Hydraulic Roller Valvetrains - Buzz It Up!

Two things to note: the COMP beehive springs with their small retainers, and the base of the Crane shaft rocker setup.

Cylinder Heads and Intake
Normally for a 383 street driver we would use heads with a 200cc port volume, but in this case, top-end output with a relatively big cam was the primary consideration. This prompted the use of a set of Dart's Platinum 215cc runner heads. With strong flow curves right out of the box, these heads have what it takes to allow a 383 to usefully turn as much as 7,000 rpm-if the valvetrain allows it.

For an intake manifold, an Edelbrock Victor Jr. with a built-in 1-inch spacer (PN 2999) was used. This, together with an 850 Barry Grant vacuum secondary Demon carb, rounded out the induction system.

Here is the completed Crane shaft rocker setup. These rockers deliver a net valve lift of over .590 inch on our test engine.

Ignition
The ignition system is a little different than the norm. Instead of a regular distributor, a Crane "all-electronic" unit was used. Some testing a while back showed the unit to be a very functional item with the convenience of adjustability not possessed by a regular distributor. The built-in timing curve module has nine rpm-related computer-controlled mechanical-advance curves, and these are supplemented by three vacuum-advance curves. Having such a range to choose from is going to allow the timing curves for part-throttle cruise to be optimally set. What this does is allow us to set up the low-speed and idle parameters so that the negative effects of a relatively big cam are somewhat held in check. Just to give an up-front idea of what this was worth, the engine's minimum idle speed without the aid of vacuum advance was a lopey 900 rpm. With the vacuum, it was 780 rpm, with only about half the lope. Also worth noting is that the amount of fuel used at idle with the vacuum advance is about 30 percent less than without.

To complete the ignition system, we used a Crane HI-6 multiple spark ignition box and the appropriate hi-output coil. The last item on the list is to plumb in the plug cable harness. The "down under" routing was used in case we had to make multiple visits to the rockers for adjustments, should we fail to reach our target rpm by the regular quarter-turn valve adjustment.

The 215cc runner Dart Pro 1 Platinum heads deliver strong flow right through the lift range, right up to the targeted .600-inch valve lift.

Test Time!
At this point, we were ready the take the engine over to T and L Engines for the dyno test. Using T and L's Innovate wide-band fuel mixture data acquisition system, carburetion was dialed in after a few exploratory pulls. Getting the best rpm and vacuum advance curves for the job was even quicker, courtesy of Crane's all-electronic distributor. All the pre-test setup work was done with an upper rpm limit set to 5,700, which is just below the accepted limit for a typical stock hydraulic roller valvetrain.

Before looking at results, let's restate our goals. First, we assembled a valvetrain with typically .050 inch more lift than normal for a 6,000 rpm valvetrain. Second, by targeting 6,600 rpm, we are attempting to get the valvetrain to turn to some 600 to 800 rpm more. Third, we hoped getting those extra rpm would be instrumental in achieving a target output of 530 hp.

The first dyno pull with the upper rpm limit at 6,500 showed we had already exceeded our target power with 531 hp at 6,300 rpm. For the next pull, the upper limit was set at 6,600 rpm, but the system refused to go 20 rpm above the 6,500 point. At 6,500, the valvetrain appeared to be totally under control, yet 20 rpm later it was in complete disarray. But we did have another card up the old sleeve. Extensive testing showed that Mobil 1 was among the best off-the-shelf oils when it came to fending off lifter collapse. Armed with the knowledge that some oils can leak faster than others and thereby greatly affect where lifter collapse starts, we switched our traditional mineral-based oil over to Mobil 1 synthetic. After bringing up the motor to temperature, some runs were made. Nothing changed until about 5,800 rpm, where power started to look better. Peak power at 6,300 went up by 4 hp, and at 6,500, it rose by 7 hp. That was all good, but the valvetrain crash threshold did not appear to change-everything still came unglued at 6,520! The nearby chart shows our final test results to the nearest whole number.

Conclusions
Although all the parts of the valvetrain played a significant role toward making the power, it has to be said that a solid 500 rpm of the 6,500 rpm seen was achieved by the use of the AFR Rev Kit. By adopting this, we were able to make the most of the power producing capabilities of COMP's Xtreme cam and the Crane high-lift shaft rockers. After running all our tests, we tore the engine down to check that nothing had been hurt.