Cylinder compression on LS1
04-22-2010, 05:28 PM
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Cylinder compression on LS1 I'm going to do a compression test on my ls1 this weekend. What is normal pressure? I have stock cam and heads yet. Just a bolt on car. For now. lol
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04-22-2010, 07:57 PM
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From the service manual:
Engine Compression Test
Charge the battery if the battery is not fully charged.
Disable the ignition system.
Disable the fuel injection system.
Remove all the spark plugs.
Block the throttle plate wide open.
Start with the compression gage at zero, and crank the engine through 4 compression strokes, 4 puffs.
Make the compression check for each cylinder. Record the reading.
If a cylinder has low compression, inject approximately 15 ml (1 tablespoon) of engine oil into the combustion chamber through the spark plug hole.
Recheck the compression and record the reading.
The minimum compression in any one cylinder should not be less than 70 percent of the highest cylinder. No cylinder should read less than 690 kPa (100 psi). For example, if the highest pressure in any one cylinder is 1035 kPa (150 psi), the lowest allowable pressure for any other cylinder would be 725 kPa (105 psi). (1035 x 70% = 725) (150 x 70% = 105).
Normal -- Compression builds up quickly and evenly to the specified compression for each cylinder.
Piston Rings Leaking -- Compression is low on the first stroke. Compression then builds up with the following strokes but does not reach normal. Compression improves considerably when you add oil.
Valves Leaking -- Compression is low on the first stroke. Compression usually does not build up on the following strokes. Compression does not improve much when you add oil.
If two adjacent cylinders have lower than normal compression and injecting oil into the cylinders does not increase the compression, the cause may be a head gasket leaking between the cylinders.
Engine Compression Test
Charge the battery if the battery is not fully charged.
Disable the ignition system.
Disable the fuel injection system.
Remove all the spark plugs.
Block the throttle plate wide open.
Start with the compression gage at zero, and crank the engine through 4 compression strokes, 4 puffs.
Make the compression check for each cylinder. Record the reading.
If a cylinder has low compression, inject approximately 15 ml (1 tablespoon) of engine oil into the combustion chamber through the spark plug hole.
Recheck the compression and record the reading.
The minimum compression in any one cylinder should not be less than 70 percent of the highest cylinder. No cylinder should read less than 690 kPa (100 psi). For example, if the highest pressure in any one cylinder is 1035 kPa (150 psi), the lowest allowable pressure for any other cylinder would be 725 kPa (105 psi). (1035 x 70% = 725) (150 x 70% = 105).
Normal -- Compression builds up quickly and evenly to the specified compression for each cylinder.
Piston Rings Leaking -- Compression is low on the first stroke. Compression then builds up with the following strokes but does not reach normal. Compression improves considerably when you add oil.
Valves Leaking -- Compression is low on the first stroke. Compression usually does not build up on the following strokes. Compression does not improve much when you add oil.
If two adjacent cylinders have lower than normal compression and injecting oil into the cylinders does not increase the compression, the cause may be a head gasket leaking between the cylinders.
04-22-2010, 07:57 PM
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not on these motors, it mostly has to do with the compression ration in the engine. not all engine have the same compression ratio
my turbo 347 pumps out only 120 psi, that is because i have lowered the CR of the engine to 8.6:1 from 10.25:1
my turbo 347 pumps out only 120 psi, that is because i have lowered the CR of the engine to 8.6:1 from 10.25:1
04-22-2010, 08:00 PM
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From the service manual:
Engine Compression Test
Charge the battery if the battery is not fully charged.
Disable the ignition system.
Disable the fuel injection system.
Remove all the spark plugs.
Block the throttle plate wide open.
Start with the compression gage at zero, and crank the engine through 4 compression strokes, 4 puffs.
Make the compression check for each cylinder. Record the reading.
If a cylinder has low compression, inject approximately 15 ml (1 tablespoon) of engine oil into the combustion chamber through the spark plug hole.
Recheck the compression and record the reading.
The minimum compression in any one cylinder should not be less than 70 percent of the highest cylinder. No cylinder should read less than 690 kPa (100 psi). For example, if the highest pressure in any one cylinder is 1035 kPa (150 psi), the lowest allowable pressure for any other cylinder would be 725 kPa (105 psi). (1035 x 70% = 725) (150 x 70% = 105).
Normal -- Compression builds up quickly and evenly to the specified compression for each cylinder.
Piston Rings Leaking -- Compression is low on the first stroke. Compression then builds up with the following strokes but does not reach normal. Compression improves considerably when you add oil.
Valves Leaking -- Compression is low on the first stroke. Compression usually does not build up on the following strokes.Compression does not improve much when you add oil.
If two adjacent cylinders have lower than normal compression and injecting oil into the cylinders does not increase the compression, the cause may be a head gasket leaking between the cylinders.
Engine Compression Test
Charge the battery if the battery is not fully charged.
Disable the ignition system.
Disable the fuel injection system.
Remove all the spark plugs.
Block the throttle plate wide open.
Start with the compression gage at zero, and crank the engine through 4 compression strokes, 4 puffs.
Make the compression check for each cylinder. Record the reading.
If a cylinder has low compression, inject approximately 15 ml (1 tablespoon) of engine oil into the combustion chamber through the spark plug hole.
Recheck the compression and record the reading.
The minimum compression in any one cylinder should not be less than 70 percent of the highest cylinder. No cylinder should read less than 690 kPa (100 psi). For example, if the highest pressure in any one cylinder is 1035 kPa (150 psi), the lowest allowable pressure for any other cylinder would be 725 kPa (105 psi). (1035 x 70% = 725) (150 x 70% = 105).
Normal -- Compression builds up quickly and evenly to the specified compression for each cylinder.
Piston Rings Leaking -- Compression is low on the first stroke. Compression then builds up with the following strokes but does not reach normal. Compression improves considerably when you add oil.
Valves Leaking -- Compression is low on the first stroke. Compression usually does not build up on the following strokes.Compression does not improve much when you add oil.
If two adjacent cylinders have lower than normal compression and injecting oil into the cylinders does not increase the compression, the cause may be a head gasket leaking between the cylinders.
why would you do that if the throtle plate already has a hole in it ?
04-22-2010, 08:10 PM
#14
and no, i seen what you edited, the IAC controls idle air flow, not just the hole in the throttle body. also, your looking for the cylinders FULL capacity, its not going to get that with the throttle body closed. the hole in the TB is not sufficient enough to feed the engine for a compression test.
04-22-2010, 08:26 PM
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and no, i seen what you edited, the IAC controls idle air flow, not just the hole in the throttle body. also, your looking for the cylinders FULL capacity, its not going to get that with the throttle body closed. the hole in the TB is not sufficient enough to feed the engine for a compression test.
turning the motor over with the starter will not spin it faster then that, so it will get all the air it needs
what is iac ?
these engine do not have an idle control valve
04-22-2010, 08:42 PM
#16
our engines idle at about 600rpm with the throttle plate closed, it gets all the air from the small hole that is in the throttle plate
turning the motor over with the starter will not spin it faster then that, so it will get all the air it needs
what is iac ?
these engine do not have an idle control valve
turning the motor over with the starter will not spin it faster then that, so it will get all the air it needs
what is iac ?
these engine do not have an idle control valve
the throttle plate needs to be all the way open. were not measuring idle air compression, your measuring the compression at FULL cylinder capacity. just so you know, an engine does not take in all the air it can hold at idle. if it did it would run extremely lean at idle.
04-22-2010, 09:21 PM
#18
first you need a leak down tester, then pull all the plugs, block the throttle open, open the oil cap, radiator cap as well as be able to listen to the exhaust.
make sure the cylinder you are testing is at TDC compression, and follow your tester's instructions for line pressure and cylinder pressure settings, set the valves on the tester as instructed and watch your gauge. it should have a
"go, no-go" area on the face of the dial.
if you have a "no-go" reading, listen through the throttle, radiator, crankcase, and exhaust for leaks. it helps to have a few little sandwich bags on hand to strap over each opening to "see" the leaks.
1. leaking out oil cap = rings or valve seals leaking
2. leaking out radiator = head gasket
3. leaking out TB = intake valves
4. leaking out exhaust = exhaust
any combination of the 4 and you have bigger problems.
make sure the cylinder you are testing is at TDC compression, and follow your tester's instructions for line pressure and cylinder pressure settings, set the valves on the tester as instructed and watch your gauge. it should have a
"go, no-go" area on the face of the dial.
if you have a "no-go" reading, listen through the throttle, radiator, crankcase, and exhaust for leaks. it helps to have a few little sandwich bags on hand to strap over each opening to "see" the leaks.
1. leaking out oil cap = rings or valve seals leaking
2. leaking out radiator = head gasket
3. leaking out TB = intake valves
4. leaking out exhaust = exhaust
any combination of the 4 and you have bigger problems.
04-22-2010, 09:52 PM
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wow...you need to open the hood of your car. the idle air controler allows air to enter the engine at idle, yes LS1's DO have an IAC motor. the hole is just for a little more air that it needs above what the IAC can handle.
the throttle plate needs to be all the way open. were not measuring idle air compression, your measuring the compression at FULL cylinder capacity. just so you know, an engine does not take in all the air it can hold at idle. if it did it would run extremely lean at idle.
the throttle plate needs to be all the way open. were not measuring idle air compression, your measuring the compression at FULL cylinder capacity. just so you know, an engine does not take in all the air it can hold at idle. if it did it would run extremely lean at idle.
i fucked up