Welcome to Godzilla, HOT ROD's latest Rat motor mutation. In its first go-round with a relatively docile hydraulic roller cam, the 540 has already churned out a pavement-melting 665 lb-ft of torque and 604 hp on Speed-O-Motive's conservative DTS engine dyno.
Time was, anyone with a 454 big-block was sitting pretty. But with aftermarket small-blocks upsizing to 450-plus cubes, big-block lovers have to raise the ante. Even a 502 is no longer sufficient; today's Chevrolet Rat motor of choice is rapidly becoming the 540. Everyone and his uncle is now building these megamotors, and they're beside themselves with just how much power and torque these babies are capable of making. HOT ROD decided to get on the bandwagon and build a stout 540 to evaluate a whole series of mild to wild power recipes. Even in its initial mild street form, this stout engine makes more than 650 lb-ft at 4,200 rpm with Brodix oval-port heads, an Edelbrock RPM Air-Gap intake, and a Lunati hydraulic roller cam with 230-ish (at 0.050) duration. And that's just Phase 1. Future plans for our multi-installment flog include progressively more radical Lunati solid roller cams and valvetrain components, bigger Holley Dominator carbs, a full range of Edelbrock intakes, ever-larger Brodix rectangular-port heads, and a variety of Hooker headers. Read on as we put the pedal to the metal.
The Short-Block
For this project, we chose to work with Speed-O-Motive, long known for its expertise in building stout stroker engines of all makes and flavors. With a complete, state-of-the art machine shop, assembly facilities, and a DTS engine dyno all under one roof, it was the perfect choice to handle an extensive and complicated engine-flog. Now all we needed were parts. That used to be a big deal requiring a bunch of hard-to-get special-order items, but these motors have become so routine that nowadays all the components are just about standard issue.
Dart's Big M Sportsman block is available in either the standard passenger (9.800-inch nominal) or truck (10.200-inch) deck heights, and-thanks to its beefy siamesed cylinder walls-with a variety of bore sizes from 4.250 inches through 4.600 inches.
What makes these giant Rat motors viable is the ready availability of thick, siamesed-wall, aftermarket cylinder blocks like Dart Machinery's Big M Sportsman series that are re-engineered in critical areas to easily accommodate stroker rotating assemblies. Starting with a 4.5-inch-bore, 9.8-inch (nominal) deck height, Big M, Speed-O-Motive dropped in a Scat 4340-steel, 4.25-inch-stroke crank that swings Scat I-beam rods hooked to JE/Sportsman Racing Products (SRP) pistons. Depending on the final deck height, cylinder head selection, and head-gasket thickness, the result is a pump-gas-friendly 9.9 to 10.9:1 compression ratio.
Federal-Mogul's Speed-Pro division threw in a set of its premium Competition Series main, rod, and cam bearings, while its Fel-Pro division supplied all the gaskets. The high-volume oil pump is also a Speed-Pro item, but the rest of the lubrication system (as well as the distributor driveshaft and the valve covers) are all Milodon. Critical fasteners not included by Dart with the block were supplied by ARP.
Baseline: Stock Oval-Port Heads, Lunati Hydraulic Cam
Starting off in truly mild form, we baselined our initial configuration using stock GM large oval-port heads. GM Casting No. 353049 was used on some '73 cars and trucks and reputedly ranks among the best-flowing factory oval-port heads. We scored a set of the relatively rare castings at Cylinder Head Exchange, a Southern California core bank.
Also installed for the baseline was a mild (for so many cubic inches) 233/241 degrees duration (at 0.050) Lunati Voodoo-series hydraulic flat-tappet cam, an Edelbrock Performer intake, a Holley 750 carb, and Hooker headers with 2-inch primaries.
One thing to watch out for on Rat motors when running a hydraulic cam is premature valve float. With their canted valves, long pushrods, heavy valvetrain, and high 1.7:1 rocker-arm ratio, big-block Chevys skate on the fine edge of upper-end distress. Spring pressures satisfactory in a typical small-block may not cut the mustard on a Rat motor. Yet running overly stiff springs with a hydraulic cam can cause the lifters to bleed down overnight, leading to noisy lifters and possibly impacting lifter longevity.
This engine uses an all-MSD ignition system, including a Pro-Billet Chevrolet V-8 distributor, a Blaster SS coil, red 8mm Super Conductor spark plug wires, and (for those steel-billet roller cams requiring it) a bronze distributor gear.
Another problem is the declining quality of hydraulic flat tappets combined with most modern street motor oils' lack of the zinc-based extreme-pressure lubricants needed to keep flat tappets happy. Some old-school builders don't like running hydraulic or hydraulic roller cams in any serious Rat motor, opting to move up to a serious mechanical flat tappet or roller grind. Nevertheless, most guys are running hydraulics on milder motors nowadays, so that's what we started off with.
To avoid durability problems on the dyno and speed up the test process, the stiffer springs specified for the Lunati hydraulic roller cam we intended to run next were installed on the flat tappet. However, the engine was first run in with EOS additive on the outer springs only. This procedure worked OK on the dyno, but (as noted above) running stiffer springs than those officially specified for a given cam may not be the ticket for a street driver. Instead, consider going with a slightly softer but modern high-tech ovate valvespring (such as Lunati PN 71817).
Speed-O-Motive uses a DTS dyno for testing. Its design enabled us to easily pull from 2,000 to 6,000 rpm for all tests in this series, which were run with 35 degrees total advance in a locked-out MSD distributor on 91-octane pump gas. Speed-O-Motive also used the conservative SAE J1349 net dyno correction factor; while about 5 percent lower than we're used to, it's more representative of real-world in-car operating conditions.
The baseline setup uses a 750-cfm carburetor, a Performer RPM intake with a 1-inch spacer, and a Lunati Voodoo hydraulic flat-tappet cam to make more than 575 lb-ft and 480 hp. It made more than 500 lb-ft from 2,200 to 5,000 rpm and more than 400 hp from 3,700 to 6,000 rpm.
Speed-O-Motive pressure-checked our GM 049 castings before treating them to a performance three-angle valve job. The castings' semi-open chambers are superior to early bathtub chambers, yet-unlike later peanut-port castings-they still have fullsize 1 3/4 x 2-inch intake runners.
Right from the get-go, we knew we had a winner on our hands: Generating 576.2 lb-ft and 480.5 hp, even with obsolete factory castings, this engine would make a great towing package in a heavy vehicle.
The street-friendly Lunati hydraulic roller cam's pressed-on iron distributor gear eliminates the need for a bronze distributor drive gear usually required with steel roller cams.
Lunati Hydraulic Roller Cam
What could we gain using a hydraulic roller cam with similar 0.050-inch tappet lift duration to the hydraulic cam, but having considerably more lift? Namely, 35 hp and 26 lb-ft of torque at the peaks and 21 hp and 25 lb-ft on average. Still, with the same Edelbrock Performer and 1-inch spacer, the engine now clearly preferred a larger 950-cfm carb, making 603 lb-ft and 515 hp in this configuration. Next we tried both the single-plane Victor Jr. and the RPM Air-Gap high-rise dual-plane, both with 1-inch spacers. The Victor Jr. raised output to 611.9 lb-ft and 542.4 hp but lost torque and power below 3,500 rpm. Still, the Victor Jr.'s average torque and power production of 551.1 lb-ft and 419.3 hp was worth about 7 lb-ft and 10 hp over the Performer's 543.9-lb-ft/409.1hp average. At the peaks, the Air-Gap made 2.7 lb-ft more torque, but 6.6 hp less, than the Victor Jr. The Victor Jr. was a tad better than the Air-Gap from 4,100 through 5,900. But looking at overall area under the curve, the RPM did edge out the Victor, generating 4.4 lb-ft and 0.6 hp more throughout the rpm range. The Performer only slightly outperformed the Air-Gap at 2,000, as well as from 2,600 to 3,100 rpm. Advantage: Air-Gap (barely).
Brodix Oval-Port Heads
With early-'70s oval-port heads performing so well, we couldn't wait to see what the benefits of 30 years of cylinder head technological evolution could bring to the table. It was time to bolt on a set of Brodix's Race-Rite oval-port heads. With the RPM Air-Gap intake, they raised peak output to 665.3 lb-ft and 604.4 hp, a gain of 50.7 lb-ft and 68.5 hp. On average, the engine was now making 603.3 lb-ft and 460.4 hp, an increase of 47.8 and 40.5 numbers, respectively, over the iron heads. And would you believe more than 525 lb-ft at just 2,100 rpm?
Summing up, our progress so far verifies the clich that there's no substitute for cubic inches. It's also apparent that a big engine like this wants more plenum volume than provided by intakes originally designed for 396-454 mills. In every test to date, the engine has run better with a 1-inch open carb spacer. So far the engine has also run best with Hooker 2-inch primary-tube headers (PN 2217-1HKR, listed as fitting '70-'72 Camaros), preferring them to 1 3/4-, 1 7/8-, and 2 1/8-inch sets. We expect larger headers to come into their own at some point as we move up the food chain.
Next we planned to try the larger 2 1/8-inch primary-tube headers and then the Victor Jr. again, but power mysteriously started falling off. It turned out there was water in the oil. Time to regroup before the next go-round. There could be another 30 number in the present combo alone, and we haven't even gotten to mechanical roller cams or rectangular-port-head combos. Never fear, Godzilla will return, headed for 800 hp.
Blueprint Data
Except as noted, all dimensions are in linear inches. For cam specs, see the separate Camshaft table.
Engine type: Chevrolet Mark IV big V-8
Engine builder: Speed-O-Motive
Measures And Volumes
Advertised displacement: 540 ci
Actual displacement: 540.7 ci
Bore x stroke: 4.50 x 4.25
Compression ratio (GM 049 heads): 9.90:1
Compression ratio (Brodix heads): 10.93:1
Main bearing clearance: 0.0025
Crankshaft thrust clearance: 0.0065
Rod bearing clearance: 0.0022
Rod side clearance: 0.018
Rod center to center: 6.385
Rod/stroke ratio: 1.50:1
Crank centerline to deck: 9.7805
Piston-to-bore clearance: 0.006
Piston compression distance: 1.270
Piston deck height: 0.005 below
Piston dome volume: 10 cc
Head gasket compressed volume: 11.2 cc
Chamber volume (GM 049 heads): 122 cc
Chamber volume (Brodix heads): 109 cc
Piston ring gap, 1st groove: 0.020
Piston ring gap, 2nd groove: 0.022
Piston ring gap, oil groove support rail: 0.015 minimum
Camshaft thrust clearance: 0 (Torrington bearing installed behind cam sprocket)
Piston-to-valve clearance: 0.100-plus
Valvespring seat pressure (Lunati PN 73121): 142 lbs @ 1.940
Valvespring open pressure: 402 lbs @ 1.250
Valvespring coil-bind: 1.130
Critical Tightening Values
Values not listed are the same as production.
With ARP assembly lube:
ARP capscrews in Scat rods: 70 lb-ft
ARP damper bolt: 80 lb-ft
ARP head bolts: 70 lb-ft
Dart main bolts: 105 lb-ft With SAE 30 engine oil
ARP oil pump stud: 65 lb-ft
Rocker studs: 60 lb-ft
APPLICATION-SPECIFIC PARTS: GM OVAL-PORT HEADS Fel-Pro Header gasket set 1.88x1.88 square ports 1410 1 Fel-Pro Intake gasket set Embossed, steel-core laminate, oval-port, 1.82 x 2.05 x 0.060, no heat 1210 1 GM Cylinder head Iron, 2.06/1.72 valves (used, supplied by Cylinder Head Exchange) Cast 353049 2 Lunati Valve seal For 3/8-stem valves and 0.530-od guides 78385 1 set Manley Exhaust valve Pro Flow, 1.72 head, 3/8 stem 11517-8 1 set Manley Intake Valve Race Flow, 2.065 head, 3/8 stem 11514-8 1 set
APPLICATION-SPECIFIC PARTS: BRODIX OVAL-PORT HEADS Brodix Cylinder head Race-Rite, oval-port, 270cc intake, 115cc chamber 2060004 2 Fel-Pro Header gasket set 1.94 round ports 1411 1 Fel-Pro Intake gasket set Composite w/Printoseal, oval-port, 1.82 x 2.05 x 0.060, w/heat 1212 1
APPLICATION-SPECIFIC PARTS: LUNATI HYDRAULIC FLAT-TAPPET CAM Edelbrock Intake manifold Performer 2-O, no EGR 2161 1 Holley Carburetor 4150 HP, 750-cfm, mechanical secondaries, gasoline 0-80528-1 1 Lunati Camshaft Hydraulic flat-tappet, Voodoo-series, ’65-’96 {{{Chevrolet}}} big V-8 60204 1 Lunati Lifter Hydraulic flat-tappet Micro-Trol, 0.842-od, ’55-’96 Chevrolet V-8 71817 1 set Lunati Lubricant Assembly lubricant, 10-gram tube 99010 1 Lunati Pushrods Bracket Master II series, 3/8-inch od 80144 1 set
APPLICATION-SPECIFIC PARTS: LUNATI HYDRAULIC ROLLER CAM Edelbrock Intake manifold RPM Air-Gap 2-O 7561 1 Holley Carburetor 4150 HP Ultra, 950-cfm, mechanical secondaries, gasoline 0-80676 1 Lunati Camshaft Hydraulic roller, Voodoo Retrofit, '65-'96 Chevrolet big V-8 60212 1 Lunati Lifter Hydraulic roller retrofit, 0.842-od, big-block Chevy 72431LUN 1 set Lunati Pushrods Bracket Master II series, 3/8-inch od 80160 1
