Author Topic: cyclinder pressure  (Read 6221 times)

dab67

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cyclinder pressure
« on: March 04, 2007, 11:51:52 PM »
Can someone tell me what is considered good cylinder pressure for a 40 year old 350 v8?    200 p.s.i. 185 p.s.i.??? I looked through my Chassis service manual for 1967 and it shows how to test but doesn't say what the cylinders should be, unless I am looking in the wrong place, what is considered good pressure?  If I remember correctly all eight cylinders should be within 10 percent of each other. Is that correct? For that matter, what was the pressure for a new 350 back in 67?

dab67

Steve68

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Re: cyclinder pressure
« Reply #1 on: March 05, 2007, 12:52:04 AM »
150 would be good then and now.

Steve

dab67

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Re: cyclinder pressure
« Reply #2 on: March 05, 2007, 01:02:54 AM »
Thanks Steve

Steve68

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Re: cyclinder pressure
« Reply #3 on: March 05, 2007, 01:10:32 AM »
BTW, I think the max variation between cylinders was/is 20 lbs.

Steve

1968RSZ28

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Re: cyclinder pressure
« Reply #4 on: March 05, 2007, 05:49:14 AM »
dab67 -

You can find that information in your chassis service manual in the specifications section.  Compression specifications are found in the tune up chart specs.  The compression spec in my 1968 chassis service manual for a 350 is 160 psi at cranking speed, throttle wide open with a maximum variation of 20 lbs. between cylinders.

Paul        


dab67

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Re: cyclinder pressure
« Reply #5 on: March 05, 2007, 10:36:50 AM »
Steve and Paul:

Thanks for the info!

Dave

Jerry@CHP

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Re: cyclinder pressure
« Reply #6 on: March 05, 2007, 03:43:26 PM »
Dave,

It might be a better idea to do a leak down test instead of a compression test.  This is more of an exact science and will give you the percentage of leakage in each cylinder.  In a race car, these engines leak about 2-3 percent.  In a street car, it's more like 6-10 percent which is about normal.  Just some food for thought.

Jerry

dab67

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Re: cyclinder pressure
« Reply #7 on: March 05, 2007, 03:45:42 PM »
Jerry:

No clue what a leak down test is. Enlighten me!!!!!!!!!!!!!!!!!!!!!!!!!!!

Dave

Jerry@CHP

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Re: cyclinder pressure
« Reply #8 on: March 05, 2007, 04:51:32 PM »
You pump air into the cylinders from an air compressor source.  Most leak down tester kits have a hose with a threaded fitting that screws into the spark plug hole.  Once installed, it measures the amount of leakage from the cylinder on a gauge. 

This is by far the best way to tell if your rings are good or bad.........and if the cylinder has good seal.  Here is a link to one on Ebay right now.  Good luck!

http://cgi.ebay.com/ebaymotors/NEW-CYLINDER-LEAK-DOWN-TESTER-TEST-DIAGNOSTIC-AUTO-TOOL_W0QQcmdZViewItemQQcategoryZ43989QQihZ014QQitemZ330093865626QQrdZ1QQsspagenameZWDVW

Jerry

JohnZ

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Re: cyclinder pressure
« Reply #9 on: March 05, 2007, 06:11:33 PM »
The beauty of the leakdown tester is that in addition to the actual leakage rate, it allows you to identify the source of the leakage; if you hear noise through the carb, it's an intake valve; if you hear noise through the exhaust, it's an exhaust valve; if you hear noise through the oil fill hole, it's rings, etc. Much better diagnostic tool than a simple compression tester.
'69 Z/28
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1968RSZ28

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Re: cyclinder pressure
« Reply #10 on: March 05, 2007, 10:49:28 PM »
Dave -

If you decide to check the state of your engine with a cylinder leakage test each cylinder to be tested must have the piston at TDC (top dead center) on the compression stroke, so that both valves are closed.  If the piston is not in this position you will get a reading of 100% leakage!  Have fun.   :)

Paul  

dab67

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Re: cyclinder pressure
« Reply #11 on: March 06, 2007, 10:54:43 AM »
thanks for the info John and Paul, I will find out if my partner in crime has a leak down tester or if he knows someone that does.

Dave

Mr12771

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Re: cyclinder pressure
« Reply #12 on: March 06, 2007, 02:10:45 PM »
Dave
  I have two if you what, you can take one to play with.

Mike

dab67

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Re: cyclinder pressure
« Reply #13 on: March 07, 2007, 11:13:28 AM »
Mike:

Thanks for the offer, greatly appreciated. My friend has access to one. Once we get everything put back together on my car we may do both tests just for the heck of it.

Dave

Wallace

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Re: cyclinder pressure
« Reply #14 on: March 15, 2007, 04:13:40 PM »
I built my own leak down tester and it works well.  For those of you wanting to tinker a bit check out this web site.


http://www.xs11.com/tips/misc/misc3.shtml

Wallace