That has usually been my problem with similar issues.
Small block compression readings
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Safety Car
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Small block compression readings
I am checking the compression on my 67 300 hp engine and coming up with a range between 150 and 180. Can someone please tell me what I should be getting for readings.
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Those sound pretty normal to me. What are you looking for? Misfire? Running rough?
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Le Mans Master
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A cylinder will fire fine all the way down to 120 compression. I think your issue is elsewhere. A solid engine will normally have compression within 10% on all 8 holes.
Yours is a little out of that spec but not terrible.
Yours is a little out of that spec but not terrible.
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The numbers can vary based on CR and cam (valve overlap).. it's more important that there are no "outliers".
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Thread Starter
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Thanks for all of the reply's.
Burning Brakes
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IMO, yes - that's typically how it's done. And BTW, it's been my experience that oiling the cylinders will yield a false high reading on the first stroke.
Last edited by CrossedUp; Oct 15, 2017 at 11:33 AM.
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Safety Car
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Just for clarification one plug out at a time or all of the plugs out at the same time and then check.
Last edited by deejaydu; Oct 15, 2017 at 11:36 AM.
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All plugs out at the same time. Turn motor over until you get the highest reading. 
I never block the throttle open. To me that just dumps gas in the cylinders, washes down the cylinders, and pollutes the oil.
.
I never block the throttle open. To me that just dumps gas in the cylinders, washes down the cylinders, and pollutes the oil.
.
Last edited by Kerrmudgeon; Oct 15, 2017 at 11:42 AM.
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Wow - all over the board here.
My 2 cents:
- warm motor up - doesn't have to be blistering hot. If aluminum heads back the spark plugs off first while the engine is cold, so they are just snug but not fully tight.
- pull all plugs out.
- wire the throttle open and leave it open. The one stroke won't pump enough gas down to do much more than wet the intake which will evap quickly in a warm engine.
- put a batter charger on (not trickle charger)
- install gage and spin motor at least 3 revolutions. I think it's OK to spin until highest reading but you should be there within 3 complete revolutions.
- after all readings if you have a low one you can squirt a bit of oil in it and repeat. If it comes up that is a sign of rings not sealing.
My 2 cents:
- warm motor up - doesn't have to be blistering hot. If aluminum heads back the spark plugs off first while the engine is cold, so they are just snug but not fully tight.
- pull all plugs out.
- wire the throttle open and leave it open. The one stroke won't pump enough gas down to do much more than wet the intake which will evap quickly in a warm engine.
- put a batter charger on (not trickle charger)
- install gage and spin motor at least 3 revolutions. I think it's OK to spin until highest reading but you should be there within 3 complete revolutions.
- after all readings if you have a low one you can squirt a bit of oil in it and repeat. If it comes up that is a sign of rings not sealing.
Last edited by DansYellow66; Oct 15, 2017 at 11:59 AM.
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This is the wrong way to do a compression test. As stated, you need the engine warmed up, remove all spark plugs, disable the ignition, block the carb open, and crank the engine the same number of revolutions with each cylinder. Usually about 4 or 5 revolutions. Also, you don't want a lot of variance between the cylinders...more than 20-30 psi will give you roughness. Most of the time a car with a weak or dead hole due to mechanical issues can be diagnosed when starting....it will crank faster as the weak cylinder comes up on Top Dead Center, causing a skip in the cadence......Instead of "na-na-na-na-na" it'll sound like na-na-NA-na-na". You can also connect a vacuum gauge and see if the needle jumps while cranking.