By David Reher-Morrison Racing Engines
The road to high technology is often a two-way street. People who are involved in motorsports maintain that racing improves the breed, from the invention of the rearview mirror by Ray Harroun, the first Indianapolis 500 winner, to the disc brakes and low-profile tires that are commonplace on cars today. But the improvements that are made on everyday automobiles and trucks can pay dividends for racers, too. The extended lifter bosses in the sixth-generation (Gen VI) big-block Chevrolet V8 are an example of production engine technology that has benefited hardcore drag racers.
GM engineers lengthened the lifter bosses in late-model small-block and big-block V8 engines to accommodate hydraulic roller lifters. The switch from flat tappets to roller lifters was primarily intended to reduce friction and to improve fuel economy on the highway. It had the additional benefit of allowing faster, more aggressive camshaft profiles that boosted horsepower in high-performance street engines like the LT1 and LT4 small-blocks.
When the first Gen VI big-block with tall lifter bosses arrived in our shop, we were dismayed. There weren’t any commercially available solid roller lifters that would fit the extended bores. Our first impulse was to machine the tops of the bosses to accept the shorter lifters we’d used for years, but then we realized that would be a big step backward. We recognized that the longer bosses would stabilize the lifters in their bores – a real advantage in big-block Chevy engines with angled pushrods.
Crower stepped up with a redesigned roller tappet with a longer body and a raised tie bar that cleared the taller lifter bosses. Now “long body” lifters are available from many performance camshaft companies.
When we overhauled the first race engines built with Gen VI blocks, we discovered that lifter bore wear was dramatically reduced. With the old short lifter bosses, the tops of the bores were often bellmouthed after a season of racing. That’s because the big-block Chevy’s sharply angled pushrods subject the lifters to strong side loads. This sideways thrust is especially apparent in engines with Dart Big Chief and Brodix Big Duke spread-port cylinder heads because they have more severe pushrod angles than conventional siamesed port heads.
When Richard Maskin was developing the aftermarket Dart Big M big-block, I recommended that he use extended lifter bosses because of our positive results with this design. In fact, we now use Big M blocks with tall lifter bosses for almost all of our Super Series engines. I was surprised to learn recently that Dart also offers Big M blocks with the lifter bosses machined down to standard height. When I quizzed Maskin about this, he told me that many racers still want to use their old short-body lifters.
In my opinion, short lifters are the wrong approach. If a racer is going to spend the money on a brand-new block, he should take advantage of the latest technology that’s available. Yes, a set of long-body lifters costs more than a set of standard lifters, but the benefits they offer in longer service life and improved reliability are well worth the relatively minor additional expense. It’s false economy to save a few dollars on lifters when you consider the thousands it can cost to repair an engine after a catastrophic lifter failure.
There are also instances in engine design when the racers have the right idea. One of the major shortcomings of the production big-block Chevrolet V8 is its four “missing” head bolts on the intake side of cylinders No. 2, 3, 6 and 7. While the other four cylinders have six head bolts arranged symmetrically around each bore, there is a 4.550-inch span between the upper head bolt holes on these four cylinders which have only five fasteners. Since the four missing bolt holes would be located underneath the intake ports in a stock big-block head, I can only assume that these bolts were eliminated because of the difficulty of installing them on an assembly line and servicing the cylinder heads in the field.
When the first aluminum versions of the Chevy big-block V8 were released for Can-Am road racing in the late ’60s, they featured four bolt bosses in the lifter valley. These bosses engaged studs or bolts that threaded into holes underneath the intake ports to provide the clamping force that is required to seal the head gaskets in a competition engine. Today most big-block cylinder heads have provisions for these studs, even if the bosses aren’t drilled and tapped.
Unfortunately, these lifter valley head bolt bosses were never incorporated in production cast-iron blocks. When we built our first big-block racing engines with Mark IV blocks, we dimpled the deck surfaces with a centerpunch in an attempt to hold the gasket in place. Later we fabricated steel head lugs and mounted them in the lifter valley with bolts and dowel pins. The first option really wasn’t very effective, and the second was expensive and time-consuming.
We see evidence of seepage past the head gaskets in almost every competition big-block Chevy V8 that does not have these four additional head fasteners. When the power level reaches 850 to 900 horsepower, the head gaskets are almost certain to fail in the long span between the upper head bolts.
In the past, the most practical solution was to machine the block for O-rings and use soft copper head gaskets. This is an expensive proposition, however, when your goal is to build affordable engines for sportsman racers. Fortunately, GM’s CNC-machined Gen VI competition cylinder case, some Merlin blocks and all Dart Big M blocks now incorporate head bolt lugs in their lifter valleys – a real improvement over production castings. Among these alternatives, the Big M block is the most affordable choice for sportsman racers.
It doesn’t take much clamping force to solve the big-block’s head gasket problems. We use a 3/8-inch stud torqued to 45 ft./lbs. on our Super Series engines. This has proven to be so effective that we have eliminated O-rings on all but our most powerful big-block bracket engines.
There is a common misconception that more torque on the head fasteners improves head gasket sealing. We use imprint paper to measure the load on the head gaskets, and we have learned that less is better in many instances. The length of the fasteners (bolts or studs) and the distance between them affects the clamping force they produce on the gasket. On our Pro Stock DRCE engines, for example, we torque the outer row of studs to 55 ft./lbs., the valley bolts to 42 ft./lbs. and the long center studs to 70 ft./lbs. We have found that these different torque specifications produce the most uniform loads on the head gasket and keep the head as flat as possible on the block’s deck surface.
Racing is about finding solutions to problems, whether it’s seeing the guy behind you with a rearview mirror or keeping the lifters and head gaskets alive in a big-block V8. In most instances, it’s not rocket science, but simply common sense.