what are the best performance mods for this car?

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Accepted Answer

Great question! Your 1987 Mustang GT Convertible is a fantastic starting point for modifications, and the Fox body 5.0 responds incredibly well to bolt-ons.

**About Your Starting Point:**
Stock, your 5.0 HO is rated at **225 horsepower and 300 lb-ft of torque** - though it's common for these engines to put down less at the wheels after 35+ years. The good news? That Flowmaster and short throw shifter are solid upgrades already in place!

**Best Modification Path for Your Convertible:**

**1. Chassis/Safety First (Convertible-Specific)**
Since you have a convertible, **subframe connectors** should be your absolute first mod. Fox body convertibles are notorious for chassis flex - the body can sag and twist under power, plus the torque box (where the rear control arms mount) is prone to cracking. Full-length, weld-in connectors are best, but bolt-ons work too. This isn't a "power" mod, but it makes every other mod work better and preserves the car's structural integrity.

**2. Gearing (Biggest "Bang for Buck")**
Most '87 GTs came with 2.73 or 3.08 rear gears. Swapping to **3.73 gears** transforms acceleration - you'll feel like you gained 30+ horsepower. With your 5-speed, 3.73s are perfect for street driving without excessive highway RPM. Cost is usually $400-600 installed, and it's the single best "seat of pants" improvement for a stock-powered Fox.

**3. Complete Your Exhaust**
Since you've got Flowmasters out back, consider **1 5/8" shorty headers** (better ground clearance for convertibles) and an **off-road H-pipe or X-pipe** to match. Shorty headers bolt to your stock cats; long tubes require more work and clearance considerations. This combo pairs perfectly with those Flowmasters and can net 15-20hp with better sound up top.

**4. GT40 Intake Swap (Best Value Engine Mod)**
The stock intake manifold is restrictive. A **GT40 or GT40P intake** from a 1996-2001 Ford Explorer is the cost-effective classic - often found for $200-400 used. This alone is worth **15-30hp at the top end**. Pair it with a **65mm throttle body** and matching EGR spacer to match the airflow. The GT40P heads are actually a nice upgrade too if you find them cheap, but the intake alone is the big win.

**5. Strut Tower Brace**
Cheap, bolt-on, and helps reduce front-end flex on launches. Maximum Motorsports and others make nice pieces specifically for convertibles.

**What to Skip for Now:**
- Skip the E303 cam unless you're planning heads/intake together - it's great for sound, but with stock heads, the gains are modest for the money.
- Skip underdrive pulleys on a convertible - your alternator works hard with the top motor.
- Skip "cold air intakes" - a K&N drop-in with the stock airbox is actually plenty.

**The 43,000-Mile Factor:**
Since your car is low-mileage and carries "Original & Highly Original" status, consider reversible mods or keep the stock parts if possible. The GT40 intake, gears, and exhaust are all easily swapped back if you ever want to return to stock.

**Recommended priority:** Subframe connectors → 3.73 gears → Headers/mid-pipe → GT40 intake + 65mm TB.

What's your goal - spirited street driving, track days, or chasing a specific horsepower number? That'll help me narrow down whether you should prioritize the intake swap or focus on suspension next!

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