We can remember the days when a 454 big-block was considered, well, big. But today you can hit that displacement number with a small-block and save a ton of weight. So, if you’re going to go with a big-block you might as well start thinking, well, big. Of course, using a factory GM block stifles dreams of huge displacement, but luckily for us the aftermarket offers blocks capable of cubic inches once only available to the pros. And, in the world of stroker engines, it’s not much more expensive to build a block big rather than err on the small side. Besides, more displacement equates to more torque, and more torque is always a good time.
When we formulated this big-block build we decided on a few parameters. First, it needed to be geared to the street. This meant it had to have a decent idle, make some vacuum for power brakes, and live on the 91-octane swill that passes as premium here in sunny California. Second, it had to have a flat as Kansas torque curve, especially in the low to midrange area most street engines spend their time. Third, it had to have a standard deck height so that we could find off-the-shelf headers and an intake manifold. After pondering a bit, it seemed like a big-displacement roller engine was in order.
Going really big meant turning to an aftermarket block and Dart makes some of the best stuff out there. Their line of Big-M blocks can be built into many tasty combinations from a diminutive 454 up to a 582 and beyond. With that in mind the formula gelled into a bore of 4.600 inches and a stroke of 4.375 inches. Do the math and it rounds up to 582 cubes of power and torque, making goodness.
After ordering up our block, we contacted JR Twedt, of JR Competition Engines, to help us with the machine work and assembly. As Twedt says, “The Dart Big-M block is hands down the best choice for big-inch engines. The main lines on these blocks are always spot on from Dart, which is really nice considering the labor intensiveness that goes into having to line-bore the mains. Another great thing about the Dart Big-M is its strength and versatility. You can take these blocks out to 4.600 with ease and not have to worry about thin cylinder walls because of the extra-thick siamese cylinder walls.” We also decided to stick with our “street-friendly” philosophy and run a hydraulic roller camshaft. Now having a big stack of spendy parts should theoretically yield a killer engine, but only if the parts are fitted together correctly; that’s why we turned to Twedt for the build. Follow along as we carefully assemble the short block of our 582 big-block. Next issue we’ll finish it up and then wind it out on Westech’s SuperFlow engine dyno.
As shipped, the Dart blocks are pretty clean, but they do require some TLC. JR Twedt, owner of JR Competition Engines, explained, “We deburred all the casting flash, which can eventually chip away causing heat and stress risers. Even with the big stroke, no clearancing was needed to account for rod swing.”
Our Dart Big-M block is like a stock GM block, but better. Since Dart started the design on a clean sheet of paper, they were able to address some the issues found with the OEM block. Extra-thick siamesed cylinder walls resist cracking and have improved ring seal, scalloped outer water jacket walls help improve coolant flow, stronger steel caps incorporate splayed outer bolts, and improved lifter valley head bosses are just a few of the refinements. Other items like true “priority main” oiling and a crank tunnel pre-clearanced for big strokes just makes life easier. JR punched the cylinder bores out to 4.600 inches, and we were ready to rock.
Prepping the block and taking lots of measurements is key when the goal is a solid and trouble-free engine. Twedt then explained how he prepped the block, “First we calculated our assembly height. This was done by checking our connecting rod length, adding half the stroke, and then adding our pistons compression height. This gave us our assembly height. We don’t trial assemble or mock-up engine assemblies since we were using quality parts. We simply square decked the surface of the block 90 degrees off the crankshaft centerline and 45 degrees off the cam centerline. Using torque plates, we bored the block to within 0.0055 inch of our finish size before honing. We then honed each cylinder in five stages.”
If you’re going to make big (and reliable) power then skimping on the crank isn’t the best idea. To make sure our 582 would hold up to abuse we picked up this Scat 4.375-inch stroke forged 4340 steel crank. This crank was precision-ground, heat-treated, shot-peened, and micro polished at Scat to ensure tight tolerances. It’s also nitride-hardened to resist wear and has straight-shot and chamfered oil holes. Lastly, it features large radius on all journals for improved wear resistance and strength.
With the crank in place we went ahead and torqued down the steel billet main caps using the bolts supplied by Dart. If you want to save a few hundred bucks you can order the Sportsman version of this block, which has ductile iron mains. No matter which material you go with, the outer bolts are splayed for extra strength.
Twedt then checked the thrust on the crank. “We want to make sure that the thrust bearing isn’t too tight and doesn’t wipe out the crankshaft,” he says. Some builders do this by hand, but the right way is with some precision measuring equipment.
Now if all we cared about was wowing you with big dyno numbers, we could have tossed in an insanely rowdy camshaft that would be cumbersome to live with on the street. But we live in the real world where idle characteristics are nearly as important as how much peak power an engine puts out. To that end, we selected a hydraulic roller camshaft from COMP that’s a good mix between power and manner. Duration numbers (at 0.050) came in at 275/279 with lift of 0.680 inch on a 112 LSA.
Connecting rods take a ton of abuse so we went with these Scat H-beam pieces. These are the strongest rods Scat makes, and if they can stand up to blower and nitrous abuse then they should have no problems living in our big-block. These 6.535-inch forged 4340 rods incorporate special doweled caps for specific cap-to-rod alignment and are profiled for extra stroker clearance. Each rod came fitted with ARP 8740 chromoly rod bolts rated to 200,000 psi.
When building a 582 there’s no way we were going to find off-the-shelf slugs that would work, so we ordered up some custom pistons from Mahle. They came ready to rock in our 4.600-inch bore big-block and were fully phosphate dry film lubricated and the skirts had Mahle’s Grafal coating to reduce frictional drag. Our target compression ratio was 10.8:1 so they had an 8cc dome and a compression height of 1.070 inches.
After file fitting the rings, and mating the Mahle pistons to the Scat rods, we slid the assemblies into their new homes using our handy Summit guide sleeve.
After torquing down the Scat rods, Twedt checked how much play there was between the rods. “I do this for a couple of reasons. First being that side clearance plays a critical role in maintaining correct oil flow to each rod journal. Typically, I’m looking for a minimum of four times the actual bearing clearance on a street engine. Also I do this to check the consistency of the rod journal radius,” JR says.
Degreeing the camshaft is critical if you want to make optimum power with any engine you might be building. As Twedt explained, “Roller lifters walk the crankshaft back and forth so you need a button with a little bit of clearance so that the cam doesn’t walk out the front of the timing cover.”
When building an engine from a new block it’s easy to overlook small, but needed, items like a fuel pump block-off plate or this Mr. Gasket oil filter adapter. Luckily, we remembered before getting to the dyno and trying to screw on a filter.
A broken timing chain can wreak havoc on an engine’s valvetrain, so we bought this double-roller COMP chain and gearset. It features billet steel sprockets and a nine-keyway crank sprocket for 2-degree incremental adjustability. It’s pre-stretched, heat-treated, and included the Torrington roller thrust bearing; what’s not to love?
Billet front covers look great, but there’s more to them than just looks. Even with a thrust button, a stock stamped-steel front cover can flex under pressure, causing erratic ignition timing. This COMP two-piece billet aluminum cover is super rigid and will hold our cam in place where it belongs. It also made endplay adjustment a snap due to its handy access hole. For racers the two-piece design makes cam swaps that much easier.
If you’re going to spin a big-stroke engine hard then you need a good damper to keep all the internals spinning happily. For this engine we called up Summit and ordered an ATI Super Damper. Their elastomer is designed and tuned to eliminate harmful crank harmonics, reduce wear, and stop horsepower loss. They also exceed SFI 18.1 specs.
A sketchy oiling system can quickly kill even the best build engine. To keep the Texas Tea flowing we picked up this high-volume pump from Moroso. This pump is designed for an 8-inch-deep pan, and the pickup is fully welded in place.
The other big player in our rock-solid oiling system was this fully baffled 6-quart pan from Moroso. It features a kicked out sump for improved oil control and an integrated windage tray. We bolted it in place using a Fel-Pro gasket set and stainless fasteners from our ARP accessory bolt kit.
And with that, our 582 short-block is done and ready for a top end capable of feeding the necessary atmosphere to the eight hungry cylinders. Once together we’ll strap it down to Westech’s SuperFlow 902 dyno and let it feed.
|Dart Big-M block
|Scat 4.375-inch stroke forged crank
|COMP hydraulic camshaft
|Scat H-beam rods
|Mahle forged custom pistons
|Mr. Gasket oil filter adapter
|COMP double-roller chain and gearset
|COMP billet aluminum cover
|ATI Super Damper
|Moroso high-volume pump
|Moroso 6-quart pan
|Fel-Pro gasket set
|ARP accessory bolt kit