Dart Short-Block Motor - Power in a Package

At the filter mount, a Moroso Oil Bypass Eliminator was used. This takes the place of the standard bypass style adapter, ensuring that the oil goes through the filter at all times. A standard bypass filter adapter can allow debris to pass around the filter, and cause damage.

To ensure the engine will look good for a long time to come (and stand out on our cover), we used Dupli-Color's high-quality engine enamel in traditional Chevy orange. We have found this paint to offer outstanding long-term durability, and it's good up to 500 degrees F.

Though the SHP block will accept all of the OEM hydraulic roller components, we went with COMP's new short-travel retrofit-style lifters to minimize the potential for hydraulic instability at high rpm. These units cut down plunger travel from .200 inch, to just .012 inch. The benefit is easy valve lash adjustment (just set it and forget it like a normal hydraulic lifter), with the high-rpm reliability and extended lift of a solid roller lifter. The sweet solid roller valvetrain tone is just icing on the cake.

We originally ordered the heads with springs spec'd for a solid roller, and revised the springs to accommodate our final choice of a hydraulic. (The short answer for this is that we plan on trying a solid roller later on, and special ordered the heads with these stiffer springs.) The COMP 930 springs deliver 145-pound spring load on the seat, and 325 pounds over the nose of our Thumpr cam.

We ordered our Dart Pro-1 Platinum cylinder heads with a 64cc combustion chamber, which provides a final compression ratio of 10.66:1 with a Fel-Pro .039-inch- thick head gasket. Dart says their Platinum line has demonstrated a 25 hp improvement over their previous Pro-1 head, which takes the place of a lot of manual porting work. Our dyno test showed their worth in box-stock form.

When you order a Dart top end kit with your SHP short-block as we did, you'll have a choice of head and intake combinations. As you can see from our price breakdown, there are cost savings that result from this. Our combo consisted of the Pro-1 Platinum heads and dual-plane intake; the valve covers, head gaskets, valve cover gaskets, head bolts, intake bolts, spark plugs, and 3/8-inch rocker studs are also included at the $1,848.78 price. You'll note that we did step up to stronger 7/16-inch rocker studs, and substituted Totally Stainless fasteners where they would be visible.

There are a number of checks that should be preformed before the heads are ready for final installation. The valvetrain will need to be set up to determine the optimal pushrod length for the best geometry and sweep on the valve tip. A pushrod length checking tool is used to arrive at the optimal sweep pattern-in our case a 7.250-inch-long pushrod produced the tightest sweep pattern on the rocker tip.

Valve-to-piston clearance is another vital check, performed here by mocking up the head (at the same time you do this to check the pushrod length) using the clay impression technique. The head is bolted on and the valvetrain is set up, followed by rolling the engine through the valve events, then the head is removed and the clearance is verified in the impressions made to the clay.

With all of the preliminaries out of the way, Dart's Pro-1 cylinder heads with 200cc intake runners and 64cc chambers were bolted to the decks using the ARP bolts and Fel-Pro gaskets provided in the Dart top end kit.

COMP's Ultra Gold aluminum rocker arms in the stock 1.5:1 ratio cleared the big 930 springs. We upgraded to ARP 7/16-inch rocker studs, and the rockers were adjusted to 1/4-turn past zero lash preload-just as with any other hydraulic lifter setup.

After considerable deliberation, a Dart two-plane intake manifold was selected over a single-plane design. In a street application, the overall power curve of this style intake seems to prove superior in virtually every test we've seen. When we saw nearly 500 lb-ft of torque right at the hit, we knew it was the right choice.

We had two new Holley carbs at our disposal, an 850 Street HP, and the new 750 Ultra Double Pumper. We bolted on the bigger carb to start with as our baseline. Also, take note of our Moroso HEI distributor and Blue Max wires-both of them contributing to the simplicity, cost effectiveness, power, and cosmetic needs of our build.

On the dyno, we ran the engine to seat the rings, then went into the power-tuning procedure. We bumped the jetting in several steps until we found the perfect mixture, then zeroed in on the best timing at 36 degrees total.

With a set of 13/4-inch Hedman dyno headers installed, our 400 rewarded us with 523 lb-ft of torque and 523 hp, and about the fattest power curve we have ever seen. The engine produced massive torque right at the bottom, and pulled more than the power we hoped for up top.

With an 850-cfm carb as the baseline, we wondered how much power might be lost going to a smaller 750 cfm. We had the new Holley 750 Ultra Double Pumper on deck, and it made power very nearly in lockstep with the bigger carb. These new Holley carbs are manufactured in aluminum, representing a weight savings of approximately seven pounds compared to their traditional cast zinc counterparts. The 750 Ultra runs about $522.69 through Summit, or about $4 less than the 850. Besides the all-aluminum construction, the Ultra also has sight glasses in the fuel bowls and an electronic choke for improved driveability. You also get your choice of black, red, or blue anodized baseplate and metering blocks.