Jeff Huneycutt
December 1, 2009

When Ford debuted the modular engine family in the early '90s, the overhead cam V-8 was quite a technological advancement compared to the cam-in-block small-block that had been around for decades. But, the Two-Valve layout doesn't work as well with the engine's smaller 100mm bore spacing. The cylinder heads just couldn't pull in enough air for high-performance applications.

That changed with the birth of the Four-Valve head in 1993. Even though they are slightly smaller, the increased curtain area of two intake valves in each combustion chamber significantly increases how well the engine can breathe, and performance as a result is also greatly improved. In naturally aspirated form, the same block with Two-Valve versus Four-Valve heads jumps from 260 hp to over 300!

So it's no wonder speed freaks and sprocketheads love the Four-Valve modular in their Mustangs. It's even the foundation for Ford's fantastic supercharged Shelby GT500 with 500 hp and 480 lb-ft of torque. So despite the complexity of an extra set of valves-and the rest of the valvetrain that comes with it-there is definitely an advantage of going with four valves per cylinder in this application versus two.

A downside of the Four-Valve cylinder heads is it can be tricky to properly degree in the camshafts. We are talking four camshafts, four different timing chains, four tensioners, and seven sprockets (counting the crank sprocket). Worse yet, Ford doesn't build any adjustability into the system! That might be excusable if the cams always arrived spot-on from the factory, but in different engine builds we've found cam timing in stock engines can be off by several degrees. That's like leaving horsepower on the showroom floor.

Degreeing your cams is the process of making sure your camshaft is correctly positioned relative to the crankshaft. In plain English, this means the cam opens the valves when the pistons are in the correct positions in the cylinders. Although cam timing is normally good when the timing set is installed as directed, cam-timing errors can crop up unexpectedly because of machining errors with the timing set, the cylinder heads, the block or even the camshafts themselves. No matter what engine you are working with, you should always take the time to degree in the cams any time you are building a new engine, installing new cams in an existing engine, or doing any other work that requires you to pull the timing assembly off the engine. Heck, if you have a Four-Valve engine in your Mustang, it might be a good idea to degree the cams just to make sure you aren't giving up any horsepower from a setup that came improperly degreed in from the factory.

Just be aware that degreeing in the camshafts on your Four-Valve Modular motor is a bit more complex that what you might have seen before on a Two- or Three-Valve modular engine, or even a cam-in-block push-rod engine. To do the job correctly requires a few specialty tools and a lot of patience.

To get the full scoop, we traveled to the shops of KT Engine Development in Concord, North Carolina, where engine builder Craig Hibdon was completing the build on a Four-Valve that had been bored and stroked to 351 ci. Even though this is a new build, the process is the same even if you are working on an engine still in your car.

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