VW Air-Cooled Engines: How to Build Max-Performance: How to Build Max-Performance

CHAPTER 1

ENGINE DESIGN

The basic design of the VW air-cooled engine has not changed much. To increase power, stronger parts are required, and more displacement, supercharging or turbocharging, and nitrous oxide can be used. Ferdinand Porsche made the original Volkswagen engine design, and the car was set up to transport a family of four every day at about 60 mph. However, today’s world requires something with more horsepower.

Air-Cooled and Liquid-Cooled Engine Basics

Automotive air-cooled engines require an auxiliary fan to adequately cool the engine. A shroud directs the airflow so that it circulates around the heads and cylinders efficiently. A thermostat opens and closes either the fan’s air intake or outlet (depending on design) so that the engine warms up quickly and the operating temperature doesn’t vary over a wide range.

Most automotive air-cooled engines require an oil cooler for extra engine heat reduction, which in the case of a Type 1 or Type 2 is under the fan shroud. These oil coolers are small radiators that the oil circulates through after being pumped through the engine before returning to the crankcase. Air-cooled engines rely on the oil supply to help maintain the designed engine temperature. When making performance upgrades, upgrade the oil cooler and filtration system.

When building a high-performance Beetle engine, upgrade the air-cooling systems to accommodate the increased engine heat that will be produced. Heat is thermal energy and cannot be destroyed; it can only be transferred. Heat always moves from a hotter object to a colder object, which is part of the second law of thermodynamics. The cooling fan in the air-cooled cooling system blows cold air across the engine to remove the heat. Air is the main heat exchanger that removes the heat of combustion through convection.

The Formula Super Vee racing series ran from 1970 to 1990. It was an offshoot of Formula Vee, which started in 1959. Formula Super Vee was a promotional platform for Volkswagen vehicles.

The Volkswagen military Kübelwagen Command bucket-seat car (also called the tub car) was a light military vehicle designed by Ferdinand Porsche and built by Volkswagen during World War II for use by the German military (both Wehrmacht and Waffen SS). It was based heavily on the Volkswagen Beetle, and it was prototyped as the Type 62 but eventually became known internally as the Type 82. Volkswagen built a similar vehicle in the 1970s called the Thing. (Photo Courtesy Shutterstock)

Volkswagen air-cooled engines use deeply finned heads and cylinders similar to many motorcycles. The fins provide more surface area to absorb heat and draw it away from the cylinders and combustion chambers. The fins also expose more surface area to the air to help dissipate the heat. The engine crankcases of some air-cooled engines have internal and external fins that reduce oil temperature to maintain the overall engine temperature. The internal fins speed heat absorption from the oil to the crankcase, and the external fins dissipate the heat to the air.

The Volkswagen engine cooling fan blows air inside the shroud, which is directly over the cooling fins on the cylinders and heads. This removes the heat of combustion like a heat sink. This passive heat exchanger transfers the heat generated by the engine to the air, where it is dissipated away from the engine. (Photo Courtesy Shutterstock)

Convection is heat transfer by the molecular motion within the heated substance itself. It only takes place in liquids and gases. This gas heat transfer is by the circulation of air in motion between the cooling fan and the head and cylinder cooling fins, which act as heat sinks. Combustion heat is transferred to the cylinder wall and is blown by the cooling fan into the heater boxes to either heat the vehicle or go into the atmosphere.

There are two sorts of convection heat transfer: natural convection and forced convection. Natural convection is when air motion is caused by different air densities. Forced convection is when air motion is caused by a fan, which is the method employed by most air-cooled engines. Heat transfers between the air and the fins of the heads and cylinders in relative motion, and the motion is caused by the cooling fan.

Motorcycles have used air-cooled engines for many years. However, Asian manufacturers used water-cooled engines for most of their motorcycles since the 1990s. Even Harley-Davidson engines have used liquid-cooled heads on many models for a few years now. Air-cooled engines remove engine heat by using the airflow that hits the engine when the bike is moving. This is why they have fins on the outside to create more surface area for the air to pass over. This cooling method is lightweight and simple. It usually requires no cooling fan and also has an engine oil cooler mounted in front of the engine to cool the oil. An engine-powered fan is sometimes used to send air to the fins for forced air cooling, which is similar to the Volkswagen engines. (Photo Courtesy Shutterstock)

The definition of convection is the action or process of conveying movement in a gas. In this case, air in the warmer parts rises. This graphic shows the heat transfer by molecular movement in the heated substance itself and heat transfer by circulation through the air.

Porsche 911–style cooling fans are used with ultra-high-performance builds using a Bergman Porsche 911–style shroud kit. If it is a milder build, a stronger-than-stock fan is available. It has 56 welds (28 on each side in an alternating pattern), is statically balanced for higher-RPM engines, and will fit all doghouse fan shrouds. A welded race fan with a 34.7-mm inner fan width and a 36.9-mm outer fan width is shown. (Photo Courtesy the Dub Shop)

The cooling fan is one of the most important parts of an air-cooled engine. Bent or cracked fins, a worn hub, or out-of-round fan hubs are issues that can cause overheating. The later-style factory fan and aftermarket fans are wider than the original unit.

Air-cooled engines do not provide a consistent and controllable engine-operating temperature that allows for precise fuel metering to provide lower exhaust emissions. This was one of the primary reasons that Volkswagen abandoned the air-cooled engine in favor of a water-cooled design.

Planning

When beginning a high-performance build on a Volkswagen air-cooled engine, decide what level of performance you want and assess your engine project finances. Are bolt-on options okay, or is performing a complete engine blueprint rebuild needed?

A liquid-cooled system is the most common automotive cooling system. The coolant circulates outside of the engine and is exposed indirectly to the air by a radiator. The air absorbs heat from the coolant so that the coolant can flow back into the engine and absorb more heat. The greater the difference in temperature between the coolant and the air, the more heat will be absorbed by the air. Uniform engine temperatures reduce thermal stress. The consistent temperatures also allow very precise fuel metering, which helps keep exhaust emissions low. In 1985, Volkswagen abandoned the air-cooled pancake engine in the Type 2 Microbus and Vanagan and replaced it with a water-cooled boxer pancake engine called the Waterboxer. (Graphic Courtesy Shutterstock)

Volkswagen Origins

The very start of Volkswagen and its engine begins with some politics in pre–World War II Germany.

Porsche engineers Karl Rabe and Xavier Reimspiess, under the direction of Dr. Ferdinand Porsche, designed an air-cooled, horizontally opposed, 985-cc, 4-cylinder engine to power Adolf Hitler’s KdF-Wagen, which became the Volkswagen, or “People’s Car.” A variety of engines were tried but were shelved in 1936 in favor of the now-classic VW Beetle engine.

The 985-cc engine was replaced by the 1,130-cc engine with a 75-mm bore and 64-mm stroke. This engine was originally developed for the military KübelwagenCommand (bucket-seat) cars, Model 62 and Model 82 that can be seen in old World War II movies.

The final decision to build the Volkswagen came after a discussion between Hitler and Porsche, where Hitler stated that the vehicle must be able to cruise at 60 mph, have fuel economy of 40 mpg, be air-cooled, have space for five people, and be priced at 1,000 Marks. Porsche felt this was unrealistic, and there was no existing plant.

In 1937, at the Berlin Motor Show, it was stated that Opel (GM owned) would build the Volkswagen. Hitler was not happy about Opel building the car and issued a command to build a factory just for the KdF-Wagen in Wolfsburg. Now with unlimited funds, Porsche built the historic Volkswagen Beetle. ■

Engine performance building is a series of concessions because it likely will not be able to do everything. Decide which parts of engine building and performance are most important and prioritize them. Ask yourself the following questions:

What is the funding for the engine project?

What is the purpose of the engine (street vehicle, modified stock, track race car, dune buggy, etc.)?

What level of reliability does the engine need? Do you want to remove the engine after every run? (For the range of 150 to 200 bhp, air-cooled engines need routine maintenance.)

Performance air-cooled engine building is not simple. Information regarding these old engine designs may be difficult to find online, and some of it may be misleading.

This performance kit from the Dub Shop provides complete performance-based components to install electronic fuel injection. It includes high-flow intake manifolds, the throttle body, fuel injectors, the crank pulley, controller, wiring, installation hardware, and instructions for a 1,600-cc Volkswagen engine. (Photo Courtesy the Dub Shop)

Increasing Performance

One of the quickest and cheapest ways to get more power out of an air-cooled VW engine is to make it breathe better. Larger cylinder heads, larger valves, and larger and smoother ports can be used to get more power. Another option is to replace the factory air-intake system with a higher-flow system without engine disassembly. This can increase horsepower by allowing more air to flow into the engine. A new air intake system is one of the easiest performance modifications that can be done, and it is not expensive. All of these modifications can be done without removing the engine. Although, these engines are easy to remove and reinstall. So, you may still do that, especially if you are changing the cylinder heads.

When building an engine, complete upgrade kits are available with everything needed to build a specific engine except the external components and induction system. (Photo Courtesy Scat Enterprises)

To improve engine breathing, the air must exit the engine as fast as it goes in. Installing a performance exhaust system increases horsepower by allowing hot air to exit the cylinders more efficiently. Performance exhaust systems are generally bolt-on and inexpensive. A supercharger or a turbocharger can be added to improve the engine air capacity and provide a denser charge, giving a boost in power if there is a strong bottom end. These can be costly and require engine modifications. However, there are bolt-on kits from numerous aftermarket performance-parts suppliers.

Thermodynamics

Thermodynamics is the subject of the relation of heat to forces acting within the combustion chamber of an internal-combustion engine. The main thermodynamic point is energy, which is the ability to do work. Thermodynamics works with heat and temperature and their relationship to energy and work. For example, energy can move from one object to another due to a difference in pressure, volume, and temperature. When heat moves an object through a distance, work is done.

Knowledge of thermodynamics assists in the design of a high-performance air-cooled engine because enough heat needs to be generated to develop enough power for the desired performance. The science of thermodynamics developed out of a desire to increase the efficiency of early steam engines from the work of French physicist Nicolas Léonard Sadi Carnot (1824).

Thermodynamics is a broad field and includes different systems: chemical, thermal, and mechanical. The combustion of air and fuel is called a system, and everything else is called its surroundings. This internal-combustion-engine system is closed because there is no interchange of matter between the system and its surroundings. Any change within the system that it may undergo is called a process. Any process or series of processes where the system returns to its original state is called a cycle, such as the four-stroke Otto cycle.

Heat is energy in transit from one mass to another because of a difference in temperature between the two. Whenever a force of any kind acts through a distance, work is performed. Just like heat, work is also energy in transit. The early application of thermodynamics was to mechanical heat engines.

Thermodynamics is simply heat that is used to generate power and cause motion. It is an increase in internal energy of a closed system that is equal to the total energy added to the system. If the energy that is entering the system is supplied as heat and leaves the system as work, the heat is accounted for as positive and the work as negative.

Temperature is worth measuring because it predicts whether heat will transfer between objects. This is true regardless of how the objects interact. If two objects are not in physical contact, heat still can flow between them by means of radiation heat transfer. If the systems are in thermal balance, no heat flow will occur.

The first law of thermodynamics states that when energy passes as work, as heat, or with matter into or out of a system, the system’s internal energy changes in accord with the law of conservation of energy. This pertains to the internal-combustion engine as well as perpetual-motion machines of the first kind. This means that machines that produce work with no energy input are not possible.

The second law of thermodynamics establishes that perpetual-motion machines of the second kind (machines that spontaneously convert thermal energy into mechanical work) are impossible.

Temperature is a measure of the degree of heat that an object possesses. It is the measure of the speed of the molecule vibrating. An increase in temperature indicates that the speed of the molecules has increased. When heat is removed from a body, it becomes cold because heat always flows from a warmer object to a colder object. A drop in temperature means a decrease in molecular speed.

The first law of thermodynamics is part of the conservation law of energy, which states that energy cannot be created or destroyed. It can only change. Whenever energy is transformed from one form to another, energy is always conserved as stated energy. The sum total of all energy remains the same. The first law concerns the analysis of systems involving heat transfer and work.

The second law of thermodynamics states that the conversion of heat to work is limited by the temperature at which the conversion takes place. It can be roughly related to the level of disorder, the loss of information, or the amount of useless energy (energy that cannot be used to perform work). The second law is an observation of the fact that over time, differences in temperature, pressure, and chemical potential tend to even out in a physical system that is isolated from the outside world. The conversion of heat to work is limited by the temperature at which the conversion occurs.

The internal-combustion engine burns its fuel inside a combustion chamber. One side of this chamber is open to a piston. When the fuel burns, the hot gases expand very rapidly and push the piston away from the combustion chamber. This basic action of heated gases expanding and pushing is the source of power for all internal-combustion engines.

Engine Combustion

The oldest engine known to man was the simple lever. Food fuels the muscle pushing the lever to move objects that the muscle alone could never budge. The automotive engine uses fuel to perform work. The Volkswagen air-cooled engine is fueled by gasoline. The automotive engine is an internal-combustion engine. It is internal because the fuel it uses is burned inside a combustion chamber. An external combustion engine burns fuel outside the engine, such as a steam engine. Fuel is burned to produce heat to make steam, and the steam powers pistons to move the vehicle.

The engine converts part of the fuel energy to useful power, which is used to move the vehicle. The chemical energy in fuel is converted to heat due to the burning of the fuel at a controlled rate, which is called combustion. Heat energy released in the combustion chamber raises the temperature of the combustion gases within the chamber. The increase in gas temperature causes the pressure of the gases to increase. The pressure developed within the combustion chamber pushes on the head of a piston to produce a usable mechanical force, which is converted into mechanical power. The trick in building a high-performance engine is to increase this explosive pressure to push harder against the piston to develop more torque or twisting force to move the vehicle faster.

In a spark-ignition air-cooled engine, a homogenous mixture of fuel and air is inducted into the engine. This gas mixes with the exhaust gas remaining from the previous cycle, which results in a slightly diluted mixture. To start combustion, a spark with a duration of about 0.001 second is discharged. A short delay of about 0.001 second follows, during which chemical reactions started by the spark produce a small flame kernel that is able to propagate across the combustion chamber. The speed with which the flame moves across the combustion chamber is determined by three main factors: laminar flame speed, turbulent enhancement of the flame speed, and the expansion ration of the burned gas.

Laminar flame speed is the speed at which a flame will burn though a calm air-fuel mixture. A laminar flame burns as a flat flame sheet as it moves through the mixture. Laminar burning velocities for gasoline range from about 3 centimeters per second for a very lean mixture up to 150 centimeters for a stoichiometric mixture at 14.7 parts air to 1 part fuel at a high temperature.

For turbulent enhancement, the flame does not propagate across the combustion chamber as a smooth flame sheet. Rather, turbulence in the gases twists and distorts the flame shape into a wrinkled sheet that greatly increases its surface area. The effect of this turbulence increases the