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327 compression test

15K views 8 replies 7 participants last post by  ular284 
#1 ·
I have just become the proud owner of a 327 engine that looks to be in really clean shape, but everybody knows that clean and good are not the same. I would like to do a compression test but am unsure of what the numbers should be when testing from an engine stand, hand turning the crank. Any info out there on what the numbers should be? Also I am planning to remove all the plugs except the cylinder I am testing to make it easier to turn the crank.
Any flaws in my plan? Any suggestions to do it better?
Thanks in advance for all opinions and advice.
Captn Jim
 
#2 ·
You wont have much luck doing a compression test while turning the engine by hand. If it is a decent stand connect a starter to it to run the test. As far as what to expect it is hard to say because there are a lot of variables. I would look for at least 120 or so and consistency., +- 10
 
#3 ·
As T-Bucket said, there's no way it will work doing it by hand, you need to really spin it over 4 or 5 times to get a good reading. Ideally the engine should be warmed up before the comp. check but if that's not feasable then oh well. Some guys will even pour boiling hot water into the block (remove thermostat) to expand things a bit for a better read.

Hold open the choke and carb butterflys (or just remove the carb.) with a screw driver or whatever you have so the engine can breath. If you get 120-125 psi consistantly across all cyl. then it should be ok.

You'll really never know what you have though until you tear it down, might be .030/.060 overbored. Old engine, could have been rebuilt numerous times. I love the 327 but I switched to 500" Cadillacs. Here's an old pic of my last 327 and my newest 507" Cad.
 

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#4 ·
The compression results will vary depending on a lot of things. Just to give an example on my 350 with 9:1 compression and a 270/278 219/227 @ 50 515/530 lift hydraulic roller cam with a 106/112 lsa with out opening the carburetor up to wide open throttle and just turning the engine over I get about 160 to 170 on all 8 cylinders as an example. The bigger the cam to a certain degree the less psi it will register depending on what its compression ratio is.
 
#5 ·
Thanks guys for all the comments, good idea on using the starter motor. I was mostly wanting to determine if the motor would need serious work or if I could clean it up and use it as-is for a while while I get the rest of this project on the road. Since it was given to me I do not know what I have, the heads are camel back (2 humps) so I am assuming that they are 2.02 exhaust and the engine block number is V0405EA. I haven't researched that to see what it originally was but for sure it could have who knows what modifications inside.

Bottom line after spraying a little WD40 in each cylinder, pressure was a consistent 117-118 on all cylinders so the rings and valves must be OK at least. I am going to go ahead and use it as-is for now and use the cash on an IF suspension kit.

Thanks again for all the help.
 
#7 ·
Camel Humps do not automatically denote 2.02" intake valves, in fact about 96% of these castings are 1.94" valves....every 250, 275, and 300hp 327 had the 1.94" valve versions...only the true high performance engines got them machined for 2.02" valve....325hp or higher stock engines.

"EA" is a 1965 327 250hp, from a Chevelle or Chevy II/Nova...so 1.94" valves would be stock.
 
#9 ·
Again, I'm new to this forum, but not to pulling wrenches on things that go boom in the night. Actually, there's so many variables that can affect cylinder pressure that I wouldn't worry about a number, but rather uniformity. If all your cylinders check out within 10 PSI, I'd call it good and run it and see how it performs. If it's worn out you should see pretty quick in oil consumption and leakage. Other wise I'd run hell out of that baby. That's what it was born for.
 
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