This is for all the guys who are addicted to super sizing. You know, the largest soda at the 7-11, the Camaro with the widest rear tires on the planet, and a Rat motor that must displace at least 500 ci. While the small-block has enjoyed plenty of attention when it comes to displacement enhancement, the Rat continues to be King of the Street.
So this got us thinking about what kind of street-driven, pump-gas, normally aspirated big-block we could build that would automatically be branded Neolithic by the tree-huggers and blasted as anything but cost-effective by the monetarily challenged. If you are either of these and are considering firing up your poison pen, save yourself the trouble because we'll ignore your bleating. This is an in-your-face Rat that we wanted to build mainly because we could.
To begin our 540ci buildup, we started with a used Gen VI Bow Tie block that Tim discovered at a swap meet. After Jim Grubbs Motorsports completed the machine work, Tim dropped in the Scat one-piece rear-main-seal stroker crank with Federal-Mogul bearings.
OK, so our pal Tim Moore stumbled across a good deal on a Gen VI 502 iron-block at a swap meet, so right away we were off to a good start. That led to the selection of a Scat 4340 steel crank with a 4.250-inch stroke to add a quarter-inch arm to a stock 454's swing. Since this had to be a pump-gas motor, we went with Sportsman Racing Pistons' (SRP) streetable forged aluminum-alloy pistons with a flat top to keep the compression realistic. With a 4.500-inch bore allowed by the 502 block and the coffee-can-sized pistons, we ended up with Max the Rat at 540 cubic inches.
Flow Chart
The key to power with any engine, from the lowliest four-cylinder to the manliest supercharged Top Fuel engine, is cylinder head flow. But while ultimate flow is always attractive, there are other considerations that often become critical. The most important for us was to retain the street nature of the cylinder head. Many good Rat heads raise the exhaust ports to improve the exhaust flow. While this is an excellent plan for power, it requires very expensive custom headers-something we wanted to avoid.
A 540 creates its displacement not only from the 4.25-inch-stroke increase but also from the monstrous 4.500-inch bore. This called for SRP forged pistons featuring a Total Seal 1⁄16-inch ring package with a 3⁄16-inch oil ring. Tim pinned the pistons to a set of Scat 4340 forged H-beam 6.135-inch rods to complete the rotating assembly.
This led us to Edelbrock's Victor Jr. Chapman CNC heads. These heads feature a stock-location exhaust port, yet sport a healthy 320cc intake-port volume and a fully CNC-machined 112cc chamber. The valve sizes come in at a manly 2.250/1.90 inches. The heads are shipped with valves but without springs, because Edelbrock realizes that a head like this will require custom springs to match the cam.
Next it was time for a camshaft. Tim is good buddies with Flowmaster's Kevin McClelland, who also did us the favor of helping spec the camshaft. The idea was that we didn't want to worry about detonation, but we also didn't want to short-change the heads with a wimpy cam. Tim was also smart enough to realize that the cam would have to be ground on a Gen VI-style cam blank in order to properly mate with the Gen VI block. We ended up with a custom grind from Crane.
This may sound expensive and time-threatening, but the truth is that Crane handles custom orders like this every day and got us the cam in a few days. You can find the specs in the accompanying spec chart, but needless to say, it's a thumper.
The key power point of any buildup has to be the cylinder heads. For our fat Rat, we chose a set of Edelbrock Victor Jr. CNC'd rectangle-port heads. With 320cc Chapman-ported intake ports, the Vicor Jr. CNC'd heads are based on the Performer 1.5 degrees before machining to decrease the chamber size and unshround the valves. | 
We also flow-tested these Edelbrock heads on Westech's Superflow 600 bench to give us an idea of how well these castings will move air. |
The fully CNC-machined chambers measure a mere 112 cc's but are crammed with monstrous 2.250/1.90-inch valves. To keep the weight down, they use smaller 11⁄32-inch versus 3⁄8-inch stems. The heads come complete with Serdi-machined ductile iron seats. | |
| Test Numbers |
| Test 1: The 540ci Rat complete with 2-inch primary tube headers with an open exhaust system |
| Test 2: The same as Test 1 except the addition of a complete 3-inch exhaust system and Flowmaster mufflers |
| TEST 1 | | TEST 2 |
| RPM | TQ | HP | TQ | HP |
| 2,600 | 503 | 249 | 488 | 241 |
| 2,800 | 522 | 278 | 508 | 271 |
| 3,000 | 538 | 307 | 535 | 306 |
| 3,200 | 595 | 362 | 581 | 354 |
| 3,400 | 627 | 406 | 618 | 400 |
| 3,600 | 618 | 424 | 609 | 417 |
| 3,800 | 602 | 436 | 609 | 440 |
| 4,000 | 600 | 457 | 617 | 466 |
| 4,200 | 616 | 493 | 622 | 493 |
| 4,400 | 631 | 529 | 623 | 526 |
| 4,600 | 643 | 563 | 625 | 553 |
| 4,800 | 638 | 583 | 635 | 570 |
| 5,000 | 644 | 613 | 632 | 598 |
| 5,200 | 645 | 639 | 630 | 623 |
| 5,400 | 643 | 661 | 630 | 647 |
| 5,600 | 637 | 679 | 623 | 664 |
| 5,800 | 630 | 696 | 615 | 679 |
| 6,000 | 619 | 707 | 609 | 696 |
| 6,200 | 608 | 718 | 602 | 711 |
| 6,400 | 584 | 711 | 580 | 706 |
| 6,600 | 573 | 720 | - | - |
| 6,800 | 547 | 709 | - | - |
| 7,000 | 523 | 697 | - | - |
| AVG. | 607 | 525 | 599 | 518 |
| Note: Averages were calculated only between 2,600 and 6,400 rpm. |
