15

The power of an engine is not determined by the difference in pressure between the combustion chamber and the exhaust. Power is determined by how much energy one can put into the combustion chamber and the efficiency of how that energy is applied. When one is compressing the intake air, additional oxygen is being included in the "mix" allowing for ...


12

OP's question states: It should follow that turbocharging should be equally effective pumping air out the exhaust, than in the inlet. No, it is not as effective. You can't reduce the pressure to less than 0 psi. So the maximum "suck" you can get is 1 bar. The boost pressure on high performance engines can be 2 to 3 bar. But working from the ...


9

You just hold the rubber ended bit against the plug hole whilst cranking the engine. No, it does not blow out of the hole due to pressure build up. This is how such a unit is designed to be used. The different designs of tube allow use on different designs of engines, choose the one which feels most appropriate to the vehicle you are testing.


9

IMO this is not a stupid idea, however it doesn't actually make sense for multiple reasons: A naturally-aspirated Otto or Diesel engine by itself doesn't expand the gas even to atmospheric pressure. When opening the exhaust valve, there's an overpressure escaping – thus wasting energy – before the exhaus stroke itself starts. (This is the concrete reason ...


8

You asked What do these compression figures mean Response Not that much when the engine is cold. Background Based upon the information you have provided I see no indication that the rings are bad. You aren't burning any oil You do not have oily carbon buildup on your spark plugs Bad rings will almost always give you those two symptoms, if they aren't ...


7

Put simply, an engine's compression ratio is the ratio between the volume of a cylinder with the piston at the down position (position 1 and 4 in the pic below) and the volume of the same cylinder with the piston in the up position (position 2 and 3 in the pic below). So, basically, the volume of the cylinder with the piston in the down position is the ...


6

Those numbers do not seem horrible, unless the 140psi is low. You might want to repeat the test with the engine warm. I generally feel that a cold test only reveals inter-cylinder differnces (in your worst case only 18psi), but dynamic compression after everything is warmed up and expanded might be much better.


6

Yes, it does lead to a loss of a power, but your compression is not worth worrying about. Every engine will loose some compression after a few years. New rings wear out faster at the beginning and later they wears out slowly, so probably you won't see a difference for another 2 years.


6

I am guessing that the smaller engine has a turbocharger and the larger engine doesn’t. This would fit with the smaller engine having a lower compression ratio. The turbo compresses the air entering the engine allowing more fuel to be added. The small engine will therefore in effect have a larger capacity and will therefore be more powerful. The smaller ...


6

There is no direct path from the intake to the exhaust, at least one set of valves will be closed at all times. The exhaust valves open and the piston pushes the exhaust out of the cylinder, then the exhaust valves close and the intake valves open to allow fresh fuel-air mix in. Low pressure on the exhaust may pull the exhaust out a bit quicker but it won't ...


5

There is no such thing as an octane sensor. Octane is analyzed in two ways. Analysis of the chemical composition, they call this Research. They place the fuel into a test engine and run it until it pings, they call this Motor. If you look at a gas pump it will usually show for example, 87 octane (R + M)/2. This is an average of Research and Motor. A modern ...


5

Yes it can. The reason is, these are two different tests, done differently, reading different things. To understand this, you need to understand how the tool works for each test. For the compression test, the test apparatus captures and holds the compression as it builds through several, but counted revolutions of the crankshaft. You will get so much ...


5

First... find another garage. White smoke and low compression are NOT symptoms of a bent connecting rod. Also, you CANNOT inspect the connecting rods by removing the head - they're on the opposite (bottom) ends of the pistons. White smoke and low compression are both symptoms of a blown head gasket. That's very classic. It doesn't sound like it's very bad, ...


5

You cannot assume just because it starts it has good compression. It can have minimal compression and still start and run just fine. That minimal compression is going to be different for every engine, so you'd have to look up the specifications for the exact engine you're looking at. The deal with it is, the more compression the better it will run (make more ...


4

Why was it redone? And was your block checked for warping? If it was warped, and not corrected, you could be facing the same problem.


4

I always assumed that the less "square" (or more "undersquare") a motorcycle engine was, the higher the compression ratios it can have. In order to maintain the same in-cylinder displacement a smaller bore will require a larger stroke, so the distance between top-dead-center (TDC) and bottom-dead-center (BDC) will be larger. However, this does not ...


3

TL;DR: Either there's a problem with the head gasket, or with the piston rings. Remember, the piston rings fly over the openings in the cylinder wall, and there's no radial force onto the section exposed to the opening, pushing it into its groove. Shortly after, this section touches the cylinder wall again and experiences the radial force pushing it back. ...


3

So searching the Internet, I've found some conflicting opinions, with an occasional person saying either that cold leak down tests are completely invalid, or that cold numbers will be two to three times warm numbers. Some people relate the numbers to how big your ring gap is: I just did a cold test on my fresh off the dyno engine, over the past 20 yrs I'...


3

What you are proposing has been done a few times: there are cars that run on compressed air. The problem with that is that compressed air has a low energy density, comparable to lead-acid batteries and 30 times lower than petrol or diesel. So compressed air cars have short range. They're also harder to refuel than an electric car. This combination means ...


3

One pump; one pump only. Which test we perform determines the procedure used. Three procedures are described and each test has a different purpose. But keep in mind when the engine is running it only gets one pump per cycle. Running compression test: A decent way to estimate volumetric efficiency (VE). This is not technically a compression test. Install ...


3

From the looks of it, you're going about your compression test incorrectly. You should rotate the engine, using the starter, for the same number of revolutions with each cylinder. This will give you a truer tale of what's going on. Usually 4-5 revolutions gets the job done. The reason you want the same amount of revolutions for each cylinder is so the tests ...


3

Rings generally wear at the same rate meaning that when it's time to replace one you should be replacing them all as they're not seating with the cylinder properly any more. Burning oil does not always imply a loss of compression. Cars with good rings will burn oil due to bad valve guides or bad valve guide seals. A compression test should help you ...


3

Caveat lector: I am neither an engineer nor engine builder. I just read a lot. You have received correct descriptions of static CR. But you framed the question with concerns about preignition and how it is effected by under- or over- square configurations and fuel quality. Unfortunately no one is going to be able to answer the questions to your satisfaction....


3

how is it possible? Turbo/ Supercharging, higher tuning, there are a lot of possibilities to make more power out of an engine. what are the advantages & disadvantages of less cc more power vehicles Advantages of the "smaller" engine: Possibly less weight. Better fuel efficentcy Less material consumed in making it (but could be offset by added ...


3

The pressure gauge has a one way valve in it so that it does not follow the pressure in the cylinder at all times - it is designed to record the maximum pressure over several cycles of the engine. The pressure gauge used for this test also has a button on the side (back or connecting tube) to release the pressure. This also allows for the reading to be read ...


3

Since the question doesn't specify any type of engine... Funnily enough, there are engines which pull a vacuum on the exhaust. They are steam engines, so the vacuum is created by simply adding cold water in a condensor, without wasting power (*) to create the vacuum. This extracts energy from the steam down to about 30C instead of the 100C boiling point at ...


3

Pumping air into an engine requires work, but each joule spent pumping in pre-combustion air will increase the amount of work that is produced downstream by more than a joule. The effective power increase is the difference between the added input work and the increase in output work. If one were to pump out the exhaust, one could reduce the amount of work ...


3

You state you "lapped the valves" when replacing them? If you have replaced the valves, you need to do more than just lap the valves. You actually have to do a valve job. This entails machining both the valve seat and the valve itself so they will mate properly. Once this is done, then you lap the valves in to provide the seal you're looking for. ...


2

Wow! Textbook case of worn rings. The oil helps seal the ringland area. That's a large increase on cylinders 2, 3, and 4. Your fuel efficiency should be pretty poor with those compression numbers. Is it? If your fuel efficiency is miserable, it's time for a rebuild. Depending on the car it might be cheaper just to replace the engine with one from a engine ...


2

You should have checked the flatness of the block deck with a feeler gauge and a straight edge before installing your new equipment. For instance one of my engines has a maximum value of .002" of "warp-age" when measured at any location on the surface of the block deck. If out of spec, the block deck would need to be resurfaced, which when all is said and ...


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