Dart 427w Engine Build - Brawn Dart
A tough new 427 short-block from Dart Machinery
From the August, 2011 issue of 5.0 Mustang & Super Fords
By Dale Amy
Photography by Dale Amy
Nope, you can't buy a complete...
Nope, you can't buy a complete engine like this from Dart Machinery, but it does now assemble a heck of a Windsor-style 427-inch short-block as a bull-strong starting point for your own creation. And, yes, some deep-breathing Dart heads couldn't hurt.
Dart Machinery has a long and successful history of producing both horsepower and brute strength for Blue Oval and Brand C gearheads. The Motor City-based firm is perhaps best known for its high-flow cylinder heads and race-oriented Iron Eagle engine blocks, but has recently begun production of 427-inch short-block assemblies based on Dart's Special High Performance series of 9.5-inch-deck Windsor-style blocks. These robust iron-blocks are decidedly more street-friendly (and affordable) than the racy Iron Eagle, yet offer a humongous strength increase over a stock 351 casting. They are targeted at the high-performance street and sportsman crowd.
Dart now teams these American-cast-and-machined SHP blocks with quality rotating/reciprocating hardware from top-line performance manufacturers, and even more importantly, harnesses the talents of experienced in-house engine builders to hand-assemble each and every 427 short-block.
Let's be clear: Dart is not in the business of building long-blocks or crate motors. Rather, with this new Windsor-style 427, the company has created a strongly spec'd and precision-assembled short-block foundation. It's the trickiest and most critical aspect of any powerplant, and one you or your favorite engine shop can build upon. In essence, Dart has done the hard, precise work so you can finish it off and bolt together whatever combo suits your purposes, knowing the bottom end will be up to the task.
Still, where's the fun in just showing you some short-block images? Instead, we prevailed upon the talented crew at Dart to show us not just their 427 bottom end going together, but to finish the big-bore beast off with cam, heads, and induction, then lock it all down in the company's in-house dyno cell and generate some real-world numbers for your consideration. For this exercise, the Dart dudes opted to put together a sort of street-bruiser combo with torque aplenty that would be happy to rumble around on a diet of pump gas.
Horse Sense: Drag-racing enthusiast Richard Maskin founded Dart Machinery some 30 years ago in a humble Detroit-area two-car garage. Its growth over the past three decades has been nothing short of phenomenal.
Dart's high-nickel-content SHP iron-blocks are cast in Wisconsin and machined on ultra-modern hardware in one of the company's two Detroit-area facilities. For 427 cubes, the bore is 4.125 with a 4.000-inch stroke (though the SHP block is said to support combos up to a maximum of 4.185 x 4.250). Bores are Siamesed for rigidity, while the distinctive scalloped outer-jacket shape provides plenty of coolant flow around the cylinders. Decks have a minimum of 0.675-inch thickness.
The business end of Dart's...
The business end of Dart's SHP short-block looks like it could survive a nuclear strike. Thick internal bulkheads are matched by massive steel main caps, the second, third, and fourth of which have four bolts, with the outer pair being slightly splayed. Like the blocks, these caps are machined in-house at Dart. Notice how far the bore castings extend into the crankcase for piston support throughout its stroke. Main-journal diameter is a Cleveland-style 2.749 inches, and the muscular bare block weighs in at 195 pounds.
Dart doesn't mess around when...
Dart doesn't mess around when it comes to the 427's crank, going with Eagle's forged 4340-alloy unit with 4.000-inch stroke as the sole offering. Engineered for internal balance, this thing is rated for up to 1,500 hp. 'Nuff said?
It's the same with the rods...
It's the same with the rods in that Eagle's 4340 H-beams (in 6.250-inch length) are the only choice--and they are strong.
If all this seems rather dictatorial,...
If all this seems rather dictatorial, there are alternatives on the piston front as a choice between flat-top or dished (26cc) variants is available. Paired with heads having 62cc chambers, the former would result in around 11.04:1 compression on the 427, while the dished slugs would yield about 9.5:1. In either case, the piston manufacturer is Mahle, with 1.245-inch compression height, utilizing a common 1.5mm/1.5mm/3mm ring package. Dart will work with you or your engine builder on desired compression. For our subject build, Dart opted to use the flat-top pistons, but opened up the accompanying cylinder heads' combustion chambers to 65cc for 10.5:1 compression.
Dart's pair of veteran builders,...
Dart's pair of veteran builders, Tony McAfee (shown, here wielding the Sunnen dial bore gauge) and Jeff Lake, assemble each and every 427 short-block. These guys are experienced pros. They used to build and maintain the race bullets for Dart's recently terminated Pro Stock drag program. And when it comes to a short-block, the skill and precision with which it is assembled is at least as important as its components.
Ring-end gap is critical for...
Ring-end gap is critical for proper combustion sealing, so be sure to tell Dart's order desk if you are planning, say, nitrous or boost, which would dictate a wider gap than a purely naturally aspirated application.
A shot of an installed piston...
A shot of an installed piston at bottom dead center shows how little of the skirt extends beneath the Dart block's cylinder-wall casting. Such full-length lateral support for the piston is critically important on long-stroke combinations.
Should you or your engine...
Should you or your engine builder order Dart's 427 short-block assembly, it will arrive looking something like this. Dart will optionally paint the block on request. Note that a cam is not included, as that choice should be specific to your intended application.
For our buildup and dyno testing,...
For our buildup and dyno testing, Dart's crew decided to go relatively mild and street-friendly with a Comp Cams (www.compcams.com) hydraulic-roller bumpstick having gross valve lift of 0.585/0.580 inches, and a duration of 0.050 at 242/248 degrees. Lobe separation is 110 degrees, and it was installed straight up. Displacement has a calming effect on camshafts, so this piece is way tamer ministering to 427 cubes than it would be conducting a 351.
Dart's SHP block is fully...
Dart's SHP block is fully machined to accept roller lifters and their associated hardware, so a full OEM setup was installed, as shown here.
Dart is perhaps best known...
Dart is perhaps best known for its free-flowing cylinder heads, and we went with its top-dog Pro1 CNC model with 225cc intake ports because ... well, just because we could. As made obvious by their designation, these virgin 355-T61 aluminum alloy castings are CNC-ported, flow like fire hoses, and probably didn't even break a sweat on our fairly mild combo.
Normally 62cc on the Pro1...
Normally 62cc on the Pro1 or Pro1 CNC heads, Dart machined the heart-shaped chambers on our test set to 65cc, which, when teamed with the short-block's flat-top pistons, provided a pump gas-civilized 10.5:1 compression.
Compared to factory heads,...
Compared to factory heads, the Pro1 lineup has large raised exhaust ports with a spread bolt pattern (3-inch centers). This is to allow for large primary headers and correct the restricted port shape of the stock-style 351 castings.
New from Dart are these two-piece,...
New from Dart are these two-piece, adjustable pushrod guideplates, which Tony and Jeff put to good use...
...mounting a set of Comp...
...mounting a set of Comp Cams High Energy die-cast 1.6:1 aluminum rocker arms--nothing exotic, and certainly matching the overall street/strip personality of our test engine combo.
Likewise there's nothing particularly...
Likewise there's nothing particularly exotic about the intake that was on hand for our dyno mule, though the Professional Products Hurricane is of single-plane configuration and favors revs above the 3,500-rpm mark.
Dart had a variety of "dyno...
Dart had a variety of "dyno carbs" on hand, and we decided to start testing with this 650-cfm Demon. It did well but was ultimately replaced with its 850-cfm bigger brother. Check out our dyno sidebar to see how it all did.
With efficiency that stems from years of experience, Tony McAfee and Jeff Lake had our street-friendly 427 test mule strapped down and hooked up in the dyno cell in short order, plumbing it with a set of Kooks long-tubes with primaries large enough to take advantage of the heads' cavernous exhaust ports. To be honest, little time was spent "perfecting" the combo--it wasn't necessary.
We started with a 650-cfm Demon carb, made two or three pulls while experimenting with ignition timing (the combo seemed to prefer about 31 degrees total timing), then bolted on an 850 Demon for a couple final pulls. As you can see, the result is oodles of torque and better than 1.4 peak horsepower per cubic inch. This is excellent performance from a naturally aspirated bullet with pump gas-friendly 10.5:1 compression and civilized cam specs. Equally important, however, is the longevity that can be expected from the high-quality components and fastidious assembly of the Dart 427 short-block.
|w/650 Demon||w/850 Demon|