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.
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.
To begin our 540ci buildup, we started with a used Gen VI Bow Tie block that Tim discovere
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.
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.
A 540 creates its displacement not only from the 4.25-inch-stroke increase but also from t
We also lined up a Victor Jr. 4500-style intake along with a Demon 1,090-cfm Race Demon carburetor-a big-inch motor like this wouldn't be happy with an 850- or 900-cfm square-bore carburetor. We also acknowledge that it will take some effort to ensure that this big Dominator gets a little attention when it comes to part-throttle tuning for the street.
Along with the induction system, we also added a complete MSD billet-aluminum distributor, wires, and an MSD-6A box to boldly light the fire. On the exhaust side, we chose a set of Dynatech 2 1/4-inch headers to vent the exhaust along with a Flowmaster 3-inch exhaust system and a pair of matching mufflers. After Ed Taylor bolted all these parts in place on Ken Duttweiler's dyno, and after gently warming up and breaking in Max the Rat, we were ready to make some noise.
The key power point of any buildup has to be the cylinder heads. For our fat Rat, we chose
Big-inch Rats have a sound all their own. This motor doesn't thump at idle like some you've heard mainly because with a big cam and only 9.5:1 compression, the cylinder pressure's not overpowering. But the cam matched nicely with the rest of the package, and this allowed Ed to pull this rotund rodent all the way down to 2,500 rpm. If you've ever wondered why many dyno-tests start at 3,500 or 4,000, it's often because the cam is so rowdy that the engine literally won't hold a wide-open-throttle (WOT) load at that low of an engine speed. Tim's super-sized Rat, on the other hand, was more than happy at 2,500, so our test data starts at 2,600.
The first minor difficulty our gallant testers ran into was that Max wanted a bunch more fuel. Even using the largest jets we had in the 1,090-cfm Demon, our Innovate air/fuel-ratio meter reported a lean 13.5:1. This necessitated increasing the power-valve feed restrictors in the primary as well as increasing the restrictor size in the Demon's intermediate fuel-delivery circuit. This was worth sufficient fuel to bring the air/fuel ratio closer to 12.9 to 13.0:1, where we felt the engine would be safe and also make the best power.
And power is what we had. We ran Max both with open headers and with 3-inch Flowmasters, but we'll deal with the muffled exhaust numbers for the sake of our street intentions. Our big-stick big-block started out at 2,600 rpm with over 500 lb-ft of torque and then pushed peak torque up to 632 lb-ft at 4,900 rpm, with peak horsepower coming in with 711 hp at a reasonable 6,200 rpm. That's a 1,300-rpm powerband, which is a little narrower than we would have liked-but hey, we're talking about 711 big ones here.
The fully CNC-machined chambers measure a mere 112 cc's but are crammed with monstrous 2.2
For fun, we plugged that power into the Quarter Pro simulation for a 3,500-pound body style with a TH400 automatic and a conservative 3,500-rpm stall, 5 percent slippage, a 3.91 gear pushing sticky 18-inch tall slicks that are 10.5 inches wide on a decent 72-degree-F day at sea level with a 29.00 barometer. The simulation spit out a 10.55/132-mph number using a 1.60-second sixty-foot time while shifting at 6,500 rpm. That's a great effort from a heavy car, but certainly achievable-and that's without any power adder. Imagine pumping a 150 or 200hp shot on top of that! Yahoo!
So what have we learned here? Max the Rat isn't cheap and it isn't conservative. But it does make excellent power, and since it only spins to 6,500 rpm, it should be dead reliable. With 500 lb-ft of torque on demand at 2,600, traction will be difficult to achieve. But that's the kind of problem that every car crafter dreams of. So there you have it-a Rat for all seasons, because it's never too hot or too cold to go fast.
Most performance Rat heads also raise the exhaust ports in an effort to gain flow. The exh
We also flow-tested these Edelbrock heads on Westech's Superflow 600 bench to give us an i
Since this is a big-inch motor, the long stroke can accommodate a very healthy cam. This l
The Gen VI block incorporates a taller lifter body, so we used Crane's taller solid-lifter
Ed Taylor bolted our rotund Rodent on the dyno at Duttweiler Performance using an Edelbroc
Tim and Ed discovered that even with the biggest jets in the Demon carb, the 540ci Rat wan
The solution for feeding this thirsty Rat was increasing the size of the power-valve chann
To reinforce that this is no max-compression, race-gas-only motor, Ed performed a quickie
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
|RPM ||TEST 1 ||TEST 2 |
|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.
Edelbrock Victor Jr.
320cc Intake Port
E/I @ 0.400: 87%
|Lift ||Intake ||Exhaust w/ |
|0.050 || 34 || 37 |
|0.100 || 71 || 65 |
|0.200 ||142 ||130 |
|0.300 ||200 ||173 |
|0.400 ||246 ||214 |
|0.500 ||270 ||249 |
|0.600 ||282 ||273 |
|0.700 ||289 ||283 |
|0.800 ||296 ||293 |
Note: This head was flowed on a 4.250-inch bore fixture. Our 540 sports a much larger 4.50-inch bore that unshrouds the intake valve considerably. This is why our flow numbers are smaller than Edelbrock's published flow numbers.
The cam we used was a Crane custom mechanical roller with the following specs, installed 3 degrees advanced at a 109-degree intake centerline.
|Camshaft ||Adv. Dur. ||Dur. @ 0.050 ||Valve Lift ||Lobe |
|Crane custom, Int. ||302 ||270 ||0.714 ||112 |
|Mech. roller, Exh. ||312 ||280 ||0.714 |
|Parts List |
|Component ||Source ||PN ||Price |
|GM Gen VI 502 block ||used ||(10237292) ||$1,200 |
|Crank ||Scat ||4-454-4250-6385-L ||$913 |
|Connecting rods, H-beam ||Scat ||2-454-6385-2200 ||$536 |
|Balancer ||Scat ||D-80005 ||$109 |
|Pistons ||SRP ||139521 ||call |
|Piston rings ||Total Seal ||MT9190 255 ||$244 |
|Main bearings ||Federal-Mogul ||141M ||$50 |
|Rod bearings ||Federal-Mogul ||8-7200CH ||$55 |
|Cam bearings ||Federal-Mogul ||1404M ||n/a |
|Head bolts ||ARP ||135-3610 ||$99 |
|Main studs ||ARP ||235-5606 ||$100 |
|Engine accessory kit ||ARP ||535-9601 ||$94 |
|Rocker studs ||ARP ||135-7202 ||$62 |
|Oil pump drive ||ARP ||135-7901 ||$14 |
|Oil pan stud kit ||ARP ||435-1901 ||$43 |
|Harmonic balance bolt ||ARP ||235-2501 ||$22 |
|Camshaft, mechanical roller ||Crane ||custom for GEN VI ||call |
|Roller lifters ||Crane ||16510-16 ||$363 |
|Pushrods, intake (custom) ||Crane ||95632-8 ||$72 |
|Pushrods, exhaust (custom) ||Crane ||95652-8 ||$72 |
|Roller rockers, 1.7:1 ||Crane ||13750-16 ||$286 |
|Valvesprings ||Crane ||99877-16 ||n/a |
|Retainers, titanium ||Crane ||99679-16 ||$250 |
|Timing set, hydraulic-roller style ||GMPP ||12371053 ||$40 |
|Heads, Victor Jr. CNC (2) ||Edelbrock ||60419 ||$2,480 |
|Intake manifold, Victor Jr. 454R ||Edelbrock ||2907 ||$246 |
|Valve covers ||Edelbrock ||4680 ||$48 |
|Guideplates ||Edelbrock ||9666 ||$58 |
|Water pump ||Edelbrock ||8850 ||$163 |
|Carburetor, 1,090 Race Demon ||Demon ||8728030 ||$923 |
|Distributor, Street Pro Billet ||MSD ||8361 ||$190 |
|Ignition box, 6A ||MSD ||6200 ||$150 |
|Plug wires, universal ||MSD ||3118 ||$50 |
|Oil pan ||Milodon ||31186 ||$446 |
|Oil pump ||Milodon ||18760 ||$67 |
|Pickup ||Milodon ||18301 ||$35 |
|Head gasket ||Fel-Pro ||1037 ||$37 |
|Intake gasket ||Fel-Pro ||1275 ||$14 |
|Headers, 2.25-inch ||DynaTech ||500-906700 ||n/a |
Automotive Racing Products (ARP)
531 Spectrum Circle
P.O. Box 1966
Autotronic Controls Corp. (MSD)
B&M Performance Products
GM Performance Parts
530 Fentress Blvd.
Jim Grubbs Motorsports
28130 Crocker Ave.
Demon Carburetion/Barry Grant
2250 Agate Ct.
2700 California St.
Sportsman Racing Pistons (SRP)