Compression test?
Team Owner
Joined: May 2002
Posts: 24,337
Likes: 25
From: San Diego , CA Double Yellow DirtBags 1985..Z51..6-speed
Re: Compression test? (MLLRTYM)
Warm up engine, shut it off, zip tie the throttle plates wide open, get some good leather gloves, pull all spark plugs out, pull fuel injection fuse, hook up gage, crank it over,
Also, you may want to have a battery charger handy to hook up between your measurements. If the battery gets low, the compression readings will drop also.
Watch how fast it builds up on each revolution... this is a good indication of rings condition.
Try to do the test at least twice, but do the cylinders in the opposite order the second time... compression numbers will drop significantly as the engine block cools down.
That's just a quicky to getcha started... :seeya
Also, you may want to have a battery charger handy to hook up between your measurements. If the battery gets low, the compression readings will drop also.
Watch how fast it builds up on each revolution... this is a good indication of rings condition.
Try to do the test at least twice, but do the cylinders in the opposite order the second time... compression numbers will drop significantly as the engine block cools down.
That's just a quicky to getcha started... :seeya
Drifting
Joined: Aug 2000
Posts: 1,521
Likes: 0
From: West Islip New York
Re: Compression test? (MLLRTYM)
How is this done on a 95 LT1 ?
Usually two or three revolutions are required to obtain max compression.
Whats important to look for is an consistant reading across all cylinders. There should not be more than a 10% differnence from one cylinder to another. Do you suspect something ?
Melting Slicks
Joined: Jun 2000
Posts: 3,215
Likes: 6
From: Tampa Florida
Re: Compression test? (MLLRTYM)
Just like they said.
I just did this on my LT4 and ended up with 225 psi! Wow is all I can say...also running 11.2 CR...:)
I do wish I did this when stock for good comparison.
:)
I just did this on my LT4 and ended up with 225 psi! Wow is all I can say...also running 11.2 CR...:)
I do wish I did this when stock for good comparison.
:)
Team Owner
Joined: May 2002
Posts: 24,337
Likes: 25
From: San Diego , CA Double Yellow DirtBags 1985..Z51..6-speed
Re: Compression test? (1MoorTym)
I've got to disagree with pulling the plugs on a warm engine with aluminum heads though, and doing it twice from different directions.
Also, Don't the aluminum holes grow faster than the steel spark plugs as it heats up? I don't see the problem with pulling the plugs on a warm engine, besides, you really have to do this, if you wanna do a compression test. If other plugs are in, it will have to compress those cylinders, so the cranking speed will decrease, and compression values will be low.
[Modified by CentralCoaster, 12:53 AM 8/9/2003]
Drifting
Joined: Aug 2000
Posts: 1,521
Likes: 0
From: West Islip New York
Re: Compression test? (CentralCoaster)
I'm not suggesting to leave any plugs in, I'm saying do not pull them on a warm engine. I don't think it good practice to work on aluminum when "warmed up".
I don't think it neccessary to do a compression check on a warm engine. As you know, what your looking for is a difference between max and min cylinder readings. I don't get the point of having to factor in any temperature decreases from the first to the last cylinder. If they consistently drop 5psi (probably won't be that linear or that much) from the first (warm) to the last (cold) cylinder you check, what are you proving? Once you calculate the differences related to temperature drop your still left with a max to min comparision.
:cheers:
[Modified by 1MoorTym, 2:30 PM 8/9/2003]
I don't think it neccessary to do a compression check on a warm engine. As you know, what your looking for is a difference between max and min cylinder readings. I don't get the point of having to factor in any temperature decreases from the first to the last cylinder. If they consistently drop 5psi (probably won't be that linear or that much) from the first (warm) to the last (cold) cylinder you check, what are you proving? Once you calculate the differences related to temperature drop your still left with a max to min comparision.
:cheers:
[Modified by 1MoorTym, 2:30 PM 8/9/2003]
