One horsepower per cubic inch. Back in the 1950s, that was the target. Those newfangled overhead pushrod engines that revolutionized how passenger car engines were created only served to heat up the power-per-cube race. When the new Chevrolet big-block engine was introduced in 1965, it lit the fuse for bigger power and renewed the focus on the power-per-cubic-inch wars.
Today, making big horsepower is still the ultimate goal; the one-horsepower-per-one-cube of displacement target is but a mere dot in the rearview mirror of old aspirations. But complications to the engine-building process have surfaced recently. For many builders, the engines they create must make excellent power and still be compatible with today's low-quality pump gas (91-octane). In addition, they must be able to generate adequate vacuum and excellent daily-use drivability. Just as today's performance cars are compatible with formerly antiperformance style options, such as A/C and power steering, most current engines don't need 114-octane race fuel to avoid detonation while hitting the big power figures. The fact is that no engine builder wants to tell his clients that their freshly built engines require such coddling. Why should they when proper component selection will help them avoid such behavior?
A Little Big-Block History
The big-block Chevy engines of today come in a variety of shapes and styles. While the Mark IV, as introduced in 1965, went through some initial changes, it was not until 1991 that the Mark V engine came to be. Today, the Mark V and its brother, the Mark VI, which debuted in 1996, are great platforms for engine builders, offering great versatility and availability over the seemingly harder-to-find Mark IV engines. Featuring a strong internal webbing, integrated oil pan gasket, and one-piece round rear main seal to avoid oil pan drips, the Mark V was perfect for our needs. Paired with the hot performing RHS Pro Action aluminum cylinder heads, we were excited about the potential for what we believed would be an excellent combination for our street-based project.
The selection of the Mark V platform was the work of engine builder Jim Shewbert, who was hired to create the potent big-cube engine for Ted Yurek's '70 Chevelle. The car, while outfitted with a number of advanced suspension upgrades, was a true dual-purpose machine; both track and cruise time were planned for the beautiful blue-and-SS-stripe-clad heavy Chevy. While the engine was assembled in Southern California, the Chevelle was expected to run on pump gas once dropped between the inner fenderwells of the Coeur d'Alene, Idaho-based Chevy. Owing to the huge amount of distance between L.A. and Idaho, it was imperative that the engine be powerful and reliable.
The Build Up
The building of the Mark V engine was not unique, for the most part-a fairly straightforward assembly using Scat 6.385-inch 4340 H-beam connecting rods, Akerly & Childs extreme rings, and 4.5-inch bore Keith Black Hypereutectic aluminum pistons. The pistons feature a 1/16-inch top moly piston ring and similar-sized cast-iron second ring. The pistons have a flat-top, making for excellent flame propagation, and when used with a 9.800-inch deck block, generate 10.25:1 compression. An Eagle forged steel crankshaft was used with a 4.250-inch stroke, making for 532 cid total displacement (540 cid for you government workers).
The cylinder heads were state-of-the-art RHS Pro Action 360cc aluminum heads. The heads started plenty clean from the factory with excellent airflow and internal water-jacketing for consistent temperature control, and were ported to the next level by Toby Allison. Because of the high horsepower that Jim wished to generate, he felt a Toby porting job would help to eek out the engine's top horsepower numbers.
In the valvetrain department, Shewbert clearly wanted a big camshaft to take advantage of the high-flow cylinder heads and horsepower and torque-handling attributes of the super-strong Mark V short-block (see CamQuest 6 sidebar). To that end, he selected a camshaft that featured large lift and duration numbers requiring a mechanical roller valvetrain, which included COMP's new Endure-X mechanical roller lifters. In combination with the big camshaft, the COMP Cams tech line folks (1-800-999-0853) helped him select appropriate valvesprings, retainers, lifters, spring cups, lash caps, and even the Pro Magnum roller rockers that were to be used with this combination.
Topping the engine was a Dart intake ported by Allison and a Demon reworked 850-cfm carburetor. Big-tube exhaust headers and low-restriction Flowmaster tailpipes were slated for use, along with a five-speed manual transmission and high-performance clutch.
On To the Dyno
The folks at Westech Performance were hired to test the limits of our engine. Engine builder Jim Shewbert installed the camshaft with 4 degrees of advance, along with the Dart intake, Demon 850-cfm carburetor, and MSD ignition. Using 91-octane fuel, Westech's Steve Brule fired the engine and spent a considerable amount of time warming the engine, then resetting the valves and warming the engine again with some short low-rpm pulls. After an hour of break-in time, they proceeded to make some test runs to see if we had done the proper homework.
The Mark V required a few jetting changes, and we adjusted the timing slightly during our four test pulls. In the end, our 540-cid Mark V big-block turned out an impressive 649.2 hp at 6,200 rpm and 613 lb-ft of torque at 4,900 rpm. The most impressive part of the engine's power and torque output was the consistent power delivery. From 5,700 through 6,700 rpm, the engine maintained a minimum of 640 hp-less than a 10hp variance for over 1,000 rpm. In addition, the torque level reached 590 lb-ft of torque starting at 4,100 rpm, and stayed above that level through 5,700 rpm. This is usable street horsepower that would be more than up to any race challenge encountered by the classic Chevelle.
In the end, we were quite happy with the performance level of the 540-cid engine. Making 650 hp on pump gas is no small accomplishment, and one that proved-street or race-big-block Chevrolets have deservedly earned their reputation for relatable power, even the often-overlooked Mark V.
Why the Mark V?
The Mark V engine was an intermediate step in the evolution of the big-block Chevy, fixing problems encountered with the Mark IV engine, most notably, leaky mains, and oil pan gaskets. The Mark V engine does not use a bolt-on oil filter bypass and required installation of check valves into the engine to make it work with such systems (If you forget, the engine will appear to make proper oil pressure, only it will be missing the engine and only circulating through the oil filter system-for the time your engine will continue to run.)
Mark V Quick Spotter Guide:
* One-piece oil pan gasket
* 10-bolt timing cover with gasket (Mark VI uses six-bolt cover with an O-ring)
* Includes oil cooler option in the galleys for a remote oil cooler
540-cid Engine BuildUp - Specs and Parts List:
Fuel: Pump gas
Block: GM Mark V block with 4.5 bore and 9.800 deck
Crankshaft: Eagle forged crankshaft - 4.250-inch stroke
Connecting rods: Scat - 6.385-inch length
Pistons: KB Hypereutectic - 10.25:1 compression, flat top
Heads: RHS Pro Action 360cc aluminum - Mark IV style, 360cc intake runners
Akerly & Childs rings
1/16 top moly ring
1/16 top second cast-iron
3/16inch stainless expander
COMP Cams 306AR-10 mechanical roller camshaft
Lift: 0.680/0.680-inch intake/exhaust
Duration: 306-degrees intake/ 319-degrees exhaust
Lobe centers: 110-degrees
COMP Cams Valvetrain:
COMP timing chain with degreeable off-set key - degreed at 4 degrees advanced
COMP Cams rocker studs, guideplates, and lash caps, 10-degree machined keepers
COMP Cams Pro Magnum Roller rockers
COMP Cams titanium retainers - COMP Cams PN#731-16
COMP Cams 10-degree machined keepers
COMP Valvesprings COMP Cams PN#944-16
COMP Cams Endure-X mechanical roller lifters - PN#866-16
COMP Cams heavy-duty pushrods - PN#7131-8 intake, PN#7141-8 exhaust
Additional parts list:
RHS Pro Action cylinder heads 360cc - intake runners - all Mark IV style, 116cc chambers, ported by Toby Allison
Manley valves - 2.250-inch intake stainless steel valve, severe duty (0.250-inch long valves); exhaust valve - 1.880-inch stainless by 11/32-inch exhaust valves (0.100-inch long valve stems)
Heads ported and polished by Toby Allison, match ported the intake, did the bowl, blended the intake bowl to the seats, also ported the entire exhaust port and shaped the guidesCompetition Specialties - rear main seal adaptor (converts Mark V to Mark IV crankshaft)
Fel-Pro head gasket (allows a Mark IV cylinder head to adapt to Mark V block); Teflon-coated gasket includes 0.041-inch stainless steel o-ring embedded in the gasket
Dart single plane intake manifold - port matched by Toby Allison
NGK spark plugs - 5/8-inch head - requires small plug
Hooker headers 2/125-inch primary tube - length to be determined
ARP head bolts
Competition Specialties - Mark V front cover
ATI front dampener
MSD plug wire 8.8mm and billet distributor 6AL ignition box
Demon 850-cfm jets - 88 primary and 94 secondary jets, original power valve used Akerly & Childs bearings - rod and crank, special chamfered bearing because of big radium in the crankshaft
Milodon - oil pan, (30951), pickup (18310) and pump
Adams Machine, Lancaster, CA - all engine machining and balancing (owner Mark Adams)
CamQuest 6 Asks - Can We Do Better?Our 540-cid Chevy big-block Mark V engine was a standout performer. It did everything we asked it to do. But did we optimize the performance? Did we get everything we could from the combination? Knowing that we were up for anything the learning curve might throw our way, we decided to test our camshaft knowledge against the newest programming available from COMP Cams-the CamQuest 6 Cam Selection Software.
As touted in the ad materials, the CamQuest 6 is a PC-based camshaft selection program that allows the user to find the right camshaft by answering a few application-specific question from the program's dropdown menus. Sounds simple enough, so we took the program for a testdrive.
First, we input the parameters required by the program, such as engine type, compression, carburetion, cylinder head type, etc. The program offers up an amazing number of possibilities. For our Mark V big-block engine, the program was easy to understand and required little intuitive thinking on our part to fill in the grids accordingly. Our only "gray" area occurred with regard to the flow figures of our ported RHS Pro Action 360cc cylinder heads. Having the exact measurements here would give us more accurate information in terms of the total calculation, but we were comfortable in running the simulation with the data we had in hand. The CamQuest 6 calculated the data and kicked out a number of good, better, and best camshaft choices. Interestingly enough, our model RA306-10, (0680-inch lift and 306/319-degrees duration, 110-degree lobe centers), the one that generated the 649 hp on the Westech dyno, was not the top CamQuest 6 camshaft selection. So what did the CamQuest 6 recommend? Camshaft (grind number RA296ER-8) with less duration and more lift on 108-degree lobe centers.
To determine how much better the smaller duration camshaft would be, we did two virtual installs using CamQuest 6. As it was the top pick, the program used grind RA296ER-8 and displayed the results, along with all of the recommended ancillary COMP Cams parts like lifters, retainers, springs, locks, and other parts that should be used to achieve optimum performance. Grind RA296ER-8 (the top CamQuest 6 camshaft selection) features 108-degree lobe centers, with only 296-degree intake duration (304-degree exhaust). Lift was increased to 0.714 inches. Our new estimated horsepower-nearly 689 hp. Torque-655. So why the 30hp difference? We decided to investigate.
According to Westech's Steve Brule, the camshaft chosen for the dyno test featured a large amount of duration-too much for the application due to the engine's limited compression. With a pump gas-compatible engine such as this, the increased duration actually allows cylinder pressure to be reduced, slightly lowering peak power.
"This type of engine (540-cid Mark V) can handle a lot of lift, but too much duration is a detriment," says Brule. "The excessive duration, however slight, actually bleeds off intake charge. It negatively affects the volumetric efficiency and increases the exhaust gas temperatures. But the higher lift is not a problem; in fact, it gets the valve moving slightly quicker, helping fill the cylinder more fully making more power. As long as you don't have valve to piston problems, lift is only a positive thing."
The camshaft selection process has long been a black art by both pro and novice engine builders, leaving lots of room for interpretation. How do you know you have purchased exactly the right camshaft for your engine? In the past there has been only one way-to trust in the expertise of those who are believed to be experts. Today, real experts are easy to find, such as those answering the phone at the COMP Cams Cam Help hotline. Unfortunately, many builders don't make the call and rely on their friends and pseudo experts to advise them. With engine building requiring not only cubic inches, but also cubic dollars to build big power, it's safe to believe there are now two very reliable sources for camshaft advice-Cam Help and CamQuest 6.