop the hop Kit". It will put the reinforcements where you need them, especially having a vert, and will work with the IRS subframe you already have. This setup will truly eliminate any movement or hop. Will also help you grip out of corners.

 

[MustangMitch69]

@MustangMitch69 :I would also advise "Steeda stop the hop Kit". It will put the reinforcements where you need them, especially having a vert, and will work with the IRS subframe you already have. This setup will truly eliminate any movement or hop. Will also help you grip out of corners.

Steeda’s Stop the Hop Kit is not a single, unique part, rather a pre-packaged marketing bundle of several different rear suspension components sold under one part number.

It is strictly listed as "Coupe Only" because every single tier of that kit includes the Steeda IRS Subframe Support Braces.

The underside of the convertible chassis features massive, factory-installed cross-bracing which physically blocks the Steeda IRS Subframe Support Braces from bolting up.

Because I could not fit the rear IRS braces, I focused on stiffening the front half of the chassis by utilizing the G-Trac K-Brace.

 

[Ninjak]

@MustangMitch69 : Ahh Ok. In truth, I never looked to see if it was coupe only....Heh, I have a coupe, so I was like yeah.

Makes sense, the verts have the extras. Honestly, I have not seen underneath a Vert Mustang since my 97 Vert GT.

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