Jim Smart
December 1, 2003

Six-cylinder performance. Sounds like an oxymoron, doesn't it? But don't underestimate the humble Mustang six because there's a lot of performance potential. Pound for pound, the 170, 200, and 250ci sixes make more torque than a small-block 302 or a 351 V-8 because they have six cylinders in a row on a common crankshaft for smooth application of firepower. Inline engines-be they four-, six-, or even eight-cylinder-apply power more smoothly and effectively on a long, common crankshaft than V-type engines. The one big exception to this theory is four-cylinder engines, which struggle with vibration and harmonics issues, depending on the design

Inline-sixes were heavily drag-raced back in the '60s. In many parts of the world, such as Australia, they still are. Ford and Chrysler took inline-sixes to Daytona in the early '60s-Ford with the Falcon and Chrysler with the Valiant. Racers successfully spun these sixes to 7,000 rpm, making lots of power. Forty years later, that great potential for power still exists in these hearty powerplants.

The Mustang's 170/200/250ci six has its roots in the 144ci six introduced in the '60 Falcon. The 144 is a lightweight, gray-wall iron powerplant with six 3.5-inch cylinder bores and a 2.50-inch stroke along a four-main-bearing crankshaft. Ford took the 144's modest stroke and increased it to 2.94 inches to arrive at 170 ci for 1961. This made the little Ford six more crisp right off the idle circuit, getting Falcons and Comets off to a good start. When Ford introduced the Mustang in April 1964, the 170ci six was standard equipment, with 105 hp at 4,400 rpm. But journalists of the period weren't impressed with the Mustang's anemic standard offering. The 170ci six, coupled with a 2.77 unsynchronized three-speed manual transmission, was disappointing at best. The package simply didn't perform very well.

In 1964, Ford pumped up the bore and stroke to arrive at 200 ci. The 200's bore was 3.68 inches, with a 3.126-inch stroke. Externally, the 200 didn't look much different from the 144 and 170ci sixes it surpassed. That first year, the 200 had a four-main-bearing crankshaft and was available only in the Fairlane. A year later, the 200 would have seven main bearings and hydraulic lifters in a more rigid block. In August 1964, Ford began offering the 200 as standard equipment in the Mustang. The 200 was more peppy with 120 hp at 4,400 rpm. Torque improved dramatically to 190 lb-ft. In 1966, the 170/200's standard 2.77 crash-box was phased out in favor of the fully synchronized 3.03 three-speed "Top Loader" manual transmission.

In 1969, Ford raised the 200's deck some 1.66 inches, using the same 3.68-inch bore, and stroked the taller block to 3.91 inches to achieve 250 ci. What this meant for the little six was big-six torque, with 240 lb-ft of twist at 1,600 rpm. The 250ci six was a nice Mustang option in 1969-'70 for those who didn't want a V-8. From 1971-'73, it became the standard Mustang power offering. From 1974-'79, the venerable inline Ford six was dropped from the Mustang, returning for 1980-'82 as the 3.3L inline-six due to a critical shortage of 2.8L Vulcan V-6s.

At first glance, the 170/200/250ci sixes all look the same. Closer inspection reveals the differences. The 170ci six has three freeze plugs in the block. The 200ci six has five freeze plugs. The 250ci six is 1.66 inches taller than the 200ci six and is easily identified by its taller design and a four-bolt water pump. The 200ci has a three-bolt water pump. The 250 is 31/44 inch wider than the 170 and 200.

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Ford Six Performance Basics

When you're building a Mustang six, it can get quite confusing when it comes to cylinder heads because they can all look the same. But there are clear differences you should be aware of. Here's how they stack up.

Model YearDisplacementIntake Valve SizeExhaust Valve SizeCombustion Chamber Size
'60-'64144 ci1.467 in1.266 in44-51 cc
'61-'63170 ci1.522 in1.266 in48-53 cc
'64-'72170 ci1.649 in1.380 in48-53 cc
'64-'73200 ci1.649 in1.380 in51-53 cc
'78-'82200 ci1.750 in1.380 in62 cc
'69-'75250 ci1.649 in1.380 in62 cc
'76-'80250 ci1.750 in1.380 in62 cc