Understanding Camshaft Basics for Racing Applications

A camshaft is the brain of an engine’s valvetrain, dictating when and how long the intake and exhaust valves open. For racers, selecting the right cam profile is one of the most critical decisions because it directly influences power delivery, rpm range, and overall engine durability. Camshafts are defined by three primary specifications: lift, duration, and lobe separation angle. Lift measures how far the valve is pushed off its seat, controlling how much air-fuel mixture enters and how much exhaust exits. Duration is the total number of crankshaft degrees the valve remains open, affecting the engine’s power band. Overlap—the period when both valves are open simultaneously—helps scavenge exhaust gases but can create idle stability challenges. The lobe separation angle (LSA) impacts these characteristics by altering the overlap window. For racing, aggressive profiles with higher lift and longer duration are common, but they introduce potential interference issues that must be managed carefully. Comp Cams and other manufacturers provide detailed cam cards that list all these parameters.

Common Camshaft Selection Problems in Race Engines

Racers often overlook the mechanical limits of their valvetrain when choosing a cam. The most frequent issues include:

  • Valve Spring Interference: The cam’s lobe profile can physically contact the spring coils, especially with high-lift designs. This leads to spring bind, rapid wear, or catastrophic failure.
  • Retainer-to-Guide Clearance: Excessive lift may cause the valve retainer to hit the top of the valve guide, bending valves or destroying the guide.
  • Piston-to-Valve Clearance: With long duration and early intake closing, the piston can strike an open valve if the timing is not checked.
  • Coil Bind: When the spring is compressed solid before the valve reaches full lift, the valve can float or break the spring.
  • Harmonic Imbalance: Improper spring rates can cause valve float at high rpm, reducing power and risking piston contact.

Understanding these pitfalls helps racers avoid expensive mistakes when pairing a camshaft with valve springs and other valvetrain components.

Why Valve Spring Interference Happens with High-Lift Cams

Valve spring interference typically occurs when the cam’s lobe lift exceeds the spring’s installed height or when the spring’s coil pitch is too tight. As the cam rotates, the follower pushes the valve down, compressing the spring. If the spring coils stack solid before the valve reaches maximum lift, the spring cannot compress further—this is coil bind. The result is extreme loads on the valvetrain, often bending pushrods, cracking rocker arms, or shattering the camshaft itself. Racer Grant cams, known for aggressive profiles used in circle track and drag racing, often have lobe lifts exceeding 0.400 inch. Without matching spring specs, interference is almost guaranteed. PAC Racing Springs offers many options designed specifically for high-lift cams.

Strategies to Avoid Valve Spring Interference

Preventing valve spring interference requires meticulous measurement and selection. Here are actionable solutions:

  • Measure Installed Spring Height: Use a micrometer to confirm the spring pocket depth and installed height. For a typical small-block Chevrolet, installed height is around 1.700–1.800 inches. If the cam lift plus retainer thickness exceeds the available space, you need taller valve springs or shorter retainers.
  • Check Coil Bind Clearance: Calculate the spring’s compressed length at max lift. Leave at least 0.050 inch between coils to prevent bind. Many spring manufacturers list coil bind height on their spec sheets.
  • Select Springs with Proper Pressure: Use springs that provide enough seat pressure to control the valve without being so stiff they cause excessive friction. For a 0.650-inch lift cam, dual springs with 130–160 psi on the seat and 350–400 psi open are typical.
  • Upgrade Retainers and Locks: Use steel or titanium retainers that are shorter than stock to gain additional clearance. Seven-degree locks can further reduce the stack height.
  • Adjust Rocker Arm Ratio: Running a lower rocker ratio reduces net valve lift, which sidesteps interference. For instance, switching from 1.6:1 to 1.5:1 rockers cuts lift by about 6%.
  • Consult the Cam Grinder: Racer Grant provides cam cards with recommended spring specs. Follow these exactly. Racer Grant Cams publishes detailed application guides.

Step-by-Step Guide to Selecting Racer Grant Cams

Racer Grant cams are popular in circle track, drag racing, and oval track classes because of their proven power gains. To choose the right one and avoid interference, follow this process:

1. Define Your Engine Build and RPM Range

Racer Grant offers cams ranging from mild street/strip profiles to all-out competition grinds. Determine where you want peak power. A cam with 280–300 degrees of duration (advertised) will peak around 6500–7000 rpm, while a 310+ duration grind shifts the power to 7500+ rpm. Higher rpm demands stronger springs and more clearance.

2. Check Piston-to-Valve Clearance

Before ordering, measure the valve to piston clearance at TDC overlap. Use modeling clay or a dial indicator. For a 0.650-inch lift cam with 106° LSA, you need at least 0.100 inch on the intake and 0.125 inch on the exhaust. If clearances are tight, you may need flycut pistons or an adjustable timing set.

3. Match Springs to the Cam Profile

Select valve springs that have a coil bind height lower than the maximum valve lift plus a 0.050-inch safety margin. For example, if the cam lift is 0.720 inch and the installed height is 1.750 inch, the spring’s coil bind height must be at or below 0.980 inch (1.750 – 0.720 – 0.050). Many racers use 1.550-inch height springs to allow more room. Check Isky Cams for spring recommendations compatible with Racer Grant profiles.

4. Verify Retainer-to-Guide Clearance

With the spring removed, install the retainer and locks on the valve. Slide the valve down until the retainer contacts the guide boss. Measure the gap. If it’s less than 0.100 inch at full lift, you risk contact. Solutions include using a shorter retainer, cutting down the guide boss, or switching to a higher-quality guide material.

5. Perform a Virtual Assembly Test

Before final assembly, use a checking spring (low-pressure spring) to cycle the valvetrain by hand. Rotate the engine with a torque wrench and listen for any clicking or binding. This confirms that all components work together without interference. Racer Grant camshafts often require double checking because of their aggressive lobes.

Testing and Fine-Tuning After Installation

Even with careful selection, you must validate the setup on the engine stand and on the dyno.

  • Dyno Testing: Run the engine up to the intended redline. Monitor valve float—a sharp drop in power or erratic exhaust note indicates spring pressure is insufficient or coil bind is occurring. Recheck spring pressures after the first few pulls.
  • Clearance Rechecks: After initial break-in, pull the valve covers and measure the installed height again. High heat and cycling can settle the retainers or compress the springs slightly.
  • Timing Adjustments: Cam timing (advance or retard) can affect valve clearance. If you advance the cam, piston-to-valve clearance on the intake decreases. Use an adjustable timing set to dial in the optimal cam position. Typically, retarding the cam by 2–4 degrees increases top-end power but may tighten clearance.
  • Spring Pressure Testing: Use a spring tester to verify seat and open pressures. If pressures have dropped more than 10% from new, replace the springs. Spring fatigue accelerates with aggressive cams.

Real-World Examples of Valve Spring Interference with Racer Grant Cams

A common scenario involves a racer using a Racer Grant 306H grind (306° advertised duration, 0.620-inch lift with 1.6 rockers) in a 355ci small-block Chevy. The builder installed standard dual springs with a 1.800-inch installed height and a coil bind height of 1.200 inches. At full lift (0.620 inch), the spring compressed to 1.180 inches, causing coil bind. The result: broken springs and a bent pushrod after only one race. The fix was switching to a shorter spring with a 1.150-inch coil bind height (e.g., Comp Cams 987-16) and a shorter retainer, restoring clearance. Another racer used a 0.720-lift Racer Grant cam in a 400ci Ford with stock valve guides. The retainer contacted the guide at 0.650 inch of lift, requiring guide boss machining. These examples underscore the need for precision. Crane Cams also provides helpful interference checklists on their website.

Long-Term Reliability and Maintenance

Once the cam and valve springs are properly matched, maintain them with regular inspections. Replace springs every 25–50 race hours, depending on rpm and spring pressure. Use a quality break-in oil for flat tappet cams to prevent lobe wear. For roller cams, ensure the roller lifters are correctly aligned with the lobes. Keep the valvetrain geometry correct by using adjustable rocker arms and checking pushrod length. A small interference issue that goes unnoticed can destroy the entire engine. Regularly check for signs of coil bind by examining the spring coils for polished marks or flat spots. If you see evidence of contact, address it immediately.

Conclusion

Selecting the right camshaft for your race engine—especially Racer Grant cams—is a science that demands attention to valve spring interference. By understanding the key dimensions like installed height, coil bind, and retainer clearance, racers can avoid costly failures. Measure everything, follow the cam manufacturer’s spring recommendations, and validate with assembly tests and dyno runs. With the correct preparation, Racer Grant cams deliver impressive power gains without the risk of valve spring interference. Remember that a few extra hours of measurement can save thousands of dollars in engine repairs and lost track time.