Cylinder Compression Questions

Swarzkopf

Member

Sep 23, 2004

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16

Pittsburgh

Feb 10, 2006

#1

• Feb 10, 2006

• #1

This was previously posted in 94-95. It doesn't seem to be getting much attention so if it's okay, I'm putting it here as well.

So I did a quick compression test on my stock, 90,000 mile 95 5.0 shortblock yesterday.

I did the test on a cold engine.

Here's what I got:

1- 121
2- 126
3- 125
4- 124
5- 125
6- 122
7- 122
8- 112

According to the Hayne's manual, the cylinder compression should be over 100 and the minium cylinder should be at least 75% of the maximum cylinder, so I'm at least "okay".

However, I wonder how much performance I'm losing and how down my compression really is from stock?

Should I continue to mess with this motor, or save up and buy a new bottom end and new heads?

What do you guys have for cylinder compression? What was it stock?

Input is appreciated.

 

JBeezy53

Member

Dec 28, 2003

559

1

19

Sacramento, Ca

Feb 10, 2006

#2

• Feb 10, 2006

• #2

Subscribing.....

 

1

1SLO306

My 97 GTP owns you ALL!

Mar 31, 2005

904

1

17

Muhlenberg, ky

Feb 10, 2006

#3

• Feb 10, 2006

• #3

JBeezy53 said:

Subscribing.....

Click to expand...

Me too!

 

M

Marlboro_Man

Member

Sep 30, 2005

437

1

18

Houston, TX

Feb 10, 2006

#4

• Feb 10, 2006

• #4

Well I believe you should redo the compression test with your motor up to normal running temps. But thats about all I know about compression tests.

I wish someone would do a write up on exactly how a compression test should be performed on our cars and what kind of results we should look for.

Subscribing....

 

JBeezy53

Member

Dec 28, 2003

559

1

19

Sacramento, Ca

Feb 10, 2006

#5

• Feb 10, 2006

• #5

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S

Stang D

Member

Jan 23, 2006

122

6

18

Quad Cities, Iowa

Feb 10, 2006

#6

• Feb 10, 2006

• #6

You guys might check the 94-95 tech forum. Thread is getting a response there now.

 

Swarzkopf

Member

Sep 23, 2004

973

0

16

Pittsburgh

Feb 10, 2006

#7

• Feb 10, 2006

• #7

Yeah, I feel bad about cross-posting this now.

 

1

1SLO306

My 97 GTP owns you ALL!

Mar 31, 2005

904

1

17

Muhlenberg, ky

Feb 10, 2006

#8

• Feb 10, 2006

• #8

Swarzkopf said:

Yeah, I feel bad about cross-posting this now.

Click to expand...

mane, its fine. i went and checked it out over there!!!

 

3

304billet

Member

Sep 16, 2005

315

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16

Feb 10, 2006

#9

• Feb 10, 2006

• #9

More important than a compression check is a leakdown test. It determines how much compression is getting past the rings. A good engine s/h between 2%-10% leakdown in any cylinder. More than 10% leakdown is indicative of needing refreshed.

A leakdown test costs about $200 and is well worth it. It will not tell u that u have bad scraper rings though, a condition that consumes oil. U could have all the cylinders below 10% but still be consuming oil because of bad scraper rings. The scraper rings scrape the oil off the cylinder walls.

I would not even think about building a motor around a 90,000 mile shortblock. I would just take the 302 bore it out .030 over and reuse the stock rods and polished stock crank, forged 11:1 SRP, Probe pistons, Comp cam XE282HR, AFR 185 stud mount heads, port matched RPM ll intake, LT ceramic coated 1 5/8", 24lbers, accufab 70mm TB, PMAS 75mm MAF. easy 375/375rwhp, NA on pump gas.

Or go 9:1 forged pistons and thow on some boost from a s-trim and have close to 500rwhp.

 

Swarzkopf

Member

Sep 23, 2004

973

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16

Pittsburgh

Feb 13, 2006

#10

• Feb 13, 2006

• #10

Problem solved...check out the other thread for details. LOL