Ford Mustang Six-Cylinder Performance Guide
Making The Most Of Your Mustang's Inline-Six Begins With Jack Clifford's Performance Products
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.