Jim Smart
February 1, 2009

Mustangs are closely tied to V-8 engines, and it's been that way for nearly a half-century. However, six-cylinder Mustangs reign supreme when it comes to raw production numbers. Ford built a lot of them, encouraging dealers to sell even more when V-8 engines were in short supply during the mid-'60s. Buyers snapped them up in great numbers just to get into a Mustang.

With so many six-cylinder Mustangs out there, why aren't we building more of them today? As a rule, enthusiasts like the way a V-8 sounds and responds. But what if you want something that doesn't require radical surgery?

When it's time to buy a Mustang, six-cylinder hardtops are the cheapest available, making them terrific restomod bargain rides. When you build a six-cylinder Mustang, you're building something different. It isn't just another V-8 Mustang, but rather something with a lot of room for imagination because inline engines look sharp when they're dressed to the nines. A six built with an array of goodies from Classic Inlines provides an engine compartment nearly everyone will stop to admire.

This is a 250ci block being built for a turbocharged application by McLearran Racing in Southern Arizona. Notice the O-ring sealing around each bore for an artificially aspirated (turbo or supercharged) application. The 250 is long on torque thanks to its generous stroke.

Build a classic Ford six intelligently and it will sport a throaty European sound. By the way, inline Ford sixes don't have to sound buzzy. Give them an Italian opera tenor voice with the right induction, cam profile, cylinder head, and exhaust tuning. Along with the right exhaust tuning, your Mustang six will come alive.

Some History
The Mustang's "Getaway Six" was originally known as the "Thrift Power Six" before it became known as the Falcon Six. When the compact, lightweight Thrift Power Six was introduced in the fall of 1959 in the all-new '60 Falcon, there was only one displacement: 144 ci with a 3.50-inch bore and 2.50-inch stroke sporting 90 hp. The 144 wasn't much on torque. In fact, it was a gutless wonder that needed a good running start, but it was certainly practical for any commute. A year later, Ford stroked the 144 to 170 ci for 1961, giving the Falcon a pinch more punch at 105 hp.

The 250ci six has main bearing journals that are the same size as those in the 289/302ci small-block V-8. That, coupled with seven-main bearing construction, makes the Mustang's largest six quite rugged and easy to build. When you build a Ford six, you can make the same improvements as you would with a V-8: chamfer the oil passages, dynamic-balance the bottom end, recondition and shot-peen the connecting rods, install ARP rod bolts, opt for forged pistons if you're going to spin it high, install hardened exhaust valve seats, increase rocker arm ratio, choose the right performance camshaft, and improve breathing.

Ford increased the 144/170 bore and stroke to 3.86/3.126 inches in 1963 to create 200 ci with 120 hp and 190 lb-ft of torque. Originally, the 200 six had four main journals like the 144 and 170, but Ford made significant block improvements for 1964, including seven main bearings to eliminate crank oscillation, which had caused noise, vibration, and harshness. You can tell the difference between a four-main bearing and seven-main bearing block by the number of core plugs. Four-main bearing blocks have three while the later seven-main bearing blocks have five. Seven-main bearing blocks also have hydraulic lifters instead of the solids used with four-main bearing blocks.

A lame cylinder head with an integral intake manifold and a mix of Autolite, Holley, and Carter one-barrel carburetors greatly limited the 144/170/200ci engines. Because the integral log manifold was a raw, unmachined casting inside, fuel distribution was never a strong suit with these engines. Most didn't idle well and throttle response was poor at best.

Ford took the 200ci six's architecture and raised the block deck 1.66 inches in order to reach 250 ci for 1969. To achieve the extra 50 ci, Ford increased the stroke to 3.91 inches, which improved torque to 240 lb-ft. What made the 250 different from previous sixes was its larger main journal, bolt-on intake manifold, and bellhousing/starter arrangement like a small-block V-8. It also had a new cylinder head for improved breathing and easier service. Available in the Mustang from '69 to '73, the 250 remained in production through 1976 in other Fords.

Compression is controlled primarily through piston dishing--the deeper the dish, the lower the compression. Compression is also controlled via piston compression height and how much volume there is above the piston. Combustion chamber size and gasket thickness also contribute to compression ratio.

Hot Six Performance
Building a powerful Ford six-shooter is a matter of getting back to old-fashioned hot-rodding basics. The more air and fuel you can huff into the chambers, and the higher you can tweak compression without harming the engine, the more power you're going to make. Nothing makes horsepower and torque like increased compression. These days, the most compression a street six can handle on pump gas is 10.0:1 to 10.5:1, depending on ignition timing, fuel mixture, and where you live (elevation, humidity, average temperature, and highest fuel octane rating available).

All 144/170/200/250ci cylinder heads are interchangeable. The main difference is valve and combustion chamber size. If you're seeking real performance from your Mustang six, it's a good idea to get acquainted with the 250ci cylinder head because of its bolt-on intake manifold. The 144/170/200 heads are limited from an induction standpoint because their integral intake manifold limits breathing potential. As you shop for a cylinder head, closely examine chamber and valve size.

As you might imagine, camshaft selection for Ford sixes is limited. However, look to Crane, Comp Cams, Clifford Performance, Clay Smith, Crower Cams, and Isky Cams for plenty of choices. There are also valvetrain options from Classic Inlines, such as roller rockers, one-piece pushrods, and dual-roller timing sets.

Classic Inlines offers a line of induction systems for vintage six-cylinder Mustangs. The bolt-on FSP-250-IMC intake for the 250 iron and aluminum head is designed for just about any kind of fuel distribution system imaginable, including carburetion and fuel injection. There are six fuel injection bungs for port fuel injection, or you can go with throttle-body injection. Classic Inlines also offers an FSP-250-IMW manifold for Weber carburetors or triple throttle bodies.

Pony Carburetors offers Ford six enthusiasts a number of options, including a new Autolite 1100 reproduction one-barrel carburetor. Known as the Vaporizer 1100, Pony Carburetors goes the classic Autolite 1100 one better with Annular Fuel Discharge for an improved fuel/air mix and better distribution. The result is smoother idle and better throttle response. Pony Carburetors also suggests 10-15-percent better fuel economy with the Vaporizer.

There's no excuse for a lame ignition system when there are plenty of options that eliminate points entirely, including the D.U.I. system from Performance Distributors. However, if you're on a budget, the PerTronix Ignitor II works wonderfully in an old Autolite single-point distributor, eliminating point-triggered ignition in 30 minutes. Opt for a PerTronix ignition wire set while you're at it.

Classic Inlines' aluminum cylinder head was designed to yield dramatic increases in horsepower and torque. Based on the Australian 250-2V cast-iron cylinder head, this new head is the result of extensive research and development. Classic Inlines' goal was to improve airflow to offer the most advanced aluminum head ever for Ford sixes.

Down Under Performance
There's a lot of street chatter about Australian Ford sixes. However, Ford six history Down Under isn't much different from that of North America. Early on, Australia and New Zealand got the same sixes as North America, and so did South America, with some variations in displacement. The game changer is what Ford Australia and South America did with this six later on. In 1976 Ford Australia fitted the venerable 250 with a new cast-iron crossflow cylinder head, which improved performance dramatically. This new crossflow design improved flow and also moved exhaust manifold heat away from the induction system. It may surprise you to know the crossflow head was a spin-off of the 351C head concept with the same valvetrain components and combustion chamber design.

In 1978 Ford Australia fitted the 250 with a new aluminum crossflow head for cleaner emissions and better performance. Instead of Autolite or Motorcraft carburetion, they got Webers. Bosch Jetronic Fuel Injection followed in the '80s.

The Aussie Ford 250ci six became an overhead cam design in 1988, yielding greater torque. The 250 was enlarged to 4.0 liters in 1991, and in 1998 Ford Australia made significant improvements to make the engine more durable, including larger main journals, cast aluminum oil pan, and variable valve timing. What's more, double overhead cam technology is coming for Australia's inline-six.

Here's a cutaway of the induction side that shows long intake runners for improved velocity (air speed and volume). With velocity comes pressure and torque.
Cylinder Head Specifications Intake Airflow In CFM
Head TypeValve Lift 
 @ 0.{{{100}}}”0.{{{200}}}”0.{{{300}}}”0.400”0.500”0.{{{600}}}”
144/170/2004587108119124127
OZ 25063101133155156156
Classic Inlines 5299143180201210
Ported55103159196223231
This is a close look at the exhaust runner, also longer for improved scavenging. Hot gases have a much smoother trip here than in a vintage iron head.
Cylinder Head Specifications Exhaust Airflow In CFM
Head TypeValve Lift 
 @ 0.100”0.200”0.300”0.400”0.500”0.600”
144/170/20036689198103105
OZ 25036689198103105
Classic Inlines 4079111144{{{164}}}174
Ported4487122159179184