Shop troll, Lewy D, blows...
Shop troll, Lewy D, blows the intake off during one of the swaps. Despite having over .550-inch lift on the exhaust, 110 pounds of spring force on the seat and 330 pounds open, the budget long-slot 1.6-ratio stamped rockers held up without any signs of wear. Thanks to the easy lobes on the COMP cam, a few trips to the 7,000-rpm mark never showed any signs of valve float.
After crunching numbers and half a bag of chips, our fearless crew dove into the dyno room on the quest for knowledge. Several successively higher rpm pulls were made, finally topping out at 6,700 rpm. It’s impressive that the little engine showed no signs of valve float at all. A group of three runs was made and the numbers were averaged in order to reduce any chance of skewing the results by an outlier in the bunch. The happy little mill churned out a respectable 367 lb-ft and 354 horsies. This was with a “factory” valve job consisting of a 30-degree top cut, 45-degree seat, 60-degree bottom cut, and the bone-stock valves.
Three hours is the amount of time needed to finish a dyno pull, pull the top end off a small-block, cut a valve job, flow test a head, reassemble the engine, and make another dyno pull. Ask me how I know. In this second round, the heads were treated to a 35-degree valve job, with the cylinder head having a 15-degree top cut, 35-degree seat, and 45-degree bottom cut. The valves were treated to a 35-degree seat, and 19.5-degree back cut. As expected, the low-lift flow numbers rose, while the upper lift flow numbers suffered slightly. The combination ended up giving up a little midrange torque, but picking up a little up top while widening the rpm range. The results: 363 lb-ft and an equal 363 hp proved the shallow angles could work.
Drawing an imaginary wall...
Drawing an imaginary wall coming down from the edge of the valve straight down to the cylinder head is considered the curtain area. This wall area changes as the valve opens and closes, and determines the absolute maximum amount of air that can pass through.
Another three hours was burned as the heads came off for another round. This time a 45-degree top cut, 50-degree seat, and 70-degree bottom cut were performed, and a fresh set of valves was ground with a 50-degree seat and a 37.5-degree back cut. True to expectations, the steep angle hurt low-lift flow while picking up on the high end. What was not expected was the increase in torque and horsepower. At 387 lb-ft and 369 hp, the 50-degree seat typically reserved for high-lift cams put the others to shame. Conventional wisdom may say that the 45-degree valve job is best for a street engine, but our tests showed without a doubt that the more “obstructive” 50-degree valve job is worth an extra 15 peak horsepower, and at 500 rpm lower. Perfect for a street engine.
Aside from the horsepower changes, perhaps the more important trend to spot was that it appeared the steeper the valve job, the more it made it look like the engine had a shorter-duration, higher-lift cam. This was exactly the behavior the Ferberts predicted. “The steep angle chokes the flow down low, acting like a smaller cam, but when the piston really starts to move, the higher flow makes more torque,” Randy Ferbert says. It was this trend that led the brothers to use that 50-degree valve job in their EMC entry along with a long-duration camshaft. Durability of a 50-degree valve job in a daily driver may come into question, but cammed properly it appears the uncommon valve job proved uncommonly good, and for a weekend warrior, it may just be the next big thing.
“Having steeper seats is going to close up the curtain area, especially down at low lift.” —Rick Ferbert
During the end of the exhaust cycle as the exhaust valve is closing (left) and the intake valve is opening, there is still positive pressure in the combustion chamber and so a small amount of reversion creeps around the intake valve, contaminating the incoming air/fuel charge with exhaust gasses. Signs of that reversion are seen when removing the intake valves from an engine and seeing black, sooty bowl areas and intake runners. During testing, low-lift reverse flow of the three valve jobs at .050 and .100 lift was measured, and it was found that the 50-degree cut reduced that flow significantly. That reduction most likely resulted in less contamination in the incoming air, and helped with the increase in power seen.