Figure 2b: Shown here are a pair of Crane roller rockers, with a 1.6 ratio on the left an
Figure 3: The hole that the pushrod passes through in the head is not a critical toleranc
This is the critical part to the whole roller rocker installation--Crane's guideplate and
Here, you can see the differences between Crane's roller rockers and the stock Mopar piece
No matter what we drive, we all want the same thing from our enginesmore power. Unless were building it from the oil pan to the air cleaner wing nut, a proven bolt-on part is always preferred. Whether its a 440-6 or a Magnum V-6, if we can find ways to squeak out more grunt with minimum effort, were all over it.
One proven way to increase power is by decreasing the amount of valvetrain friction. The biggest friction hot spots in any valvetrain are those where the lifter comes in contact with the cam lobe, where the rocker fulcrum rides on the shaft or stud, and where the tip of the rocker comes in contact with the valve stem. In basic, simplified terms, the more energy your engine exerts by overcoming these high-friction contact points, the less torque is exerted to the rear wheels. Replace the rubbing metal-to-metal contact with a bearing of some type, and the engine is going to spend less energy doing the same work. Hence, the creation of roller lifters and roller-tipped rockers.
With roller cams, two benefits are noted: (1) the friction reduction of a roller lifter and (2) the radical cam profiles the roller allows. Even if total lift is the same, the higher velocities are possible with a roller tappet lifter as opposed to a flat tappet lifter. The roller lifters higher velo-city is the key to achieving higher lifts sooner in the lift curve. While acceleration is quicker with a flat tappet, the velocity of the flat tappet lifter is limited by the lifters diameter.
While most will assume that the only benefit of roller rockers is reduction in friction, the other benefits of aftermarket roller rockers include true, blueprinted, at-the-valve ratios and precision motion.
By placing a roller on the tip of the rocker where it comes in contact with the valve stem, the rocker is able to roll across the valve as it travels through its cycle, instead of sliding back and forth across the valve stem. Beside the obvious friction created here by non-roller tips, serious side loads are placed on the valve stem as the tip drags across the top of it while the valve travels up and down in the valve guide, contributing to worn guides (Fig. 1).
Another time-honored way to increase power with rocker arms is to change the ratio of the rocker (Figs. 2a, 2b). The ratio of a rocker is determined by dividing the length of the centerline of the fulcrum to the rocker tip (A) by the length of the pushrod end to the fulcrum centerline (B). To increase the ratio, shorten length B. Its like moving the centerline of a seesaw on a playground.
The benefit of increased rocker arm ratio is the valve is opened a little further and faster, allowing more air in and out of the engine, thus creating more power. According to the guys at Crane Cams, changing from a rocker ratio of 1.5 to 1.6 generally adds about 3 degrees of valve duration, and changing from 1.6 to 1.7 rockers adds another 1-2 degrees. The net result is you are effectively changing your cam specs without changing your cam.
Traditionally, stock rocker ratios are right around 1.5, with a standard increase being a change to 1.6 rockers. The rockers found on Dodges Magnum motors are already 1.6 from the factory. If bigger is almost always better, why not swap in a 1.7? On the old LA engines, this swap created pushrod clearance problems, because the pushrods angle of attack was changed enough to make contact with its hole in the head, meaning that 1.7 rockers required machining the heads. Magnum engines have enough clearance for the pushrod (Fig. 3), but there is a possibility that you could run into piston-to-valve clearance problems because the valve is opening further and faster. If youre building a motor from scratch, clay on the top of the piston will let you know if the pistons should be fly-cut. Crane tested 1.7 rockers on an engine and didnt encounter any clearance problems. Usually, when you go from stock 1.5 rockers to 1.6, there is enough clearance that you can get away with it, so it would seem that going from a factory 1.6 to 1.7 would have the same result. But if the engine was in the vehicle, and it was our vehicle, we wouldnt chance it.
Crane Cams offers a roller rocker kit for V-6 and V-8 Magnum motors that is a real nice bolt-in. The full kit (several different part numbers) includes real pushrod guideplates, a stud kit, stronger pushrods, and your choice of extruded or die-formed aluminum rockers, both with needle-bearing fulcrums and roller tips. The difference between the die-formed and extruded models boils down to, roughly, the difference between cast and billet parts. The billet (extruded) pieces are stronger for race-only applications, while the cast pieces are designed for hard-street and moderate race use. Crane is an OE supplier, and their cast pieces live up to stringent 100,000 mile durability testing with no problems. For our own personal vehicles, wed save a little cash and take the die-formed pieces any day. Crane recommends swapping out the stock valve springs on Magnum motors, and upgrading to the Mopar Performance pieces, as well as MP valve covers to clear the new rockers. A full length baffle runs the length of the stock valve cover that interferes (Fig. 4). You could modify the stock baffle, but why?
Crane provided us with before-and-after dyno tests of their rockers on a 95 V-6 Magnum. As you can see, the engine made more torque and horsepower all the way throughout the rpm band. Since they are two cylinders ahead, V-8 owners can expect to see proportional increases in both categories.
We buzzed over to Crane in Daytona Beach and bolted a set of their rockers, studs, and guideplates onto a V-8 Magnum on an engine stand, to show you the process. After doing it, there is no doubt in our minds you could do this in your garage. Plan on spending the weekend to do itafter torquing the new studs in place, allow the Loc-Tite to set overnight.
|Magnum V-6 Rockers|
|Stock Rockers vs. Crane Roller|
|RPM||baseline TQ||1.6:1 Rockers||1.7:1 Rockers|
|Magnum V-6 Rockers|
|Stock Rockers vs. Crane Roller|
|RPM||baseline HP||1.6:1 Rockers||1.7:1 Rockers|
The differences between the stud-mounted Crane piece and the OE piece are self evident. Wh
The difference between the Crane pushrods and the factory pieces is also dramatic. The fol
Here, you can see the differences between Crane's Energizer die-formed rockers (right) and
Begin by removing the stock Magnum rockers. Their mounts are a light press fit on the asse
Crane recommends replacing the stock springs with the Mopar Performance units. This can be
The stock guideplate is on the left, and Crane's guideplate base is on the right. The stoc
This is the important piece of the valve guide. The insert presses into the fingers. The p
The guideplate base rests on the rocker bolt bosses. The base is a shallow U-channel, and
This step is vitally important. Crane supplies a pair of stud installers with its kit. The
After the studs and guideplates are in, drop the pushrods into place. Be sure to hit the c
Drop the rockers in place on the studs. The fulcrum has a top and bottom, so pay attention
Tighten up the rockers according to the instructions, and you're done. The rockers should