It’s over 200 cubic inches too big for Pro Stock, 55 inches over the limit for Fastest Street Car competition and the equivalent of two 350 small-blocks. If you’re into new cars, it’s an 11.5L. That’s 705 cubic inches of big-block Chevy made possible by World Products’ Merlin Superblock cast-iron block. Mountain motors of this stature have been possible for years but only with exotic and incredibly expensive aluminum race blocks. The Merlin is the first iron block available that allows 700-plus cubes in a (sorta) practical package.
The Merlin block’s main claim to fame is its skyscraper 11.625-inch deck height. With enough stroke, it’s possible to squeeze out over 750 cubic inches in a package roughly similar to a big-block Chevy. And with some fancy (and very expensive) machine work, the bore centers can be changed to yield upward of 800 inches. The Merlin Superblock is based on a big-block Chevy, and all the accessories from a Rat motor (water pump, mechanical fuel pump, motor mounts, clutch pivot ball and bellhousing) will bolt up to the Merlin. But the Merlin block carries a lot more cast-iron meat than even a Bow-Tie block, and even though the Merlin is based on a big-block Chevy, it can be machined to accept Pontiac, Ford or Chrysler heads, making off-the-wall hybrids fairly easy.
We wanted to see just what was involved in building one of these mountain motors and were curious about the kind of streetable, pump-gas power that could be had with a 700-inch engine. Jack Chisenhall, the owner of Vintage Air, is building a Bonneville-bound ’53 Studebaker street car (Roddin At Random, February ’94) and will be relying on a Merlin motor to push his Stude to 200 mph. We followed along while designated engine builder Donnie Anderson at Performance Engineering in San Antonio, Texas, went through the laborious process of getting everything to fit.
Initially, the idea was to shoot the moon and go for as many cubes as possible, but after some consideration, it was decided to be a bit more conservative with displacement. When the stroke starts getting ridiculous, stability becomes a problem. Since this was meant to be a driveable, long-term engine, durability was mandatory. Also, a 5.300-stroke crank was readily available from Bryant Racing. A longer-stroke crank would have taken two to three months to build, and the project was moving along too fast to wait.
The parts in the short-block assembly could almost be measured in feet instead of thousandths of an inch. The Bryant Racing crank is a 4330 billet piece with a 5.300-inch stroke, cross-drilled oiling and knife-edged counterweights. The steel rods are from Cunningham, and they measure a whopping 7.600 inches. The forged JE pistons fit the 4.600-inch bore and wear 1/16-inch Childs & Albert rings. The block was in pretty good shape right out of the box, but Anderson did have to do some machining and clearance grinding for the rods.
Production-based heads have no hope of adequately feeding an engine of this size, so the 705 was topped with Dart’s Big Chief aluminum cylinder heads. The monster 395cc intake ports and 2.400-inch intake valves flow enough atmosphere to keep an airliner at 20,000 feet. The combustion chambers are a mere 88 cc, which means lots of compression. But Chisenhall doesn’t want his Stude to be a single-purpose race car—he plans on cruising it through the streets of San Antonio on a semiregular basis—so a pump-gas-friendly compression ratio was required. With the aluminum Dart heads, Anderson figured that the motor could handle about 11.0:1 with 92-octane pump gas, providing the camshaft was big enough to bleed off some cylinder pressure. To get the desired compression with 88cc chambers required deep dishes in the pistons. The JE slugs used here have a 42cc dish, which brings the compression to 10.97:1.
The valvetrain consists of a Competition Cams solid roller bumpstick (part No. 11-703-9) with titanium retainers, triple valvesprings, long Smiths Brothers pushrods and T&D aluminum shaft-mounted rockers. Specs on the cam are 278/282 degrees of duration at .050, .714/.680 lift and 110-degree lobe-separation angle.
The biggest hassle with an engine of this magnitude is that you can’t just walk down to the local speed shop for the parts. Very few of the components in this engine are off-the-shelf items. Most are hard-core race parts, some need to be fabricated by an engine builder who really knows what he’s doing, and machine work is critical. Because of this, the engine doesn’t just bolt together, and it’s anything but low-buck. The retail cost on the parts alone is over $20,000, so when you add labor and machine work, you’re looking at a $25,000 to $30,000 price tag to duplicate this package. If you’re looking to build a (comparatively) low-dollar example using production iron heads, you’ll still have well over $15,000 invested in just parts.
Then comes the problem of actually installing the engine into a car. At the exhaust flanges on the heads, the Merlin block/Dart head combination is 4 inches wider than a stock big-block Chevy, and fabricating the 23/8-inch headers required to let this thing breathe is a true test of talent and patience. Run with the big dogs or cower under the porch.
And boy are those dogs big. After about 40 dyno pulls and some serious hair-pulling episodes concerning fuel delivery, the 705 ingested enough 92-octane to shake the dyno cell to the tune of 961 horsepower and 950 lbs-ft of torque. That’s real close to 1000 horsepower, with a single four-barrel and no nitrous! Plus, there’s power left in the combination that we didn’t have time to get. Still, 961 horsepower should be enough to propel Chisenhall and the ’53 to two bills on the salt!
