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Topic: Compression ratio

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	Howstuffworks "What does octane mean?"
		One of the strokes is the compression stroke, where the engine compresses a cylinder-full of air and gas into a much smaller volume before igniting it with a spark plug.
		The compression ratio of your engine determines the octane rating of the gas you must use in the car.
		The advantage of a high compression ratio is that it gives your engine a higher horsepower rating for a given engine weight -- that is what makes the engine "high performance." The disadvantage is that the gasoline for your engine costs more.
	auto.howstuffworks.com /question90.htm (621 words)

	How To Calculate Compression Ratio- Car Craft Magazine
		Compression ratio is the relationship of cylinder volume (or displacement) with the piston at BDC to cylinder volume with the piston at TDC.
		For the purposes of calculating compression, we prefer to view the cc's of a dish as a positive number because a dish adds volume to the cylinder (and reduces the compression ratio); a dome is a negative number because it subtracts volume from the cylinder (and increases the compression ratio).
		Compression ratio aside, a good reason to have a small clearance volume is to tighten up the quench area (arrow).
	www.carcraft.com /techarticles/calculate_compression_ratio (1688 words)

	Compression Ratio - Page 1
		We know that in general a high compression ratio is good for performance and efficiency, but that it can also lead to "knocking" or "detonation".
		Therefore high compression ratios are usually associated with the requirement for high octane fuel and careful engine management.
		Compression ratio is also dependent on cam duration, as we shall see.
	e30m3performance.com /myths/more_myths1/comp_ratio/comp_ratio.htm (387 words)

	Compression ratio - Wikipedia, the free encyclopedia
		The compression ratio is a single number that can be used to predict the performance of any engine (such as an internal-combustion engine or a Stirling Engine).
		It is a ratio between the volume of a combustion chamber and cylinder, when the piston is at the bottom of its stroke and the volume when the piston is at the top of its stroke.
		Measuring the compression pressure of an engine, with a pressure gauge connected to the spark plug opening, gives an indication of the engine's state and quality.
	en.wikipedia.org /wiki/Compression_ratio (757 words)

	Isentropic Compression or Expansion
		During the compression process, as the pressure is increased from p1 to p2, the temperature increases from T1 to T2 according to this exponential equation.
		The quantity (v1 / v2) is the ratio of the volume at state 1 and state 2 and is called the compression ratio.
		The value of the compression ratio is a function of the design of the bore and stroke of the piston.
	www.grc.nasa.gov /WWW/K-12/airplane/compexp.html (804 words)

	Cisco - WAN Compression FAQs
		Compression is very processor-intensive, and processor utilization is proportional to the amount of traffic you wish to compress.
		A compression ratio of less than one means that the compression algorithm increases the size of the data.
		Compression ratios of less than one can result from an overly taxed CPU. If you run software compression on a router that does not have the cycles in order to perform the necessary calculations, the process stops.
	www.cisco.com /warp/public/116/wan_compression_faq.html (1773 words)

	Setting Compression Ratio - Tech Review - VW Trends Magazine
		This compression has a ratio, which can be anywhere from six- or seven-parts-to-one on a stock engine, all the way up to 16- or 17-parts -to-one in race-only engines.
		The higher the compression ratio, the more heat will be generated, which is why, with today's less-than-perfect fuels, most builders of street engines keep the compression down below 9-1/2-to-one, or lower.
		All three items (compression ratio, deck height, and the ccs in the combustion chamber of the head) can be "tweaked" to affect the other.
	www.vwtrendsweb.com /tech/0303vwt_compression_ratio/index.html (988 words)

	Axis Communications - Compression standards
		The downside is that the compression ratio, i.e.
		Since the compression ratio is so limited, these formats are impractical for use in network video solutions where large amounts of images need to be stored and transmitted.
		For example, a white wall may produce a relatively small image file (and a higher compression ratio), while the same compression level applied on a very complex and patterned scene will produce a larger file size, with a lower compression ratio.
	www.axis.com /products/video/about_networkvideo/compression.htm (1823 words)

	Data compression ratio - Wikipedia, the free encyclopedia
		Data compression ratio is a computer term used to quantify the reduction in data quantity produced by a data compression algorithm.
		Compression ratios are generally expressed as size>:, or as a percentage.
		Data compression ratios are also closely related to the concept of coding rates, which express the same concept but relate the ratio to more tangible quantities.
	en.wikipedia.org /wiki/Data_compression_ratio (292 words)

	Dynamic CR
		Determining what the compression ratio is after the intake valve closes provides valuable information about how the engine will perform with a particular cam and octane.
		Dynamic Compression Ratio, on the other hand, uses the position of the piston at intake valve closing rather than BDC of the crank stroke to determine the sweep volume of the cylinder.
		This lowering of the compression ratio, due to the late closing of the intake valve, is the primary reason cam manufactures specify a higher static compression ratio for their larger cams: to get the running or dynamic CR into the proper range.
	cochise.uia.net /pkelley2/DynamicCR.html (2291 words)

	JPEG2000-3D for Medical Imaging - Aware, Inc. (Site not responding. Last check: 2007-10-26)
		For lossy compression, the results are more dramatic: at a specific compression ratio, JPEG2000-3D increased the average pSNR (quality) of the image sequence by 5-18 dB than by compressing each image independently.
		Compression of all the images independently using JPEG2000 at a ratio of 10:1 yields average quality, or pSNR of 77 dB.
		The result is that at a compression ratio of 25:1, JPEG2000-3D yields images of the same average quality, or pSNR, as JPEG2000 at a compression ratio of 10:1.
	www.aware.com /products/compression/J2K3D.html (339 words)

	Compression in Audio Recordings
		Compression ratios of perhaps 2:1 are common, so the output will rise (or fall) by one unit for every two units of input change.
		Compression is commonly used in the final mix, and this is where things can go seriously wrong - everything is at the same volume, peak to average ratio is minimal, and the resulting sound is almost always worse than it was before the compression was applied.
		A ratio of 20dB is at the other extreme, so the same 50W amplifier will only produce an average power of 0.5W - this is where the use of high powered amplifiers for hi-fi is important - by the time the average power is high enough, the peak power is massive.
	sound.westhost.com /compression.htm (4146 words)

	Compression Ratios
		Increasing the compression ratio of an engine is one of the best ways to increase horse power and torque.
		Compression ratio's higher than this can be prone to detonation, even with long duration camshafts.
		When modifying an engine, it is important to match the compression ratio with the duration of the cam.
	www.nightrider.com /biketech/hdhead_compression.htm (437 words)

	Compressing Web Content with mod_gzip and mod_deflate \| Linux Journal
		To emphasize the value of compression further, I ran a test on a Web server to see what the average compression ratio would be when requesting a large number of files.
		The compression ratio for the test files ranged from no compression for files that were less than 300 bytes to 15% of the original file size for two Linux SCSI Programming HOWTOs.
		Compression ratios do not increase in a linear fashion when compared to file size; rather, compression depends heavily on the repetition of content within a file to gain its greatest successes.
	www.linuxjournal.com /article/6802 (2368 words)

	Erbman's Engine Emporium, Part III
		Higher compression ratios give a higher thermal efficiency, allowing the engine to get more useful work out of the heat energy in the fuel.
		Compression ratio has only a small effect on the volumetric efficiency of four-stroke engines.
		(Ref 1) The upper limit on compression ratio is set by detonation, where the fuel/air charge is heated sufficiently in the compression stroke to self ignite.
	www.eaa1000.av.org /technicl/engemp/engemp3.htm (1556 words)

	Compression Ratio - Page 2
		It is instructive to remember that the static compression ratio that your engine displays on paper does not translate directly to higher cylinder pressures.
		An engine with a performance cam operating at low RPM will suffer a loss of torque due to the fact that the effective compression ratio is reduced by the late intake valve closing point.
		In order to ensure that the mixture is still compressed sufficiently over the reduced effective compression stroke it is necessary to increase the static compression ratio.
	e30m3performance.com /myths/more_myths1/comp_ratio/comp_ratio2.htm (729 words)

	Halfbakery: Variable compression ratio engine
		Then, the compression ratio would be continuously variable, by sliding the crankshaft so that the con rod slides to the "bottom" end (for higher compression ratio), or vice versa.
		Modern variable valve timing and variable lift/duration systems are good enough that it has some of the same effect as variable compression, as the dynamic compression ratio varies with the engine speed and valve opening and closing profile.
		You do need to consider the physical effect of changing the compression ratio and hence the torque output whilst the engine is running, which will most likely result in a shock being felt through the car.
	www.halfbakery.com /idea/Variable_20compression_20ratio_20engine (743 words)

	Audio Box Inc. - Compression on a Windows PC
		There are various compression schemes to achieve different results; for example, many codecs remove portions of the audio signal that human hearing is less sensitive to.
		The compression ratio for MPEG compression can be adjusted across a wide range of quality levels, however sound quality drops as the compression is increased.
		ATELP yields a compression ratio of 12:1, 20:1, or 30:1.
	www.audioboxinc.com /compression.html (1061 words)

	Blaine Technologies - Articles
		Calculating compression ratio is essential for any performance engine buildup, but the process can sometimes be confusing.
		Compression ratio is defined as the volume above the piston at bottom dead center (BDC) as compared to the volume above the piston at top dead center (TDC).
		Even the lowly head gasket contributes to compression ratio through its compressed thickness and its bore (gasket bore is typically larger than cylinder bore.) The formula is shown below—note that the gasket bore and compressed gasket thickness figures are typically available from the head gasket manufacturer.
	www.blainetech.net /articles (1085 words)

	Boost Compression Ratio Calculator
		To see what the effect of bore, stroke, rod length, cam timing, compression ratio, boost pressure and altitude is on your dynamic compression ratio, simply enter the seven variables and the calculator will display the results in a new pop-up window.
		When you play around with this you may see why RB Racing has run "high" compression ratios on certain turbo bikes when we were running at Bonneville which is at an altitude of 4500 feet.
		Building a motor that sacrifices torque for peak power by running too low a compression ratio can be a mistake in some cases, especially if you live at higher elevations like in Denver, Colorado.
	www.rbracing-rsr.com /comprAdvHD.htm (606 words)

	Aspect Ratio and the Screen Compression Ratio for the TI-85 (Site not responding. Last check: 2007-10-26)
		Imagine rescaling the window W by compressing (or stretching) it in the horizontal direction so that it has width 1, and then compressing (or stretching) in the vertical direction so that it also has height 1.
		Under the transformation, a circle in the window W is rescaled into an ellipse whose axes are horizontal and vertical, and where the ratio of the length of the vertical axes divided by the length of the horizontal is AR(W)
		A screen compression ratio of CR(W) = 1 indicates there is no distortion in the calculator's picture, so that circles look round and the graph of a line with slope one meets the horizontal at a 45 degree angle.
	www.math.ou.edu /~amiller/ti85/cratio.htm (512 words)

	Andrews Products - COMPRESSION RATIO CHANGES
		As long as fuel with a high enough octane rating is available (so it will burn without detonation), raising the compression ratio can be a very effective performance boost.
		The amount of material which must be milled from heads (or cylinders) to change compression ratios may be easily determined.
		Only the stroke length, the original and new compression ratios need to be known.
	www.andrews-products.com /motorcycle/cams/compression_ratio_changes.htm (227 words)

	Drastic Video Math/Compression White Paper
		The ratio of a megabyte or megabit throughput can be calculated by dividing the appropriate value for uncompressed video by the specified data rate.
		To convert a ratio to the amount of time that can be recorded per gigabyte of hard drive space, simply use the total amount of time available for uncompressed video per gigabyte, and multiply by the ratio.
		To calculate the compression ratio given the number of minutes per gigabyte, simply use the number of uncompressed minutes that can be stored in a gigabyte and divide that into the number specified.
	www.drastictech.com /wp_compression.html (1620 words)

	DataCompression.info - Huffman Coding (Site not responding. Last check: 2007-10-26)
		The decoder is one pass and uses a huffman code table at the beginning of the compressed file to decode the file.
		Compression is based on Burrows Wheeler Transformation and modified Huffman entropy coder.
		The compression ratio is in par with most of the commercial grade compression utilities.
	datacompression.info /Huffman.shtml (3319 words)

	Engine Compression Ratio — Tech — Popular Hot Rodding Magazine
		Raising the compression to 12:1 would theoretically pump that up 387 lbs.-ft. However, unless other problems are encountered by virtue of the compression increase, such a gain would be toward the minimum end of the scale.
		The key to being able to utilize high compression ratios and have the engine survive is to understand what factors can accelerate its early onset.
		Although intended CR ratio may be achieved, the combustion process may be severely compromised by the presence of the dome.
	www.popularhotrodding.com /tech/0311_phr_compression_ratio_tech (3737 words)

	Compression ratio - NASIOC
		Assume that the compression ratio is how much the stroke of the piston compresses the air/fuel mixture.
		So, you in fact need a compression ratio that is lower than for a NA engine, so that you have room for the turbo to increase the pressure.
		So, is that mean if I replace the stock head gasket to a thicker one, I lower the compression ratio -->make more room for the turbo to have higer boost --->but will lost a lot at the bottom-end torque.
	forums.nasioc.com /forums/showthread.php?t=129129 (1327 words)

	Compression Ratio - Dirt Rider . Net, Dirt Bikes - Motocross - Off-Road - Supercross
		Increase the compression a little and under a load (under way) it will rev higher as long as the compression isn't too high and start to hinder that.
		By changing the gasket under the jug to a thinner one you are altering compression ratio and port timing.
		By dropping the ports, you are increasing compression ratio, retarding port opening, advancing port closure and decreasing port duration.
	www.dirtrider.net /forums3/showthread.php?t=76036 (1100 words)

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