ANDRA Fastlane 20 - Page 11

with. As a result, there’s a big move toward large diameter, ellipsoidal or tapered pushrods. Pushrod column strength is the key. You can pretty much rate the overall performance of different cams this way. The best is a solid roller cam, followed by solid flat tappet, hydraulic roller, then hydraulic flat tappet. How can a solid flat tappet cam outpower a hydraulic roller? It’s the weight of the lifter. A hydraulic roller lifter is a rather hefty component; add the weight of the oil and you can see why a solid flat tappet cam with a lighter lifter can outperform a hydraulic roller cam. Loft is something else to consider. Loft is where the engine actually sees more lift than the cam provides. It’s like controlled valve float. It occurs in many flat tappet NHRA Stock Eliminator engine combinations. Loft can increase both lift and duration. In practice, it is possible to really “hit” a flat tappet cam to achieve loft, particularly a solid cam. It’s also possible to achieve loft with a hydraulic if you use short travel (small preload) hydraulic race lifters. Bottom line, loft is good for power if it can be controlled. Lifter-to-bore tolerances and overall geometry are critical, particularly when you consider many of the engines using flat tappet lifters have been around for decades. It’s not uncommon to sleeve a set of lifter bores to fix wear, past block damage, and geometry issues. When lifter bore sleeves are installed, the machine shop sets the block up in a fixture, which in turn determines the angle of the reaming tool. Once the bores have been aligned and opened oversize, sleeves (most often bronze) are pressed into place. The sleeves are then trimmed and beveled before they’re finish honed to size. This “blueprints” the bores, providing proper lifter-to-bore clearance along with correct geometry. I should point out that if the geometry is spot on, and the bores and lifter-to-bore clearance are good, then all the bores need is a quick touch with a lifter-honing tool. The idea is to create a smooth, crosshatched finish. Each machine shop will have their own concepts of how smooth the crosshatch will be, so keep that in mind. Finally, oil is key when working with a flat tappet combination. As the motor vehicle manufacturers moved away from flat tappet cams to rollers, the major oil companies altered the additive packages in motor oil. One additive that went away was a compound called Zinc Dialkyl Dithio Phosphate, or ZDDP for short. Zinc-based additives have excellent anti-wear/anti-oxidant properties, which is critical to flat tappet cams due to the lifter-to- lobe contact. There was an issue with ZDDP: the phosphorous found in the additive doesn’t agree with catalytic converters. Coupled with the OEMs’ move to roller 11