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Performance Principles of Power and Acceleration


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Old 06-20-2006, 12:00 PM
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Performance Principles of Power and Acceleration

Performance Principles of Power and Acceleration
- Ned Erkman, Author of The Read for Speed
http://www.rollingthunderz.com/index.shtml

It is often considered that the performance potential for a high performance vehicle is primarily determined by engine power. Although horsepower and torque are key ingredients, the power of an engine is not the only requirement for improving vehicle performance. The acceleration rate of an engine also contributes to performance by producing a rapid rate of vehicle acceleration.

The engine acceleration rate is determined by the speed in which the crankshaft rotates. The faster the engine rotates or spins the crankshaft, the faster the vehicle will accelerate. Although engine power creates energy to turn the crankshaft, the acceleration rate is what determines how fast the crankshaft rotates. A faster rotation of the crankshaft helps to turn the drive train components faster, which then rotate the drive wheels faster, thereby creating quicker acceleration for a high performance vehicle.

To better understand the difference between power and acceleration, consider that a Diesel engine can produce a lot of power, but diesel engines are not used for high performance vehicles because they do not create rapid acceleration

Power alone is not enough to achieve superior performance. Power and acceleration are required for faster and quicker vehicle performance.

Engine Power

The high performance engines that produce power for sports cars and racecars are known as internal combustion engines. As the name implies, an internal combustion engine produces power by combusting fuel and air inside cylinder walls that are designed to contain combustion. Although the production of power is primarily considered dependent on the amount of fuel and air that is consumed, there is much more to total power output that requires further review.

The total power produced by an internal combustion engine is determined by the following dynamic events that occur in the engine:
Volume of air and fuel consumed
Air and fuel mixture quality
Air fuel ratio
Efficiency of combustion process
Ignition intensity and spark timing sequences
Flame propagation and burn rate
Type and quality of fuel consumed
Mechanical and frictional losses
In order to produce more power, the following events should occur:
Increase consumption of air and fuel
Improve air fuel mixture quality
Increase combustion burn rate
Improve combustion efficiency
Improve mechanical efficiency
Reduce friction
The power production of an internal combustion engine is primarily determined by the size and operating range of the engine, the quality of the cylinder head, the flow capability of the intake manifold and the valve timing events and valve lift produced by the camshaft.

Increasing engine displacement can help to generate more power by being able to consume more air and fuel. Increasing the crankshaft stroke can help to develop more power, but the acceleration rate may be reduced as the longer stroke requires more time to complete a full crankshaft rotation. The associated frictional and mechanical losses of the rotating assembly, for an engine with a bigger stroke crankshaft, can also contribute to reducing engine efficiency.

Horsepower Per Cubic Inch of Displacement Formulas

The measure of a good high performance engine can be calculated by a horsepower to cubic inch formula.

A good high performance engine should be capable of producing one horsepower per cubic inch. Examples of this are the Corvette LS1 engine that is rated at 350 hp with a 346 cid engine or a 505 cid Viper engine that is rated at 500 hp.

Properly modified high performance street engines should be able to produce 1.3 horsepower per cubic inch.

Technologically advanced street engines can produce over 1.5 horsepower per cubic inch, naturally aspirated.

Maximum effort street engines that run on pump gasoline can produce over 1.6 horsepower per cubic inch of displacement

High technology Pro Stock race engines can produce over 2.6 horsepower per cubic inch, where a 500 cid engine generates 1300 horsepower, naturally aspirated.

Nitrous oxide injected V8 race engine can produce 3.5 horsepower per cubic inch of displacement.

Centrifugal Supercharged V8 Race Engines can produce 4.5 horsepower per cubic inch.

Turbo Charged V8 Race Engines can produce 5.5 horsepower per cid.

Evaluating engine power output, by using a horsepower per cubic inch formula, provides a quantifiable measure to determine reasonable horsepower objectives based on engine size.

Engine Acceleration

In the world of high performance, we have heard that power is nothing without control. Now we can also consider that power is nothing without acceleration.

The example that a diesel engine can produce a lot of power, but is unable to produce a fast rate of acceleration, demonstrates the significance of acceleration. Further examples of high power levels with low levels of acceleration can be seen in a racing competition between an elephant and a horse; the one horsepower animal is faster.

In animals, the rapid movement of feet produces a fast run, and in a high performance car, the rapid rotation of the crankshaft produces acceleration.

The effects of engine acceleration on the performance of a sports car can be seen in vehicles that produce high power on a dyno, but fail to produce the desired result on the race track. High power engines that are poor performers at the track are usually lacking a rapid rate of engine acceleration.

Acceleration has much to do with the combustion process. Combustion is primarily dependent on the quality of the cylinder head, along with the working relationship between the cylinder head, intake manifold, exhaust system, camshaft and piston. The faster the combustion process occurs and the greater the force of energy applied to the top of the piston, the better the rate of engine acceleration. Achieving an equal balance of power production in each cylinder will also help to produce smoother and faster engine acceleration.

Technically, acceleration is an increase in velocity measured in time and an object will accelerate only if a force is applied to increase the velocity. In a high performance engine, the quality of combustion determines the force that will be applied to the piston and a rapid rate of combustion can help to increase the velocity of the piston, thereby increasing the acceleration rate of the engine.

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Old 06-20-2006, 06:47 PM
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Quote:
Originally Posted by Bone
Performance Principles of Power and Acceleration
- Ned Erkman, Author of The Read for Speed
http://www.rollingthunderz.com/index.shtml

To better understand the difference between power and acceleration, consider that a Diesel engine can produce a lot of power, but diesel engines are not used for high performance vehicles because they do not create rapid acceleration


The example that a diesel engine can produce a lot of power, but is unable to produce a fast rate of acceleration, demonstrates the significance of acceleration. Further examples of high power levels with low levels of acceleration can be seen in a racing competition between an elephant and a horse; the one horsepower animal is faster.
Very good and interesting article.

I do have to point out one item. It was a Diesel in an Audi that won Sebring and LeMans this year. Not sure but I think they also won Daytona. Not sure on that one though.
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Old 06-20-2006, 08:52 PM
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Lightbulb often overlooked

I agree with the Hairy old Gorilla, good post

There is a couple of things that I have seldom heard discused involving engine internals: Rod angels, deck hieghts and long rod /short rod and piston pin/wrist pin offsets. All can affectivley change an engines performance!!!

Short rods seem to rev faster and have less tourque while long rods (with thier increased Hang time) seem to produce more , but rev a little slower.
When Stroking an engine(useing stock rod length) the rod angle increases.
If stroke is lengthened enough the rod angle becomes Terminal or to say
shoves the piston against the cylinder wall so hard that it don't last to long.

Deck heights, distance from center line of crank to top of block:
Many engines are available with different deck heights, again the rod lenght
( available in differant lenghts) and or wrist pin location / offset (or combination of ) can change engine performance!!
Gets a little complicated don't it????
I just can't type fast enough to give a good explination, or I would go into this farther for you all

Mr. Ape maybe you or some other engeneer LOL could enlighten the masses on this topic before I need stiches in my forehead
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Old 06-21-2006, 09:12 PM
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Question Mr. Engeneer aka Maggilla

Silver, Help my forehead is Bleeding

Quote:
Originally Posted by includemeout
I agree with the Hairy old Gorilla, good post

There is a couple of things that I have seldom heard discused involving engine internals: Rod angels, deck hieghts and long rod /short rod and piston pin/wrist pin offsets. All can affectivley change an engines performance!!!

Short rods seem to rev faster and have less tourque while long rods (with thier increased Hang / blowdown time) seem to produce more , but rev a little slower.
When Stroking an engine(useing stock rod length) the rod angle increases.
If stroke is lengthened enough the rod angle becomes Terminal or to say
shoves the piston against the cylinder wall so hard that it don't last to long.

Deck heights, distance from center line of crank to top of block:
Many engines are available with different deck heights, again the rod lenght
( available in differant lenghts) and or wrist pin location / offset (or combination of ) can change engine performance!!
Gets a little complicated don't it????
I just can't type fast enough to give a good explination, or I would go into this farther for you all

Mr. Ape maybe you or some other engeneer LOL could enlighten the masses on this topic before I need stiches in my forehead
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Old 06-21-2006, 11:16 PM
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So what you're saying is "hit gas, go fast," right?
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Old 06-22-2006, 06:32 AM
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Quote:
Originally Posted by includemeout
Silver, Help my forehead is Bleeding
Big ass bandaid is in the mail.

WARNING: Be sure to not put it over your mouth and nose at the same time. Severe Death Could Occure.
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Old 06-22-2006, 08:21 AM
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So your saying minor death is OK?

Bill
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Old 06-22-2006, 05:42 PM
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Quote:
Originally Posted by Begood
So your saying minor death is OK?

Bill
I have been told occasionally that I look like Death Warmed Over. Does that count.
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