Dart Short-Block Motor - Power in a Package

While a crate is certainly the most time effective way to a high-performance engine, this approach typically comes with some compromises. Often, the engine combinations are "one size fits all," or based upon a limited number of combination choices. With the SHP short-block, what you get is a brand-new Dart SHP iron block filled with a brand-new balanced rotating assembly. When you really look at a short-block assembly as an alternative to a full build or a crate, there are some real advantages. With the bottom end built, the most time-consuming aspect of the engine project is already done and ready to go, but the options on heads, cam, valvetrain, and other go-fast ingredients are still wide open to build the combination any way you want. Really, the combinations are virtually limitless, resulting in an engine equipped with the components that are right on target for your combination.

These Siamese-bore castings have the extra meat where it counts, with thick cylinder wall spec'd out at a minimum of .230 inch at a bore size of 4.165 inches, heavier main webs and deck, and all poured from a superior grade of iron alloy. All of the boltholes are blind, eliminating the need to slop sealer on the cylinder head fasteners, and the bottom end is secured with splayed-cap four-bolt mains. Add in the priority-main oiling system, revised cooling jackets, and you've got a foundation that puts the engine in another league compared to a junkyard block.

Build It
We were looking to put together a nice 400-cube small-block Chevy, to build a hot-street pump-gas combination with a minimum of 500 hp and reliability that we could count on for the long haul. After exploring the options, the Dart SHP short just made sense as the starting point. Considering the scarcity of production big-bore 400 blocks, and weighing that against the improvements with the Dart unit, it really didn't take much to tip the scales to favor the SHP block as the basis of the build. Ultimately, we went all the way with the assembled short, considering it to present a good value for machining and assembly given the quality components used. Working the numbers, we would have a hard time equaling the short-block assembly for the money, not even accounting for the additional time required when starting from a bare block. To make the bottom end as stout as possible, we ticked all of the option boxes when making the order, upgrading to the forged crank and pistons with H-beam rods (bringing the short-block total to $4,184.66). And while we didn't see these upgrades as an absolute necessity for the power level achieved in this story, we do have our eyes set on upgrading to a more potent top end and valvetrain at a later date.

As with the camshaft, by starting with the short-block, that left the cylinder head options wide open. Here, we looked no further than the Dart catalog, going with the Dart Pro-1 200cc aluminum heads with 64cc chambers. These as-cast Pro-1 heads offer a good balance of cost, flow, and runner size, putting them right on target for our displacement and rpm range. To accommodate the heads, the springs were upgraded to COMP number 930-16 pieces (a 1.550-inch diameter dual-spring assembly). The large-diameter springs can create clearance issues with some rockers, but we found they worked fine with a set of COMP Ultra Gold aluminum rockers in a 1.5:1 ratio. To provide the link between the rockers and the lifters, we went with a set of Manley hardened 5/16-inch pushrods in a length of 7.250 inches.

With the major components of the build selected, the parts were taken to Andy Mitchell's Outlaw Racing Engines for final assembly. Having a complete short-block as a starting point, the assembly process was completed very quickly, with no undue surprises. Mitchell degreed the cam in to an installed centerline of 102 degrees, using a COMP timing set, and locked it down with an OEM GM thrust plate. A COMP two-piece aluminum timing cover (to aid future cam swaps) was use to seal the front of the engine, with a TCI Rattler damper hung on the nose of the crank. The heads went on with a set of ARP bolts, giving a compression ratio calculated at 10.66 by Mitchell based on 64cc combustion chambers, .039-inch thick Fel-Pro gaskets, and .028-inch piston deck. Providing for the lubrication, Mitchell used all Moroso components, including an Eliminator seven-quart pan and standard-volume pump. Turning back upstairs, a Moroso DuraFire HEI distributor and Blue Max wires put the final touches to our completed engine.

On The Dyno
Anytime a new combination is put together it comes down to the power numbers to gauge the success of the effort. We have to admit that this engine assembly all came together with out-of-the-box parts, with none of the custom "massaging" that some of our engines get. Really, to all of us involved, it just seemed too easy this way, and it made us wonder if it could really "turn a number." This apprehension was at its peak the day the engine was bolted to the Westech engine dyno. Editor Johnny Hunkins was responsible for most of the parts selection, and it did look good on paper. With the cubes, heads, cam, and compression, the ingredients were there for power. We were looking for an honest 500 hp on pump gas, and I reassured Hunkins that "anything we see over 500 hp is pure gravy."

Westech's Steve Brule, our dyno operator, had first-hand experience with these Dart SHP engine combinations in the past, having personally put together and tested a 372-cube version. As he put it, "These Dart short-blocks are nice. It's the highest-quality crate short-block I've ever seen." Needless to say, Brule confidently predicted that the engine would make our target with ease.

We still had the 750 Ultra Double Pumper to test, a new lightweight aluminum-bodied carb from Holley that features an electronic choke for street driving. The 400-cube Chevrolet certainly did seem to like our big 850-cfm baseline carb, and we had to expect a power penalty going with the smaller 750. As we went into the pulls, the mixture numbers were virtually dead-on, and the 750 Ultra's power was within a kitty cat's hair of the bigger Holley. Even with a 750-cfm carb, the combination delivered.