Motor Vehicle Maintenance & Repair Stack Exchange
Motor Vehicle Maintenance & Repair Stack Exchange

Questions tagged [compression]

One of the four internal combustion engine strokes necessary for the complete combustion process to occur. The compression stroke compresses an air fuel mixture and prepares for it ignition by spark.

Image depiction the compression stroke of the 4 stroke engine cycle

enter image description here

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Static vs. Effective compression: Why does higher effective compression not require higher octane gas?

Background I've been trying to do a lot of research on boost lately because I'm planning on running a moderate turbo setup on my daily/light-duty-autox car in the future. I'm trying to get into the physics of things so that when I do my build, I'm…
Annath
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What do these compression figures mean

This is a follow up question to What are the causes of fluctuating intake manifold vacuum I have a 2005 Honda CBR600 F4i which suffers from occasional hesitation at low rpm when accelerating. After a compression test on a hot engine I got the…
Ian Oakes
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Why is it that when supercharging, it's preferred to compress the input, rather than pull a vacuum on the exhaust?

It's a strange dilemma, but if the power of an engine is determined by the difference in pressure between the combustion chamber and the exhaust, it should follow that turbocharging should be equally effective pumping air out the exhaust, than in…
tuskiomi
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More In Cylinder Pressure Testing Questions

So I was looking at a 06 Pontiac G6 2.4l with a complaint of low power on hills. Had been at another shop to have the transmission checked and they referred the customer to us. Road test confirms car doesn't go anywhere fast. I didn't really think…
Ben
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Shouldn't a loss of compression equal a loss of power?

I recently did a compression test on a Nissan B13 GA16DE and got 125, 127, 122 and 140 PSI (cold). A few years ago, all 4 cylinders got 135-140 PSI, cold. Shouldn't this loss of compression have led to a commensurate loss of power?
tlhIngan
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How to leak down test a cold engine?

I'm thinking of doing a leakdown test on an engine before I install it in my car. Of course the problem is that the engine will be cold and things won't seal the way they do when they are hot. So how does the leak down testing procedure change when…
Robert S. Barnes
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What are these two rubber-ended attachments used for in a compression tester kit?

I'm looking to buy a compression tester kit and am a little puzzled by the purpose of the two rubber-ended attachments shown below. Am I right in assuming that these two attachments can be jammed into the spark plug hole without threading to perform…
Zaid
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Is cylinder leak down test needed if compression test results are fine?

If I compression test my engine and the results are fine, could there ever be any need to leak-down test it as well? IOW, can a leak down test ever fail if the compression test is fine. RELATED: Cylinder Leak-down vs Compression Test
amphibient
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What actually affects engine compression ratios?

I always assumed that the less "square" (or more "undersquare") a motorcycle engine was, the higher the compression ratios it can have. But a survey of several bikes -- from cruisers to supersports, seems to reveal that it's not necessarily the…
ManRow
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Cylinder 1 and 4 has low compresion, after engine has been redone

I have a Opel Corsa 1999 B type. We had a mechanic redo the engine about 4 months ago, but this week it just does not want to start. Today had other mechanic look at the engine, and did a quick compression test, cyclinder 1 and 4 where under the…
ZioN
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No compression on my two stroke

I was recently riding racing my Honda 250R (1986) (informally), and, all of a sudden, the engine quit completely. I tried letting out the clutch in second gear (push starting) with my momentum, but although the engine turned over freely, there was…
Cullub
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Engine consuming oil and white smoke comes out when starting the engine while cold

my car has been consuming oil for a while now but only recently has started to smoke when it is started while the engine is cold. I thought that maybe because I am using a synthetic oil in a high mileage car but after switching to non-synthetic one…
method
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Corsa Sport (2007) low compression cylinders 2 & 4

I have been having trouble with my Corsa. It sometimes just cuts out or does not want to start at random times. I have had the car serviced, I have had the starter motor replaced & am now having a new fuel pump relay replaced. I was told today,…
Benita
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Motorcycle 125cc question about PISTON condition and battery

Last year I bought a 125cc bike, Modenas brand, most likely unknown to you. It is a moped. http://www.modenas.com.my/v2motorcycle.asp?id=70 It can go as fast as 110 km/h enough for the city, However, I gave it to a family person for a while and…
GorillaApe
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If an engine starts does that mean compression is fine?

I am looking at buying a second hand 2-stroke engine. I have seen a lot online about checking compression before buying used engines. I don't have a compression tester, but will buy one if necessary. My question is, if the engine starts and runs…
Swag_B
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