Assembled engine packages have become popular items among hot rodders in the last few years. While most sources for these engines are in the aftermarket, new-car manufacturers are also interested in these engine packages, as evidenced by Chevrolet's 350 H.O. engine package. While Ford continues to develop its 351 Windsor H.O. response, Ford Authorized Remanufacturers (FAR) are already in the hunt with a late-model Remanufactured High Output (RHO) 5.0-liter engine that's available through a number of sources, including select Ford and Lincoln-Mercury dealerships and Ford Motorsport dealerships.
As the RHO 5.0-liter name suggests, this engine is not new, but a remanufactured small-block that features a number of power-producing modification. The RHO 5.0 comes as a complete, assembled long-block with heads, all the valvetrain components (including the timing chain and gears), and an oil pump. It does not include the oil pan, timing chain cover, water pump, intake manifold, exhaust, or distributor.
The RHO was developed with a couple of interesting departures from the normal rebuilt-engine approach, such as the cam FAR chose to use. With assistance from Ed Lyons and John Vermeersch at Ford's Special Vehicles Operations (SVO), the RHO engine is fitted with the Ford Motorsport M-6250-B303 roller camshaft. With specs of 284-degrees advertised duration, 224 degrees at 0.050-inch tappet lift, a 0.480-inch valve lift with the stock H.O. 5.0-liter cam. As you might assume, it's a little lumpy when it comes to idle quality. Our sources claim that it is not recommended for engines equipped with the early Ford speed-density electronic-fuel-injection system, unless you use the Ford Motorsport Mass Air Flow conversion kit. The idle quality on our carbureted dyno engine revealed 13.5 inches of vacuum at 850 rpm.
The other major modification made to this engine is significant port-work to the exhaust side of the heads. As any Windsor Ford fanatic knows the exhaust side of most small-block Ford heads is weak in comparison with the intake ports and constitutes an area for improvement. The cast-in comparison with the intake ports and constitutes an area for improvement. The cast-in EGR bump in the port roof of these otherwise-stock heads is completely removed by the rebuilders, which appears to significantly improve the exhaust-port flow and to complement the potential of the B303 camshaft.
The remainder of the engine is a close-tolerance rebuild of a select late-model, roller-cam H.O. 5.0-liter small-block, featuring 0.030-inch overbore (making this engine 306 cubic inches), low-tension oil rings, forged four-eyebrow pistons, a reground H.O. crankshaft, rebuilt H.O. rods with ARP rod bolts, and a Ford Motorsport oil pump. The heads are also completely rebuilt with new 1.78 / 1.48-inch valves, guides, seals, steel retainers (without the rotators), and a 3-angle valve job. The heads on our engine were '78 70cc castings that produced an 8.5:1 compression ratio (weak - Fletch). Later-model fuel-injection truck heads are the preferred castings, as they offer smaller chambers that increase the static compression ratio.
The RHO engine looked impressive enough on paper to warrant an in-depth look, so we enlisted the help of our friends at McFarland & Associates, who put one of these engines on the dyno to see shat kind of power it could produce. Chris Kaufmann of Kaufmann Products also lent his technical assistance in the effort. In addition, we had a chance to test two intake manifolds, including Edelbrock's brand-new Performer RPM intake for the 5.0 engine and the brand-new World Products / Dart II iron cylinder head.
To begin the test we outfitted the RHO 5.0 engine with a stock '85 Ford dual-plane intake manifold, and a 650-cfm Holley double-pumper carburetor, an '85 electronic ignition distributor from Ford Motorsport with an MSD-6A amplifier and MSD wires, stock stainless-steel factory headers, and a 2 1/2-inch-diameter dual exhaust system with a pair of turbo-style mufflers. Once the engine was sufficiently broken in, dyno operator Kevin McClelland experimented with the total timing and jetting on the 650 Holley carburetor until power was optimized. In this "stock" configuration, the RHO engine generated 296 lbs.-ft. of torque at 3,500 rpm and a respectable 244 horsepower at 5,250 rpm.
Even with the enhanced exhaust ports, Kevin felt that the factory-style exhaust headers left much to be desired, so the first change was installing a set of Headman 1 5/8-inch headers, originally designed for an early small-block Fairlane. Retaining the same exhaust system and mufflers, the RHO engine responded to the change with an across-the-board increase in torque, especially below 4,000 rpm where the increase was never less than seven lbs.-ft. with a whopping 16 lbs.-ft. increase at 3,000 rpm! The increase in horsepower was not as significant, with a 9-horsepower increase at 5,250 rpm, indicating that the factory intake was too restrictive to allow the engine to take advantage of the improved exhaust system.
Naturally, the next step was to try Edelbrock’s newest high-rise Performer RPM intake. Once the intake was installed, Kevin again went through the optimization drill before coming up with a power comparison. The major increases were in the above-3,000-rpm range, since the larger RPM intake lost small amounts of power below 3,250 rpm. From 3,250 rpm on up, the torque increased at lease 17 lbs.-ft., with the largest increases at 5,500 rpm, where the RHO engine with intake and headers cranked out a whopping 38 lbs.-ft. more torque and 40 horsepower over the stock configuration. Looking at just the intake change alone (not including the headers), the Edelbrock RPM intake was worth 34 horsepower over the stock intake and header combination at 5,750 rpm! With just an intake and header swap, the RHO engine cranked out an impressive 282 horsepower at 5,500 rpm and 315 lbs.-ft. of torque at 3,750 rpm!
Just as we were about to yank the engine off the dyno, Bill Mitchell sent us a set of his latest Dart II iron heads for the Windsor Ford. With a stout 195cc intake port, 2.02 / 1.60 inch valve diameters, and a decent exhaust-to-intake-port flow relationship, the heads appeared to be worth some power. There was some concern, however, that the large intake port would create a slight power loss below the torque peak. But once the heads were installed, the numbers told an amazing story.
The new Dart II iron heads require dedicated small-block Ford 1.6:1 rocker arms, which Kaufmann supplied. The RHO cam also necessitated a valvespring change, since the Dart II heads are supplied with stock-type small-block Chevy valvesprings, which would never have cut it with the Ford roller cam. Bill Mitchell supplied a set of stronger valvesprings and retainers, and once they were installed, we were ready to test.
Again, after the requisite tuning process, our first full pull on the RHO engine with the Dart II heads resulted in an amazing 60 horsepower increase over the previous combination. The Dart II heads lost only six lbs.-ft. of torque at 2,500 and gained no less than nine lbs.-ft. of torque from 3,000 rpm up to 6,000 rpm! With this combination, the RHO made maximums of 330 horsepower at 6,000 rpm and 334 lbs.-ft. of torque at 4,000 rpm, increasing the airflow through the engine by well over 40 cfm at 6,000 rpm! Even at the RHO head's peak horsepower point, the Dart II heads cranked out 39 more horsepower. Keep in mind, too, that the Dart II heads enjoyed the advantage of roughly half a point of compression increase over the RHO heads, which is worth some power. To be fair we should mention that by using the 1.6:1 roller rockers on the Dart II heads, some power was no doubt gained over the stock, stamped rockers used with the RHO heads.
As you can see from this test, the RHO small-block Ford responded to every modification we cranked into it. Remember this test was performed with a complete muffled exhaust system and pump gasoline, which means these numbers represent what you could expect from this engine installed in a car. Even more power could be obtained by pocket porting the heads, experimenting with camshafts, and choosing a more efficient muffler such as the Borla (I would go with MAC or Flowmaster personally - Fletch). Perhaps the best part of this entire engine deal is the price range; at this writing, the RHO engine costs approximately $1,800. Regardless of whether you like your small-block mild or wild, the Ford RHO 5.0 engine is a great deal on a great deal of engine.