Programmable ECUs

A special category of ECUs are those which are programmable. These units do not have a fixed behaviour and can be reprogrammed by the user.

Programmable ECUs are required where significant aftermarket modifications have been made to a vehicle's engine. Examples include adding or changing of a turbocharger, adding or changing of an intercooler, changing of the exhaust system or a conversion to run on alternative fuel. As a consequence of these changes, the old ECU may not provide appropriate control for the new configuration. In these situations, a programmable ECU can be wired in. These can be programmed/mapped with a laptop connected using a serial or USB cable, while the engine is running.

The programmable ECU may control the amount of fuel to be injected into each cylinder. This varies depending on the engine's RPM and the position of the accelerator pedal (or the manifold air pressure). The engine tuner can adjust this by bringing up a spreadsheet-like page on the laptop where each cell represents an intersection between a specific RPM value and an accelerator pedal position (or the throttle position, as it is called). In this cell a number corresponding to the amount of fuel to be injected is entered. This spreadsheet is often referred to as a fuel table or fuel map.

By modifying these values while monitoring the exhausts using a wide band lambda probe to see if the engine runs rich or lean, the tuner can find the optimal amount of fuel to inject to the engine at every different combination of RPM and throttle position. This process is often carried out at a dynamometer, giving the tuner a controlled environment to work in. An engine dynamometer gives a more precise calibration for racing applications. Tuners often utilize a chassis dynamometer for street and other high performance applications.

Other parameters that are often mappable are:

• Ignition Timing: Defines at what point in the engine cycle the spark plug should fire for each cylinder. Modern systems allow for individual trim on each cylinder for per-cylinder optimization of the ignition timing.
• Rev. limit: Defines the maximum RPM that the engine is allowed to reach. After this fuel and/or ignition is cut. Some vehicles have a "soft" cut-off before the "hard" cut-off. This "soft cut" generally functions by retarding ignition timing to reduce power output and thereby slow the acceleration rate just before the "hard cut" is hit.
• Water temperature correction: Allows for additional fuel to be added when the engine is cold, such as in a winter cold-start scenario or when the engine is dangerously hot, to allow for additional cylinder cooling (though not in a very efficient manner, as an emergency only).
• Transient fueling: Tells the ECU to add a specific amount of fuel when throttle is applied. The is referred to as "acceleration enrichment".
• Low fuel pressure modifier: Tells the ECU to increase the injector fire time to compensate for an increase or loss of fuel pressure.
• Closed loop lambda: Lets the ECU monitor a permanently installed lambda probe and modify the fueling to achieve the targeted air/fuel ratio desired. This is often the stoichiometric (ideal) air fuel ratio, which on traditional petrol (gasoline) powered vehicles this air:fuel ratio is 14.7:1. This can also be a much richer ratio for when the engine is under high load, or possibly a leaner ratio for when the engine is operating under low load cruise conditions for maximum fuel efficiency.

Some of the more advanced standalone/race ECUs include functionality such as launch control, operating as a rev limiter while the car is at the starting line to keep the engine revs in a 'sweet spot', waiting for the clutch to be released to launch the car as quickly and efficiently as possible. Other examples of advanced functions are:

• Wastegate control: Controls the behavior of a turbocharger's wastegate, controlling boost. This can be mapped to command a specific duty cycle on the valve, or can use a PID based closed-loop control algorithm.
• Staged injection: Allows for an additional injector per cylinder, used to get a finer fuel injection control and atomization over a wide RPM range. And example being the use of small injectors for smooth idle and low load conditions, and a second, larger set of injectors that are 'staged in' at higher loads, such as when the turbo boost climbs above a set point.
• Variable cam timing: Allows for control variable intake and exhaust cams (VVT), mapping the exact advance/retard curve positioning the camshafts for maximum benefit at all load/rpm positions in the map. This functionality is often used to optimize power output at high load/rpms, and to maximize fuel efficiency and emissions as lower loads/rpms.
• Gear control: Tells the ECU to cut ignition during (sequential gearbox) upshifts or blip the throttle during downshifts.

A race ECU is often equipped with a data logger recording all sensors for later analysis using special software in a PC. This can be useful to track down engine stalls, misfires or other undesired behaviors during a race by downloading the log data and looking for anomalies after the event. The data logger usually has a capacity between 0.5 and 16 megabytes.

In order to communicate with the driver, a race ECU can often be connected to a "data stack", which is a simple dash board presenting the driver with the current RPM, speed and other basic engine data. These race stacks, which are almost always digital, talk to the ECU using one of several proprietary protocols running over RS232 or CANbus, connecting to the DLC connector (Data Link Connector) usually located on the underside of the dash, inline with the steering wheel

ECU

Engine Control Unit

An ECU is a computer that runs the engine in all moderd day vehicles, Introduced in the early 1980s with the advent of electronic fuel injection systems, these early systems where very primitive they just monitored the revolution of the engine, air flow in to the engine and engine temperature. The ECU then used this information gathered from these sensors to inject the right amount of fuel at the right time. The advantages of fuel injection over a carburettured engine was the degree of control that a computer had over fuel delivery, 1000s of times more accurate than that of a carburetor.

An engine control unit (ECU), most commonly called the powertrain control module (PCM), is a type of electronic control unit that controls a series of actuators on an internal combustion engineto ensure the optimum running. It does this by reading values from a multitude of sensors within the engine bay, interpreting the data using multidimensional performance maps (called Look-up tables), and adjusting the engine actuators accordingly.

Before ECUs, air/fuel mixture, ignition timing, and idle speed were mechanically set and dynamically controlled by mechanical and pneumatic means. One of the earliest attempts to use such a unitized and automated device to manage multiple engine control functions simultaneously was the "Kommandogerät" created by BMW in 1939, for their 801 14-cylinder aviation radial engine

In the present day an ECU is a very powerful control system capable of gathering hundreds of channels of information to control every aspect of the engine, even its own efficiency. 
The worse place in the world that you could put a sophisticated piece of electronics is under the bonnet of a car due to massive vibration, constant heat variations and intense radio interference from the ignition system added to the fact that the manufacturers must produce on a huge scale, this causes so many problems and design flaws with modern day ECUs.

  Intake Manifolds for Carburetors

There are countless options for choosing an intake manifold. Some intakes will help you make power down low, while others will help with top end power. Choosing the right intake is a matter of your application and the kind of horsepower your engine will potentially make. We'll give you Intake Manifold basics and then get more technical at the end.

Intake Manifold Format

You've heard the terms: High rise manifold, dual plane, single plane, tunnel ram....Each manifold type has a purpose in the performance world.

Dual Plane Intake Manifolds

Dual plane intake manifolds are named for their split plenum opening in the intake where the carb sits. Each side of the opening feeds 4 cylinders on a V8. Dual plane intake manifolds are the most popular for high performance street and mild racing because they generally build power across a wider range and start at 1,500 RPM, depending on the dual plane manifold. Each intake manifold has its own performance characteristics. It's best to know how you'll use your vehicle and select from there. To be clear: Dual plane has nothing to do with the number of carburetors that the intake will accept. You can have a dual plane manifold that accepts 1 or 2 carburetors.

Single Plane Intakes

Single plane manifolds are named for their intake opening where the carb is bolted on. A single plane intake has one "hole", in the plenum where the carburetor sits on the intake. Fuel from the carburetor enters the intake through one opening with no separation. That single hole feeds all 8 cylinders on a V8. They are typically less restrictive and work best to build power between 3,000 and 8,000 RPM's. Because of the RPM range, the single plane intake manifold is best suited for racing applications.

Square Bore Intakes

Carburetors have venturis that open and close as you apply the throttle. A 4 barrel square bore carb has 4 equal sized venturis that you can more easily see from the underside ofthe carb. Square bore intake manifolds match the square bore shape of the carburetor base and venturis.

Spread Bore Intakes

Spread bore carburetors have 2 small venturis up front that are the primaries and 2 larger secondaries on the rear of the carb. Spread bore intake manifolds match that shape to accomodate the larger venturis toward the back.

Low Rise Intakes

Low Rise refers to the height of the intake. Low rise is a general term used to describe intake manifolds. There is no clear distinction between a low rise and a medium rise intake. It's pretty easy to describe an intake manifold as low or high rise. Low riseintakes fit under hoods better and offer certain performance advantages over taller intakes.

High Rise Intakes

High rise intakes are taller than low rise. High rise is a general term to describe an intake. There is no standard height where low rise intakes end and high rise intakes begin. High rise intakes are better at building horsepower in the upper RPM range and usually have a wider power band.

Tunnel Rams

Tunnel ram intakes are extreme Hi Rise intakes that accomodate one or two 4 barrel carburetors. They are made for high RPM and big horsepower setups. You see tunnel rams on the street, but they are best suited at the track where you can really get into the higher RPM's.

So, How do I select the right manifold for my application?

As with many situations in building an engine, it should match your intended purpose. Everyone wants the big tunnel ram dual quad intake sticking out of the hood, but it may not be practical, or best, for maximum performance. All intakes advertise an RPM range that identifies where they are most efficient. As an example, the intake may advertise "1,500-6,500 RPM". This RPM range must be considered and is the easiest guide to choosing the right intake for you. Street cars work best with a dual plane intake, most advertised "idle to 6,000 RPM" or "1500-6500 RPM". Race cars that work more in the upper RPM ranges will require a single plane, ?2,500-7,000 RPM? or "3,500-8,000 RPM". Next, the intake and camshaft selection should go hand in hand. The camshaft will also state an RPM range for its best performance. The RPM range of the camshaft and intake should match or be very close. A minimal low RPM difference of 500 RPM is acceptable, but should not exceed 1000 RPM. If this is the case in your selections it is better for the intake RPM range to start lower than the camshaft. The reverse may cause low end instability, thus an off throttle hesitation. Lastly you need to consider the physical fitment. Most obviously, be sure to select the appropriate part number for the engine and cylinder head design. Consideration for engine vacuum ports, water coolant ports, carburetor flange fitment, and be sure to check for proper hood clearance.

Fuel Injectors

There are a few important factors that you must take into account when modifying an electronic fuel injection engine. These car aceessories factors are: the pulse duration of the injectors and the duty cycle. The injector pulse duration is the amount of time that the injector is held open so that it can inject fuel into the combustion chamber. The pulse duration is controlled by the engine control unit (ECU) and is dependent on various sensors in the electronic fuel injection (EFI) system. The longer the pulse duration, the more fuel is added to the air/fuel mixture. The amount of fuel required at any one time varies by the amount of air flow, the air density, the engine load, and the engine temperature. Therefore the pulse duration will vary. However, there is only a limited amount of time that the injector can be held open at each revolution of the engine. This amount of time is reduced as engine speed increases. For example, at 600 RPM the available time is 0.1 seconds (60 seconds in a minute divided by 600 revolutions) but at 6,000 RPM it is only 0.01 seconds. The pulse duration relative to the available time at the engine red line is called the duty cycle and is expressed as a percentage. Thus a duty cycle of 80% means that at the engine red line the pulse duration (the amount of time the injector is help open) is 80% of the available time.

Some engine tuners will tell you that if your car has a duty cycle of 80%, you have a possible gain of 20%. However, the injector is an electronic solenoid and cannot be held open for too long or it will overheat and fail. In practice most Nippon Denso and Rochester injectors will remain reliable at up to an 80% duty cycle; most Bosch injectors will remain reliable at up to an 85% duty cycle; and most Lucas injectors will remain reliable at up to a 92% duty cycle. Though even at these duty cycles it is still advisable to test the injectors. Test them specifically for their spray pattern and their flow volumes at the maximum duty cycle you require. On a race engine I wouldn't exceed a maximum duty cycle of 80% as dyno-testing on various have shown that a duty cycle in the region of 60% to 70% produces the best power. This is because a shorter duty cycle does not allow for the proper atomization of the fuel, and proper atomization is important for the proper burning of the air/fuel mixture. I usually aim for a duty cycle at the point where maximum power is reached so as to ensure the longevity and reliability of the injectors. So, how do you adjust the duty cycle? By adjusting the fuel pressure and the injector nozzle size. On an OEM EFI system there are certain limitations on increasing the fuel pressure and the injector nozzle size. I'll discuss increasing the injector size in a while, but you can read more about increasing fuel pressure here.

Increasing the injector nozzle size will result in increased fuel delivery all the time. As "Langer" mentioned in engine basics, a rich fuel mixture results in power loss. Therefore, increasing the nozzle size could have a negative effect on performance and economy. The oxygen Sensor (O2S) will correct the fuel mixture for an injector that is about 20% larger than stock. However, on a pre-1996 EFI system, the ECU will ignore the O2S sensor under full throttle conditions. Furthermore, the OEM ECU will not be able to handle an injector that is more than 20% larger than stock and will suspect that one or more of its sensors are faulty and will revert to its programmed settings, which means that the fuel air mixture will not be optimal and will probably be rich as this is the failsafe setting on the ECU when it suspects that its sensors are faulty.

Another option is to increase the number of injectors. You can do this by adding auxiliary injectors that are controlled by a separate ECU, or by adding a second ECU to control both the existing injectors as well as the additional injectors, leaving the OEM ECU to control the other engine management functions. The latter is called "staged" injection and requires an extra injector for each engine cylinder. With auxiliary injectors you don't need an extra injector per cylinder; instead you can place one or two extra injectors upstream in the air intake path. To achieve the best performance, you should install the extra injectors ahead of the throttle body in the intake path as this allows for better fuel distribution and aids fuel vaporization. However, with positive-displacement superchargers, such as Roots, Eaton, or Lysholm superchargers this is not possible because the throttle body must be placed ahead of the supercharger.

While the additional ECU in both systems are fully programmable, and while staged injection is more expressive and a bit more complicated than auxiliary injectors, it does give you far more tuning control and better fuel distribution as you have full programming control over both sets of injectors. Usually, the new injectors are larger than the stock injectors and become the primary injectors with the stock injectors becoming the secondary injectors. The secondary injectors only come online at high engine loads, when extra fuel in required. This setup allows for greater tolerance of minor variations in the air/fuel mixture, and a smoother transition when the secondary injectors are in use. Whenever I need to run larger injectors, and when my budget allows it, I'd go for staged injection every time.

carburetor

carburetor, also spelled carburettor ,  device for supplying a spark-ignitionengine with a mixture of fuel and air. Components of carburetors usually include a storage chamber for liquid fuel, a choke, an idling (or slow-running) jet, a main jet, a venturi-shaped air-flow restriction, and an accelerator pump. The quantity offuel in the storage chamber is controlled by a valve actuated by a float. Thechoke, a butterfly valve, reduces the intake of air and allows a fuel-rich charge to be drawn into the cylinders when a cold engine is started. As the engine warms up, the choke is gradually opened either by hand or automatically by heat- and engine-speed-responsive controllers. The fuel flows out of the idling jet into the intake air as a result of reduced pressure near the partially closedthrottle valve. The main fuel jet comes into action when the throttle valve is further open. Then theventuri-shaped air-flow restriction creates a reduced pressure for drawing fuel from the main jet into the air stream at a rate related to the air flow so that a nearly constant fuel-air ratio is obtained. The accelerator pump injects fuel into the inlet air when the throttle is opened suddenly.

In the 1970s, new legislation and consumer preferences led automobile manufacturers to improvefuel efficiency and lower pollutant emissions. To accomplish these objectives, engineers developedfuel injection management systems based on new computer technologies. Soon, fuel injection systems replaced carbureted fuel systems in virtually all gasoline engines except for two-cycle and small four-cycle gasoline engines, such as those used in lawn mowers.

Things to Remember When Buying a Carburetor

Things to Remember When Buying a Carburetor

If you drive or own a vintage car, it's probably equipped with a carburetor. The carburetor is yesteryear's version of today's fuel injection systems. Invented by Karl Benz in 1800, this component is continued to be trusted by millions of car owners all over the globe. The carburetor's main function is to mix the right amount of gasoline with air to make your engine run properly. It works by metering, vaporizing the fuel, and equally distributing the air-fuel mixture. If the carburetor fails and the air-fuel mixture is incorrect, your engine will have a hard time functioning. This can lead to an engine that's running lean or rich. If there is less fuel than the amount required in the mixture, this is the time when the engine runs lean. On the other hand, if there is more fuel than the required amount, this is when the engine runs rich. An engine that's running on incorrect air-fuel ratio will usually produce a lot of smoke, bog down, stall, waste fuel, or at times, it may even not run at all. If you think your good old carburetor is malfunctioning and causing you trouble on the road, you'd better address it right away to get your vehicle back on track ASAP.

Finding a Carburetor

If you want to get a carburetor that will deliver exceptional functionality and efficiency when you drive, you are going to find a lot of options out there today. A lot of carburetors are intended for high-performance applications. And whether you are going to use your vehicle on the streets or on the race track, the market offers a wide selection of carburetors that will help you fix or upgrade your ride.

Choose a carburetor that has exceptional throttle response to make the most out of your engine's power. There are tons of OEM options that you can choose from with prices ranging from 250 to 500 USD. It may seem a bit pricey, but the performance that you are going to get once you've installed will make it worth every penny you spend.

Buying a Carburetor

More than anything else, your first priority when getting a carburetor should be acquiring one that's easy to install and tune. This will make it easy for you to fix the component according to your vehicle's specs and settings. Also, make sure you get a carburetor that is completely compatible with your system to ensure that your vehicle parts will coexist and work well with another. To make sure you get your money's worth, never settle for anything less and buy only from a brand that you can trust. Choose a brand that is backed by a good reputation to lessen your worries while performing your vehicle repairs.

How to Replace your Vehicle's Carburetor

How to Replace your Vehicle's Carburetor

Dirt, debris, and varnish are the most common types of contaminants that can damage your carburetor. Over time, these tiny particles can accumulate and clog up your fuel and air passages. When left unchecked, it can cause your carburetor some serious problems. Below are the tools and steps that you can follow to get your vehicle back on track ASAP.

Difficulty Level: Easy

What You'll Need:

• Rags
• Metric wrench set
• Metric socket set
• Gasket sealer
• Replacement carburetor
• Replacement gasket
• Gasket sealer

Step 1: Using your wrenches and sockets, disconnect your battery, vacuum, and fuel lines from the carburetor. If your vehicle has an automatic transmission, don't forget to disconnect the throttle linkage as well. Mark or tag all the lines to make it easier for you to return them back later.

Step 2: Take out the carburetor by removing the nuts that connect it to the intake manifold. To keep other parts from falling, place some rags in the opened intake ports.

Step 3: Clean the area where you're going to mount the new carburetor and gasket. Before cleaning the gasket surface, make sure you remove the rags first.

Step 4: Put the gasket in place and spread over a light coating of gasket sealer on both sides.

Step 5: Attach your replacement carburetor, and secure it in place by tightening the nuts in a crisscross torque pattern. Do not overdo it and remember to apply just the right amount of pressure for each nut.

Step 6: Reconnect your vacuum and fuel lines before attaching your battery back.

Step 7: Before starting the engine, prime your carburetor with some gas. You might need to prime it a couple of times before the gas reaches the carburetor.

Step 8: Check your system for any vacuum or gas leaks and replace gaskets when needed.

Single OverHead Camshaft

If you have read the article How Car Engines Work, you know about the valves that let the air/fuel mixture into the engine and the exhaust out of the engine. The camshaft uses lobes (called cams) that push against the valves to open them as the camshaft rotates; springs on the valves return them to their closed position. This is a critical job, and can have a great impact on an engine's performance at different speeds. On the next page of this article you can see the animation we built to really show you the difference between a performance camshaft and a standard one.

In this article, you will learn how the camshaft affects engine performance. We've got some great animations that show you how different engine layouts, like single overhead cam(SOHC) and double overhead cam (DOHC), really work. And then we'll go over a few of the neat ways that some cars adjust the camshaft so that it can handle different engine speeds more efficiently.

Let's start with the basics.

Camshaft Basics

The key parts of any camshaft are the lobes. As the camshaft spins, the lobes open and close the intake and exhaust valves in time with the motion of the piston. It turns out that there is a direct relationship between the shape of the cam lobes and the way the engine performs in different speed ranges.

To understand why this is the case, imagine that we are running an engine extremely slowly -- at just 10 or 20 revolutions per minute (RPM) -- so that it takes the piston a couple of seconds to complete a cycle. It would be impossible to actually run a normal engine this slowly, but let's imagine that we could. At this slow speed, we would want cam lobes shaped so that:

• Just as the piston starts moving downward in the intake stroke (called top dead center, or TDC), the intake valve would open. The intake valve would close right as the piston bottoms out.
• The exhaust valve would open right as the piston bottoms out (called bottom dead center, or BDC) at the end of the combustion stroke, and would close as the piston completes the exhaust stroke.

This setup would work really well for the engine as long as it ran at this very slow speed. But what happens if you increase the RPM? Let's find out.

When you increase the RPM, the 10 to 20 RPM configuration for the camshaft does not work well. If the engine is running at 4,000 RPM, the valves are opening and closing 2,000 times every minute, or 33 times every second. At these speeds, the piston is moving very quickly, so the air/fuel mixture rushing into the cylinder is moving very quickly as well.

When the intake valve opens and the piston starts its intake stroke, the air/fuel mixture in the intake runner starts to accelerate into the cylinder. By the time the piston reaches the bottom of its intake stroke, the air/fuel is moving at a pretty high speed. If we were to slam the intake valve shut, all of that air/fuel would come to a stop and not enter the cylinder. By leaving the intake valve open a little longer, the momentum of the fast-moving air/fuel continues to force air/fuel into the cylinder as the piston starts its compression stroke. So the faster the engine goes, the faster the air/fuel moves, and the longer we want the intake valve to stay open. We also want the valve to open wider at higher speeds -- this parameter, called valve lift, is governed by the cam lobe profile.

The animation below shows how a regular cam and a performance cam have different valve timing. Notice that the exhaust (red circle) and intake (blue circle) cycles overlap a lot more on the performance cam. Because of this, cars with this type of cam tend to run very roughly at idle.

Two different cam profiles: Click the button under the play button to toggle between cams. The circles show how long the valves stay open, blue for intake, red for exhaust. The valve overlap (when both the intake and exhaust valves are open at the same time) is highlighted at the beginning of each animation.Any given camshaft will be perfect only at one engine speed. At every other engine speed, the engine won't perform to its full potential. A fixed camshaft is, therefore, always a compromise. This is why carmakers have developed schemes to vary the cam profile as the engine speed changes.There are several different arrangements of camshafts on engines. We'll talk about some of the most common ones. You've probably heard the terminology:

OverHead Camshaft

In modern engines, the pushrod system is being replaced by the simpler overhead camshaft arrangement.

The overhead camshaft is located in the cylinder head. There can be 1 or 2 camshafts. Let’s look at a single overhead camshaft arrangement.

Single overhead camshafts can use rocker arms. The cam can lift one end of the rocker arm, or it can press down on the rocker arm.

On double overhead camshaft systems, the most common arrangement is to use a bucket tappet or lifter. It operates in a guide that protects the valve against side thrusts which it would receive if the cam operated directly against the valve.

The adjustment of valve clearance is usually done by changing accurately machined spacers. Spacers are available in a range of thicknesses, and they’re exchanged to obtain the correct clearance.

Some overhead cam engines use a hydraulic lash adjuster to reduce lash in the valve train. They have zero clearance at the valve stem so there’s no need for tappet adjustment.

It can be put in the valve end of the rocker arm. Like the hydraulic valve lifter, it has a body with plunger held against the valve stem by a spring.

Oil supplied to the adjuster keeps the plunger in contact with the valve and eliminates lash.

Lash adjusters can be put in the cylinder head at the end of the rocker arm. The lash adjusters are stationary and have a pivot for the end of the rocker arm. The plunger in the adjuster holds the rocker up against the cam.

In the lash adjuster inside the bucket tappet, the plunger’s hydraulic action holds the bucket body against the cam on the camshaft and also against the tip of the valve stem so that there is zero clearance.

DOHC (Double Over Head Camshaft)

DOHC

DOHC or double overhead camshaft engines are very popular now in all brands of cars. They used to be considered special and used mostly in pricey foreign cars. Most of the time a DOHC engine is a V-6, although V-8 models are starting to find themselves nestled in the engine compartments of the larger American cars and Foreign luxury cars.

The basis of DOHC engines comes from the fact that they make more horsepower because they are more efficient. In general the DOHC engine is used more than ever now, because the trend is to have smaller cars with engines that make lots of power and get good fuel mileage..

A double overhead camshaft engine succeeds the trusty pushrod engine. Pushrod engines have been in use for 100 years plus. It is the original valve train setup. Pushrod engines can be made to produce plenty of power. Nascarengines have pusrods and they make incredible amounts of power. The reality is it cost less for the factory to manufacture the DOHC engines and put them into cars on the assembly line than spice up a pushrod engine. It is what the future is bringing us.

Briefly, in a DOHC engine there is one camshaft per row of cylinders. If the engine is not a V-6 or V-8 it can’t be DOHC. If there is just one row of cylinders it has to be a single overhead camshaft engine (SOHC). Just because it does not have pushrods does not make it simpler. In reality they are more complicated and expensive to fix than a pushrod engine. Most of the DOHC and SOHC engines use a timing belt or chain to operate the camshafts.

I wish to discuss pushrod and SOHC engines in the GotEngines.com Blog. Becoming an educated consumer is of prime importance in making engine replacement decisions. We have a bunch of good information on our blog and it grows everyday.