For a gearhead it’s always interesting to look at the upper echelons of motorsports to see what’s ticking under the hood. F1, Sprint Cup, and endurance cars are all fairly engaging from an engine perspective, but nothing tops drag racing for its sheer power, variety and ingenuity. In a single event you have vehicles competing from 8,000 hp Top Fuelers to 300 hp Stock Eliminator cars.
But the most intense class for any serious engine builder is NHRA Pro Stock. With these naturally aspirated 500 cid engines spinning 10,500 rpm and producing upwards of 1,450 hp and 800 ft.lbs. of torque, you have to ask yourself – how’s that possible?
Getting that much power out of a two-valve, normally aspirated 500 cid V8, has taken years of development – five horsepower at a time. Who does that? The answer is a very small circle of engine builders and parts suppliers who devote their lives to building the quickest and fastest normally aspirated door-slammer engines. It’s a tight-knit community of 100 people or less dedicated to extracting every last horsepower out of a production OE-based 500 cid engine.
This level of performance and dedication doesn’t come cheap. In fact, you can “rent” one of these engines (and many teams do), for $50,000 per race or $1.2M per season. The way the rental program works is that you show up for a race and the engine builder delivers the engine to your pit. The engine builder handles all required maintenance at the racetrack (valve spring replacement, tuning, etc.). After the race, the engine builder picks up the engine and takes it back to his shop. While $1.2M may sound like an astronomical amount of money (the parts and labor cost to build one cost about $100,000), the technology required to field a competitive motor is priceless.
We spoke to some of the most notable racers, engine builders and parts suppliers to get an idea of what goes into a Pro Stock engine. Kurt Johnson out the famous Warren Johnson Racing stable, Roy Johnson, dad and engine builder for Allen Johnson Racing, Joe Squires from Bryant Racing, Nick Ferri of the newly formed Jeg’s engine shop (JNR Racing), Scooter Brothers from Comp Cams and Dan Jesel of Jesel Valvetrain Innovation. This all-star lineup gave us a good idea of what goes into a current NHRA Pro Stock engine.
The current HRA Pro Stock record holders are Rodger Brogdon with a 6.495 ET and Erica Enders who holds the MPH end of the record at 213.57mph.
Many of the front-runners produce enough power to win. The Pro Stock winner on any given day is the racer who can apply that power to the ground in the most effective manner. Tuning the clutch and chassis to make a smooth, hooked-up run from start to finish is the challenge. Taking advantage of the 8,500-10,500 rpm powerband is key to a successful run.
So let’s get down to the nuts and bolts. All three marques – GM, Dodge and Ford – start with a factory-sourced Pro Stock engine block. Of the current engines, GM has been around the longest with the DRCE2 and DRCE3 both still in use. The Dodge folks have the Hemi 99 and the Hemi 06, and Ford’s latest engine is called the 2009 Pro Stock. Most of these blocks are made out of compacted graphite iron (CGI) that resist bore distortion and crankshaft deflection. It’s safe to say that all three 4.900? bore-spacing blocks are very similar, having been homogenized by the rules, and virtually everyone we spoke with claimed that no single design had a clear advantage over the other. Several people thought that the Hemi was a little stronger at high rpm, but right now nobody is complaining. That was somewhat of a surprise that a race sanctioning body had finally achieved parity between the dueling manufacturers.
The most important thing to mention about these Pro Stock blocks is the cam placement. The higher, the better – in fact one of the significant changes between the DRCE2 and DRCE3 blocks is that the cam has been moved up in the DRCE3 more than a full inch. With a typical stroke of 3.500?-3.600? and the fact that virtually everyone uses steel rods, why is a high cam position so important? It all comes down to valvetrain rigidity.
After spending countless hours on Spintrons and back and forth to the dyno, valvetrain manufacturers and engine builders discovered that the stiffer a camshaft was, the more power the engine made. Not so difficult to understand when you consider the 1,000-pound open valve spring pressures and their effect on camshaft torsional rigidity and cam timing. So not only is the cam positioned higher, the diameters of these steel billet cams have grown to 60-70 mm and even 80 mm in some cases. Another aspect of higher cam placement is that the pushrod is shortened making it stiffer and the valvetrain more rigid.
We spoke to Scooter Brothers at Comp Cams who gave us a very interesting look at the evolution of Pro Stock camshafts and valvetrain designs (see sidebar in Figure 2). According to Brothers, Comp was one of the companies that helped develop the Spintron that has led to huge improvements in valvetrain performance. Early on, the lightest parts and the highest spring pressures were thought to be the best – now the stiffest and correctly designed parts are recognized as better.
As the stiffness of the system evolved, the valve springs changed. Not only did the quality of springs greatly increase, but the understanding of springs as a part of the system began to emerge. When the cam, pushrod and rocker arm were bending and flexing under the extreme 1,300-lb.-plus spring pressures, the system acted like a “pole vault.” When the valve opened the system flexed, and when the lifter went over the nose of the cam, it slammed back to normal, releasing all of that energy right back into the spring. The old solution was to add spring, but that turned out to be exactly the wrong direction. Today’s Pro Stock (in fact, most race) engines use the stiffest components available up to the valve, and the valve, retainer, locks, and springs are the lightest possible. These same theories and designs are used today in almost every racing application and are now creeping into production engines.
Dan Jesel founder of Jesel Valvetrain Innovation has been a driving force behind many of the gains in Pro Stock valvetrain technology. He has advocated large diameter billet cams for many years for both increased rigidity and the fact that you can run less rocker ratio due to the availability of more “lobe lift.” He recommends 1.85-1.90 rocker ratios that make the valvetrain easier to control. Jesel also believes that you can grind a smoother cam profile on a large diameter cam that is also much easier on the valvetrain at high rpm.
Many teams run Jesel’s keyway style roller lifters that are extremely light because they eliminate the weight of the traditional tie-bar or extended body necessary in a dog-bone style lifter. They are aligned to the cam lobe with a slotted bronze bushing that a tab on the lifter keeps it from rotating. Jesel recommends his 1.095? lifters for Pro Stock because they increase the axle and roller bearing length, spreading out the incredible load they are under. Also, the bigger lifter body allows the use of a larger .940? roller.
We were surprised to hear that the majority of Jesel’s Pro Stock customers are still using aluminum body rocker arms. Jesel offers steel Pro Stock rockers, but there seems to be no advantage in this application. Dan Jesel pointed out that one of the biggest gains in valvetrain performance came from “tying the rocker stand down to the head.” When he invented his “box-style” stands, racers saw improvement in all aspects of the valvetrain, including spring life.
Pro Stock pushrods look more like telephone poles than pushrods. Not only does the raised cam make them shorter, but the 1/2?-9/16? diameter .200?-wall thickness makes them virtually impossible to flex ensuring total advertised cam timing at the valve. And in case you’re wondering, Comp Cams puts the timing in the neighborhood of 276-300 degrees duration at .050? lift, 1.100?-1.300? of lift and lobe centers around 120 degrees.
Joe Squires from Bryant Racing took us through the crankshaft specs for a typical 500 cid Pro Stock crank. They start out with a huge block of Timken 4330M double-melt steel and machine it into a work of art. Typical strokes are 3.575?-3.600?, and the main bearing journals are 2.500? in diameter (accepts readily available 409 Chevy bearings), and 1.888? rod journals. Every trick is used (rifle drilling, scalloped flywheel flange, etc.) to reduce weight to around 51 pounds, compared to a stock BBC crank weight of 70 pounds.
Each engine builder has a different preference for counterweight shape, (knife edging or an aero contour), not a problem as every crank is a custom order. All operations are done in house at Bryant including up to 4-weeks of heat-treating, cryo and nitride hardening processes and REM super finishing. Typical lead-time is 12 weeks to build a crank from start to finish.
Nick Ferri is a noted Pro Stock engine builder who has built engines for various racers including the dominant Mike Edwards. Now he is starting a Pro Stock engine program at Jegs Performance with Roy Simmons. They will supply Jeg Coughlin Jr. engines along with leasing engines to other teams. We asked Ferri about a basic short block assembly. He said that most engine builders use a short stroke 3.500? x 4.750? or longer stroke 3.600? x 4.700? combination. An interesting fact is that the rod/stroke ratio is in 1.66 – 1.75 range, and Ferri prefers the 1.66 ratio or even lower ratio if he could physically do it. For many years the ideal rod/stroke ratio was thought to be a 1.9 allowing the piston to “dwell” at TDC for a longer period. Not the case in NHRA Pro Stock.
Another interesting point is that a few years ago NHRA mandated minimum weights for valves, pistons and other reciprocating parts, to keep the ultra-exotic F1 materials out of Pro Stock. Ferri said that he doesn’t come close to minimum piston weight, and has gone for rigidity and stability over light weight. An informal survey between Kurt Johnson, Roy Johnson and Ferri “ball-parked” a typical compression ratio at 14.5:1 – 15.5:1.
These same gentlemen weighed in on where some of the biggest gains have come from in Pro Stock over the past several years and Ferri pointed to raised cam placement and improvements in piston rings by companies like Total Seal. Kurt voted for overall improvements in valvetrain components, and Roy said that improvements in cylinder heads and simply the improvement in the quality of the materials they get to work on has pushed their performance forward.
The final and probably most important pieces of the puzzle are the cylinder heads and manifold. This is where the power is made. The secrecy surrounding both is amazing – for years racers like Warren Johnson would cover their manifold runners with sheet metal to exclude prying eyes and cameras. We couldn’t get racers, engine builders and especially cylinder head guys to talk about the subject, even in the most general terms. However, the center of attention is Carl Foltz’s CFE Racing Products. Both record holders Brogdon and Enders run CFE as does recent winner Allen Johnson and the ever-dominant Mike Edwards. Several teams have their own cylinder head program, but it is a big undertaking for some of the smaller teams.
What we have gleaned about Pro Stock cylinder heads is that the chambers are extremely small in the 50-60cc range. Valve sizes are as big as possible with up to 2.5? diameter intakes and 1.80? exhausts. Some engine builders will sacrifice exhaust valve diameter for larger intake valves. The intake manifolds are CNC-whittled out of billet, fabbed out of welded sheetmetal or a combination of both. A pair 2.3?-throttle bore Holley Dominator carbs typically prepped by tuners like Braswell feed these monsters high-octane race gas and huge amounts of air.
There are many areas that we did not have room to touch on such as oil pans, dry sumps, ignition systems, headers and hood scoops. But hopefully we have provided some insight into these incredible race engines. Much of what goes on in Pro Stock can be applied to virtually any performance or race engine – five horsepower at a time!