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1990 Ford Mustang Head Swap - Back In Business
RHS is back, and we find big horsepower using its newest casts on a 331 stroker.
Last November at the SEMA show, the Comp Performance Group announced it was bringing back the Racing Head Service (RHS) brand in Spring 2006. It was through RHS (which built racing cylinder heads, crate engines, and sold performance components) that the Competition Cams brand was born during the '80s. RHS created the Comp Cams company because of a need for quality valvetrain and camshafts to support its crate engine and cylinder head business.
Over the years, RHS had changed management and ownership, which led to it closing its doors in the early '90s. But the ever-growing Comp Performance Group decided it was time to get into the cylinder head business again, and it revived RHS. The announcement coincided with the company's purchase of Pro Topline. SEMA was the coming-out party and RHS had several small-block Ford cylinder heads on display.
Through the acquisition of Pro Topline, the new line of heads take aim at the street car mar-ket, with cylinder heads in the 180cc, 200cc, and 215cc variations, and they are available in both aluminum and cast-iron versions. These three cylinder heads cover everything from mild street engines to serious street/strip stroker Windsor or 302-based motors. The 180cc and 200cc heads feature 2.020-inch intake valves, and the 215cc heads use 2.080-inch intake valves. All heads utilize a 1.600-inch exhaust valve to efficiently expel exhaust gasses. A thick deck ensures proper sealing with power adders. All heads are available in 58cc or 64cc combustion chambers.
This month we picked up a set of RHS 180cc heads to test on a fairly mild 331ci engine. We chose an aluminum set that had the 58cc chamber because that is what closely represented what was on this running engine. JPC Racing (Glen Burnie, Maryland) was more than happy to install the cylinder heads. It didn't build the car, but had sold the short-block to the car's owner-the JPC crew didn't mind updating the cylinder heads to something better.
The 331 was from RGR/JPC and had a TFS Stage 1 camshaft with a pair of Ford Racing GT-40Y heads. In this trim, the '90 Mustang LX kicked out 302 hp and 342 lb-ft of torque at the rear tires on a Mustang dyno. We expected more from this combination, but the car did feature a pair of shorty headers, which were undoubtedly scrubbing off torque and horsepower. A stroker engine needs to breathe, especially one with 331 cubes.
The camshaft was a bit too mild for this engine; it was chosen when the customer had a stock 302 bottom end. The TFS people designed it for use in a mild 302 bottom end and its TFS Twisted Wedge heads. Those heads don't allow for a radical camshaft when installed on a stock short-block. The Stage 1 cam probably wasn't the best choice for this combination. but we were willing to give this test a shot despite our different ideas with regards to this combination. We set out to do an A-B comparison of these cylinder heads on what we'd call a budget 331ci engine combo. Just like some of the other components, the GT-40Y heads were a bit out of the norm for the stouter short-block combination. But the A-B comparison was accomplished with outstanding success, as we picked up 37 hp at the rear tires. Total output jumped to 339 rwhp and 367 rwtq.
Swapping cylinder heads on a 5-liter-style engine has become quite routine and easy, to be totally honest. Our installation was fairly straight-forward, and there weren't any hidden surprises or mysteries. Given the aftermarket short-block, we knew piston-to-valve clearance wasn't going to be an issue. We used a set of Fel-Pro 1011-2 head gaskets. The GT-40Y heads' combustion chambers checked in at 60 cc. All accessory holes on the RHS heads were in the stock location, making the pulleys and accessories a simple bolt-on procedure.
Included with the assembled heads are the pushrod guideplates and rocker arm studs. The RHS-supplied guideplates were not used. The Comp Cams Pro Magnum 1.6:1 ratio rocker arms (PN 1334-16) are self-aligning, meaning we didn't need the guideplates.
The only parts we couldn't get before our installation date were the pushrods. A pushrod-measuring tool was used to determine the exact length. It was decided a 6.350-inch-long pushrod would work perfectly in this application. We spec'd out some different lengths, but the 6.350-inch had zero clearance issues with the pushrod holes in the heads, and rocker arm geometry was correct.
The stock 6.250-inch pushrods did work but were a bit close to the side of the pushrod hole. It could have worked, but using Comp Cams' hardened pushrods that were 0.100 inch larger made more sense. Using stock pushrods with aftermarket camshafts and higher rpm is just asking for trouble. Deflection during valvetrain events will lead to less horsepower and eventually broken parts. A hardened pushrod will stay straight and true when the cam lobes are rotating at higher rpm levels.
By all accounts, the RHS heads can be added to the list of aftermarket heads that will add horsepower to your 5-liter engine. RHS 180cc heads are perfect for a street/strip combination like the one we tested. If your engine is a bit more radical, check out either the 200cc version or have your cylinder-head porter massage these heads.
If a big-inch Windsor engine is being pieced together, then RHS 215cc heads could satisfy the airflow requirements. RHS offers CNC-ported versions for other heads in its catalog, and it is our guess that it will only be a matter of time before that option is available for the SBF heads.