How to Get 674 lb-ft of Torque From a 540ci Big-Block - Fire In The Hole
From the September, 2011 issue of Chevy High Performance
By Steven Rupp
Photography by Steven Rupp
As they say, “bigger is better,” and today, with the ever-increasing displacement of small-block engines, it applies even more to big-blocks. After all, why build a 396 or 454 big-block when it’s fairly easy to get that sort of displacement from a lighter weight small-block? Besides, the overall cost to build bigger isn’t that much higher and the benefits in overall power potential, especially torque, is huge.
When we started penciling down this big-block build we decided on a few parameters. First, it needed to be geared for the street. Meaning it had to have a decent idle and live on 91 octane that passes as premium here in California. Second, it had to have a broad, flat torque curve, especially in the low to midrange area most street engines live in. After pondering a bit, it seemed like a big-displacement hydraulic-roller engine was in order.
If you haven’t noticed, good condition big-block cores are becoming increasingly hard to find, but fortunately Dart Machinery offers Big-M blocks that are perfect for someone who wants to shun the LS trend and do something a bit more retro. Their Sportsman line is well suited for a street engine build and at around $2,000 it’s pretty affordable as well. But, the most important aspect of the Dart block is that it’s able to go to displacements unobtainable for OEM offerings from the General.
After chatting with Jack McInnis over at Dart, we came up with a 540ci big-block. Sure, we could have gone even bigger, but 540 is a lot of cubes and more than enough for the typical street bruiser. All the parts are available right off the shelf, and it’s a proven reliable combination. After ordering our block we contacted JR Twedt of JR Competition Engines, to help us with the machine work and assembly. 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. A couple more great things about the Dart Big-M are its strength and versatility. You can take these blocks out to 4.600 inches with ease and not have to worry about thin cylinder walls because of the extra-thick siamese cylinder walls.” We also decided to make life easy and stick with a hydraulic-roller camshaft. Sure, this leaves some of the 540’s potential on the table, but we feel that for a street engine it’s a trade-off worth making.
When Dart designed their Big-M...
When Dart designed their Big-M blocks they did more than just make the GM offering bigger, they addressed a host of issues. Extra-thick siamesed cylinder walls resist cracking and have improved ring seal; scalloped outer water jacket walls help improve coolant flow, stronger steel or ductile main 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 preclearanced for big strokes just makes it better.
Twedt says big-inch 540ci engines love compression and camshaft. Now this is a street application, so it needed to stay in the 91-octane range at 10.5:1 compression. The whole street aspect also dictated the general size of the camshaft. As Twedt says, “Combination is everything—not just the cylinder heads and cam combination, but how all the parts work together. The big lift, big duration, and huge cfm flow numbers are cool to look at, but it doesn’t mean much if it’s used incorrectly. After all, nobody drives a flow bench down the road or racetrack.” This is why it’s important to think about how an engine will be used before ordering parts and piecing it all together. If our goal was a quarter-mile race car then this big-block would have been built completely different. The goal here is a well-mannered street engine that could hit the occasional dragstrip or autocross. This isn’t a cookie-cutter build, which is why we used an engine builder rather than flipping open a catalog and buying someone else’s idea of what we need. Besides, doing it this way is much more fun.
While the block that ships...
While the block that ships from Dart is pretty clean, it does require some work. As JR Twedt of JR Competition Engines says, “We first deburred all the casting flash, which over time can chip away causing heat and stress risers. No clearancing was needed for the 540 on the bottom of the cylinder walls for rod swing; Dart took care of that when the block was made.
Twedt then explained how he...
Twedt then explained how he prepped the block, “First we calculated our assembly height. This was done by checking our connecting rod (6.385 inches), adding half the stroke (2.125 inches), and then adding our pistons’ compression height (1.270 inches). This gave us a 9.780-inch assembly height. From Dart, the block measures roughly 9.810 inches. We don’t trial assemble or mock up engine assemblies. If you buy good components from trusted manufacturers and use proper machining processes, you don’t have to worry about being off when you assemble the engine. 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. For this engine we set the piston-to-wall clearance at 0.0045 inch.
When building a stroker, one...
When building a stroker, one key player is the crank. When we called up Lunati we wanted to order one of their Sledgehammer engine kits (PN EA55-540-S, $2,670). They feature a nitride heat-treated crank forged from 4340 non-twist steel. The bad news for us was that the crank in the kit (PN BP425IN, $740) was on back order. Since we had a deadline, Lunati substituted their Pro Series crank (PN BP421IN, $1,680). The Pro Series crank is the best they make, since it can handle over 1,500 hp. Granted it’s overkill for this build, but man it sure is a sexy American-made crank. Hey, at least we know we’re set if we decide to toss in a big shot of nitrous. If you’re looking to duplicate this build, pick up the wallet-friendly Sledgehammer kit that includes the crank, rods, pistons, bearings, and rings.
Rods take a lot of punishment,...
Rods take a lot of punishment, so skimping here wasn’t going to happen. The 6.385-inch H-beam Lunati rods (PN 6385H) that came in our kit were just what we needed. They’re forged from aircraft-grade 4340 steel and then heat treated, stress relieved, shot-peened, and magnafluxed to perfection.
Packaged in our Lunati kit...
Packaged in our Lunati kit were these Wiseco pistons (PN WISPT102HS). The forged 15cc domed pistons have a compression height of 1.270 inches and came with fully coated skirts.
After file fitting all the...
After file fitting all the rings, Twedt went about mating all the Lunati H-beam rods to the forged Wiseco pistons using the included spiral locks.
Time to start filling the...
Time to start filling the Dart block; first up was this Lunati hydraulic roller tappet camshaft (PN LUN-60213, $320). Choosing the right camshaft can be a daunting task. After talking with Dart and Twedt we settled on this 241/239 duration, 0.625 lift, 110 LSA stick. As Twedt says, “We could have added more duration, but that would have moved our powerband to a higher level, and with this cylinder head all we would have done is post a larger horsepower number, but sacrifice the good mid-level torque number we were shooting for.” The cam was then degreed by checking the valve’s opening and closing figures at 0.050-inch lift. Twedt found that our numbers were spot on with what Lunati specified.
With the cam in place we could...
With the cam in place we could then install and secure the Lunati crank. The Dart block came with high-grade main cap bolts, so that did save us a few bucks.
To keep everything in good...
To keep everything in good time we then installed this double-roller timing set from Lunati (PN 93114LUN, $69). It came with a Torrington bearing to prevent wear to the block face and won’t stretch out over time like other cheaper offerings.