Dirt track modifieds aren’t much to look at – they have an appearance that only a fabricator could love – but don’t let their simple flat panels fool you. Underneath these plain-Jane exteriors lies a marvel of contradictions. Take the power train for example – these mods typically use first generation small block Chevy 350 or 400 cubic inch engines, circa the late ’60s and early ’70s. Taking these forty-year-old engines and blending in a mix of technically advanced components, to achieve more horsepower than the power plant was ever designed to make, is nothing short of a modern miracle.
The OneDirt project car, a sport modified chassis with an SBC 350, is undergoing a heart transplant of sorts. We called our friends at Scorpion Race Products (SRP) to help us get our heads right – cylinder heads, that is. Not even brain transplants can help our driver or crew, so we would have to settle on getting some serious performance for the top end of this ancient engine.
Watch the Video on our Scorpion Racing Products Head Build:
We were starting with a bare set of heads that we sent out to Torres Machining and Performance for a good cleaning and dress up of the valve seats and guides. We had the 3947041 (head casting number) heads from the 1969-1970 year models, which are closed chamber heads that came stock with 1.94 intake and 1.5 exhaust valves. We wanted to keep these heads as stock as possible, while integrating the latest technology available, to produce as much power as possible and make it as dependable as a dirt track race motor needs to be – all while keeping it affordable for the average Saturday night sportsman racer.
We selected Scorpion Race Products for this build, and were ready to update our worn out heads with new technology and a full valve train from SRP.
Scorpion Racing Products began life as Rob Stopanio’s engine building company – Blue Thunder Racing – in Fort Lauderdale, Florida. Blue Thunder’s engines were primarily built for the the marine industry, and the US Drug Enforcement Agency bought these racing engines for their Ocean Interceptor Boats (that were used to chase and apprehend drug smugglers).
Stopanio founded Scorpion Racing Inc. in 1999, and began manufacturing rocker arms for high performance automotive engines. Continuously refining the manufacturing process, Stopanio increased production and reliability of the parts to the point where Scorpion Racing Parts were in high demand from high performance race engine builders. In 2008, Scorpion Racing Products was created as the marketing and distribution company of Scorpion Performance manufacturing.
Scorpion Racing Products has enjoyed success with the straight line racers on the drag strips around the world. However, they’ve also had success on circle tracks. “We’re still one of the best kept secrets in circle track racing,” Luke Whalen, General Manager of Scorpion Racing Products, tells us. “Racing teams that get an advantage by using our products don’t really share the information and keep that under a rock, so that the other teams won’t catch up easily.” SRP is able to keep and maintain their quality control by “committing to updating and replacing our sophisticated tooling at least every three years,” states Whalen. “Every part is tested before it leaves the factory. Each component is treated like it’s an egg, so that when it arrives at the customer’s door, it’s flawless.”
The goal of our project was to build a set of heads that complied with the local race rules and could be competitive on the track, yet stay within the budget of a grassroots racer. Some of the considerations that we took into account when selecting parts for this build were based on the age and condition of the cylinder heads themselves, as well as the bottom end internal components. Careful selection of a camshaft that will work with the valve train is critical to the prolonged life of the completed engine.
While the camshaft may be considered the “brain” of the engine because it controls all of the timing events, the valve train components also affect performance. Understanding the requirements of the components that make up a good system is essential to making dependable horsepower. Choosing from the Scorpion Race Products line to fill our need for performance parts at reasonable prices was an easy decision. They only offer one line of parts – there is no budget line, no sportsman line, and no economy line. Scorpion only sells the race product line that they have become known for, and that meant that we only had to decide the technical aspects of the build.
Playing by the Rules
The track rules that we would be competing under state that the block must be American-made with steel heads – original equipment manufacturer (OEM) passenger vehicle production only, no bowtie, SVO, or Chrysler W blocks and heads. The rules also specified flat tappet cam and lifters with stud mounted rocker arms only – no stud girdles, no mushroom lifters, and no altering the lifter bores. Fuel delivery system is through a Holley 4412 (two-barrel) carburetor. All engines must be able to be used in conventional passenger cars without alterations. Finally, only wet sump oil systems are permitted.
Armed with these guidelines, we selected a mechanical flat tappet camshaft and lifters. The specs of the cam are not important for the purposes of this article, but understanding why we selected the mechanical flat tappet cam and lifters is important. A hydraulic cam and lifters will experience valve float at higher RPMs and they restrict your top range to about 6,500 rpm. We selected the mechanical (solid) cam and lifters to give us a wider range of usable rpm. Scorpion Lifters are a great choice overall, and they really shine in the mechanical flat tappet valve trains. “These are type 3 lifters, the same thing that is in the NASCAR cars,” explains Whalen.
About Scorpion’s Lifters:
- High Concentration of Acicular Carbides for extreme wear resistance.
- Proprietary iron formula, cast in Scorpion’s own foundry.
- Every lifter is tested before it leaves the factory, not just batch testing.
SRP is really proud of their pushrods, which are formed out of 4135 chromoly seamless steel tubing and are designed to last forever. Whalen describes the pushrods as, “a bad ass piece that is finished in a salt bath nitride surface treatment for outstanding wear properties, and rated at 180,000 psi tensile strength.” The tips of the push rods are constructed of 8260 bar stock, and are case hardened and cyrogenically treated and tempered for greater impact/wear resistance. Offered off the shelf in 5/16” and 3/8” with 5/16” ball tip or custom-made, these push rods can be ordered from SRP.
- Finished in salt bath nitride surface treatment for higher wear properties.
- Rated at 180,000 psi tensile strength.
- Manufactured out of 8260 Bar Stock.
- Cryogenically Treated.
Scorpion Racing Products offers a variety of race valve springs for every application, including motorcycle and ATV valve springs. Advertising that their valve springs have been made in America for six generations, SRP has every application covered. We chose the endurance valve springs for our circle track race car because of the strength and design features. All of Scorpion’s valve springs are checked for any imperfections with an X-ray diffraction machine (which checks the alloy’s atomic spacing of the crystalline structure). This ensures that the inherent stresses in the metal from the manufacturing process fall within an acceptable level for race springs, under extreme conditions and aggressive camshaft profiles.
About the Endurance Valve Springs:
- Manufactured on CNC spring making equipment.
- Specific Pitch profiles for the rate of the engine application.
- Ground on CNC machines for tighter coil bind height.
- Nano peened to reduce residual stresses within the metal.
SRP’s racing valves cover big and small block Chevys, Corvette LS1 valves, and Fords. “SRP valves are the same valves that are used in F1 race cars, and this stainless steel valve line is manufactured from a one-piece forging,” explains Whalen.
Metals tend to fatigue and creep at higher temperatures, depending on the temperature, time and loads being applied to the metal. Metal fatigue is the weakening of the metal until it fractures, and creep is the movement or deformation of metal under extreme conditions. According to Whalen, this alloy combination can, “withstand serious exhaust temperatures before fatigue.” You get exactly what you ask for when you order these valves.
About the Race Valves:
- Back cut for improved flow.
- Undercut valve stems that further improve flow characteristics.
- Intake Valves are manufactured out of 21-4N Stainless Steel material.
- Exhaust Valves are manufactured out of 23-8N Stainless Steel to withstand higher temps.
- Robotically Manufactured for tightly controlled tolerances.
Scorpion rocker arms are a work of art, and are the flagship of Scorpion Racing Products. “We started out making racing rocker arms, and now we’ve taken them a step further,” explains Whalen. “All of our experience combined equals 500-600 years of experience in manufacturing these.” All of Scorpion Racing Products’ rocker arms have a lifetime warranty, which means (to us) that you can buy one set and race for a lifetime.
We chose the race series 1.5 ratio Platinum Series rockers for our small block Chevy. “We set the ratio of the rocker under 400 pounds of open spring pressure, where most rocker arms ratios are set statically,” Whalen explained, giving us the real lowdown on these rockers. “Setting the ratio under pressure ensures that you will get 1.5 ratio when they are installed and working. 1.5 means 1.5 to us”.
About the Race Series Rocker Arms:
- Lifetime Warranty.
- Manufactured out of Aerospace Aluminum.
- 100% CNC Machined in-house.
- Tighter Tolerances and rated to handle .950″ lift and 950 lbs of open spring pressure.
We took our brand new Scorpion Racing Products valve train and our slightly used twenty-nine-year-old cylinder heads to our favorite machine shop – Torres Machining and Performance in Murrieta, California. We had them clean, surface and cut the valve seats on our heads. They also checked the valve guides for wear while they were there, and fortunately for us, we were well within limits. The first step was to clean the cylinder heads with the jet cleaner, so that the heads could be checked really well for any problems like cracks and excessive wear.
After the heads came out of the jet cleaning machine, Luis Torres checked the valve stem height with a height gauge, to ensure that we would be within limits prior to cutting the valve seats. Any adjustments that might be needed could be handled by installing valve seat spacers. However, our heads weren’t as beaten as we thought they might have been and we were using stock style components, so we were well within limits. Luis then set the heads up on the valve seat cutting mill.
We were looking for the most flow available for a stock setup with the small faced valves, so Luis set up for a performance three angle valve seat job. This would take advantage of the angles cut into the Scorpion Race valves – specifically, the back cut on the valves and the valve stems. This increased flow will improve the port flow at all engine speeds. The thirty degree back cut to the underside of the intake valves further increases air flow, which also has the added benefit of keeping the valve heads cooler.
Once the seats were cut for the Scorpion Racing Products Endurance valves, Luis applied assembly lubrication on the valve stems and installed the valves into the valve guides. The valves were numbered after the valve seat grinding, assembled into the correct order, and the sealing properties checked using a vacuum tester. Proper sealing of the valves is essential to making good power. With the valves installed in the correct order, Luis assembled the valve springs, umbrella, and retainer in place over the valve stems.
Using a hydraulic compressor, he compressed the springs in order until the keeper groove was visible, and inserted the keepers into place. Once all sixteen valves were completely assembled, we test fit the rocker arms, checking for any visual interference, and for safe keeping until the heads are assembled on the short block. With that, our top end was ready for installation.
Completing the Install
Back at the garage, we installed the heads on the short block, making sure to torque the head bolts to the correct specifications using a multi-step process. Starting with 50% of the final torque value, we progressively increased the torque value in 10 ft/lb increments, until the final torque value was met.
Applying a coating of assembly lube on each pushrod, we inserted the pushrods through the guide slots to the lifters, making sure that each end of the pushrod was coated with lubrication. Each rocker arm was then installed with a good amount of lubrication in the push rod pocket of the rocker arm, and the poly locks were installed on the studs (without tightening them to the point where they made full contact with the rocker arm trunnion). Once all the components were in place, we could start setting the valve clearance.
Using mechanical lifters means that you have to be religious with your routine maintenance, starting with the initial valve clearance setting. Mechanical lifters tend to be a little noisy compared to hydraulic flat tappet lifters. However, the noise can be minimized by very specific clearance adjustment.
Your camshaft should come with a spec card that specifies the acceptable clearance adjustment for intake and exhaust valves. We have found that following these recommendations will save a lot of heartache and broken valve train parts. Using the appropriate size feeler gauge blade, the valve clearance should be set following the spec card. We strongly recommend repeating the valve clearance procedure to ensure that the clearances are correct.
When we completed our valve clearance adjustment, we turned the engine over to top dead center with the #1 cylinder firing, so that installing the distributor would be an easier procedure.
Our #K9 Sport Modified was one step closer to the track with a new and improved valve train. The Scorpion valve train components are “full-on” race parts, so we had no doubt about the ability of these pieces to withstand the rigors of dirt track racing. The only hesitation we had after this install was whether the driver could actually perform as well as the Scorpion components. With all the excuses taken away from the engine operation, the driver is the bridge between success and failure.