15
votes
Why is it that when supercharging, it's preferred to compress the input, rather than pull a vacuum on the exhaust?
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 ...
- 4,455
12
votes
Why is it that when supercharging, it's preferred to compress the input, rather than pull a vacuum on the exhaust?
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 ...
- 1,848
9
votes
Accepted
What are these two rubber-ended attachments used for in a compression tester kit?
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.
...
- 23.5k
9
votes
Accepted
Why is it that when supercharging, it's preferred to compress the input, rather than pull a vacuum on the exhaust?
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. ...
- 435
8
votes
What do these compression figures mean
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.
...
- 33k
7
votes
What actually affects engine compression ratios?
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 ...
- 12.2k
6
votes
Shouldn't a loss of compression equal a loss of power?
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 ...
- 12.4k
6
votes
Accepted
Shouldn't a loss of compression equal a loss of power?
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 ...
- 1,448
6
votes
How can a model with a smaller engine produce more power?
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 ...
- 24.9k
6
votes
Why is it that when supercharging, it's preferred to compress the input, rather than pull a vacuum on the exhaust?
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 ...
- 16.2k
5
votes
Accepted
Premium vs. regular in medium compression engines
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 ...
- 16k
5
votes
Accepted
If an engine starts does that mean compression is fine?
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, ...
- 153k
4
votes
Accepted
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.
In order to maintain the same in-cylinder displacement a ...
- 39.1k
3
votes
What actually affects engine compression ratios?
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 ...
3
votes
Accepted
How to leak down test a cold engine?
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 ...
- 15.7k
3
votes
Accepted
Why can't they add more gas particles to the pressure higher to force a piston down!
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 ...
- 4,422
3
votes
Accepted
No compression on my two stroke
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 ...
- 7,047
3
votes
How Many Times to Crank During a Compression Test
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 ...
- 11.6k
3
votes
Accepted
Interpreting Cylinder Compression Readings
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 ...
- 153k
3
votes
How can a model with a smaller engine produce more power?
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 ...
- 1,062
3
votes
Accepted
How does compression tests work inside of an engine?
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.
...
- 34.6k
3
votes
Why is it that when supercharging, it's preferred to compress the input, rather than pull a vacuum on the exhaust?
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 ...
- 131
3
votes
Why is it that when supercharging, it's preferred to compress the input, rather than pull a vacuum on the exhaust?
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 ...
- 291
3
votes
Accepted
Leakdown Test | EJ205 on Engine Stand and replaced all Valves
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 ...
- 153k
2
votes
Corsa Sport (2007) low compression cylinders 2 & 4
Background
The Corsa has dual overhead cams. The cam rides directly on a bucket that sites above the valve stem and valve spring. In order to adjust your valves you have to properly size shims that ...
- 33k
2
votes
Does a warped engine block affect compression test?
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 "...
- 121
2
votes
Why can't they add more gas particles to the pressure higher to force a piston down!
The amount of energy required to force that amount of gas into the cylinder is immense. Causing a large enough pressure difference to force the piston down and drive the engine, and also the vehicle, ...
- 3,012
2
votes
What actually affects engine compression ratios?
There's actually another factor to consider in addition to the bore and stroke - the size of the space above the piston when the piston is at TDC is also a factor. (that dome shaped area you see ...
- 121
2
votes
Honda dirt bike with clone engine lots of problems
Your bike is full of deposits -- carbon and varnish -- that are byproducts of petrochemical fuel and years of combustion. Deposits clog fuel lines and carburetor jets, cause piston rings to stick, ...
- 1,882
2
votes
Accepted
Simple Question: During combustion stsgep do the piston go up all the way?
TL DR: You are absolutely correct: the piston does not completely close the gap.
There are two points in the rotation of the crankshaft where the piston stops momentarily as it changes direction:
...
- 153k
Only top scored, non community-wiki answers of a minimum length are eligible