Jim Smart
March 9, 2011

We see it all the time-Mustangs that aren't safe, nor road-ready, because not enough thought went into their execution. This includes V-8 conversions with wimpy six-cylinder rear axles, 500hp small-blocks with manual drum brakes and 5/16-inch fuel line, mega-horsepower rides with less than adequate steering and suspension systems, and clogged two-row core radiators that cause chronic overheating in new engines. We've also seen high-amp subwoofer sound systems, power windows, video systems, climate control, discharge headlights, and more installed in Mustangs with 45-amp Autolite alternators and Group 24 batteries where owners wonder why their lights are dim. There are also canyon-carving rocket ships with little more than lap belts for safety equipment.

How ready is your Mustang for what you're asking it to do? How safe is it? A boatload of ponies in a Mustang ill-equipped to accommodate all those horses is a good way to get maimed or killed. It also puts others at risk who share the road with you.

How do you get all of your Mustang's components on the same page so they work together like a Swiss watch? What's the best way to plan and execute your dream ride?

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Brakes & Suspension

Regardless of how much power you build into a classic Mustang, it must have braking and handling that will help you avoid trouble or get you out quickly. You want a Mustang that will take you in the direction it is steered, hold the road, and stop safely. The best accident is the one you avoid.

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Suspension and brakes must be matched to the amount of power you intend to have along with engine and driveline weight. You can have all the braking and handling in the world, yet come up short because you misjudged engine and driveline weight. Big-blocks, due to size and weight, call for a heavy-duty suspension with stiffer spring rates along with larger brakes. They also call for more cautious driving technique because you can't cheat physics. Braking and suspension choices are also determined by how you intend to drive the car. Road racers require a different approach than drag racers or cruisers.

Fuel System

You can build power into your Mustang's engine compartment. However, without adequate fuel delivery, you're wasting your engine's potential. Your engine must have adequate fuel volume in gallons per hour (GPH) and pressure pounds per square inch (PSI) to perform. This means you need a fuel system that delivers. First and foremost is fuel line size (diameter) followed by adequate fuel pressure. Most classic Mustangs prior to 1969 have 5/16-inch fuel lines designed for six-cylinder engines or small-block V-8s. However, when horsepower rises above 300, your Mustang needs a 3/8-inch line from fuel tank to carburetor. This means sending unit, body fuel lines, all hoses and filters, and fuel pump to carburetor line. If you have a 5/16-inch pathway anywhere in the fuel system, such as the tank-sending unit, you still have 5/16 inch.

Some carburetors, such as the Holley 4150/4160, have fuel filters and fittings at the carb inlet. This has the same effect as a 5/16-inch fuel line. It limits fuel flow and can cause fuel starvation at wide-open throttle.

Carburetor sizing and jetting are also important issues to consider because they have a direct bearing on performance. Popular logic says larger is better, but that's not always true. Too much carburetor along with too much jetting hinders power and pollutes the air. However, we'd rather have too much jetting than too little. A lean mixture at wide-open throttle can harm an engine. We suggest a spark plug reading after a good wide-open throttle run. If the spark plug is snow white, your jetting is too lean. Light tan is the optimum color.

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Fuel capacity also depends on demand, which is determined by fuel consumption at wide-open throttle. Holley tells us your engine is going to need 0.5 pound of fuel per horsepower every hour. A gallon of gasoline weighs six pounds. If your small-block Ford makes 350 hp at wide-open throttle, it's going to mandate 175 pounds of fuel an hour, which is 29 gallons. Use this formula to determine fuel pump needs: 350 hp x 0.5 pound = 175 pounds of fuel; 175 pounds/6 pounds = 29 gallons per hour.

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Ignition & Electrical

We take our ignition and electrical systems for granted as if they happen by magic. A Mustang's electrical system follows the fundamental laws of physics and there are no exceptions. Fall short in your electrical and ignition system planning and you can count on winding up roadside.

The first area to address is proper grounding. We will even suggest taking grounding even further than Ford because it's that important. Because your engine and transmission sit on rubber mounts, they must be grounded to the firewall in order for both ignition and charging systems to work properly. If you've converted your classic Mustang to electronic fuel injection, it's even more important to be redundant in your grounding program.

One old law of physics is electricity. It will always find the path of least resistance, sometimes with befuddling results. A poorly grounded ignition system offers hit-and-miss operation. Sometimes your engine starts. Sometimes it won't. And sometimes it will just quit. Charging may be intermittent with erratic voltage regulator operation. It is suggested you have two forms of engine grounding-the factory cylinder head to firewall ground and another ground from block to chassis.

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Don't forget distributor grounding, which is a small ground lead inside your distributor. Too many of us forget that little guy during tune-ups or PerTronix Ignitor retrofits. Because the breaker plate floats on nylon rub pads, you can't count on sufficient grounding any other way but the ground strap.

Ignition system selection depends on how you intend to drive your Mustang and the level of expected performance. Cruisers and weekend show cars are good to go with high-quality ignition points or a PerTronix Ignitor conversion, which eliminates old-fashioned ignition points. The Ignitor is the easiest upgrade you can make to a classic Mustang and it never requires maintenance. Install it, set the gap, and forget it.

If your Mustang project is more about high-performance driving, you may want to consider an MSD Ignition system or PerTronix's billet distributor, which is fitted with the new Ignitor III system for exceptional performance. Street Mustangs should get a distributor with vacuum advance, which helps the engine deliver both efficiency and low-end torque.

Regardless of the distributor you use, always have it curved to expected driving conditions. In other words, have a qualified technician set up your distributor for your engine and how you intend to drive. MCE Engines does complete distributor rebuilds along with proper tuning for your application. There are also other professional distributor rebuilders and tuners out there such as Tim O'Connor, a Ford service technician, who has been rebuilding and tuning Ford ignition systems since 1966.

Exhaust System

This is another area we tend to overlook. However, it is important to both performance and reliability. You want a low-restriction exhaust system, yet with enough restriction that will give you back pressure and scavenging. Velocity through header primary and secondary tubes along with low-restriction mufflers is key to the smooth flow of exhaust gasses and delivery of power. The choice of long- or short-tube headers depends on the amount of power your engine is going to make. As horsepower increases at high rpm, you're going to want long-tube headers. Shorty headers yield some improvement in exhaust scavenging because they do away with the restrictive roughcast surfaces and passages of stock exhaust manifolds. However, don't expect a huge gain in performance from shorty headers. Long-tube headers will give you better scavenging and velocity as rpm increase.

It can be challenging to choose the right type of long-tube headers. You want custom-tuned headers with uniform length primary tubes and right-sized collectors for optimum performance at high rpm. Yet, equal-length header tubes can make things a bit crowded. It is all about compromise. One of the best long-tube header manufacturers we've worked with is Ford Powertrain Applications (FPA), which offers Ford buffs perfect-fit long-tube headers with ball and socket collectors that don't require collector gaskets. These headers tuck close beside your engine to take up minimal space.

Muffler choice and pipe size depends on how much power you intend to make. Pipe size should be proportional to power output. Pipes that are too large will lose precious torque. Pipes that are too small will cause excessive backpressure and heat.

Another important consideration is cabin noise levels. Although loud exhaust systems have been fashionable with hot rodders for generations, we're also a generation of deaf people from rock 'n' roll music and hotrods. You want good sound deadening and user-friendly mufflers for your road-going Mustang cruiser.

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Cooling System

Cooling systems are another area we tend to fudge on, mainly due to expense. High-quality radiators and related components are expensive yet vital to engine survival and longevity. Power comes from BTUs (British Thermal Units). The more power your Mustang's engine makes, the more crucial adequate cooling becomes.

Start your cooling system regiment with a good radiator. A clean, right-sized radiator removes excess heat and helps maintain proper operating temperature. You don't have to have a high-end aluminum radiator to get the job done unless you're making 400 hp or more. A quality three- or four-row copper/brass radiator will do the job well depending on engine power and other demands like air conditioning. However, it takes more than a good radiator because this is a team effort. You need the right fan for your application along with a fan shroud to improve air velocity through your radiator.

An electric cooling fan is an excellent option if you're building a restomod because it is reliable and effective. Just make sure you have enough fan (cfm) to get the job done. The main concern is to order the right capacity for your application. You can order too little fan capacity (CFM) and wind up with overheating. We're not convinced you could ever order too much capacity.


Transmission and axle selection depends on how much power you're going to make coupled with the type of driving you intend to do. If old-fashioned hot rodding is what you want, a Ford Top Loader four-speed or three-speed automatic will get the job done. Reliving the good old days isn't always about fuel economy or reducing wear and tear, but instead about the nostalgic experience. There's nothing quite like the whine of first gear in an old four-speed to get your motor running.

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If you want a road-going cruiser for long distance driving, you probably want to take advantage of overdrive with a Tremec World Class T-5. If you're planning 400-500 hp, think about a TKO version to stand up to that kind of power.

If you're thinking automatic transmission, you have three basic choices-Ford's C4, C6, or AOD/AODE. The C4 offers reliability and less weight for those with sixes and small-block V-8s. A small-block C6 offers durability, but with a weight penalty and more rotating mass to whirl around inside. Although there's also the FMX three-speed automatic, it's not recommended unless your Mustang came with it and you're sticking to originality. The C6 is your only choice for a three-speed automatic if you have a big-block. You would choose the AOD or AODE for the same reasons you'd choose a five-speed-overdrive. The AOD has mechanical modulation where the AODE/4R70W is electronic control.

Driveshaft selection depends upon the amount of power you're considering. Although we can offer a lot of pointers on driveshaft selection, you're better off consulting with Inland Empire Driveline Service for the best choice. There are three basic choices depending upon budget and power-steel, aluminum, or composite.

Whenever horsepower and torque rise above 250, you're going to want Ford's tough 9-inch rear axle. How you configure the 9-inch depends on the kind of power you're going to build. For horsepower and torque numbers between 250 and 300, a standard 9-inch Limited-Slip or Traction-Lok with 28-spline axles is plenty. When power goes above 300, you need 31-spline axles. When numbers begin courting the 450-500-horse mark, choose 35-spline axles along with larger bearings.

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Size Formula

Here's a basic formula to use for determining proper carburetor and fuel line sizing. Remember-sizing should go higher as expected performance and combination of engine parts (heads, camshaft, intake manifold, compression) increases. This table is based on stock or mild restomod condition. Carburetor jetting is based on where you live and the level of performance expected. As always, do a spark plug reading.

One more thing-what about fuel pump capacity in gallons per hour (GPH)? Visit www.holley.com for accurate information about fuel pump sizing for your application. What you're concerned with most is fuel demand at wide-open throttle. When fuel demand goes up, consider the use of a fuel pressure regulator between the fuel pump and carburetor.

DisplacementSuggested Carburetor Size RangeSuggested Fuel Line Size From Tank To Carburetor
250-300 ci480-600 cfm5/16 inch
300-350 ci600-650 cfm5/16 or 3/8 inch
350-400 ci650-750 cfm3/8 inch
400-500 ci750-950 cfm3/8 inch or 1/2 inch