Mustang Cylinder Heads - Bolt On A Pair

While the exhaust ports are slightly raised, the RHS heads are all designed as bolt-on parts. Built without a heat crossover, this wasn't designed with emissions in mind and doesn't have a CARB exemption number. Two exhaust-bolt patterns are supplied by RHS. The outer pattern is for oversize headers with wide flanges.

While not revolutionary, the combustion chamber shape in the RHS heads follows modern practice with plenty of shapes to control combustion. In the old days, this would have been a simple slanted bathtub of a chamber; the modern chamber shapes speed combustion and control detonation. The valves are 2.020x1.600 inches in stainless steel.

While weighing a claimed 20 pounds, the RHS heads feature generous metal where needed. Furthermore, steel thread inserts in the rocker-arm pedestal mounting holes add great strength without having to add more aluminum. When bought as assemblies, the RHS heads are supplied with rocker studs and guide plates.

With Comp Cams as the parent company of RHS, you don't need to worry about the valve springs on RHS heads. They proved to be up to the task of handling the 0.608-inch lift Comp camshaft we ran, and they'll certainly have no problem with less lift or duration.

The intake rocker stud holes extend all the way through the upper deck of the engine. When the valvetrain is installed, the intake rocker stud will seal this hole.

Westech is aligned with Demon Carburetors. For the RHS examination, we used a 750-cfm Mighty Demon. That's a performance carburetor with no choke horn and a more aerodynamically shaped air entry compared to the standard Street Demon. The carburetor proved well-matched to the engine's airflow, with only 1.2 in. to once-touching 1.5 in. Hg of restriction at the power peak. A single jet change, shown here, was needed to tune the amount of 100-octane Rockett Brand unleaded gasoline delivered.

Our front-engine dress has remained the same for a couple of years now. The electric water pump saved time on the dyno, but it added several more horsepower to the reading. So subtract 10 hp to be safe when thinking of the test engine in typical street trim. The ignition was by MSD.

To corroborate the dyno and flow bench findings, Westech fitted the air hat atop the Mighty Demon for a couple of runs with each cylinder head. The air vane costs next to nothing power-wise-about 2 hp-but the power figures in this article are without the air hat in place. The airflow figures from the dyno to flow bench made sense. Air consumption for both heads peaked at 612 cfm, and the curves correspond to the power curves. Having the airflow and power curves the same shape supports the idea that the small performance difference in the heads is due to the change in airflow, and not a tuning factor such as ignition timing.

At the conclusion of the cylinder head testing, Westech wanted to try this 14x4-inch round S&B air filter. Surprisingly, it didn't change power at all, posting a 460hp run.