Blown Big-Block Chevy Engine Build - Shock And Awe

If a big-block Chevy has not figured into your life yet, you probably won't understand it until you experience the apparent ease with which it will deliver a big fat output. Whereas a small-block always seems so busy on the dyno, a big-block just grunts it out, seemingly without any real effort. Adding a blower to a big-block just reinforces the whole "in your face" deal. Apart from the intimidation factor, the effortless output was why Outlaw Racing customer Alex Maldonado chose to go the blown big-block route for his '57 Chevy-it's a big, heavy car. With a basic game plan in mind, it was time for Alex to do some source searching.

Anytime we talk blown big-block, the word "budget" can no longer be used with the word "low." But that should not imply a build cost looking like a monetary black hole either. Choose an engine builder who has expertise at off-the-shelf parts selection for functional combinations, and an exotic "catalog" big-block like this one could be yours for under $21,000. But for many, $21,000 is still a lot of cash. That said, it becomes even more important to choose a reputable engine builder who has experience with such builds, and one who stands behind his work.

Andy Mitchell is the boss at the Upland, California-based Outlaw Racing Engines. It has to be said that it's easy to stick the word "Racing" into a company business name. Sometimes for the business' owner, it's no more than a flight of imagination. When contemplating an exotic high-performance engine where $21,000 is involved, success on the track looks like it should figure prominently in the decision making. Visit www.outlawracingengines.com, and you will see some of the race-winning, record-setting cars powered by Andy's engines. With a clean, smart, well-equipped full-service shop to back his efforts, Alex figured Andy looked like the guy to build his engine.

The big-bore Dart block selected... 

   

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The big-bore Dart block selected for the job has many upgrades that the stock-block does not have.

The Bottom End
A few years back, the big-block Chevy went through a popularity resurgence. This has resulted in even stock-blocks commanding premium asking prices. We have just gone through this routine ourselves, shelling out $600 for an average core 454 block. By the time we found a good late-model block, and had it machined, the bill was well into four figures. At the end of the day, we still only had a stock block. Andy's advice here is spend the money, get a Dart block, and enjoy the insurance of super strength that goes with it. For something over a grand more than stock, you get a new block with a 4.5-inch bore that will go to 4.625 if necessary. That's up to 3/8 inch bigger than stock. Additionally, the block is good for a couple of thousand horsepower, and then some. It also has the sort of reliability enhancing upgrades you would like to have on a stock-block, such as priority main oiling (unlike stock, oil is delivered to the mains first, then lifters). Also, a re-routed oil crossover passage eliminates internal oil leakage at the distributor.

Other than finishing the bores... 

   

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Other than finishing the bores to suit the pistons, the Dart block comes fully machined in all other respects to race-engine limits.

For a crank, a Callies Dragonslayer was chosen. These are best described as an all-American-made, heavy duty sportsman crank. Callies makes these cranks with a stock 2.200-inch rod journal, with stroke options of 4.000, 4.250, and 4.500 inches. With top-grade 4340 steel, a tough core, and deep-case heat treat, these cranks are about ready for anything. For shock-and-awe value, it has the ability-if required-to turn a lot of rpm. In this case, the 4-inch stroke was used, and with the 4.5-inch bore, delivered 509 inches.

Rods for this 509 took the form of a set of Howards billet BR series. This American-made 6.8-inch long two-rib cap design is (at a shade over 780 grams) lighter than you would expect of a heavy-duty rod. Riding on the rods is a set of JE's finest. These off-the-shelf pistons worked out perfectly in the tall-deck Dart block, with the 4-inch stroke and the 6.8-inch-long Howards rods providing a respectable 1.395-inch compression height. Keeping the wristpin out of the oil ring on a street engine of this power level will pay dividends in longevity for years to come. With the 28cc dish pistons just shy of flush, plus a flat mill of some .010 inch on the heads, resulted in a boost-friendly 8.2:1 compression ratio. With a compression ratio this conservative, there was room to considerably move the boost in an upward direction at a later date. The JE pistons were equipped with Total Seal Advanced Profile Gapless stainless steel rings to ensure a long life and gas-tight seal when that boosted charge lights off. Total Seal rings are, among some engine builders, a controversial subject. Andy's viewpoint: "We go faster with them, and our team car is slaughtering the opposition on the track."

Feeding the internals the necessary oil flow and pressure was a Melling high-volume pump, and to control the inevitable oil surge from high g acceleration, a six-quart pan from Big B Auto was used.

The Callies Dragonslayer crank... 

   

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The Callies Dragonslayer crank used in our 509 represents good American engineering at a sportsman price. Top-grade material and a comprehensive heat treat are all part of the deal.

Power Production Parts
We can liken the bottom end of this engine to a "case." And with the parts used, we have a case that can reliably contain the pressures and mechanically generated dynamic forces that are likely to come about during the business of producing immense power figures. It's time to look at just what power producing components Andy chose for this build.

Starting at the top is a pair of blower-spec 750 Holleys, which will be fed a diet of clean air courtesy of a Hilborn filter-equipped air scoop. Good filtration will ensure the close tolerances of the blower rotors are not compromised, and the rings and bores will have long lives.

The 750 Holleys used were of a blower-specific design. The main difference is the power valve is referenced to the manifold vacuum/pressure under the supercharger, not the area under the carbs before the supercharger. As far as the fuel delivery curves at part and wide-open throttle are concerned, Holley went through a series of calibration tests at its facility on these Weiand 6- and 8-71 blowers. An advantage of the calibration of a blower carb is that possible calibration changes, from one blower to another, are very minimal, as the induction pulses are unique to the blower, not the engine. This means once the factory calibrations are done, they won't change significantly from one GMC-blown application to another.

Because the form and amplitude of the blower pulses are measurably different than piston-induced pulses in a normally aspirated engine, the fuel delivery calibrations for these blower carbs are substantially different. To achieve the desired fuel curves in idle, transition, and wide-open mode, the main jets, air correctors, and emulsion well holes had to be re-evaluated. Just how well these near-universal calibrations would work would be revealed when this 509 hit the dyno.

Dragonslayer cranks can be...        read full caption Dragonslayer cranks can be had in three different stroke lengths. Ours was the shortest at 4.000 inches, thus allowing a high rev limit, and maximum strength from the short stroke's rod journal/main journal overlap.	Andy is seen here balancing...        read full caption Andy is seen here balancing the crank. With the chosen combination of rods and pistons, the crank balanced in without any major metal removal.	Check out these Howards rods....        read full caption Check out these Howards rods. They're beefy enough to take on a 1,000hp loading, while being light enough to eliminate the need for an expensive heavy metal balance job.
Blower motors require tough...        read full caption Blower motors require tough pistons. JE had just what was needed right off the shelf.	Rings for the 509 were the...        read full caption Rings for the 509 were the latest high-tech offering from Total Seal. These are what Andy uses to win races.

The Blower
Ultimately, it's the presence of that big 8-71 blower that gives this 509 its menacing appearance and sound. Originally designed as the scavenge pump for a GMC two-cycle diesel, this blower found notoriety when the top Gas and Fuel dragster guys started using it in the late '50s and early '60s. It has long gone out of production, and what Weiand now builds is an updated version from all-new tooling. It is in fact an improved replica of the world's most notorious blower, and falls into a category known as a "positive displacement" supercharger. If we exclude leakage past the rotors, that means (unlike a turbo) it moves a certain number of cubic feet of air per revolution, regardless of rpm. What this does is not only produce boost everywhere in the rpm range, but also produces it instantly, on demand. When everything is just right, throttle response follows suit, meaning that it's near instant. You have to believe those Top Fuel guys used this blower all those years for a reason. Maybe it's because it made them fast!

This shot shows the carbs...        read full caption This shot shows the carbs and linkage mounted on the Weiand 8-71 blower. At this stage, it's about ready to be mounted onto the intake manifold.

The fuel/air mix is delivered...        read full caption The fuel/air mix is delivered to the Weiand blower by means of a pair of special blower-spec 750 Holleys.

This vacuum take-off references...        read full caption This vacuum take-off references the power valve to the vacuum/boost below the supercharger so that the power enrichment takes place in the desired fashion.

Heads
Although iron heads can be used with a supercharger, aluminum heads have the advantage of running cooler, and with less troublesome detonation-inducing hot spots. This means they are able to accommodate a combination of more boost and higher compression. The heads chosen for the job were as-cast RHS 320cc port heads (PN 11001). These are the smaller of the two port sizes that RHS offers for the big-block. When a blower factors into the equation of a high-output street motor, the port size does not need to be configured so much for the top end output because the blower will, to a certain extent, take care of that with boost. For part-throttle driveability, there are advantages toward the use of a smaller port, and that is why this particular spec of head was chosen.

In its 320cc Pro Action head,...        read full caption In its 320cc Pro Action head, RHS chose to use a chamber shape with laid back walls to minimize valve shrouding.

Because the blower takes care...        read full caption Because the blower takes care of the top-end output, the intake port size can be on the smaller side to aid low-speed cruise and throttle response.