Shown is FAR's RHO engine straight from the factory. It's a complete longblock minus details such as an oil pan, timing chain cover, water pump, intake, flywheel and balancer, and other necessities. These pieces are left off to reduce the initial purchase price, since most enthusiasts will be using this engine to replace an existing Windsor small-block.
Details worth noting include the fact that this is a late-model 5.0-liter engine that requires the use of a late-model balancer and flywheel or flexplate. A McLeod flywheel (part No. 463106) was used for the dyno tests, along with a stock late-model balancer and a 50-percent underdrive V-belt pulley (part No. 5455) from B&B.
Here is the RHO engine in the "stock" configuration test. It was assembled complete with a set of late-model Ford stainless-steel "headers" from a Mustang with a true 2 1/4-inch dual exhaust system feeding into a pair of turbo-style mufflers.
On the intake side of this first test, we used a stock '85 Ford aluminum intake, along with a 650 Holley double-pumper. The 650 Holley was used only because we didn't have a 600-cfm-vacuum secondary carburetor at the time of the test! On the street, a 600-vacuum secondary carb would be perfect for this engine. The distributor is an '85 Ford electronic unit with a steel drive gear (part No. M-12390-F) available through SVO Motorsport (no longer available but you can get a rebuilt unit at the local Ford dealership - ask for an '85 Mustang with a 5-speed - Fletch). This gear is a must for any distributor, since an iron gear will wear out in a matter of hours when combined with a steel-billet roller camshaft. We also used MSD wires and an MSD-6A amplifier in all of the tests.
The first change was to outfit the RHO engine with a set of "real" 1 5/8-inch headers from Headman. They were installed on the dyno in "boat" fashion in order to clear the dyno stand. The longer-tube headers in combination with the improved exhaust ports produced dramatic improvements, especially in low-speed torque.
Our second modification was improving the induction side with the addition of an Edelbrock RPM dual-plane intake manifold. Compared with the stock Ford intake port, the RPM intake offers a substantial larger intake port. This proved to be worthwhile, for the rpm intake generated a 35-horsepower increase, when combined with the headers. A Victor Jr. would also work well in this application if you were looking to increase high-rpm power. The RPM dual plane is our choice for all but the most serious street duty.
If the B-303 roller cam that comes in the RHO engine is a bit lumpy for your taste, Kaufmann Products offers a dual-pattern roller cam with a shorter 214-duration intake profile. It provides 224 degrees of exhaust duration at 0.050-inch tappet lift and a 114-degree lobe-separation angle, which generates a much smoother idle. Power is still a strong point, since the cam offers much taller 0.520 / 0.544-inch valve-lift specs.
The Dart II iron Ford heads come completely assembled, or you can buy them bare. The camber size is 64 cc's the valves are 2.02 / 1.60, and the exhaust port is drilled for both exhaust-flange patterns. A little bowl-work on the exhaust side and some intake-port work could generate even more flow potential from these heads.
The RHO engine comes with forged, four-eyebrow pistons. When using the Dart II iron heads with a high-lift camshaft, you will probably have to remachine the valve relief pockets in the pistons, as the larger valves in the dart heads could hit the pistons. Always check the valve-to-piston clearance when changing either the heads or cam.
The Dart II heads come stock with lo-po valvesprings that are fine for basic flat-tappet cams. But to control the RHO engine's radical B-303 roller cam, Bill Mitchell supplied larger valve-springs. The Dart II heads come with 3/8-inch screw-in studs and guideplates. You should use rocker arms designed for the small-block Ford (small-block Chevy rockers won't work) (-like duh, don't you love it when these Chevy guys do a Ford article - Fletch), such as those offered by Crane, Edelbrock, or Competition Cams. The stock Ford stamped rockers will deflect horrendously, especially when used with roller-cam valvesprings.