540 Chevy Big-Block Engine Build - Toeing The Line

It's good to know what you want when you set out to build an engine. It's even better to actually get it.

As Ken Sink formulated a replacement Rat motor for his original big-block-powered '68 Chevelle SS, he wanted two things: torque and fun. It's a concise set of goals, especially since in a street car, the two are synonymous. There's a sure way to achieve lots of fun-inducing grunt, and that's with a big bore and a long stroke. Accordingly, Sink turned to Speed-O-Motive to create a muscular yet very reasonable 9.4:1 540ci fat-block. The result is a powerplant that will tolerate any type of pump-gas swill, handle anything from around-town cruising to a cross-country journey, and make a grin-inducing 659 hp and 620 lb-ft of torque while doing it.

The basis for this big-block creation was a GM Gen VI block. This piece, which is the basis of GMPP's 502 crate motors, has a number of advantages when creating this type of big-bore, big-stroke combo. Right off the bat, it has four-bolt mains and will clear up to a 4.500-inch stroke. The Gen VI block also has Siamesed bores. Put simply, this means there is thicker wall material with no water jackets between the cylinders, allowing for bores as large as 4.500 inches in diameter.

Sink set out to make the combo bulletproof, teaming the four-bolt mains with a Speed-O-Motive forged steel crank, Carrillo forged H-beam rods, and JE forged flat-top pistons. The bore-by-stroke dimensions to create 540 ci are 4.500 by 4.250 inches. It's a good combination, simply because it has more of everything. More stroke equals more torque. Bigger bore equals more power. And with a 9.4:1 compression ratio, this thing will most likely even run on California 87-octane without complaining.

While a lower end certainly costs plenty of change, the single biggest investment a big-block builder will make is the cylinder heads. Sink chose a set of Brodix Race-Rite BB-R series lungs, and they proved to be ideally matched to the rest of the combo. These heads flow plenty, as you can see in the accompanying chart, but the 294cc intake ports also maintain good air speed, meaning torque levels and low-rpm throttle response are also good. The RRs also have their exhaust ports in the stock location, so header installation in the '68 Chevelle won't be a problem. They're also drilled to accept factory-style brackets, so outfitting the new engine with accessories will be problem-free as well. In fact, except for the fact that a Gen VI block has no provision for a mechanical fuel pump, Sink figures that no one looking under the hood will be able to tell the difference between the original Rat and his new 540 brute.

In accordance with the "able to be driven anywhere" ethos Sink followed for this engine, moderation was the name of the game when it came to the camshaft. A Comp solid roller got the nod, so occasional valve lash settings are really the only (small) hitch in this mule's leave-it-alone, plug-and-play guise. In our book, the cam plays to the strength of the heads with its 0.653/0.660-inch intake and exhaust lift figures. These specs take full advantage of the heads' excellent flow numbers, getting as much mixture into the cylinders are possible. On the other hand, the cam's 248/254-degree duration figures are fairly moderate. So while this engine definitely makes good horsepower (659 at 6,200 rpm), it has a very broad torque band, averaging 556 lb-ft from 3,200 to 6,500 rpm.

On the one hand, there's no doubt that this 540 combo could make loads more power. One indication of that is the massive 54 lb-ft average torque gain we saw by adding more intake plenum space with a 2-inch open spacer; this one's a no-brainer for this engine. The other indication is the moderate cam, creating a powerband that's done by 6,500 rpm. This thing could certainly make beaucoup horsepower with a more-aggressive 'stick. On the other hand, that would defeat the whole purpose of the thing. "I don't need a screamer," Sink explained. "This is kind of a reasonable motor to build, and the whole goal is just fun." Oh, and don't forget about the torque. With what this 540 has on hand, we don't think the fun part will be a problem.

Quick Notes
What We Did
Followed along as Speed-O-Motive built a serious street 540 big-block

Bottom Line
There's grunt to spare on tap, and plenty of horsepower to go with it.

Cost (Approx)
$13,000