PONTIAC ENGINE REBUILD GUIDE: STARTUP, BREAK-IN AND TUNING

Your newly rebuilt engine is just about ready to fire! If everything was assembled correctly, it should start up relatively easily, and the sound of the exhaust pulsations smoothly bellowing out the exhaust is the best reward for your hard work. If all goes well, the improved operational and performance characteristics of your new engine should give you a great sense of self-satisfaction.

 


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Before starting your engine, you need to determine how to handle initial startup and camshaft break-in. Will it be performed on a test stand, an engine dyno, or in the vehicle? I much prefer a test stand or engine dyno to vehicle installation. The former gives you a chance to closely inspect for leaks or abnormalities and easily perform any necessary adjustments or repairs within minutes of detecting them. The latter is much more involved, however, and repairs may require several hours of frustrating work of uninstalling the engine.

 

An engine dyno is a common site at higher-end engine shops. It’s an excellent tool to start-up and break-in a new engine while checking for oil and coolant leaks. Its primary use, however, is to measure the full-throttle horsepower and torque an engine generates. A complete dyno session should include adjusting the carburetor and distributor to find the settings that produce peak power.

An engine dyno is a common site at higher-end engine shops. It’s an excellent tool to start-up and break-in a new engine while checking for oil and coolant leaks. Its primary use, however, is to measure the full-throttle horsepower and torque an engine generates. A complete dyno session should include adjusting the carburetor and distributor to find the settings that produce peak power.

 

Engine Test Stand or Dyno

An engine test stand is designed to safely cradle an engine for startup and operation. Commercially available units are available for purchase, or it can be homemade. Either should be constructed of heavy steel tubing and include a control panel with a starter button, master kill switch, complete instrumentation to monitor the engine’s vital functions during operation, radiator, and electric fan. A full exhaust can be added to provide quiet operation. The engine can be run normally and closely checked for leaks, to break in a flat-tappet camshaft, etc. If the engine checks out fine after initial startup, it’s ready to install into the vehicle and seat the piston rings.

There are two popular types of dynos commonly used to measure engine output. An engine dyno looks similar to a test stand but contains a hydrostatic “brake.” It directly connects to the crankshaft and measures how much full-throttle horsepower and torque an engine generates. The computer is programmed to let the engine accelerate at a certain number of RPM per second. The specific RPM that the computer begins recording output at is also adjustable. Output values recorded on an engine dyno are generally referred to as “at the flywheel.”

A chassis dyno measures the amount of output a vehicle generates through its entire drivetrain. With the engine installed in the vehicle and the break-in process already performed, the vehicle’s drive wheels are placed on a large, fixed-weight roller drum and output is recorded as the drum rotates. Values attained on a chassis dyno are usually significantly lower than those of an engine dyno—sometimes by 15 to 30 percent. The difference between the two is the amount of engine power consumed by transmission and rear axle operation. Results recorded “at the tire” can be converted into an approximated “flywheel” value. But because each vehicle’s drivetrain is slightly different than the next, there are too many variables to generate an exact “flywheel” conversion factor.

Step 1: Install Motor Mounts (Torque Fasteners)

SA200_FULLBOOK_RebuildPontiacV8s_Page_118_Image_0001When the engine is ready for installation into the vehicle, install the motor mounts. Depending on the year, Pontiac used rubber isolators on the engine or on the frame with a corresponding bracket on the other. New stockreplacement motor mounts were sourced from a Pontiac vendor and installed. The bolts are tightened to 70 ft-lbs with an 11/16-inch socket and 1/2-inch-drive torque wrench.

Step 2: Install Exhaust Manifolds

SA200_FULLBOOK_RebuildPontiacV8s_Page_118_Image_0002Some models allow the engine to be installed into the vehicle with the exhaust manifolds in place. Whether installing them before or after engine installation, use new exhaust gaskets. The steel shim type may be sufficient, but I recommend Fel-Pro coated gaskets; both types are included in the FelPro gasket kit. Round port gaskets are sold separately. The bolts are installed with a 9/16-inch socket and tightened to 30 ft-lbs with a 3/8-inch-drive torque wrench. I generally apply a light coating of anti-seize lubricant to the bolt threads to aid future removal.

Engine Reinstallation

The engine installation process varies for each Pontiac model, and can even vary from one year to another on similar models. I feel the best method is simply reversing the process used for engine removal. Refer to your photographs and notes for assistance, and your Pontiac Service Manual for torque specifications for any bolts, brackets, and accessories. I also strongly suggest having a capable helper assist you throughout the entire installation process. Your new rebuilt engine is very heavy and must be handled with care. Any mistake can seriously injure you, your engine, or your vehicle.

Step 3: Install Engine

SA200_FULLBOOK_RebuildPontiacV8s_Page_119_Image_0001The excited owner is ready to install his freshly rebuilt 400 into his GTO. The actual installation may vary for different vehicles, and different tools and torque specs may be required. Refer to your Pontiac Service Manual for the exact procedure. Generally, if the engine is resting between the frame rails, the transmission bellhousing dowels are aligned and the engine is bolted to the transmission. The motor-mount bolts are installed and torqued accordingly and the exhaust is connected.

Final Preparations

With the engine completely installed in the vehicle, recheck your work to ensure that every nut and bolt is tight and that the coolant hoses, fuel and vacuum lines, and all electrical wiring are properly installed. Be sure that the crankcase is full of your machinist’s recommended brand and weight of oil. Usually it is 30W premium-brand oil specifically designed for the break-in process. Such oil contains high quantities of anti-wear additives to protect surfaces and prevent scuffing. It isn’t intended for long-term use, though. Plan to replace it after the break-in process is complete.

Preventing Coolant System Air Pockets

Immediately before the initial startup, the coolant system should be completely filled with a fresh 50/50 mix of coolant and distilled water. Any air pockets trapped within the cooling system can create undesirable hot spots in the block or cylinder heads. To bleed the system of trapped air, I leave the heater core hose disconnected from its nipple at the rear of the passenger-side cylinder head and pack several old rags around it.

I pour the coolant mix directly into the radiator. The open hole allows trapped air to escape. As the cooling system nears its capacity, I begin adding small amounts of coolant while closely watching for it to trickle out of the nipple on the cylinder head. Don’t be concerned if a little bit pushes out; the rags are there to soak it up. As soon as coolant is visible at the nipple, the hose is connected and its clamp tightened. The cooling system is now primed and ready for startup.

 

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Startup

The engine is nearly ready for startup. The oiling system still must be primed from the assembly process. Verify that the number-1 piston is at top dead center (TDC) on the compression stroke and the distributor rotor tip is pointing at the number-1 terminal of the cap. Verify that the spark plug wires are oriented correctly for a firing order of 1-8-4-3- 6-5-7-2 in counterclockwise rotation.

The carburetor should be primed with fuel. With a Quadrajet, I use a disposable animal feed syringe to gently squirt some fuel into the well that houses the secondary metering rods. It provides a direct route to the float bowl. Be sure the fuel is going into the float bowl and not into the secondary barrels. The carburetor is pumped until two shots of fuel are discharged to polish the two contact surfaces. The surfaces receive no direct lubrication during normal operation, but instead are indirectly lubricated by oil seepage from the lifter bores and splash oiling from the crankshaft.

Step 4: Install Carburetor (Torque Fasteners)

SA200_FULLBOOK_RebuildPontiacV8s_Page_121_Image_0001Once the engine has been securely attached to the frame rails, remove the carburetor flange adapter from the intake manifold and install the carburetor. Its bolts are tightened to 5 ft-lbs with a 1/2-inch socket and 3/8-inch wrench. The remaining fuel lines and vacuum hoses are also installed.

 
 

Step 5: Install Accessory Brackets

SA200_FULLBOOK_RebuildPontiacV8s_Page_121_Image_0002The engine is nearly ready for startup. Install all accessories and any associated brackets, hook up the electrical connections, and install the radiator and coolant lines. Then fill the cooling system with fresh coolant. After a thorough check to be sure everything is assembled correctly, the engine is ready to start!

 
 

 

During camshaft installation, the lifter and lobe surfaces are thoroughly coated with a specific camshaft break-in lubricant, which is designed to prevent scuffing that occurs before oil circulation begins at initial startup. If prolonged cranking occurs during the initial startup process, seriously consider removing the valley pan and recoating the lifters and lobes with break-in lubricant. A failed lifter or lobe sends metallic filings throughout the engine makes complete teardown, a thorough cleaning, and new bearings required, at the minimum.

Immediately after the engine fires, its speed should be increased toward 2,500 rpm by adjusting the carburetor idle speed screw. The added RPM is necessary because it increases pressurized oil circulation and splash lubrication. It also lessens the overall inertial load on the lifters, allowing them to rotate quicker on the lobes and enhance the polishing effect. The distributor vacuum advance can be connected to full manifold vacuum to further advance spark lead and reduce the risk of overheating. There’s no risk of detonation because there is no load on the engine.

Your camshaft supplier provides you with specific break-in instructions. It might also suggest specific lubricants or physical steps be taken for the process. You should follow them closely if you expect any camshaft company to honor a warranty claim. The entire flat-tappet camshaft break-in procedure should take 20 to 30 minutes to complete. Remember: The engine should never be run at idle speed during that time.

Your helper should be watching oil pressure and coolant temperature throughout the break-in process. The engine can be shut down if coolant temperature rises above about 230 degrees F or if any operational concerns are detected. The process can continue once the engine has had ample time to cool back into the 160- to 180-degree F range. If shutdown is required, simply restart the engine and pick up where you left off until the manufacturer’s suggested run time has elapsed.

 

Roller Camshaft Break-In

Roller camshaft break-in is much simpler than flat-tappet camshaft break-in. The steel camshaft and roller lifters do not need to “mate” like flat-tappet components. If your camshaft manufacturer doesn’t provide you with specific break-in instructions, simply increase RPM to about 1,500 for a few minutes to allow the engine oil to circulate throughout the engine. Check for leaks and listen intently for any abnormal noises. Engine speed can then be reduced to where the engine doesn’t die, and the carburetor and distributor can be adjusted accordingly.

 

Engine Break-In

After the camshaft break-in process is complete, the engine should be driven for several miles to give the piston rings a chance to properly seat. The process should never include operating at a constant speed or at full-throttle for any extended length of time. The proper procedure consists of varying engine speed and engine load by continually accelerating and decelerating on an open road. Accelerate briskly and then let off the throttle. It’s best to leave the transmission in a lower gear, allowing for “engine braking” while decelerating. The process allows the rings to properly seat under acceleration and deceleration.

 

Engine Oil and Additives

Before running your new engine very hard, you should change the engine oil to rid it of any filings that result from component wear-in. It can be very thick as it cleans the heavy assembly lubricants from the internal surfaces used during assembly. Pontiac originally specified 20W oil during winter months and 30W oil during summer months. I routinely use 10W-30, 10W-40, and 15W-40 oils in our street-driven Pontiacs without any issue. The type of engine oil used depends greatly on the type of camshaft being run.

Oil companies have reduced the levels of desirable anti-wear additives present in modern-spec passenger car oil. A zinc-phosphorus compound (ZDDP) provides a high-pressure lubrication to prevent two metallic surfaces from contacting one another when the oil film is squeezed away. It’s a beneficial additive that protects such high-pressure internal engine surfaces as a flat-tappet camshaft lobe and lifter.

Modern auto manufacturers are required to warrant certain components of the emissions system of new vehicles for 8 years or 80,000 miles. It was determined that the phosphorus found in ZDDP was negatively reacting with the exhaust catalytic converter, causing premature failure. The additive is essential when using a flat-tappet camshaft, but because modern production engines use a steel camshaft and roller lifters, oil companies could remove a significant amount of the additive without any negative effects.

 

Flat-tappet camshafts can experience lobe and/or lifter failure if not properly broken-in. In addition to a specific break-in procedure, some camshaft manufacturers offer a thick paste that’s applied directly to the lobe and lifter contact surfaces during installation to prevent scuffing at initial startup. I feel that a paste is better than a liquid because it’s less likely to drip or come off the lobe or contact surfaces during initial engine operation. Ask your camshaft supplier for a recommendation.

Flat-tappet camshafts can experience lobe and/or lifter failure if not properly broken-in. In addition to a specific break-in procedure, some camshaft manufacturers offer a thick paste that’s applied directly to the lobe and lifter contact surfaces during installation to prevent scuffing at initial startup. I feel that a paste is better than a liquid because it’s less likely to drip or come off the lobe or contact surfaces during initial engine operation. Ask your camshaft supplier for a recommendation.

 

Some oil companies produce 30W oil that’s specifically designed for engine break-in. Brad Penn and Joe Gibbs Racing lubricants are quite popular with machinists and engine builders. Either lubricant provides excellent protection for initial startup and is ideal for the first few miles of driving. It isn’t intended for long-term use, so plan to change the oil shortly after the break-in process is complete.

Some oil companies produce 30W oil that’s specifically designed for engine break-in. Brad Penn and Joe Gibbs Racing lubricants are quite popular with machinists and engine builders. Either lubricant provides excellent protection for initial startup and is ideal for the first few miles of driving. It isn’t intended for long-term use, so plan to change the oil shortly after the break-in process is complete.

 

General Motors Engine Oil Supplement (E.O.S.) is a heavily concentrated lubricant that’s packed full of desirable anti-wear additives (left). It is readily available from your nearest GM dealer (number 88862586). Most camshaft manufacturers, like Comp Cams, offer a proprietary oil additive specifically designed for flat-tappet camshaft break-in (right). Either is an excellent choice that can be mixed with oil at regular change intervals to provide sufficient flat-tappet camshaft protection during normal operation.

General Motors Engine Oil Supplement (E.O.S.) is a heavily concentrated lubricant that’s packed full of desirable anti-wear additives (left). It is readily available from your nearest GM dealer (number 88862586). Most camshaft manufacturers, like Comp Cams, offer a proprietary oil additive specifically designed for flat-tappet camshaft break-in (right). Either is an excellent choice that can be mixed with oil at regular change intervals to provide sufficient flat-tappet camshaft protection during normal operation.

 

American Petroleum Institute (API) rates oil quality and regulates additives. Its ratings for oils are found in the “donut” on the back label of any oil container. Modernspec oil carries an “SN” rating, and its lubricating qualities may be the best ever. It has less of the desirable anti-wear additives than past oils, however, and that can lead to premature flat-tappet camshaft failure in older engines. If you’re using SM-spec oil, be sure to use an additive in any engine with a flat-tappet camshaft.

American Petroleum Institute (API) rates oil quality and regulates additives. Its ratings for oils are found in the “donut” on the back label of any oil container. Modernspec oil carries an “SN” rating, and its lubricating qualities may be the best ever. It has less of the desirable anti-wear additives than past oils, however, and that can lead to premature flat-tappet camshaft failure in older engines. If you’re using SM-spec oil, be sure to use an additive in any engine with a flat-tappet camshaft.


 

The reduction of ZDDP seems to have contributed to the unusually high number of flat-tappet camshaft failures in vintage engines in recent years. As the lifter or lobe wears through the hardened portion of the cast iron, whether during initial break-in or normal operation, complete failure results. That usually requires a complete teardown to clean all traces of iron filings from the engine, which might otherwise imbed into the bearings.

Many companies, including camshaft manufacturers, produce specific oil or additive packages, which contain a concentrated amount of antiwear additives, which are intended to combat flat-tappet camshaft failure. But they are generally not readily available at local auto parts stores. They must be sourced through local speed shops or machine shops, or mail-order vendors. Though these products effectively reduce the failure risk, they are simply not required when using a roller camshaft, which is constructed of steel.

In addition to any benefit related to reduced friction and slightly more aggressive lobe profiles, a hydraulic roller camshaft is an excellent choice for a street-driven Pontiac, if the budget allows. Not only is there no break-in process, there is no risk of failure and you can use most modern-spec oils that are readily available from the nearest auto parts store. I liken flat-tappet camshafts in modern engines and the associated oil concerns to high-compression engines that cannot operate on pump fuel. You just never know when you won’t be able to find what you need if you’re in a pinch, and that could potentially lead to some type of damage or failure.

 

Carburetor Tuning

The Quadrajet may be the most popular carburetor used for streetdriven Pontiacs today. Not only does it offer an excellent balance of lowspeed throttle response and fullthrottle performance, Pontiac used the Quadrajet for its performance applications in 1967 and as its only 4-barrel carburetor from 1968 forward. With the high number produced over the years, there are a number of original castings available today. They look completely original while providing excellent performance when modified correctly.

A carburetor must provide the correct mixture of atomized fuel and air for maximum performance in every operating condition. Each Quadrajet was specifically calibrated for its intended applications. Three specific fuel circuits—idle, primary (or main), and secondary—provide strong performance throughout the entire powerband. Significant engine modifications, such as camshaft or compression ratio changes, or cylinder-head port work, can require altering carburetor fueling.

When a hobbyist attempts to use a Quadrajet originally intended for a mild 301 on a highly modified 455, for instance, the carburetor simply cannot handle the fuel demand of the larger engine. While metering jet and/or rod changes can improve part-throttle and fullthrottle fueling, the engine often struggles to stay running or requires an excessive amount of initial timing to produce suitable idle quality. It is this instance that lends the Quadrajet its negative reputation. The proper repair is to completely disassemble the Quadrajet and enlarge the fixed orifices within the carburetor that control idle fueling.

That process and all the necessary information required for proper calibration can be found in CarTech’s How to Rebuild and Modify Rochester Quadrajet Carburetors by Cliff Ruggles. It’s an excellent resource that helps you identify the best Pontiac Quadrajet castings, the proper rebuild technique, and how to correctly calibrate one for most applications. Both Cliff’s High Performance and The Carburetor Shop can provide you with top-quality components compatible with ethanol-blend fuel for your project.

Tri-Power induction remains very popular with Pontiac hobbyists. The unique wail the Rochester 2-barrel trio makes at full-throttle is a sound unmatched by any 4-barrel carburetor. It is a sound many attempt to mimic by adding a Tri-Power intake manifold to their Pontiac. Many are hesitant to adjust or modify a somewhat properly working Tri-Power setup, fearing that it may operate worse than before. Tri-Power may seem complicated, but is much easier to tune if the carburetors are functioning properly.

Mike’s Tri-Powers and The Carburetor Shop are companies that are capable of handling all your Tri-Power needs. Both stock a complete line of components required to properly rebuild a Rochester 2-barrel carburetor, including rubber components compatible with ethanol-blend fuel. In addition to carburetor parts, Mike’s also carries an entire line of restoration components to properly restore your original Tri-Power setup. Both companies offer knowledgeable tech support that’s sure to help you diagnose and correct any operational issue you may experience.

 

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Distributor Types

There are two basic types of ignition systems that Pontiac used over the years: One uses contact points, and the other is electronically controlled.

The contact point set in a distributor transfers electrical energy from the coil to the spark plugs. Energy builds while the points are closed, and the duration that the points are closed is referred to as “dwell angle,” which is a degree of distributor rotation. An intense electrical spark travels the air gap across the spark plug electrode and ground strap as the points open.

Contact points distributors are quite simple and operate reliably. Dwell angle does change as the contact points wear during normal operation, however, degrading spark intensity over time. Periodic dwell angle adjustments to return it to the 28- to 32-degree range Pontiac suggests is required to maintain peak performance and minimal emissions. Once dwell exceeds that range and cannot be adjusted accordingly, the points set must be replaced, which is a relatively easy process.

Pontiac began offering its “transistorized” electronic distributor on a larger scale during the 1960s. An electronic ignition module that automatically adjusted dwell replaced the contact points set. Another electronic distributor was introduced late in the 1971 model year. The “Unitized” ignition system was marketed as a fully self-contained unit that featured an in-cap coil and required a single 12-volt power lead for normal operation. Plagued by expensive replacement parts, it was used more often during the 1972 to 1974 model years before it was replaced by the “high energy ignition” (HEI), which made its debut in May 1974.

HEI functioned similarly to Unitized, but its design was much simpler and more reliable. Produced by the AC Delco division of GM, HEI became standard equipment on most Pontiac engines toward the end of the 1974 model year. It was standard equipment on all Pontiac engines beginning in 1975. HEI remains a widely popular ignition-system choice for most GM vehicles. Many aftermarket companies still produce modern interpretations of the design, to replace worn originals or to simply replace a points-type distributor all together.

 

Effective Quadrajet modifications are more involved than simply changing metering jets and rods. Enlarging certain passages with a small drill bit often is the only way to improve idle quality and the off-idle transition. CarTech’s How to Rebuild and Modify Rochester Quadrajet Carburetors, by Cliff Ruggles, is an excellent resource that clearly describes which holes must be drilled, and how large to make them.

Effective Quadrajet modifications are more involved than simply changing metering jets and rods. Enlarging certain passages with a small drill bit often is the only way to improve idle quality and the off-idle transition. CarTech’s How to Rebuild and Modify Rochester Quadrajet Carburetors, by Cliff Ruggles, is an excellent resource that clearly describes which holes must be drilled, and how large to make them.

 

Cliff’s High Performance offers complete rebuild kits that contain virtually every piece needed to properly restore the functionality of a Rochester Quadrajet carburetor. Cliff’s kits may be more costly than those available at local auto parts stores, but they are full of top-quality components and include new gaskets, a float and filter, various small parts, and even new fasteners. The rubber parts are specially designed for use with ethanol-blend fuel.

Cliff’s High Performance offers complete rebuild kits that contain virtually every piece needed to properly restore the functionality of a Rochester Quadrajet carburetor. Cliff’s kits may be more costly than those available at local auto parts stores, but they are full of top-quality components and include new gaskets, a float and filter, various small parts, and even new fasteners. The rubber parts are specially designed for use with ethanol-blend fuel.

 

Finding complete rebuild kits for Rochester 2-barrel carburetors can be difficult enough, but finding the correct kits to properly rebuild a Pontiac Tri-Power setup can be discouraging. Mike’s Tri-Powers offers complete rebuild kits for each Tri-Power carburetor. The kits include the required gaskets and a plethora of small parts. Even better, Mike’s offers an informative DVD that walks you through the Tri-Power rebuild and tuning process.

Finding complete rebuild kits for Rochester 2-barrel carburetors can be difficult enough, but finding the correct kits to properly rebuild a Pontiac Tri-Power setup can be discouraging. Mike’s Tri-Powers offers complete rebuild kits for each Tri-Power carburetor. The kits include the required gaskets and a plethora of small parts. Even better, Mike’s offers an informative DVD that walks you through the Tri-Power rebuild and tuning process.

 

The only real drawback to an HEI distributor is its compatibility with certain Pontiac platforms and intake manifolds. Its large-cap design sometimes interferes with the firewall on such models as the first-generation Firebird or certain years of the Ventura. If a slight amount of clearance is required, a hammer can be used to lightly “massage” the firewall.

HEI is not compatible with any type of original Tri-Power intake manifold. The runners simply extend too far rearward to allow the use of an original-type HEI. Companies such as Dave’s Small Body HEI’s can produce an HEI-type distributor that uses a points-type housing at a very reasonable cost. Other companies offer complete electronic conversions for hobbyists who want to reuse a points-type distributor but use an electronic triggering system.

 

A contact points set was a common sight inside almost any new-car distributor wells into the 1970s. The coil saturates with current while the points are closed, and the resistance that occurs when the points are open is released as an electrical spark that jumps the spark plug gap. New contact points sets are available at local auto parts stores. Most hobbyists elect to convert from mechanical to electronic operation.

A contact points set was a common sight inside almost any new-car distributor wells into the 1970s. The coil saturates with current while the points are closed, and the resistance that occurs when the points are open is released as an electrical spark that jumps the spark plug gap. New contact points sets are available at local auto parts stores. Most hobbyists elect to convert from mechanical to electronic operation.

 

The HEI was Pontiac’s most common electronic ignition system. It made its debut in the mid 1970s and became standard equipment on all GM vehicles shortly after. Used units are easily found at swap meets or salvage yards, but it’s often easier to purchase a brandnew HEI than salvaging a worn original. The Pertronix D-1200 is an excellent choice. It contains topquality components and an adjustable vacuum advance unit. Pertronix also offers a few different ignitor kits to convert a points-type distributor to electronic operation.

The HEI was Pontiac’s most common electronic ignition system. It made its debut in the mid 1970s and became standard equipment on all GM vehicles shortly after. Used units are easily found at swap meets or salvage yards, but it’s often easier to purchase a brandnew HEI than salvaging a worn original. The Pertronix D-1200 is an excellent choice. It contains topquality components and an adjustable vacuum advance unit. Pertronix also offers a few different ignitor kits to convert a points-type distributor to electronic operation.

 

Most low-end HEIs available on the aftermarket contain generic mechanicaladvance curves that use lowquality pieces, and may need to be re-curved to produce peak engine output. Performance Distributors offers new top-quality HEIs that feature custom-calibrated mechanical and vacuum advance curves for your individual combination. They are delivered ready to run and offer proven success.

Most low-end HEIs available on the aftermarket contain generic mechanicaladvance curves that use lowquality pieces, and may need to be re-curved to produce peak engine output. Performance Distributors offers new top-quality HEIs that feature custom-calibrated mechanical and vacuum advance curves for your individual combination. They are delivered ready to run and offer proven success.

 

Spark Advance

Tuning An internal combustion engine generates torque by applying the combustion force as leverage, which rotates the crankshaft. Maximum torque occurs when cylinder pressure peaks at a crankshaft angle between 10 and 20 degrees after top dead center (ATDC). That range allows combustion pressure to exert as much of its force as possible over the entire length of the crankshaft’s stroke.

The crankshaft is in constant motion and total combustion takes a fixed amount of time. As engine speed increases, ignition must be initiated at an earlier crankshaft angle (before top dead center—BTDC) for peak pressure to occur within the desired ATDC crankshaft angle.

There are three basic terms often used when speaking of spark advance initial timing, mechanical advance, and vacuum advance. Each plays a distinct role in engine performance and each is very adjustable. Finding the right combination of the three can be difficult, but peak engine performance occurs only when combustion pressure is applied at the right time under every RPM and engine load. Initial timing is the base amount of spark lead an engine sees at idle with the distributor’s vacuum advance canister disconnected from any vacuum source.

 

M&H Electric Fabricators’ breakerless electronic conversion kit allows owners to eliminate the contact points set within a conventional distributor and install an electronic triggering system. The complete M&H kit fits completely within the points-type distributor cap. Its one-wire hookup lends to easy installation, while maintaining a completely original appearance. The M&H kit comes with a threeyear manufacturer warranty.

M&H Electric Fabricators’ breakerless electronic conversion kit allows owners to eliminate the contact points set within a conventional distributor and install an electronic triggering system. The complete M&H kit fits completely within the points-type distributor cap. Its one-wire hookup lends to easy installation, while maintaining a completely original appearance. The M&H kit comes with a threeyear manufacturer warranty.

 

MSD Ignitions has developed a new HEI ignition module with rev limiting capability (number 83645) that replaces the original electronic module found within an HEI distributor. It features increased output and full adjustability over its rev limiter, which can be set from 5,000 to 10,000 rpm. The MSD module installs relatively easily and retains a stock-type appearance.

MSD Ignitions has developed a new HEI ignition module with rev limiting capability (number 83645) that replaces the original electronic module found within an HEI distributor. It features increased output and full adjustability over its rev limiter, which can be set from 5,000 to 10,000 rpm. The MSD module installs relatively easily and retains a stock-type appearance.

 

Mallory Ignition offers two excellent items for Pontiac distributors. Its electronic conversion kit (number 61001M) replaces the points set in a conventional distributor. Its revlimiting HEI module (number 699) is an excellent piece that directly replaces an original HEI module, offering complete rev-limiting control. I have used the Mallory module in my own HEI for several years. I highly recommend it to anyone looking to protect an engine while retaining a completely original appearance.

Mallory Ignition offers two excellent items for Pontiac distributors. Its electronic conversion kit (number 61001M) replaces the points set in a conventional distributor. Its revlimiting HEI module (number 699) is an excellent piece that directly replaces an original HEI module, offering complete rev-limiting control. I have used the Mallory module in my own HEI for several years. I highly recommend it to anyone looking to protect an engine while retaining a completely original appearance.


 

Initial timing is measured by connecting a timing light to the number-1 spark plug wire. The timing light is aimed at the harmonic balancer. The strobe produced makes the harmonicbalancer’s TDC timing mark appear stationary with the graduated hash marks on the timing cover. Most Pontiacs are in the 8- to 12-degree range. Initial timing can be adjusted by simply loosening the hold-down clamp and rotating the distributor. Clockwise rotation advances timing; counterclockwise retards it.

A distributor is equipped with a mechanical advance system that automatically advances spark timing in relation to engine speed. Also called “centrifugal advance,” it uses a pair of weights that overcome spring tension as engine speed increases, to press on a center cam and advance the spark timing. The factorydesigned advance curves are often an excellent compromise of emissions, performance, and reliable operation on questionable-quality fuel.

Modifying the centrifugal advance curve is a popular way to increase the low-speed street manners and full-throttle performance of a particular combination. It usually involves more spark advance and/or a quicker rate of advance. The advance curve can be tested on professional equipment or with an adjustable timing light. The goal is to tailor the advance curve for peak performance by replacing weights, center cam, and/or springs. Though each combination must be addressed individually, 22 to 24 crankshaft degrees of mechanical advance that peaks between 3,000 and 3,500 rpm is an excellent starting point for a street-driven application.

Total timing is the sum of static initial timing plus mechanical advance. For instance, 10 degrees of static initial plus 24 degrees of mechanical advance produces 34 degrees of total advance. I’ve found that most Pontiacs with cast-iron cylinder heads seem to perform best with 34 to 38 degrees of total timing. You’ll have to experiment to determine the amount of timing that works best for your particular application, but listen very intently for any high-speed “ticking” or “rattling” at full throttle. Too much timing can cause engine-damaging detonation, and any testing should be immediately halted until timing can be adjusted accordingly.

 

The XR-i conversion kit from Crane Cams allows owners to easily convert a conventional distributor to electronic operation. Unlike the others, Crane’s kit includes an adjustable rev limiter (the unit specific to Pontiac is number 750- 1720). I’ve installed several XR-i modules into distributors over the years, and have found them easy to use and quite reliable.

The XR-i conversion kit from Crane Cams allows owners to easily convert a conventional distributor to electronic operation. Unlike the others, Crane’s kit includes an adjustable rev limiter (the unit specific to Pontiac is number 750- 1720). I’ve installed several XR-i modules into distributors over the years, and have found them easy to use and quite reliable.

 

Vacuum Advance Tuning

A carburetor is designed to provide the required amount of fuel to produce peak power at every engine speed under every type of load. In light-load conditions such as at partthrottle cruise, the throttle plates are almost closed, and it provides minimal amounts of fuel and air. Cylinder volume doesn’t change, however, so the fuel and air molecules within the combustion chamber aren’t as tightly compacted during the compression stroke, resulting in a less combustible mixture.

The flame front of a less combustible mixture spreads slower. Spark must be initiated much earlier for peak cylinder pressure to occur at the optimum time. This is sometimes in excess of 50 degrees BTDC depending upon the condition. It’s impossible to have a distributor mechanical advance curve properly set to provide peak performance for both part-throttle and full-throttle conditions, so a load-sensing device that uses engine vacuum to advance spark in light-load conditions was added to the distributor.

 

Electronics companies, such as Sun and Allen, offered a number of different distributor testers like this Allen Syncrograph, which was produced in the early 1980s. They were once used by service professionals to test complete functionality of a distributor. Speed shops used them to adjust the mechanical advance curve for optimum performance. Fully functional units are quite rare. If you have a distributor that you need re-curved, you may be able to find someone who has one locally by simply by asking around.

Electronics companies, such as Sun and Allen, offered a number of different distributor testers like this Allen Syncrograph, which was produced in the early 1980s. They were once used by service professionals to test complete functionality of a distributor. Speed shops used them to adjust the mechanical advance curve for optimum performance. Fully functional units are quite rare. If you have a distributor that you need re-curved, you may be able to find someone who has one locally by simply by asking around.

 

Not everyone has access to professional distributor testing equipment. Not to worry! Bob Davis Distributors can provide you with a high-quality re-curve kit that contains everything required to properly adjust your HEI’s mechanical advance.

Not everyone has access to professional distributor testing equipment. Not to worry! Bob Davis Distributors can provide you with a high-quality re-curve kit that contains everything required to properly adjust your HEI’s mechanical advance.


 

Vacuum advance tuning should be performed only after the initial and mechanical advance curves have been modified to produce peak performance. I have found that most Pontiac engines respond favorably to 10 to 15 degrees of vacuum advance, which increases the amount of spark lead to nearly 50 degrees at part throttle. Some engines may actually tolerate even more vacuum advance without detonating, but it seems the effects appear to diminish beyond about 15 degrees.

I feel that the adjustable vacuum advance kit produced by Crane is the best available choice. It allows the tuner to adjust the amount of vacuum advance and the vacuum actuation point independently of one another. Too much vacuum advance can produce audible detonation at light partthrottle. If any detonation is detected, remove 2 degrees of vacuum advance and test again. Continue the process until detonation subsides.

There are two types of engine vacuum that the vacuum advance canister can be connected to. Ported vacuum provides available engine vacuum only when the throttle plates are open. Manifold vacuum provides engine vacuum at all times, including idle and deceleration. One type isn’t necessarily better than the other and not all carburetors are equipped to provide ported vacuum.

If your carburetor contains a ported vacuum source, I recommend performing your own testing session to determine which type of vacuum advance is best suited for an application. Connect the vacuum advance canister to one type first, adjust the idle speed accordingly, trim the carburetor mixture screws to provide peak vacuum, and perform a thorough test drive.

 

Crane Cams Adjustable Vacuum Advance kit offers complete and independent adjustability of the amount of vacuum advance and the vacuum actuation point. Crane produces separate kits for pointstype and HEI distributors. They install easily and are quite simple to use. I recommend using a Crane kit in any application where vacuum advance testing is planned.

Crane Cams Adjustable Vacuum Advance kit offers complete and independent adjustability of the amount of vacuum advance and the vacuum actuation point. Crane produces separate kits for pointstype and HEI distributors. They install easily and are quite simple to use. I recommend using a Crane kit in any application where vacuum advance testing is planned.


 

After establishing a baseline, connect the vacuum canister to the other type. Adjust the idle speed and carburetor mixture screws accordingly, and perform another test drive.

You should find that a proper amount of vacuum advance is immediately noticeable at part-throttle driving conditions. The engine should be more responsive to throttle angle changes at low speed, and the improved engine efficiency can translate into a slight fuel economy increase as well as possibly reduce normal operating temperature. I have yet to find any negative results when using a reasonable amount of vacuum advance in any combination.

 

A Final Note

Your rebuild is complete! If everything went as planned, your newly rebuilt Pontiac V-8 should perform better than ever before in any driving condition. It should start easily, idle smoothly, and accelerate effortlessly. It should not run hot and should be free of any oil or coolant leaks. If you can find any spare time to dedicate to finely tuning the carburetor and distributor, you may be able to extract a few more horsepower and further improve its street manners.

 

If your rebuild was successful, your Pontiac is running better in every driving condition. Any operating concern that existed before the rebuild should no longer be an issue. It should start quickly and easily and operate very consistently. It should run better and better as more miles are added, so drive your Pontiac often!

If your rebuild was successful, your Pontiac is running better in every driving condition. Any operating concern that existed before the rebuild should no longer be an issue. It should start quickly and easily and operate very consistently. It should run better and better as more miles are added, so drive your Pontiac often!


 

The owner of the 400 rebuilt in these pages was very pleased with the result. After the 400-hp engine was reinstalled into the GTO, the car’s performance was outstanding. The 400’s operating characteristics are much different than before. It starts easily, operates reliably on 91-octane pump gas, and has provided the owner with a few thousand miles of issue-free performance so far. The car is much easier to drive in any condition, and the 400-hp engine otherwise looks just like any other beautifully detailed, original 1967 400. That’s the exact result we were after. Hopefully your rebuild is as successful!

 

Written by Rocky Rotella and Posted with Permission of CarTechBooks

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