How Horsepower Works

Whenever someone mentions horsepower the first thing that comes to mind is cars. Fast cars with extreme torque, vehicles with large power and extreme speed. But what makes horsepower measuring so meaningful? And why is it called horsepower? The word horsepower was created in 1782 by James Watt, a famous 19th century engineer while he was developing a way to improve the power of a steam engine. While watching horses haul coal out of a coal mine he came up with the idea of defining the power exerted by these animals. He calculated that a normal horse attached to a mill that ground corn or cut wood walked in a circle that was 24 feet in diameter. He then calculated that the horse pulled with a force of 180 pounds. Watt noticed the horse could make 144 trips around this circle in an hour. That is 2.4 trips per minute. Using these numbers he calculated that the horse traveled about 180.96 foot per minute then rounded up and came up with 181 foot per minute. He then multiplied the 181 foot per minute by 180 pounds of force the horse exerted and came up with the number 32,580 foot pounds per minute then rounded up again to the number 33,000 foot pounds per minute. This number equals one horsepower.

Big Block Chevy Horse Power 

Mr. Watt used his new found term to rate the power of the steam engine. Since most people were unfamiliar with the steam engine he had to come up with a comparison measurement that the normal farmer of the day would understand. As with any measurement there are different variations and different methods of measuring horsepower or hp. The normal measurement of horsepower is called mechanical horsepower.
Metric Horsepower
In Europe horsepower is measured a slightly different way. Horsepower is known by the various countries literal translation of the word horsepower. Some acronyms include PS, CV, pk and so on. Depending on the origin of the engine in question its horsepower is measured by that country's standards. Metric horsepower is defined as .73549875 kW. This is roughly 98.6% of mechanical horsepower.
Horsepower in Europe
Other countries have their own ways to measure horsepower. PS stands for Pferdestarke or horse strength. This is the German equivalent of horsepower. It is no longer used in Germany but it is in some other counties. It has since been replaced by the kilowatt but the EEC where horsepower was still used in advertisements as most people do not know the use of the kilowatt as a power measurement for combustion engines. Mathematically a PS = .73549875 kW = 0.9863201652997627 hp. The Dutch have the paardenkracht (pk). The Swedish have the hastkraft (hk). The Finnish have the hevosvoima (hv). All of these are equal to the German (ps). RAC horsepower, or taxable horsepower, is a British standard measurement of an automobile's power. It was adopted by the Royal Automobile Club. Taxable horsepower does not reflect true horsepower but it is a calculation based on the engine's bore size, the number of cylinders and a presumption of engine efficiency. The figure is no longer used as a standard in the UK but it is still put to use for the calculation of a vehicle's tax. The equation is RACh.p.= D squared * n/2.5 where D is the diameter of the bore of the cylinder in inches and n is the number of cylinders.

How Horsepower is used Measure the Power of an Engine?

1970 Chevy Chevelle SS

There are several names used to give an idea on how powerful an engine is. They are Nominal horsepower, Indicated horsepower and SAE gross horsepower. Nominal horsepower (nhp) is an early 19th century standard for estimating the power of steam engines. NHP = 7 x area of the piston x equivalent piston speed/33,000. It is measured by the size of the engine and the piston speed. Indicated horsepower (ihp) is calculated from the pressure in the cylinder. It is a misleading measurement as the actual power may be 79% to 90% of the indicated power. This was used to measure steam engine power. This measurement was open to interpretation so numbers varied. SAE gross horsepower was used by most car makers prior to 1972. It was measured with a test engine that had no accessories attached. It was a measurement of the maximum value of the engine and was often over rated to influence the sales of muscle cars. An engine that has its horsepower rating approved by the SAE will always be true to its number.  

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How Variable Cam Timing Works (VCT)

Car manufacturers have developed a variable cam timing system that adjusts  the cam to crankshaft timing depending on change in the engine speed and load.  The engine computer plays a vital role in the engine's performance as it adjusts  the camshaft timing depending on the vehicle's engine speed and load. In any  range of engine speeds only one camshaft position (in relationship to the  crankshaft) is optimum for power and economy. Pressurized engine oil is control  by the engine computer through an oil control valve which allows engine oil to  flow to the cam timing actuator (or phaser), as the oil is forced into the actuator the  camshaft timing advances, when the pressure is released a return spring supplies  force to return the actuator to standard position.

Variable Timing Camshaft

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There are many types of camshaft arrangements; some common types are single overhead  cam or SOHC, double overhead cam or DOHC and pushrod, rocker arm style of systems.  In a single overhead cam type, the engine is equipped with only one cam per cylinder head. Therefore, there is one cam in a four cylinder engine, also with straight  six cylinder engine. In v6 or v8 engine configurations there will be one camshaft  for each cylinder head, two camshafts and double the camshafts for DOHC engines.  The valve spring maintains pressure against the valve forcing the valve to contact  the valve seat, sealing the intake or exhaust port. If the valve spring is weak  or is broken the valve will lose pressure and will cause the engine to run poorly.

Variable Cam Timing Phaser Operation 
The specialty of a double overhead cam engine is that it has two cams per head.  This means that the inline engines are equipped with two cams, four cams in V style  engines. The use of double overhead cams is more common in engines which have more  than two valves per cylinder. This is because a single camshaft doesn't have the  ability to include sufficient cam lobes that can accommodate all the valves present  in a three or four valve per cylinder engine. Double overhead cams give the advantage  of adding more exhaust and intake valves. More valves allow the exhaust and intake  gases to flow freely because of the increase in the number of openings, this in  turn improves engine power and economy.

Four Valves Per Cylinder Configuration

A pushrod style of engine has a different valve opening configuration; the camshaft  is housed in the engine block instead of the cylinder head. The camshaft utilizes  lobe followers or lifters that connect to the rocker arms through a push rod.

Typical In Block Camshaft Configuration

This system is not as efficient because of the increase in weight of the system.  In turn, increases the valve springs load, slowing the engine down. Overhead camshaft  engines are more efficient and can produce more power.
A Camshaft is commonly used to operate poppet valves in a piston engine. A cylindrical  rod is situated in the cylinder block or cylinder head which has oblong lobes or  cams which push a tappet or lifter to raise and lower the intake and exhaust valves.  This force is applied on the valve directly or through an intermediate mechanism  such as a rocker arm, lifter (cam follower) and push rods are used to press against  the valve for movement. Each valve utilizes a spring which will return them to their  original position (closed) after the force is removed.

Cams are designed according to the RPM and horsepower range desired. When the  intake valve is pushed open, the piston travels down pulling an air/fuel charge  into the cylinder. This intake charge is a mixture of air and fuel and is ready  for combustion. The faster the engine is running the faster the air and fuel mixture  moves into the engine which also means that the intake and exhaust valves open and  close quicker. This parameter is known as the valve duration and is controlled by  the cam lobe width profile.

Basic Maintenance
A camshaft is driven by the crankshaft of the engine by a timing chain or timing  belt. The timing belt or chain needs to be replaced per manufacturer's specifications  because they wear out and fail without warning and stall the engine. Because a timing  chain configuration is more durable when compared to the timing belt style a timing  belt will need to be replaced more often, comparatively. Timing belts are more common  in overhead cam engines and are more easily serviced.
Cam followers or lifters have the capability to automatically adjust themselves,  removing any access clearance in the system. Maintain manufacturer recommended engine oil service.

  

Blue Smoke from Engine's Exhaust

Blue Smoke from Engine's Exhaust

Many people consider blue smoke from a vehicle to be elusive. Blue smoke is generally caused because of several specific conditions in the vehicle's engine. We will help you determine what the problem is so it can be corrected and stop the blue smoke. Blue smoke appears mostly at morning start up because oil from the vehicle's engine is mixing with the gas inside the engine's combustion chambers, then burned together with the fuel from the injectors while the engine is running. This can result in a very expensive repair, but not always. The more expensive and usually terminal reason for blue smoke is the piston rings have worn out allowing engine oil to pass into the combustion chamber.

In this case the engine is worn out and needs to be replaced, this can be expensive. There are other reasons the engine can burn oil, some engines have a small oil drain back holes in the cylinder heads, these holes allow the engine oil to drain back into the oil pan. The oil is picked up by the oil pump and returned back to the engines vital parts under pressure. If these drain back holes become plugged it can cause oil to seep down into the valves and into the combustion chamber. To repair this problem remove the valve cover and clean debris from the drain back holes, reassemble and recheck (note: after repair you must wait 2 to 4 days before the remainder of oil on the valve stems to be removed)

Most of the time producing blue smoke can be repeated since it's not usually a problem that is a single occurrence. Typically, once a vehicle starts producing blue smoke this pattern will continue to repeat until the engine is repaired. There are times when some engine additives can cause the blue smoke as well. If you are continuously adding additives to your fuel to stop smoke, you may be inadvertently covering up the smoke that your vehicle produces normally. However, if you are continuously adding engine or fuel line cleaners that are a strange color it can on occasion produce the strange colors of smoke. This condition is normal and will subside when the cleaner has run its course.

Common Problems and Solutions

The most common problems of blue smoke revolve around oil leaking into the engine's combustion chambers and burning with the fuel as discussed. However, the solutions to the problem often vary depending on the exact condition of the engine. There are times when the correction can be as simple as changing the valve stem seals or cleaning drain back holes.

It is important to note that if you decide to repair the engine you have, you are often looking at hourly repair rates plus parts and machine work to repair the engine. This is quite costly and depending on the age of the engine may well not be worth the expense of the repair. If you are highly fond of the vehicle and intend to keep it there are definitely times when a new or rebuilt engine is a better deal. Keep in mind, if you decide to change out the engine you are often able to extend the life of your vehicle by 10 years or more which can save thousands over the price of buying a new vehicle. Plus, your best bet on a new or rebuilt engine can be obtained by the dealer; surprisingly the dealer cost for the engine is close to what you will pay to have the engine rebuilt independently.

Maintenance

Maintenance for a vehicle is something that is often overlooked. From blank stares when asked when the last oil change occurred, to the even stranger looks that occur when asking when the last tire rotation was completed. It is very important to maintain oil changes and tune-ups that are performed on schedule. Proper maintenance to your car is a good way to keep all internal engine parts from becoming damaged prematurely. Without oil lubrication an engine will quickly become severely damaged. Anytime you are able to lengthen the life of the engine and help avoid breakdowns it is beneficial to the motoring experience.


Sometimes it is advisable to seek a professional ASE or other certified mechanic to trouble shoot the problem for the blue smoke condition. Never avoid engine problems as they can cause a simple and inexpensive repair to escalate to a costly repair that could have been avoided. Choosing the right mechanic or repair shop for your needs is often the biggest issue, however many times it can take just a referral from a friend or relative in order to find an appropriate repair shop.

Poorly maintained engines are much more prone to problems such as smoking. The excessive friction leads to catastrophic engine failure. Preventative maintenance is cheap insurance to ensure that your vehicle runs as smooth as possible for many miles to come.