If you read most enthusiast magazines, and especially the Chevy-only ones, you’d think that there isn’t a single person building a pre-’97 small-block Chevy anymore. With the advent of the LS series of engines, you might believe the hype that everyone has abandoned their old-style engine in favor of retrofitting the newer generation of powerplants. Camshaft makers have chucked those cores on the back lot along with flathead Ford and Buick nailhead components. Block makers have smashed those casts and Gen I small-block heads are little more than bulky doorstops.
We’re here to say that the demise of the original small-block Chevy engine is greatly exaggerated. In fact, COMP Cams sells more Gen I camshafts than LS by nearly a 2-to-1 margin. Go ahead and pop the hood on your favorite hot rod. Odds are, there’s a traditional small-block staring you in the face. If that’s the case, even if you need to replace the engine, you’ll be money ahead to put another Gen I in your car because of the cost of new headers, accessory drive, adapter bellhousing, and other miscellaneous stuff you’d need to pull off an LS engine swap. Those parts can easily set you back several thousands of dollars which you could be investing in power-making parts for your Gen I. Don’t get us wrong; we’ve done our share of LS engine buildups, and we’re not refuting the power potential of this design, the driveability, or any of the other positive characteristics. We’re just saying that there are a whole lot of people who aren’t ready to make all of the changes necessary to swap an LS engine in place of their old, trusty Gen I motor.
As is the case with every...
As is the case with every engine build, the block is the foundation. A Dart Special High Performance (SHP) short-block starts with one of the company’s new cast-iron blocks. These incorporate all of the best traits of production small-blocks and add strength, the ability to handle a 4.125-inch bore, and a 3.750-inch stroke with steel rods. They also come with four-bolt, splayed main caps.
We’ve also more than once pondered the question of just how much streetable power you can squeeze from an early design small-block with all that we’ve learned in the past 20 years about cylinder head engineering, cam timing, and combustion chamber design. Could we find an LS competitor that looked like an anemic mid-’80s 305? And which LS would we set our sights on as a target? The carbureted GM Performance Parts LS3 makes 515 hp for about $7,500, but to build it beyond that you’re replacing the pistons and doing other work to beef up the bottom end. Before you know it, you’ve got an easy $10,000 in the engine. For that much money, you can buy a GMPP crate LS7, but then you have another host of engine swap challenges, and you’re still making “only” 505 hp.
We decided that a 600hp Gen I motor would probably scare the crank right out of most LS engines. So when the engine in our Laguna gave up the ghost, it gave us the perfect opportunity to put our theories to the test.
On the top end of the SHP...
On the top end of the SHP block, the standard small-block Chevy lifter bores are retained, and mounting bosses for later-style roller tappet spiders are part of the casting. Starting with a new block removes all of the risk and guesswork of a used engine. The Dart SHP block even has blind head boltholes for zero chance of coolant seeping up the head bolts.
The first step was to find the biggest small-block we could build without getting into exotic racing parts. It didn’t take long for us to identify the Dart Special High Performance (SHP) block as a worthy candidate. It can be built in displacements from 372 up to 427, and accepts all of the original small-block paraphernalia; it even has the ’55 Chevy front lower motor mount bosses. The ability to match the LS7 in displacement with a Gen I is very desirable, and helps even out the power playing field.
A little more research unearthed that Dart offers an SHP short-block with righteous parts that produces 550 hp and 545 lb-ft of torque on pump gas. Now we were definitely interested. Strength and durability issues are shelved with a 4340 forged steel crank, aftermarket steel rods, forged pistons, and splayed main block caps. Plus, Dart builds the blocks and heads that pro racers use to make 2,500 hp or more. Their SHP line is targeted at putting that same quality and performance expertise into the hands of street guys like us who also like to pound on our equipment at the racetrack.
Unlike a purebred race block,...
Unlike a purebred race block, the deck height and cam location match stock specifications, so all of your existing sheetmetal, exhaust, and accessories will bolt right up. There are also threaded mounting holes for the late-style roller cam plates. The engine uses a priority main oiling system, which means the main bearings get lubricated first.
Dart machines all of its blocks...
Dart machines all of its blocks in-house, starting with a line hone. This assures that the main bearing journals are prepped and also perfectly perpendicular to the cylinders. Then, the cylinders are finish bored, and torque-plate honed in Dart’s computer controlled honing machine. Because these are all-new blocks and the first round of machining is done by CNC, no other machining is needed.
The oil pan side rails in...
The oil pan side rails in the Dart SHP block are clearanced using a CNC machine. There’s clearance for up to a 3.750-inch stroke with steel rods. Engine builders will rejoice in not having to spend a day grinding the block by hand, and a half day of cleaning the block after sending metal everywhere. The pan rail accepts a stock or aftermarket oil pan and gasket, although it uses an ’81-85 style pan and right-hand dipstick tube.
The exact components in a...
The exact components in a Dart SHP short-block will depend on your desired power level and how you intend to use the engine. Even though these are sold as engine assemblies, the company takes you into account and builds each engine to best suit your needs within a range of options. Think of it as custom built for a crate-motor price.
The heart of our new small-block...
The heart of our new small-block is an Eagle 4340 forged steel crank, which Dart balances using a computer-controlled dynamic spin balancer. You can build a 372 Dart SHP with a 3.480-inch stroke, a 400 with a 3.750 stroke, or the big dog 427 with a 4.000-inch stroke. With the 4.000-inch stroke, there might be rod clearance issues on the block and cam. With the CompStar H-beam steel rods in our engine, it cleared without any additional work.
Typically, a Dart 427 SHP...
Typically, a Dart 427 SHP short-block comes with 26cc dished full-floating pistons. That is part of a combo that’s good for 550 hp at 5,700. We are hoping for 600 or a tad more out of this engine build, so Mahle forged flat-tops with eyebrow valve reliefs were selected to raise the compression ratio to 11.2:1. These pistons come with Mahle’s skirt coating for durability and reduced friction.
The 372 and 400 versions of...
The 372 and 400 versions of the Dart SHP engines use ⅜-inch ARP rod bolts while the 427 steps it up to 7/16-inch bolts to deal with the additional stress of larger displacement, a longer arm, and more power. All fasteners used in this engine are ARP.
Tony McAfee assembled our...
Tony McAfee assembled our engine, and he builds most of the Dart SHP short- and long-blocks. He checks every critical measurement as he builds each engine. Here, he uses a dial-bore gauge to compare the main bore with the bearing installed to the outside diameter of the main journals of the crank. McAfee likes these clearances to be around 0.003 for an engine that will see a combination of road racing and street use, such as with our Laguna.
Gasket sealer is applied to...
Gasket sealer is applied to the rear main seal seat in the block, and McAfee set the seal in place clocked at an angle to keep the seal and block parting lines away from each other. This decreases the chances of an oil leak. The Dart SHP blocks accept the traditional two-piece seal, but can be converted to a single-piece seal as an option. A dab of grease is applied to the top of the seal so it has lubrication against the crank at start up.