Jim Smart
February 4, 2009

When you decide to convert a six-cylinder Mustang to a V-8, what do you need to get the job done? First, you need the vehicle, engine and driveline, brakes, and suspension to be cohesive. This means you cannot and should not do it half-way and on the cheap. In other words, don't just drop a V-8 into a six-cylinder Mustang without changing the rear axle and all underpinnings.

You're also going to have to decide what you're going to want from your Mustang when the conversion is complete. Be committed to what you want the car to be and stick to that plan. When you don't, it gets expensive. What's more, do your homework ahead of time and know what will work well together and what will not.

Here's what you're going to need in a nutshell:

  • A rebuildable 289/302/351ci V-8 or a new 5.0L/5.8L crate V-8
  • Appropriate transmission and related parts
  • Driveshaft
  • 8-inch or 9-inch Ford rear axle housing/differential (8.8-inch late-model optional)
  • New front and rear suspension parts
  • Front disc brakes with power assist (make sure the power booster is compatible with your clutch linkage or hydraulic clutch master cylinder)
  • Exhaust system, including headers or manifolds
  • New cooling system with high capacity radiator, water pump, hoses, 180-degree thermostat

Because we have performed a number of six to V-8 conversions in this magazine's 30-year history, you'd think we'd have it all down to a methodical process. However, each and every project brings its own challenges. Our '67 hardtop was no exception. We learned to plan better for one thing. We installed a JMC Motorsports hydraulic clutch along with a Master Power brake booster and discovered quickly the two will not work well together no matter what kind of modifications are made. That's when we went to a Modern Driveline cable clutch and Trans Am Racing power brake booster instead. Both cleared each other nicely.

We also learned about exhaust systems, headers, and pipe size. We needed a stock 2- or 2 ¼-inch dual exhaust system from Virginia Classic Mustang instead of the JBA system we ultimately went with. The JBA system is terrific and offers perfect fit. What's more, it yields a throaty bark with minimal backpressure. However, the JBA system is designed more for 400-500-horse small-block engines due to its 2 ½-inch pipes and straight-through mufflers.

Ride height is another issue we didn't address until the car was complete. We needed five-leaf mid-eye springs for more acceptable ride height. We went with four-leaf mid-eye and got less ride height than we bargained for.

The best advice we can offer to readers contemplating a six to eight conversion is to plan ahead and do your homework beforehand.

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