Cam And Crank Placement There's a design movement to position the camshaft and the crankshaft higher in the block. This begins our look at valvetrain geometry.

"You move the camshaft up to shorten the pushrods," Jenckes explains. "Obviously, with very high spring pressures, a shorter pushrod is a stiffer pushrod, is a lighter pushrod in general. In the valvetrain, you want things stiff and light. There's some kind of optimal stiffness-to-mass ratio that you're going to go after. Having a shorter pushrod that is directionally correct may actually be negatively correct for the valvetrain geometry. You have a shorter distance to go, so you make more angularity in the pushrod. Ultimately, time has proven that the shorter pushrod path is a better path to go down. In very few cases would you find arguments where you want larger pushrods.

"The second thing you'll find is that the camshaft diameter itself goes up. It increases the radius of the cam on the base circle, and the raised curvature goes up, so it is directionally correct for valvetrain dynamics. When you have a larger base circle, you have a lot more room to work, literally, with the cam profile. For the transitions, a larger radius can be smoother than a very sharp one. Having a larger base circle means you can have better valvetrain performance."

Main Strength A final topic of consideration is the number of bolts for the main caps in the block. It's the classic two-bolt versus four-bolt argument.

"A lot of power can be made out of a two-bolt main," Jenckes offers. "If you work in the world of drag racing--stock eliminator stuff--you see this. Drag racing forces people to use production blocks. With the two-bolt main stuff, they make ungodly horsepower. The question is, how long do you make it? In a Nextel Cup engine, in round numbers, you're making 800 hp now and there's a lot of cylinder pressure. Because of that, you have to retain it, and you have to retain it over time. And that's where you get into the two-bolt versus four-bolt.

"A four-bolt is a stronger combination if done properly. Almost all Nextel Cup engines use splayed main caps, which are much more satisfactory than the vertical four-bolt. Again, you're tying in more material. It's all about stability. It's more about peak performance in the long run than it is about the capability of a two-bolt block that can make power for a short period of time. Like I said, the stock eliminator blocks are a perfect example of two bolts that make power--some make as much as a Nextel Cup engine. They just don't make it last as long."