Until we get those pesky laws of physics repealed, it’s always going to take a lot of power to move a lot of car. We figured 600 naturally-aspirated horsepower from a big-block Chevy would probably do the job, and to build an engine that could run the number, yet still be happy on the street, we turned to Dart Machinery. This is the story of how they put together a 509ci rat that’s just what we needed.

Fortunately for us, big cars also mean big room between the fenderwells, and to take full advantage there was no question that we’d be running a big block. While it’s certainly possible to make 600 horsepower from a pump-gas small-block, we’d rather have the low end grunt of a lot of cubes. Dart’s build team has plenty of experience building Pro Stock engines, so we knew they wouldn’t steer us wrong when engineering our combo. 509 cubic inches topped by Pro 1 heads, a big single-plane manifold, and a Quick Fuel double-pumper would make the requisite power, while internals from Howards and SRP would ensure strength and durability. Here’s a look at Dart’s master plan:

Dart 509 BBC Build Sheet:

  • Block: Dart Big M; 9.8” Standard Deck, 4.500 Bore
  • Crank: Howards Pro Max; 4-inch stroke (PN 454061)
  • Rods: Howards Ultimate Duty Forged Billet, 6.385” length (PN BR6135)
  • Pistons: SRP 17cc Dome with JE Pro Seal Rings (PN 212140)
  • Heads: Dart Pro 1 310cc Assembled Heads (PN 19100111)
  • Rocker Arms: Harland Sharp (PN SD2001)
  • Valve Stud Girdle: Dart BBC (PN 64110001)
  • Pushrods: COMP; 8.950 Exhaust, 7.950 Intake
  • Valve Covers: Dart Cast Aluminum Inverted Flange (PN 68000040)
  • Camshaft: COMP Xtreme Energy Hydraulic Roller (PN 11-443-8)
  • Lifters: COMP Hydraulic Roller (PN 900-16)
  • Timing Set: COMP Keyway Adjustable Billet (PN 7101)
  • Timing Cover: COMP 2-Piece Billet (PN 212)
  • Balancer: Professional Products PowerForce Plus 7.6″ (PN 90036)
  • Intake: Dart Single Plane 4150 Flange (PN 41114000)
  • Carb: Quickfuel Q-850 cfm
  • Air Cleaner: K&N (PN 66-3060)
  • Oil Pan: Moroso 6-Quart Street/Strip (PN 20413)
  • Oil Pump: Moroso Standard Volume Race (PN 22150)
  • Oil Filter: K&N
  • Gaskets: Victor Reinz, Complete Set
  • Bearings: Clevite, Complete Set
  • Spark Plugs: E3 (PN E3.64)

BBC with a Capital “M”: Dart Big M Block

The foundation of our build is Dart’s Big M block, with a standard deck height of 9.8 inches (they also offer a 10.2 tall-block version) and the mid-sized 4.5-inch bore. The Big M can go as big as over 700 cubic inches, so our 509 is actually fairly conservative for this block.

Per Dart’s Jack Mcinnis, “We cast the big M block in the Midwest United States using ‘class 32′ iron for high strength.” The Big M features billet 4-bolt main caps and a revised oil gallery layout. “We machine in a priority main oiling system which feeds oil directly to the main bearings before the top end of the motor so that we always have good oil pressure and volume at high RPM,” Mcinnis explains.

Dart's Big M block is available with bores big enough to build a 700-cube monster, if so desired.

A stepped main oil gallery that goes from 9/16-inch to 1/2-inch to 7/16-inch also helps increase oil flow to the crank at high RPM. The block’s front oil crossover eliminates internal oil leaks around the distributor shaft, too, which helps keep oil where it does some good instead of being whipped around in the crankcase.

Priority main oiling and a stepped main oil gallery in the Big M protects the crank from oil starvation.

Filling in the Blanks: Howards Crank & Rods

A 4-inch stroked, internal balanced Howards Pro Max forged crank with 1-inch lightening holes in the crank throws went in first, followed by Howards Ultimate Duty forged billet rods. Brian Adix of Howards explains that the crank starts with “the finest high purity 4340 aircraft quality high nickel alloy. These forgings have high quantities of nickel and chromium, which insures strength and long service life.

The Howards Pro Max forged crank combines strength and low rotating mass.

The forgings are shipped to the leader in high performance crankshaft machining, Callies Performance Products. They are machined to the highest specifications, with roundness within 60 millionths and taper being held to within .0003” on all rod and main diameters. All journals have .125” Tru-Form fillet radii.” Looking to the future, when the 509 eventually needs freshening, Adix adds, “Callies ”Deep Case” hardening produces a wear layer that remains intact even if reground .010” under (other cranks have a hardness depth as little as .003”).”

A typical performance crank may be hardened to a depth of just three thousandths of an inch, but the Howards Pro Max is deep case hardened to the point where it can be reground as much as .010 under.

The 6.135-inch rods are made from 4340 nickel steel, and feature double-ribbed caps secured with 7/16-inch ARP 2000 capscrews. “They are specially heat-treated using a multi-phase process to produce the ultimate in strength and reliability,” Adix says. “They’re also fully stress relieved and shot peened to insure no stress risers remain, and profiled for long stroke applications and weight savings.”

Howards Ultimate Duty forged billet rods feature double-ribbed caps and ARP capscrews. Pistons are by SRP; their 17cc dome will bump compression to a pump-gas-compatible 10.1:1.

Pistons are forged from 4032 wrought aluminum alloy by SRP, and feature a 17cc dome, which will bring our compression ratio to a street-friendly 10.1:1. The nice thing about JE’s SRP line is that you get a lot of custom, race-style features at shelf-stock prices, and these pistons are no exception. Designed to work with open-chamber heads, they sport CNC-machined domes with radiused valve reliefs for improved flame travel. The ring package is a JE 1/16-1/16-7/16 Pro Seal set.

One of the nice things about running a relatively tame compression ratio is that if we decide to bump the motor later on with a little boost or nitrous, we won't have to change slugs.

Moroso Oil Pan & Pump

Buttoning things up on the bottom of our new rat is a Moroso steel 6-quart street/strip oil pan. It does more than just keep all the oil from falling out the bottom of the block, though – the deep, kicked out sump adds oil capacity and helps cool the lube, while also keeping it under control during acceleration and cornering. Dart also bolted up a matching standard-volume Moroso racing oil pump that features special internal anti-cavitation slots, feeder grooves, and an enlarged bypass area to bleed oil back to the inlet side of the pump. Combined with precision-machined gears and a precision-ground shaft, we’ve got a pump that can handle the entire rev range of our 509 without sucking wind.

Moroso's steel 6-quart street/strip pan keeps the oil off the pavement, and away from the crank as well.

Camshaft Secrets: COMP Valvetrain

With the short block together, it was time to stab in the cam, a COMP Xtreme Energy hydraulic roller unit featuring .540/.560 lift and 242/248 degree duration at .050, with a 110-degree lobe separation angle. The aggressive lobe profiles on COMP’s Xtreme Energy series cams are designed for better throttle response and more high-end power than a typical cam sharing the same specs, without killing idle vacuum. COMP’s Trent Goodwin explains, “The shorter seat timing and quicker lobe designs on our Xtreme Energy cams create more low-end torque to help move the heavier mass,” which is exactly what we’re looking for.

COMP's Xtreme Energy series cams feature aggressive lobe profiles to provide good high end power without killing vacuum at idle.

To spin the cam, Dart selected a matching COMP adjustable billet timing set, sealed up under their 2-piece billet aluminum cover. The COMP timing cover avoids the flex inherent in stock-style stamped covers that can cause erratic timing, and an access hole for a dial indicator makes endplay adjustment child’s play. From a practical standpoint, it also makes tuning and maintenance quicker and simpler. “With the two-piece cover, it’s much easier to change the cam or move the intake centerline,” Goodwin explains. “You can do all that without dropping the oil pan.” COMP lifters and pushrods (7.950 on the intake and 8.950 on the exhaust) complete the matched set of block-side valvetrain components.

A two-piece billet timing cover makes changing the keyway on the COMP billet dual roller timing set far easier.

Headline Act: Dart Pro 1 Heads

Of course, nobody reads stories like these to see what lifters we used, so we’ll get on to the main event, so to speak – the Dart Pro 1 heads. The idea behind these heads is to provide Pro Stock-derived performance in an as-cast design. “We use a C355-T61 aluminum alloy for superior strength, especially at elevated temperatures,” says Mcinnis. The intake ports measure out at 310cc (129 on the exhaust, in case you were wondering) and Dart claims 369 cubic feet per minute from them at .800 lift and 28 inches of vacuum.

Per Mcinnis, “The ports and chambers are developed to be run as-cast without requiring any additional work, and they’re modeled similar to what you’d get with a ported head, except without the extra cost involved.” 2.25-inch intake and 1.88-inch exhaust valves were specified for our build; the assembled heads can also be ordered with larger 2.30-inch intake valves for applications with bigger cubes and higher revs than our “little” 509.

Our Pro 1 heads sport 121cc combustion chambers and 2.25/1.88-inch valves.

The Pro 1 heads feature a 121cc combustion chamber volume, and put the intake ports in the stock location, but raise the exhaust ports .300-inches with a standard BBC bolt pattern. The intake valve angle is 24-degrees, and the exhaust is 15 (rolled 2-degrees), with a 4-degree cant. Though we left ours alone, these heads can be flat-milled to raise compression all the way down to 108cc chambers, with each .005 lowering volume by 1cc.

Pro 1 Features:

  • 121cc combustion chamber volume
  • 310cc intake port volume
  • 129cc exhaust port volume
  • 369CFM at .800 lift
  • 2.25-inch intake valve diameter
  • 1.88-inch exhaust valve diameter
  • Stock intake port location
  • Exhaust ports raised .300 inches (standard bolt pattern)
  • 24-degree intake valve angle
  • 15-degree exhaust valve angle with 4-degree cant

Victor Reinz MLS gaskets bridge the gap between head and block.

The heads were completed by a brace of Harland Sharp 1.7:1 ratio Diamond series stud mount rockers. These arms are designed for standard 7/16-inch studs, and are profiled to eliminate as much as 100 grams of moving mass from the valvetrain. To improve valvetrain stability, Dart added their BBC stud girdles, which clamp extra-long adjustment nuts between rigid aluminum bars. The result is deflection resistance similar to a shaft-mount rocker arm setup, without the heart-attack-inducing price tag. With the heads done, everything was capped off with a pair of Dart cast aluminum “inverted flange” valve covers.

Harland Sharp Diamond Series 1.7:1 roller rockers have a profiled main body design that reduces reciprocating weight without affecting strength.

Topping it All: Dart Intake and Quick Fuel Carb

Feeding those heads is a Dart single-plane intake manifold with a 4150-style flange. Dart offers this manifold for rectangular or oval port heads, standard and tall deck blocks, and with your choice of 4150 or Dominator flanges. Designed to make life easy for the engine builder, they feature dual distributor hold-downs to simplify timing adjustments, and the tall deck versions are set up to still use standard-length distributor shafts. Inside the plenum, extended runner dividers equalize port length and feature a radiused profiled to keep cylinder-to-cylinder fuel distribution the same. If we ever decide to spray the engine, the integral nitrous bosses will make it a straightforward deal, too.

We're going to try not to be too greedy and leave those nitrous bosses undrilled - for now.

Now that they finally had a place to put it, a Quick Fuel Q-850 carb and one-inch tall phenolic “cloverleaf” spacer topped off the intake manifold. The Q-850 is a 4150-style carburetor with a Proform aluminum main body, CNC-machined billet metering blocks, and a billet throttle baseplate, which is far less likely to warp or break an ear than a conventional cast baseplate.

To gain a little additional plenum volume, Dart added a one inch spacer. As an added bonus, the spacer helps insulate the carb from heat transmitted through the intake manifold.

The throttle uses slabbed shafts and low-profile button head screws to retain the blades, maximizing airflow, and all Q-series carbs feature an adjustable secondary pump cam bracket for fine tuning the secondary system. Notched floats and jet extensions are also standard, making this carb drag-ready out of the box.

The Q-850 is a 4150-style carb built from premium components.

Time to Light the Fire: Mallory & E3

To handle ignition duties, a Mallory Comp S/S 42-series distributor and matching plug wires were enlisted. Sporting a CNC-machined billet aluminum housing and ball bearing upper and lower bushings for longevity and stability at high RPM, it’s a direct drop-in ready-to-run piece.

The billet housing of our new Mallory distributor features dual ball bearings in place of the normal bushings to aid timing accuracy at high RPM.


The Mallory components tickle a set of eight E3 E3.64 spark plugs, which offer a patented “edge to edge” electrode design claimed to produce more power and lower emissions.

On a related note, the clear white timing marks on the Professional Products PowerForce Plus harmonic damper made it easy to set the timing. In addition to the regular timing hash marks, engraved lines every 90 degrees aid tasks like setting valve lash, and the damper is SFI 18.1-rated for safety at the drag strip.

The SFI 18.1-rated harmonic balancer from Professional Products has clear timing marks etched in the shell, which is a real bonus when trying to dial in the ignition.

The assembly process finally complete, our new best friends at Dart wheeled the newborn 509 into the dyno cell and strapped it in. Remember that our wish list for Dart was a pump-gas motor that would be happy on the street and yet still have the 600-plus horsepower.

Time to do a few carb and ignition adjustments on Dart's engine dyno...

“The objective we were given was to create a big block combination that would have good street manners, plenty of vacuum for power brakes and accessories, and yet make a lot of power to move a heavy car on the dragstrip or on a road course,” says Mcinnis.

Would our new rat run the number? Dart had chosen all the right parts, and put them together with the skill only years of racing experience can earn, but it’s all academic until the fluids get topped off and the starter turns. Everyone held their breath as the engine idled up to temperature and final adjustments were made, but when the pulls started, there were no unpleasant surprises – Dart hit the ball out of the park.

“We went with a 509 cubic inch combination, which is something that we’ve had good luck with, and we wound up producing 650 horsepower and about 613 foot-pounds of torque on the dyno,” Mcinnis proudly revealed. And it’s all in a package that will live a long and happy life. Now, we just have to do our part and get our fresh new 509 swapped in, then see how the dyno compares to the real world. As they say on TV, stay tuned for the next thrilling episode, and until next time, check out the complete photo gallery for more pictures of our build.