The intake stroke of the engine begins with the piston at the top of its travel. As the piston moves downward, it creates low pressure, or partial vacuum, in the cylinder. Outside air pressure forces air/fuel mixture and injection in through the open intake valve.
To Increase Compression Ratio, you should understand car features and also how the different parts acts for powering up the engine. I hope this guide and brief article will help you know how to improve compression ratio and power of a car and auto engine.
How the Compression Stroke Begins
The compression stroke begins with the piston reversing and moving upward, with the intake and exhaust valves closed.
The piston thus forces the air/fuel mixture up into the combustion chamber, compressing the mixture to something like 150 pounds per square inch (psi).
Process of Power Stroke
The power stroke is the one that moves the car. As the piston nears the top of its stroke, a spark jumps the gap in the spark plug and auto ignites the compressed charge.
The burning air/fuel mixture expands, increasing the compression pressure and pushing the piston down. Power developed is transmitted to the crankshaft, through the transmission, driveshaft, and differential and on to the wheels.
Exhaust Stroke and How Pistons Work
The exhaust stroke begins as the piston moves upward again, and the exhaust valve opens. The plunger forces the burned gases out of the cylinder and into the exhaust system.
The four-stroke cycle is repeated more than a thousand times a minute at highway driving speeds.
Each cylinder is at a different stage of its four-stroke cycle, resulting in a smooth flow of power impulses.
The Competition of Four Strokes Engine Compression
For the engine to develop full power, it must meet the manufacturer’s specifications for compression. The cylinder should have no leakage. Leakage can occur past the piston rings, past the intake or exhaust valves, and the cylinder head gasket.
An engine with leakage in one or more cylinders may idle roughly because of its uneven power strokes. Many factors involved in the compression test, like the head gasket and other parts of the machine, come into action.
It also will suffer a reduction in power and fuel economy (see fuel injection and compression effect part). Severe leakage past the piston rings can allow the oil to get into the combustion chamber and foul the spark plugs.
Loss of Dynamic Compression Ratio and Power: When and How
The car engine depends on three things to keep the pressure inside the cylinder:
Valves: This sits tight against the cylinder head;
Gaskets: These are located among the head and block.
Piston rings: Piston rings are expanded among the cylinder wall and the piston.
If one of these crashes, your engine will have a loss of energy or stop running. If a valve bends, it can’t sit against the head.
And, if a gasket fails, it will release pressure and if the rings fail. Also, it will apply force into the bottom of the engine and let the automotive engine to falter.
When more than one cylinders start to lose compression, the outcome is the failure of power, vibrations, and stalling of the motor.
A failure in any of these pistons, gasket, and valve parts can also cause oil or coolant to enter the cylinder, and that will cause motor problems, too.
A professional can test on the car engine and will have different tools to check the compression of the motor.
The static/dynamic compression ratio in the cylinders represents a lot about what is happening in the auto motor/engine without taking the whole thing apart.
Testing Compression Ratio and Power
Inspecting the car for testing compression is the first step in tuning the engine. You need a compression tester – simply a pressure gauge or beefy barometer – to measure combustion chamber pressures through the spark plug openings.
1st Step: Reaching Normal Engine Operating Temperature
To test compression, run the engine until it reaches normal operating temperature. Turn the engine off. Remove the spark plug cables from the plugs.
First number each cable with a bit of masking tape so you can replace them in the proper order.
The whole process has some similarities with car ac compressor testing, because two system works with compression system.
2nd Step: Removing Wires and Cables
The spark plugs are located at the ends of the heavily insulated spark cables (four, six, or eight depending on the number of cylinders).
Remove them properly by twisting the rubber boots and pulling at the same time. If you simply pull on the wire, you may break the delicate carbon track conductor inside. If a conductor breaks, it dramatically hampers the flow of electricity to the spark plug.
3rd Step: Removing the Plugs
With the wires off, slip a spark plug socket wrench over each plug and loosen it one turn. Socket accessories may be useful if your caps are hard to reach.
A hinged, offset handle, teamed with a short extension and spark plug socket, works well on most cars, jeep, and race engines. Avoid twisting the socket sideways, as this puts pressure on the brittle ceramic insulation of the plug.
To safely do the job you can use Wera or Wiha tools which will allow you do things properly.
4rth Step: Replace the Cable
Replace the cables on the loosened spark plugs, start the car or race engine, and run it at a fast idle to blow out any loosened carbon from around the plug bases.
If allowed to remain in the cylinders, carbon particles might lodge under a valve seat and give a false, low compression reading.
5th Step: Switching of the Engine for Static Compression Ratio and Dynamic
Then switch off the engine, remove the spark plug cables again, and remove all of the plugs. All spark plugs should be out when Spark Plug Removal and Installation.
The high-tension lead between the coil and the distributor should be grounded during the test. It will enable a high compression ratio. It is easy to find, even if you are not familiar with it—traceback along the spark plug wires to where they all converge at the distributor cap.
The high-tension cable emerging from the center of the distributor cap is the coil lead. Pull it out and touch its metal tip to some clean metal part of the engine.
Grounding the coil protects you from getting a shock if your hand should touch a spark plug lead, and it protects the insulation of the coil from possible damage by high-voltage buildup.
Here are Few Tips for Compression Testing on Engine:
- Gently wiggle off the rubber boot that covers each plug; never yank on the cable.
- Clean the recess before you remove the spark plug; this keeps dirt out of cylinders.
- To speed spark plug removal, team a cushioned spark plug socket (right) with a ratcheting handle (below).
- Keep the removed plugs in the correct order with some type of holder.
- Install spark plugs with a torque wrench or ratchet wrench; do not overtighten.
- Perform head gasket test of compression to know how the condition is and check if there is any leak.
- Finish the installation by replacing the rubber boot. Make sure that each boot is completely seated. You test compression. Otherwise, the reading will not be accurate unless the throttle is held open.
7th Step: Working with Compression Tester
Some compression testers are held by hand in the plug opening. Others screw in. If the plug openings are easily accessible, almost any tester will work if they are located at the bottoms of tubes, as on some Chrysler engines, you need an adaptable tester.
If you have installed a turbocharger in your car, you should make a list to check the increased power with the tester.
If your compression tester has adapters that fit into the spark plug holes, thread the proper adapter into the first or front spark plug on an in-line engine and work your way back.
On a V-engine, do the left front cylinder first and work your way back along the left cylinder bank. Then test the bottles and head gasket areas on the right side of the car, from front to back.
Check that the brake is on and the transmission is in neutral or park. If your compression tester has a remote-control switch to crank the engine, use it.
So, what about the proper uses?
The tester clips should be connected to the positive battery post and the small terminal on the starter solenoid. (The positive battery post is larger than the negative one, and sometimes it is marked with a
Connect the compression tester and crank the engine through four compression strokes with higher compression ratios; the pressure reading should rise quickly. To find the solenoid, follow the battery cable leading from the positive battery post; it leads to the solenoid.
8th Step: Testing Crank Power
Lacking a remote control, have a helper work the starter switch for you. Be sure, before each cranking, that all parts of your body and clothing are clear of the fan, pulleys, and belts.
Crank until four full compression strokes have passed the tester. This way, your car will increase horsepower and torque for the engine.
A valve inside the tester holds the compression until you read and release it. Repeat the compression test on all cylinders, recording the readings.
Understanding Compression Reading: Example and Result
If the sixth stroke readings for all cylinders are within the specified range for your car and they do not vary by more than the specified amount, compression is all right.
Suppose the compression pressure for your engine is determined at 125 to 155 pounds per square inch (psi) with a maximum variation between cylinders of 25 psi.
1st Compression Reading
If your compression readings came out like the following, you would have an engine in good breathing condition and worthy of the best tune-up you can give:
- 1-135 psi
- 2-130 psi
- 3-130 psi
- 4-135 psi
All cylinders rate close to each other, and none is as low as the minimum specified pressure.
2nd Compression Reading
But you would know you had severe breathing problems in the engine if the readings went as follows: Cylinder
- 1-155 psi
- 2-125 psi
- 3–150 psi
- 4-155 psi
While the number-two cylinder is not below the specified pressure, it is below the permissible range of pressures. Something is wrong with its breathing.
3rd Compression Reading
Here is another example of an engine that would flunk its compression test:
- 1-130 psi
- 2-115 psi
- 3-130 psi
- 4-120 psi
In this case, the variations between cylinders are within the tolerance range, but two cylinders, numbers two and four, fall below the minimum specified pressure. Chances are the engine is pretty well along in miles and needs significant work.
Reading the Power and Compression of Car Engines
Reading compression as it builds can tell you something about what repairs an engine needs. Condensation that is low on the first stroke and builds upon the following strokes, but never reaches normal, tends to indicate piston ring leakage.
To double-check, squirt a tablespoon of motor oil into the cylinder through the spark plug opening, crank several times to spread the oil, and test again. Oil seals the piston rings. A much higher second reading confirms piston ring trouble.
Compression that is low on the first stroke and stays little spells valve leakage. The reading will not change much when tested with oil in the cylinder.
If you get low readings on two adjacent cylinders, suspect cylinder head gasket leakage between the two, perform the test on all cylinders, and record the readings. Compare these figures against each other and specifications.
Pressure readings much higher than specified points to carbon buildup in the cylinders. That reduces the useful volume of the cylinders, making the mixture compress into a smaller space than it is supposed to.
That condition is harmful to the engine and should be taken care of by removing the cylinder head and scraping away the carbon deposits.
Last Few Words
Any compression deficiencies must be corrected before you can do a successful tune-up. It is not a job for the average do-it-yourself. Take your readings with you to the shop so you can show the repairman what is wrong and where. I hope this guide will also help you to gain higher compression ratios.