Chevy Big Blocks. David Vizard
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seen for engines up to approximately 7,500 rpm and 900 hp.
Fig. 2.31. This Scat non–center-counterweighted 4.5-inch-stroke crank weighed 63 pounds after balancing. This compares to about 75 pounds for a stock 4-inch-stroke forged crank.
If I’m building a cost-is-no-object engine and call the shots on a billet crank that needs to be as light as possible, I would go with the center counterweights for an endurance race engine. However, for anything short of Pro Stock or Pro Mod, the inherently lighter weight of a non-center-counterweighted crank is a good, although minor, option to consider.
The crank for one of my 598 builds (see Fig. 2.31) is a relatively high-dollar custom item, and I elected to go without center counterweights. If your application involves endurance and/or RPM at a relatively high level for extended periods, such as marine use, a center-counterweighted crank is your best option.
Fig. 2.32. This 1/4 stroker K1 crank is in the moderate price range and features center counterweights. It went into a GM-blocked street 540, 10.5:1 CR, build that netted 730 ft-lbs and 690 hp. All with a 550-rpm idle and plenty of vacuum.
Fig. 2.33. This Callies XL Magnum crank has a 4.750-inch stroke and is destined for a 632-ci build. It has three important features: hollow mains, center counterweights, and the shape of the counterweights, which are an effort to build a crank that is as light as possible while minimizing bearing loads.
The One-Piece Two-Piece Rear Seal
It would be really easy to skim right over the seemingly minor worth of the development of crank seal technology but it’s straight out of the world of Formula 1. It’s for that reason I show the rear seal type I am now using in all my builds.
The main asset of this seal is that it has extremely low friction on the crank and will run tens of thousands of race miles before leaving a visible line on the crank-seal diameter. It’s manufactured by GTS Racing Seals in Eastleigh, Hampshire, England, and available from TWPE. In addition, it seals in and out, so it makes for a better pan evacuation function. The low friction is immediately apparent as the crank spins with virtually the same ease as it did prior to installing the seal.
I have been testing these seals for about four years, and since then, nearly all of the cup car teams have switched over to them. To install it, put a single slit in a designated position, thread it into the oil seal grove in the block, and then position the cap.
Jacque builds her own race engines, and she is about to install this one-piece GTS seal on a 496 build employing a two-piece-seal crank.
This one-piece GTS seal is threaded into the block half of the rear main. The joint is positioned just below the split line. Although GTS seals call for the split to be vertical in the top half of the rear main, it seems to matter little where it is for an oil-tight seal, as long as it is not at the split line.
The inertial and gas pressure loads imparted to the crank at each rod station cause the crank to twist torsionally from end to end. When these forces are imparted at some multiple of the crank’s natural torsional frequency, they build up out of all proportion to the amount caused by the original excitation force.
A 4.75 stroke crank that was grossly under-dampened illustrates this condition. At about 4,000 rpm the crank starts to resonate and the rod journals vibrate back and forth during their rotation by almost 2 degrees. As a result, the position of the center of the rod journal on this seemingly very stiff crank is moving back and forth by an almost unbelievable 0.080 inch. This cyclic motion superimposed on the typical rotation of the crank plays havoc with the cam dynamics because the cam is coupled directly to the crank via the timing chain and gears.
Fig. 2.34. The Professional Products 7.6- or 8-inch dampener is my preference for a top-performing entry-level crank dampener. I have used them for many years and have seen good dyno results and zero problems.
Fig. 2.35. Torsional tests with dampeners from Innovators West have shown that this company knows how to build effective dampeners. The lesson is, buy direct from the company, not from a third party.
Fig. 2.36. The ATI Super Damper has a variety of elastomer rings and inertial mass rings so it can be tuned to your application. ATI offers a dampener torsional test service for which they go to the dyno being used and measure the existing torsionals. From this data, they optimize the dampener build to suit.
Fig. 2.37. This exploded view shows the internal components of an ATI dampener. These dampeners are tuned to the rotating assembly torsionals by sizing the mass and the stiffness of the rubber O-rings of the second element from the left.
In an extreme case, 50 to 75 hp is lost on a 750-hp engine, and a typical loss is 20 hp. Furthermore, the crank breaks at a fraction of its normal life. All this tells you that an effective crank dampener not only greatly extends crank life but also allows the generation of additional power.
Crankshaft Dampener installation
In all probability at least half of all conventional elastomer dampener failures are due to incorrect fitting or removal. For the dampener to be fully functional, it must be a very tight fit on the crankshaft. This tight fit plus the insurance of a top-quality crank-securing bolt are virtually mandatory for a performance power plant.
Do not hammer the dampener on or use the dampener-securing bolt to pull the dampener into place. Using a big gear puller around the dampener OD almost certainly damages or destroys the elastomer ring between the outer inertia ring and the dampener hub. Rent the right tool from one of the big auto parts chains, such as O’Reilly’s, Pep Boys, Advanced Auto Parts, etc., or purchase a really good tool, such as the one from Moroso shown here.