Mild-Mannered 440 Mauler Mayhem - Part 5, The Dyno Test

It was evident after the spring...        read full caption It was evident after the spring changes that our problem at higher rpm was related to the hydraulic lifters themselves. It stood to reason, with our demanding combo of a super-aggressive lobe and high rocker-arm ratio, and the relatively heavy valves and valvetrain, it was asking the hydraulic mechanism to cope with a lot. To put the theory to the test, we substituted a set of solid lifters for the hydraulics. It would show what the cam and valvetrain would be truly capable of, if not for the dynamic problems in the hydraulic mechanism. The combination of a juice stick and a solid tappet is not how you'd want to run the engine in the real world, but in this case served as a good diagnostic check. Note the easy access to the lifter valley provided by the Indy 440-6R valley plate.

To make the solid work on...        read full caption To make the solid work on the hydraulic cam, the valvetrain was installed and lashed to .004-inch hot. This would provide reasonable valvetrain action and allow the combination to live for testing purposes.

For the final testing with...        read full caption For the final testing with the solid tappets, the Indy single plane used in the previous test was reinstalled. With tappets that actually followed the cam's profile, the engine easily cleared the 600hp mark by 6,000 rpm, actually registering 607 hp at the top of our pull at 6,000. The test showed that there was plenty of potential in the combination, but there would be some more work involved in coming up with a happy valvetrain combo.

It seemed as if there was little we could do to correct the valvetrain instability problem, but the lower part of the power curve at which the valvetrain was operating correctly seemed normal. We had run all of our tests to this point with the ported Indy 2D two-plane intake. We also had an Indy 440-2 single-plane intake and were curious about how it would compare. The 440-2 was port matched, but not otherwise modified. The single plane manifold added marginally to output above 4,500 rpm, recording a new high in peak power of 570 hp at 5,500 rpm, while peak torque moved to 561 at 5,100 rpm. The lower end of the torque curve dropped sharply for the 10hp gain at peak torque, dropping as much as 50 lb-ft off the bottom end. Outright top-end power, however, was clearly limited by the problems we were encountering at the higher rpm.

With the limitation on rpm, despite a wide range of different springs, it began to look as though the springs' ability to control the cam's action at the valves was not really the limiting factor here. The evidence began to point to the hydraulic lifter itself. To explore this possibility, we decided to run a diagnostic check, substituting a solid lifter for the hydraulic. Can a solid lifter run on a hydraulic stick? For testing such as this, the answer is yes. Hydraulic cams lack the clearance ramps required to ease a solid lifter from lashed clearance on the base circle to the flank where the lifter begins to really accelerate. The trick is to lash the solid at .003-.004-inch lash, hot, which will effectively allow it to follow the lobe similarly to a hydraulic. The difference is, it will not have the hydraulic mechanism we suspected to be the cause of instability in our setup. The lifters were swapped and lashed, and the results were telling. The engine pulled cleanly to the 6,000-rpm limit of our test and produced 607 hp at 6,000 rpm. Peak torque was now at 549 lb-ft at 5,200 rpm. The solid lifter allowed the cam to translate its design specifications to the valve more accurately, while it appears with the hydraulic, something was being lost in the translation.

While the engine handily met our 600hp by 6,000-rpm goal, the check with the solid lifter certainly isn't a long-term solution. Actually, it just pointed to the direction where we needed to do more work. The simple conclusion here is the combination of very intense valve action, high spring loads, and a relatively heavy valve and valvetrain is just too much for the hydraulic mechanism to cope with. At higher rpm, the lifter likely just collapses the internal plunger, losing lift and duration, making the power curve nosedive. The easy solution is to substitute a solid roller in place of the hydraulic flat tappet, since the roller will allow high spring loads, while the solid body will eliminate all question of hydraulic instability. These intensities are exactly what a solid roller is designed for. Our engine did meet the goals of mild manners at idle, running smoothly at 850 rpm without a big-cam lope, while generating over 14 inches of idle vacuum at 14 degrees of initial advance.

We are uncertain exactly where this project will lead until we get more testing done on the dyno. We'd like to see peak torque edge up to the stratospheric levels and improve the high-rpm dynamics without sacrificing the great idle we have now. It'll make for some interesting testing to come.