Mustang MonthlyHow To Engine
How To Improve Six-Cylinder Performance
Make The Most Of Your Inline Mustang's Potential
Ford's lightweight six-cylinder engine debuted in the '60 Falcon and Mercury Comet as the 144ci six. It's strong on reliability but not much on power. A year later, Ford upsized the 144 to 170 ci with an increase in stroke, which improved power but didn't rock the planet. When the Mustang was introduced in April 1964, it got the Falcon's improved seven main bearing 170ci six as standard equipment. Producing 105 horsepower at 4,400 rpm, this engine's message was never about power but more about economy for buyers who needed a fuel stingy, reliable powerplant.
Detroit has come a long way over the past nearly 50 years, so it's easy to get spoiled by technology and comfort. Improvements like electronic fuel injection, roller camshafts, overdrive transmissions, and four-wheel disc brakes have made automobiles more fun to drive. Driving an old six-cylinder Mustang is more about the spirit of driving a classic than it is about comfort. These cars put you more in touch with the road than today's technological wonders. And face it, there's only so much you're going to be able to do with the classic inline sixes, including the later 200ci version. However, you can make the most of these engines if you know what to do.
The largest culprit with vintage Ford sixes is fuel distribution. Their integral log-style intake manifold, which was conceived to control manufacturing costs, makes these sixes frustrating to live with. They suffer from rough idle quality no matter how many different carburetors you try. They stumble off idle and surge or hesitate while cruising. We tend to blame these performance issues on the carburetor, but that isn't always the case. Poor fuel/air distribution along the integral intake manifold and into the cylinder head creates all kinds of performance issues. It can be the luck of the draw because no two castings are alike. Some sixes run like a clock while others can't get out of their own way.
Turbulence along the log manifold tends to upset fuel droplets in suspension, which enter intake ports erratically. End cylinders tend to run lean while inboards run rich. To add insult to injury, Ford placed the one-barrel carburetor above a hot exhaust manifold, which causes all kinds of heat-induced problems (percolation and vapor lock) in hot weather.
Autolite 1100 Carburetor
The Autolite 1100 one-barrel carburetor installed on classic six-cylinder Mustangs suffers from engineering shortcomings, with rough idle and hesitation among the biggest complaints. Jon Enyeart of Pony Carburetors tells us that these shortcomings can be engineered out with a professional rebuild and restoration. When Pony Carburetors rebuilds the 1100, it rolls in improvements that eliminate hesitation, stalling, and rough idle. However, despite Jon's best efforts, some drivability problems cannot be eliminated because fuel distribution problems transcend the carburetor. You can have the best carburetor in the world, but if air and fuel have trouble getting to the intake ports, drivability will continue to suffer.
The Autolite 1100 one-barrel carburetor was introduced in 1963 and was used on the 144, 170, and 200ci engines through 1969. Because six-cylinders are low-buck powerplants by design, Ford had to figure out the most cost effective way to produce them, hence the log manifold design. It also had to simplify carburetor design for reasons of economics. There were three basic 1100 venturi sizes-1.00, 1.10, and 1.20 inches with a common 1-7/16-inch bore. Interchangeable venturi inserts determined size-1.00 inch for the 144, 1.10 inches for 170, and 1.20 inches for the 200. This means you must be aware of which venturi size you have in your Autolite 1100. If you're running an 1100 with a 1.00-inch venturi intended for the 144ci six, you don't have enough carburetor for a 170 or 200.