The Smart Lifter

DO THE RHOADS VARI-DURATION HYDRAULIC LIFTERS REALLY MAKE MORE HP AND TORQUE? WE PUT 'EM TO THE TEST!

By Marlan Davis

Life is full of compromises. So are cars. Put in a long cam to gain more top-end horsepower and lose bottom-end tractability. Oh well, it wouldn't be a hot rod if it idled like a stocker, right?

Wrong. There is no longer a need to rationalize living with a poor compromise, thanks to the folks at Rhoads lifters, Inc. who sell one of the best kept performance secrets to come down the track in years. Their claim to fame: a uniquely designed hydraulic lifter able to change a camshaft's lift and duration as a function of rpm, valvespring pressure, Oil pressure, oil viscosity, and oil temperature. This is accomplished through a vertical slot ground top-to-bottom on the lifter's inner piston, thereby allowing the lifter to “bleed down” slightly at idle, and thus delaying valve actuation. At idle speeds, the result is an approximate decrease in valve-open duration. At idle speeds, the result is an approximate decrease in valve-open duration of 10 to 15 degrees, and .020 and .030 inch of lift. By reducing valve lift and duration, a radical cam can be civilized enough to improve low-rpm idle quality, increase vacuum for operating power accessories, and create the potential for improved gas mileage.

Even better, all this is accomplished by not sacrificing any mid-range or top end horsepower; as engine speed increases, there is less time to bleed-off oil pressure; by about 3500 rpm, bleed-off action has decreased to the point where it is virtually non-existent. Full camshaft duration and lift is restored just when it's most needed.

On the top-end the lifters have greater anti-pump-up ability compared to conventional hydraulic lifters. Excessive oil pressure buildup in conventional lifter due to their low stock bleed-off rate holds the lifter piston and plunger up against the top snap ring, in turn holding the valves open when they shouldn't be. On a Rhoads Lifter, the added bleed-off feature delays any pump-up tendencies beyond the designed operating range of currently available hydraulic camshaft profiles (not to mention most street or dual-purpose engines).

So much for the theory. Words are a dime a dozen – What'll happen on the dyno? To find out, we contacted Gale Banks Engineering, known for strong street and marine turbocharged, endurance engine packages. Banks has been using Rhoads Lifters for years. As he puts it: “In the past, my cam designs were compromised by the lack of a variable duration lifter. That compromise is now virtually eliminated. I can cam my engines for maximum power and still retain good idle quality, low-speed response, and mid-range torque.”

With Bank's cooperation we set up a dyno test to obtain real-world data. The engine selected was last year's 454 cubic-inch muffler test “dyno mule”. The 10.2:1 motor consists basically of a cast, two-bolt-main bottom end, TRW forged pistons, ported and polished ZL 1 open-chamber aluminum heads, and special annular-discharge venturi Holley carb – fully blueprinted by Gale's meticulous crew (details in sidebar). At the time of the test, the motor had nearly 200 runs on it, yet was still in good shape. That many dyno runs are equal to about 30 to 40 thousand miles of street driving, proving you don't really need four-bolt mains and forged cranks for most applications.

A radical “Banks Power” hydraulic cam with hefty valvesprings was installed for the test to prove that Rhoads Lifters could tame even the wildest cams. Also putting increased “pressure” on the Rhoads Lifters was the high-pressure oil pump, capable of supplying 65 psi hot. Apparently, the high oil pressure adversely affects the Rhoads Lifters' bleed-down rate.

The test on Gale's dyno was run using current stock hydraulic lifters (GM 52327220), adjusted per factory specs “one turn down” after cessation of audible valvetrain clatter. Despite the trick carb, with these lifters installed the engine would not idle at all below 900 rpm, where only 7 inches of vacuum was recorded. Idle quality was poor, and in fact, the dyno operator wasn't able to fully load the dyno and hit wide-open throttle (WOT) below 2000 rpm, as the engine would backfire and die. Peak torque was reached at 4500 rpm, where 567 ft.-lbs. Was produced. At 5500, the engine horsepower peaked at 552. Valve float then occurred at 6100 rpm. These results indicate real drivability problems on the street, with the low vacuum, erratic idle, and lack of bottom end power that's characteristic of radical camshafts.

The next step was to replace the conventional lifter with Rhoads Lifters (part No. RL-8178). After installation, idle vacuum increased to 10 inches at 900 rpm. However, idle speed was then satisfactorily reduced all the way down to 750 rpm, where the radically cammed motor suddenly purred like a kitten. The dyno operator could now fully load the motor and obtain a steady reading at only 1500 rpm, 500 rpm lower than previously, the vari-duration lifter was doing its job, reducing the cam's net duration.

Low-end torque increased substantially (see chart). As the run proceeded, horsepower and torque remained up slightly throughout the entire power-band. Horsepower now peaked at 6000 rpm, 500 rpm higher than before. At 6500 rpm, there were still no signs of valve float. Since the cam's power peak had already been exceeded, any additional rpm increases were unnecessary, and the test was therefore terminated.

Bottom line: In an attempt to make life tough for Rhoads, we stacked the odds with a big cam and high oil pressure. Despite there handicaps, the Rhoads Lifters performed as advertised, offering improvements on both bottom and top end. Rhoads Lifters are available for most popular American engines, and would improve the all-around response of just about anything. After all, they turn radical engines into gentlemen…and (Rhoads) scholars. HR