Introduction: Why the Comp Cams XE268H for Your Pontiac 400

The Pontiac 400 cubic-inch V8 is a legendary engine block, powering iconic vehicles from the late 1960s through the 1970s. If you are looking to wake up that big-inch motor without sacrificing daily drivability, the Comp Cams XE268H is one of the most popular and proven camshaft upgrades available. This hydraulic flat-tappet camshaft is designed to deliver a strong mid-range torque curve, a noticeable but manageable idle lope, and excellent vacuum for power brakes. Installing a camshaft is a significant mechanical project, but with careful planning and the right approach, it is a rewarding upgrade that can transform how your Pontiac 400 performs on the street. This expanded step-by-step guide covers every phase of the installation, from selecting the right supporting parts to the first start-up.

What Makes the XE268H a Smart Choice for Pontiac 400s

The XE268H is part of Comp Cams' Xtreme Energy series. It features a faster lobe ramp rate than older cam designs, which means it opens the valves more quickly and holds them open longer for a given duration at the valve. This translates to a broad power band and strong throttle response. For a Pontiac 400, this cam typically operates well in the 1,600 to 5,800 RPM range, making it ideal for street-driven cars with mild to moderate gearing. It pairs well with a stall converter around 2,500 RPM in automatic transmissions and works with most stock cylinder heads that have been upgraded with better valve springs.

Before you buy, double-check that your pistons have adequate valve relief clearance. The XE268H has an advertised duration of 268 degrees intake and 276 degrees exhaust, with a lobe lift that requires careful measurement if you are using aftermarket heads. Many builders pair this cam with 1.65:1 rocker arms for additional lift, but stock 1.50:1 rockers will still produce a noticeable performance gain.

Safety and Preparation: Setting Yourself Up for Success

A cam swap is a dirty, detailed job. Even experienced mechanics can run into trouble if they skip the preparation phase. Before you unbolt anything, make sure you understand the complete scope of work. On a Pontiac 400, the camshaft is accessed by removing the timing cover, which means you must also remove the radiator, water pump, harmonic balancer, and timing chain cover. Depending on your vehicle, you may also need to pull the intake manifold and valley pan. Plan for a full weekend if you are working in a home garage.

Gather these supplies before starting:

  • Comp Cams XE268H camshaft and matching hydraulic lifters
  • Camshaft installation lube (provided with the cam or purchased separately)
  • High-quality engine assembly oil
  • New timing chain and gears (a double-roller set is recommended for Pontiacs)
  • Intake manifold gasket set and timing cover gasket
  • Valve springs rated for the XE268H lobe profile (if reusing heads)
  • Harmonic balancer puller and installer
  • Torque wrench (both foot-pound and inch-pound ranges)
  • Dial indicator and degree wheel for verifying cam timing
  • Thread locker (medium strength)
  • Clean rags, degreaser, and a magnetic parts tray

For more details on checking valve spring pressure, consult the Comp Cams valve spring recommendations on their official website. You can also reference Pontiac-specific build forums like Pontiac Street Performance for community tips on installation torque specs.

Step 1: Disconnect and Drain

Begin by disconnecting the negative battery cable. This is non-negotiable. The starter motor is powered directly from the battery, and accidentally bumping the ignition while turning the crankshaft can cause injury or damage. Drain the coolant from the radiator by opening the petcock at the bottom. Drain the engine oil by removing the drain plug. Old oil will contain debris from the previous cam and lifters, and you do not want that circulating through the new components.

Remove the radiator, fan shroud, and fan assembly. On most Pontiac-powered cars, this gives you the clearance to reach the front of the engine. If your car has a clutch fan, you may need a special wrench to hold the water pump pulley. Set all fasteners aside in labeled bags or containers.

Step 2: Remove the Intake Manifold and Valley Pan

The intake manifold sits on top of the lifter valley. To access the lifters, you must remove the carburetor or throttle body, distributor, and intake manifold bolts. Pontiac intakes are heavy, so have a helper or a hoist available. Once the manifold is off, remove the valley pan. This stamped steel pan covers the lifter gallery and must be removed to access the pushrods and lifters. Use a new valley pan gasket when reassembling.

Label your distributor position relative to the engine block. This will save you time during reinstallation. With the valley pan removed, you can see the lifter bores. Remove each rocker arm and pushrod, keeping them in order if you plan to reuse them. Push the old lifters out from the top. Discard them. Never reuse old lifters on a new camshaft.

Step 3: Remove the Timing Cover and Old Camshaft

With the front of the engine exposed, remove the alternator and power steering pump brackets if they block the timing cover. Remove the harmonic balancer using a puller. Do not hammer on the balancer. Next, unbolt the timing cover. You may need to pry it gently from the block if the gasket is stuck.

Rotate the engine to top dead center (TDC) on cylinder number one. This ensures the timing marks on the gears align properly when you install the new cam. Remove the timing chain and gear set by unbolting the camshaft gear. The crankshaft gear can be removed with a puller or tapped gently from behind. Once the gears are off, slide the old camshaft out of the engine block. Be extremely careful not to gouge the cam bearings. The Pontiac 400 block has a tight clearance, so rotate the cam as you pull it to clear the bearings.

At this stage, inspect the cam bearings. If they show signs of scoring or excessive wear, the engine must be pulled and the bearings replaced. This is rare on a low-mileage block, but worth verifying while the cam is out.

Step 4: Pre-Lube the New Comp Cams XE268H

Before installation, coat the camshaft lobes and distributor gear with the supplied Comp Cams break-in lube. Do not skip this. Apply a generous amount to each lobe, the distributor drive gear, and the bearing journals. Also coat the bottom of each new lifter where it contacts the cam lobe. The lifter bores should be coated with engine assembly oil.

Step 5: Install the New Camshaft

Carefully slide the new XE268H into the engine block. Use a consistent rotation as you push it in to prevent binding against the bearings. Once the cam is fully seated, install the camshaft retaining plate and bolts. Torque to factory specification, usually around 20 ft-lb for a Pontiac.

Install the new timing gears. Most aftermarket double-roller timing sets allow you to degree the cam. At this stage, align the timing marks according to the instructions. The crankshaft gear mark should point straight up, and the cam gear mark should point straight down, with both marks facing each other. Install the timing chain and verify the alignment. Rotate the engine two full turns by hand and check that the marks realign. If they do not, you have a timing chain issue that must be resolved before proceeding.

For precise engine timing, use a degree wheel and dial indicator to confirm that the camshaft intake centerline matches the spec card from Comp Cams. The Comp Cams website provides the exact valve timing events for the XE268H. Degreeing the cam ensures you get the advertised power curve.

Step 6: Install the New Lifters and Pushrods

Install the new hydraulic lifters into their bores. Each lifter should drop in freely. If any lifter sticks, clean the bore with a brush and solvent. Once all lifters are in place, install the pushrods. Adjust the rocker arms to the correct preload. For hydraulic flat-tappet lifters, the typical preload is 0.020 to 0.040 inches. Use a torque wrench to tighten the rocker stud nuts to the Comp Cams spec, or adjust them with a feeler gauge if using adjustable rockers.

If you are reusing your original rocker arms, inspect the fulcrum wear surfaces. Replace them if they show pitting or galling. Pontiac rocker studs are notoriously prone to pulling out under high spring pressure. If your heads have pressed-in studs, consider upgrading to screw-in studs for safety.

Step 7: Reassemble the Front of the Engine

Install a new timing cover gasket and the timing cover. Torque the bolts in a crisscross pattern. Install the harmonic balancer using the correct installation tool. Coat the balancer seal surface with oil to prevent dry start damage. Install the water pump, alternator brackets, and accessories. Refill the cooling system with fresh 50/50 antifreeze.

Install the valley pan with a new gasket, then mount the intake manifold. Torque the intake bolts in the sequence specified for your intake manifold. A typical Pontiac intake requires 35 ft-lb on the center bolts and 30 ft-lb on the end bolts. Reinstall the distributor, ensuring the rotor aligns with the number one spark plug wire position.

Step 8: Oil Priming and First Start

Before you attempt to start the engine, prime the oil system. Install a distributor priming tool in the oil pump drive and use a heavy-duty drill to spin the pump until oil pressure registers on the gauge. This pre-lubricates the cam and lifters, preventing a dry start. Rotate the engine by hand with a breaker bar while priming to distribute oil to all bearings.

Refill the engine with high-quality break-in oil. Comp Cams recommends a conventional 10W-40 oil with high zinc and phosphorus content. Avoid synthetic oil during break-in, as synthetic oil can prevent the flat-tappet lifters from properly seating. Do not use the engine for continuous idle break-in. The cam must be broken in under load. Start the engine and immediately bring the RPM to between 2,000 and 2,500 RPM for the first 20 minutes. Vary the RPM slightly within that range. This seats the lifters to the cam lobes.

For more details on proper flat-tappet cam break-in procedures, refer to the OneDirt cam break-in guide which outlines the critical RPM range and oil requirements.

Common Pitfalls and How to Avoid Them

Even with careful planning, a few common mistakes can ruin a new camshaft. The most frequent cause of failure is insufficient break-in oil. Modern oils have reduced zinc additives. Always add a bottle of Comp Cams break-in additive or use an oil formulated for flat-tappet cams. A second common issue is incorrect lifter preload. Too much preload holds the valve open, causing a loss of compression and possible piston-to-valve contact. Too little preload creates a clattering noise and poor performance.

Another problem specific to the Pontiac 400 is the distributor gear. The XE268H uses a cast iron distributor gear. If your Pontiac has a bronze distributor gear (common with some aftermarket distributors), it will wear rapidly against the cam gear. Change to a melonized steel distributor gear or a composite gear designed for cast iron cams. This is a cheap fix that prevents catastrophic failure.

Inspect your valve springs. The XE268H requires spring pressure of at least 110 pounds on the seat and 270 pounds open. Weak springs can cause valve float at high RPM, leading to piston contact. Install new springs matched to the cam profile if your heads have unknown mileage.

Does It Require a Stall Converter?

If your Pontiac 400 is backed by an automatic transmission, the XE268H will perform best with a torque converter that stalls around 2,500 RPM. A stock stall converter (around 1,800 RPM) will feel lazy off the line. The cam does produce decent vacuum, so power brakes will still function, but a higher stall converter lets the engine reach the power band more quickly. For manual transmission cars, a 3.08 or steeper rear gear is recommended. If you run a 2.73 gear, the cam will feel soft below 2,000 RPM.

Final Check Drive and Tune

After the initial 20-minute break-in, let the engine cool completely. Retorque the intake manifold bolts and rocker arm nuts. Some settling is normal. Change the oil and filter to remove any break-in debris. Replace the break-in oil with the same high-zinc conventional oil. Do not switch to synthetic until after at least 1,000 miles.

Check and adjust the timing. The XE268H typically runs best with total timing around 34 to 36 degrees, with initial timing set between 12 and 16 degrees. Use a vacuum gauge to fine-tune idle mixture and speed. Expect a lope at idle around 750 to 850 RPM. Adjust the idle speed screw and mixture screws to achieve a stable idle with minimal surging.

Take the car for a gentle drive. Avoid full-throttle runs until you have driven 50 to 100 miles. Listen for valve train noise. A slight ticking from hydraulic lifters is normal until they pump up fully, but persistent tapping indicates a preload issue. If you hear a knocking noise from the lower end, shut the engine down immediately and inspect the oil pressure and timing chain clearance.

The Performance Difference You Will Feel

Once everything is broken in and tuned, the XE268H transforms the Pontiac 400. The mid-range torque increase is dramatic, especially between 2,500 and 4,500 RPM. The engine pulls harder through the entire RPM range, and the exhaust note becomes a deep, aggressive rumble. This cam is a proven choice for street-driven Pontiacs that see weekend cruising, autocross, or stoplight to stoplight driving. It pairs well with a 750 CFM carburetor, a dual-plane intake manifold, and headers.

For further reading on cam selection and engine building, check out the MotorTrend engine building guides which cover Pontiac-specific builds and dyno comparisons. Another good resource is the Hot Rod Network for real-world dyno results of the XE268H in a 400-inch Pontiac.

If you have an Edelbrock Performer RPM intake and a set of headers, this cam will easily produce over 400 horsepower on a well-built Pontiac 400 with 9.5:1 compression. It remains driveable with good vacuum for brakes and a reasonably smooth idle once tuned correctly. Many enthusiasts consider this cam the ultimate "street strip" compromise for the Pontiac 400.

Conclusion

Installing a Comp Cams XE268H camshaft in your Pontiac 400 is a project that rewards careful planning and attention to detail. This guide covered the full process from preparation through break-in, focusing on the steps that are most critical for a Pontiac V8. By taking your time with the installation, double checking clearances, and following the break-in procedure, you can expect a reliable and powerful street engine that performs far beyond a stock build. Always use high-quality components, change the oil frequently during the first thousand miles, and enjoy the new personality of your Pontiac 400.