When the discussion turns to making big power affordably, the Chevrolet big-block "Rat" engine has few peers. Although it was one of the longest running production passenger car powerplants, it was designed from the get-go with on-track ability in mind. Chevrolet seriously stepped up the engine program in comparison to the previous generation of W-series big-blocks with an eye toward racing. The key step here was the Rat's "Porcupine" cylinder head layout, featuring the architecture to accommodate massive ports, steep valve cant angles, and a simple but very capable stud-mounted rocker arrangement. Where man-sized helpings of horsepower are on order, the big-block Chevy is ready to serve it up.
Today, the big-block Chevy is still the foundation for massive power in a readily available package. The aftermarket has expanded on Chevrolet's original concept, with race-ready parts to build these engines in virtually any configuration imaginable. Eric Weingartner of Weingartner Racing looked no further than the big-block Chevy platform when considering an engine combination for the 2013 AMSOIL Engine Masters Challenge (EMC).
Big Bottom End
Weingartner had run big-block Chevy combinations at the EMC in prior years, and tells us, "I wanted to do something with what I already had, and I already had a big-block. I ran a big-block 496 big in a previous competition, and I wanted to take another stab at it. I knew it wouldn't be competitive in the event due to the size of it, but the goal was to make as much power as possible on pump gas. I had the Dart Big M block sitting over here complete with a rotating assembly that I bought two years ago, but I never did anything with it."
Although a production-based big-block Chevy can be modified to achieve substantial cubic-inch capacity, the big-bore aftermarket ups the ante significantly. The Dart Big M block can easily accommodate a 4.500-inch bore, and has the crankcase capacity to greatly exceed the production stroke. Most importantly, the block is built with the beefed-up structure to keep all those cubes in one piece. Weingartner's final configuration of a 4.500-inch bore and 4.250-inch stroke brought the cubic capacity to a healthy 540 ci, which is far from the maximum capability of the block. Weingartner's new engine would essentially be a bigger bore version of the popular production-based 496 combo. Weingartner explains: "With the nice long stroke, the bigger bore will unshroud the valves better than the smaller bore 496 combo."
Starting with a high-performance aftermarket block, few modifications were necessary for the block. As Weingartner relates, "There really was nothing fancy done on the block itself. It retains the bolts and parts as it comes from Dart. These blocks are said to handle 1,200 hp, and I knew this application would not be anywhere close to that, so the strength was already there. The block already had sufficient clearance for the 4.250-inch stroke crank, so that part was virtually a drop in. I went with the standard-weight Scat 4.250-inch stroke crank instead of the lightweight version, since the lighter crank can't take as much power, so it left more in the bank for reliability. Andy Key, a former Engine Masters competitor, helped me with the machine work. About the only custom work to the block was that the lifter bores were bushed and enlarged to 0.904 inch."
Weingartner's parts stash included a set of off-the-shelf 39cc dome MAHLE pistons which he modified for use in this engine: "I had the high-compression MAHLE pistons, and thankfully they had a solid dome, so I had the domes milled to get the compression ratio down to 11.5:1, and added the lateral gas ports. The rings are the gapless type from Total Seal. Part of that choice is due to anticipating nitrous on this engine after the Engine Masters Challenge. At the event you want the gap kind of narrow, but with the gapless top rings we could set the gaps wider and they will be fine. If the big-block has one drawback, it is the really big combustion chamber. You have to run a dome in it, which makes the flame travel process difficult without hampering the torque production per cubic inch."
Linking the modified pistons to the rods is a set of Scat 6.325-inch H-beam connecting rods. Weingartner tells us, "The H-beam rods are very strong, but I did upgrade the bolts to the ARP 2000 capscrews. For this application it was probably not necessary, but the upgrade gives more rpm capacity in case I ever wanted to spin it to a higher rpm in the future—plus it is added security."
The revised lubrication circuit of the Dart block alleviated the need for major oiling system modifications, though the oil pump selection did require attention. Weingartner detailed his experience, "We started with a standard-volume replacement pump, but at the top end of the pulls we saw the oil pressure start dropping off. We went back to the dyno with a Titan oil pump, and the Titan pump sure fixed it. It was just the standard volume Titan, and the oil pressure is set kind of low, but the oil pressure barely fluctuated. That Titan pump is nice." Completing the lubrication system is a Hamburger oil pan, featuring a built-in windage screen and baffles. As Weingartner tells, "It is a nice piece that bolted right on, and it does the job."
Working Top End
Of course all of the cubic inches you can pack into an engine combination will not do any good if the top end components are not up to the task of feeding them. Weingartner's specialty is cylinder head development, so this aspect of the build received the bulk of the attention. As Weingartner tells us, "The heads are the RHS 320s. I started out with a CNC program from a previous combination that had the intake ports at about 335 cc, and from there I ground them bigger and then added a ton of epoxy to the floor. The heads ended up at about 348cc total intake volume, and flowed 442 cfm. The valve combination is a 2.300-inch intake and a 1.88-inch exhaust valve. I would have liked to have gone with a bigger intake valve, but the seats weren't big enough to run the 2.350-inch size I wanted. I did not want to cut the seat inserts out to do it. When all the modifications were completed, all the runners flowed very close to the same. The short ones were down about 10-15 cfm at the very peak, but up until the top they were right there; it was pretty tight. The exhaust with a pipe was at 345 cfm."
Pistons are by MAHLE, which are readily available stocking units. The pistons were modifie
Holding the oil is a Hamburger deep-sump drag-racing–style pan. The deep pan keeps the oil
The MAHLE pistons are made for a metric 1.5/1.5/3mm ring pack, which is handled by a gaple
The Dart block was finished at a bore size of 4.500 inches, far exceeding the capacity of
RHS 320cc aluminum cylinder heads top the engine. These were extensively ported and filled
After significant experimentation, Weingartner found that a valvetrain combination of ARP