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

The greatest shortcoming of the 144/170/200ci six-cylinder is the integral intake manifold cast into the cylinder head. Although this certainly saved Ford a lot of money in manufacturing costs, it cursed these engines in terms of performance. Even box-stock, the lightweight Ford six suffers from fuel/air distribution issues that make them difficult to tune and operate. The Falcon/Mustang six suffers from idle-quality issues that are rooted in the integral intake-manifold design. Fuel doesn't always atomize consistently, which not only troubles idle quality, but causes these engines to stumble coming off idle.

When choosing a cylinder head, you have to have specific performance goals in mind. You want the ideal combination of port and valve sizing, coupled with the right chamber size. Piston deck height and cylinder-head-gasket thickness must also be considered. When we read The Ford Falcon Six Cylinder Performance Handbook, we learned the most recommended cylinder head is the '77-up 200/250ci head, with 1.760-inch intake and 1.380-inch exhaust valves. It also has a larger intake-manifold passageway, which means greater air volume. Yes, this is a '70s smog head, with the Thermactor ports and passages. But, if you're serious about performance, you'll find a sharp cylinder-head-porting professional to port your Thermactor head. Good cylinder-head porting technique not only opens up the intake and exhaust ports, it improves airflow in and out of the chambers. Larger 62cc chambers help lower compression to reduce the chance of spark knock. You can reduce chamber size by milling the head. Be careful about how much iron you remove from the cylinder head. Deck thickness is important. When we mill away iron, we lose structural integrity.

When a '77-up head becomes hard to find, there remain viable choices out there. Earlier 200 heads can be fitted with larger 1.760-inch intake valves, like we find in the later 200/250 head. Because these heads have smaller chambers, there is the advantage of high compression, which nets more power. We just need to be sure we're not running too much compression, which can lead to detonation and engine damage.

If you feel you must use the 170 head on a 200 six, remember the 170's smaller chambers and even greater compression ratios courting 11.0:1. The Ford Falcon Six Cylinder Performance Handbook tells us to use larger valves, while unshrouding the valves to give up some compression. By grinding out the valve shrouding in the 48-53cc chamber, we improve airflow and reduce compression at the same time. We suggest checking chamber volume before building the cylinder head, which helps determine where to go next.

When you're working the cylinder head, remember to install hardened exhaust-valve seats for use with today's unleaded fuels. The installation of hardened valve seats depends on how you will drive the car. If you're going to drive it daily as regular transportation, hardened valve seats are a must. And if you're going racing, hardened valve seats are necessary there too. Weekend drivers and trailered show cars don't need hardened exhaust-valve seats.

The valvetrain should include valvesprings that are compatible with the camshaft profile. This means you should order your camshaft, pushrods, valvesprings, and retainers as a kit. Because roller-tappet camshafts aren't available for the 170/200ci sixes, we have to make the most of our flat-tappet system. This means choosing a camshaft with a civilized profile for street use. You want a smooth idle, with peak torque coming on strong around 2,000 rpm. The higher we push the powerband, the rougher the idle will be. Low-end torque will also suffer with a high-rpm camshaft.

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Teasers From Australia and Clifford

For years, Australians have known about the great potential of the Ford six. Aussies are familiar with an aluminum crossflow head for 144, 170, 200, and 250ci sixes. What's more, it's happy with port fuel injection. Go to Mustang-Six@cfl.rr.com for more details.

Coming in the spring of 2004 is a crossflow aluminum cylinder head from Jack Clifford's Performance Products for 144, 170, 200, and 250ci Ford sixes. We'll have more information on this cylinder head when it arrives. Expect to see a buildup employing this cylinder head in Mustang Monthly.