705ci Chevy Big Block - Mountain Climbing
705 Cubic Inches And 961 Horsepower On Pump Gas!
- The Merlin Super- block dwarfs a Bow-Tie Chevy block, but the Merlin accepts most of the stock big-block’s accessories. The Merlin’s deck height is 11.625 inches (versus 9.800 for a production block), and at 297 pounds, it’s about 40 pounds heavier than the Bow-Tie and 80 pounds heavier than a stock production block.
- The stock oil pan won’t fit on the Superblock—it takes an Olds DRCE-patterned pan. The shorter Merlin blocks (9.800-inch and 10.200-inch deck heights) have two patterns, one for the stock pan and one for the DRCE. The Superblock also comes with 8.5-inch-wide billet steel, splayed-bolt main caps and ARP studs. The main journals are the stock 2.750-inch ones, but there’s room to open them up to 3 inches if necessary. The starter can be mounted on either side, but smaller, aftermarket gear-reduction starters are required for driver’s-side mounting. Ander- son used a Pro Start mini starter and a Moroso dry-sump pan. The oil-filter boss accepts a stock big-block adapter and filter but is moved farther out to clear the large kick-out oil pans.
- Anderson used a Bryant Racing 4330 billet crank, obtained from Scott Shafiroff Racing. Its 5.300-inch stroke, when combined with the 4.600-inch bore, yields 705 cubic inches. Notice the Mallory metal used to balance the crank. An engine this huge has very heavy reciprocating parts, and proper balancing requires real talent.
- This is one of the most dramatic illustrations of how radical the parts are on this engine. The stock 6.135-inch big-block rod on the left is miniscule compared to the 7.600-inch Cunningham steel rod used in this 705.
- Even with the Merlin’s cavernous bottom end, some grinding and clearancing still needed to be done to make the crank/rod combo fit. Anderson has invested about 15 to 20 hours just in preparing the block, including machining.
- After cutting for valve clearance, the JE pistons ended up with a 42cc dish. When squeezed into the 88cc chamber of the Big Chief heads, they yield a compression ratio of 10.97:1, which is about all pump gas can handle.
- The Manley valve sizes are 2.400-inch intake (second from right, compared to a stock 2.19-inch big-block valve) and 1.900-inch exhaust (second from left). Anderson also radiused the chamber side of the exhaust valve, which he claims is a flow technique worth about 3 to 4 cfm on the flow bench.
- Competition Cams supplied the roller cam, lifters, springs, retainers and keepers, and the pushrods came from Smiths Broth- ers. Cam specs are 278/282 duration at .050 lift, .714/ .680 lift and 110-degree lobe-separation angle.
- Three things are visible here. The altered pushrod angle dictated by the Big Chief heads makes it necessary to use longer pushrods (11.250/11.880 intake/exhaust versus 8.312/9.25 stock). The Merlin block comes with extra mounting bosses (visible between the pushrods) to accept a variety of different heads. And finally, Anderson blocked off the lifter-valley oil return. A scavenge line from the dry-sump oil pump goes through the intake and scavenges oil from this valley area. Anderson also mounted five magnets to catch any metal particles, just in case.
- The raised deck means that the heads are spaced farther apart, so Anderson had to fabricate spacers (arrows) for the intake manifold. The hard maple spacers are 17/8 inches thick and are used at the port flanges, while aluminum bar stock seals the end rails. The intake is a big single-plane from Dart. On the dyno, we discovered that wood spacers did an excellent job of isolating the manifold from heat. The intake was almost cold to the touch!
- The tall deck of the block also means that a standard-length distributor won’t fit, so Anderson convinced Mallory to make one for this application. Firing the distributor is a Mallory crank-trigger ignition, shown here. Also visible here is the Edelbrock aluminum water pump, the Fluidampr dampener and the Peterson dry-sump oil-pump drive. Not visible are the gaskets from Mr. Gasket.
- The carburetor used on the 705 is a Carburetor Shop-modified 1150 Holley Dominator. Once in the car, it will be fed by Holley’s Volumax pump and regulator. With an engine this big, a single carburetor can be a restriction, and that’s pretty much what we found. The power numbers would no doubt have been higher with more airflow, but twin Dom- inators on a sheetmetal tunnel-ram isn’t exactly streetable.
- On the Superflow 901 dyno at Kendrick Racing, Anderson, Mark Mathias and Tommy Kendrick tuned the 705 until it grunted out 961 horses and 950 lbs-ft of torque. Interestingly, the best power came with the ignition timing set at only 26 degrees total advance. The dyno headers have only 2-1/4-inch primaries, and this engine really needs 2-3/8- or even 2-1/2-inchers, so there may be another 30 or 40 horsepower right there. With bigger headers, an extra carburetor and more tuning time, we think 1000 horsepower is possible—on 92 octane!
- Not bad for a single four-barrel and pump gas. Horsepower was still climbing at 5800, but that’s as high as we wanted to spin this heavy motor. Notice the high Volumetric Efficiency (VE) numbers. At 5800 rpm, the measured airflow through the motor was 1266 cfm, which backs up our belief that the single 1150-cfm carb is creating an airflow restriction, even though The Carburetor Shop modifications allow it to flow at around 1250 cfm or higher.
The Merlin blocks main claim to fame is its skyscraper 11.625-inch deck height. With enough stroke, its 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 Darts 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 doesnt want his Stude to be a single-purpose race carhe plans on cruising it through the streets of San Antonio on a semiregular basisso 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 cant 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 hes doing, and machine work is critical. Because of this, the engine doesnt just bolt together, and its anything but low-buck. The retail cost on the parts alone is over $20,000, so when you add labor and machine work, youre looking at a $25,000 to $30,000 price tag to duplicate this package. If youre looking to build a (comparatively) low-dollar example using production iron heads, youll 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. Thats real close to 1000 horsepower, with a single four-barrel and no nitrous! Plus, theres power left in the combination that we didnt have time to get. Still, 961 horsepower should be enough to propel Chisenhall and the 53 to two bills on the salt!
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