Go Back  CorvetteForum - Chevrolet Corvette Forum Discussion > C4 Corvettes, 1984 - 1996 > C4 ZR-1 Discussion
Reload this Page >

Compression test performed: take a look at my results

Notices
C4 ZR-1 Discussion General ZR-1 Corvette Discussion, LT5 Corvette Technical Info, Performance Upgrades, Suspension Setup for Street or Track

Compression test performed: take a look at my results

 
Old 06-04-2019, 04:10 PM
  #1  
1985 Corvette
CF Senior Member
Thread Starter
 
1985 Corvette's Avatar
 
Member Since: May 2004
Location: Jacksonville Florida
Posts: 4,312
Likes: 0
Received 53 Likes on 40 Posts
Default Compression test performed: take a look at my results

I finally got around to doing this and wanted to post my results. This was done dry and with an Actron Brand compression tester (part number CP7827). All plugs removed and foot to the floor on gas pedal while cranking. The engine had been run a few hours earlier and was still hot to the touch. I'm at sea level here in Jacksonville, Florida. Take a look, let me know what you think. Car has about 84,042 miles on it as of today:

#1 - 230
#3 - 220
#5 - 229
#7 - 230

#2 - 230
#4 - 229
#6 - 227
#8 - 237

So I should've done this a lot sooner because I've been expecting the worst for weeks now but this was good to see consistency across the cylinders. What I'm curious about are other owner's tests have shown median values around 180 - 200 psi for the cylinders, so I figured the Actron tester is "happy" compared to other brand testers used? Whatever the reason, I feared the worst because I've noticed that my oil dipstick pushes out about an inch or so and has to be pushed back in after some spirited driving. I've replaced the entire PCV system EXCEPT for the PCV valves. They still rattled when I shook them but I've made it an item to just replace them. A local Chevy dealer had one of them, the other was no longer available. So what do you guys think? #8 was either 237 - 235, it's a rough estimate because gauge in only in increments of five.

Another reason I performed this test finally is because the car has become noticeably sluggish on acceleration. No trouble codes thrown but I need to replace the fuel filter anyway and while I'm at it I have decided to replace the fuel pumps in the tank. The third owner replaced the starter, coils, wires and fuel injectors before the fourth owner got the car sometime in 2017. At that point, the car was definitely stored outside and most likely not driven a lot because I found a mouse nest all around the starter, and the 4th owner just had no room in his garage to keep the car so outside it sat with a car cover. I got the car in August of 2018. The car is almost 30 years old and I believe a lot of its time since then was sitting in storage, so I wouldn't doubt one of the pumps has gone south.

Last key thing: I don't think this is a variable in the test but some cylinders, the starter turned over the engine 4 times instead of 3. I don't think this skews the results but let me know otherwise. I figured, if there was a problem, an extra crank isn't going to jack up compression and give a false reading. Sorry for the paranoia!

Last edited by 1985 Corvette; 06-04-2019 at 04:29 PM.
1985 Corvette is offline  
Old 06-04-2019, 04:44 PM
  #2  
ccmano
CF Senior Member
 
ccmano's Avatar
 
Member Since: Aug 2005
Location: Sparks NV
Posts: 1,436
Received 48 Likes on 47 Posts
Default

Looks good to me. Your at sea level so your reading will be higher. I’m at 5000ft so mine are lower around 200. Your good don’t over think it. I just did a buddies fuel filter, the car would barely get to 6k rpm without shuddering. After the filter it went straight to 7k and beyond. Also as the weather gets warmer you loose some of the performance due to heat saturation and the ecm cutting timing.
H
ccmano is offline  
Old 06-05-2019, 06:31 PM
  #3  
ghlkal
CF Senior Member
 
ghlkal's Avatar
 
Member Since: Mar 2005
Location: Fredonia WI
Posts: 2,482
Received 121 Likes on 111 Posts
2018 C4 of Year Finalist
Default

Those numbers are good.

Here's my most recent compression test:
1 - 213
3 - 213
5 - 220
7 - 220

2 - 235
4 - 215
6 - 215
8 - 215
ghlkal is offline  
Old 06-05-2019, 10:05 PM
  #4  
Kevova
CF Senior Member
 
Kevova's Avatar
 
Member Since: Sep 2013
Location: near the thumb in the mitten
Posts: 3,999
Received 375 Likes on 359 Posts
Default

Slightly high can be carbon. The readings are within 10% which is acceptable. Is there a particular condition?
Kevova is offline  
Old 06-06-2019, 10:14 PM
  #5  
1985 Corvette
CF Senior Member
Thread Starter
 
1985 Corvette's Avatar
 
Member Since: May 2004
Location: Jacksonville Florida
Posts: 4,312
Likes: 0
Received 53 Likes on 40 Posts
Default

Originally Posted by ghlkal View Post
Those numbers are good.

Here's my most recent compression test:
1 - 213
3 - 213
5 - 220
7 - 220

2 - 235
4 - 215
6 - 215
8 - 215
Looks like I'm right where I need to be. Thanks for posting your numbers!


Originally Posted by Kevova View Post
Slightly high can be carbon. The readings are within 10% which is acceptable. Is there a particular condition?
No trouble codes but I had a few seemingly too coincidental items crop up: dipstick pushing out a bit, having to add coolant, and a recent new issue with sagging acceleration pushed enough of my buttons for a popped head gasket scenario. Thankfully, my results proved I was way out in left field on it. As far as the high carbon, I'd bet you're right about that. I've had a new fuel filter sitting on the shelf that's going in the car this weekend, I have been bad about taking care of that for a while now. New stainless injectors, so after, the filter if the performance is still a miss, I'll work my way back to the register and pumps.

Last edited by 1985 Corvette; 06-06-2019 at 10:17 PM.
1985 Corvette is offline  
Old 06-09-2019, 06:37 PM
  #6  
FASTAZU
CF Senior Member
 
FASTAZU's Avatar
 
Member Since: Feb 2002
Location: Life takes Life just to understand Life
Posts: 10,186
Received 290 Likes on 263 Posts
2018 C4 of Year Finalist
2015 C4 of the Year Finalist
St. Jude Donor '16
Default

1 - 228
3 - 230
5 - 226
7 - 230

2 - 225
4 - 228
6 - 225
8 - 230
FASTAZU is offline  
Old 06-09-2019, 07:15 PM
  #7  
1985 Corvette
CF Senior Member
Thread Starter
 
1985 Corvette's Avatar
 
Member Since: May 2004
Location: Jacksonville Florida
Posts: 4,312
Likes: 0
Received 53 Likes on 40 Posts
Default

Originally Posted by FASTAZU View Post
1 - 228
3 - 230
5 - 226
7 - 230

2 - 225
4 - 228
6 - 225
8 - 230
Thanks, Steve. Looks like i'm in good company for decent results. Looks like the sky wasn't falling! (again)
1985 Corvette is offline  
Old 06-09-2019, 07:27 PM
  #8  
FASTAZU
CF Senior Member
 
FASTAZU's Avatar
 
Member Since: Feb 2002
Location: Life takes Life just to understand Life
Posts: 10,186
Received 290 Likes on 263 Posts
2018 C4 of Year Finalist
2015 C4 of the Year Finalist
St. Jude Donor '16
Default

Originally Posted by 1985 Corvette View Post
Thanks, Steve. Looks like i'm in good company for decent results. Looks like the sky wasn't falling! (again)

NP Now get out and drive the wheels off it
FASTAZU is offline  
 


Thread Tools
Search this Thread
Quick Reply: Compression test performed: take a look at my results


Contact Us - About Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service

© 2019 MH Sub I, LLC dba Internet Brands

We are a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for us to earn fees by linking to Amazon.com and affiliated sites.
 
  • Ask a Question
    Get answers from community experts
Question Title:
Description:
Your question will be posted in: