Compression and emissions -
LinkBack Thread Tools
post #1 of 4 Old 01-03-2002, 01:24 PM Thread Starter
Registered User
Join Date: Oct 2001
Location: Portland OR
Posts: 60
Compression and emissions


I am rebuilding my 4.0L and wanted to raise the compression just a tad. It's a 1988 with a lot of miles. What is the stock compression? Is it 8.8:1? If so would I pass emissions and or have problems if I raise the compression to 9.5:1. AND,.. would I have to get a new head due to the higher compression pistons? Thanks man!!

2000 Cherokee 4.0 4X4, K&N
88xj is offline  
Sponsored Links
post #2 of 4 Old 01-03-2002, 01:25 PM Thread Starter
Registered User
Join Date: Oct 2001
Location: Portland OR
Posts: 60
Me again, sorry, this is sorta the same question I asked earlier but yet different.

2000 Cherokee 4.0 4X4, K&N
88xj is offline  
post #3 of 4 Old 01-13-2002, 09:54 AM
Registered User
Join Date: Nov 2001
Location: KS
Posts: 318
You shouldnt have any problems with the 9.5:1 pistons. Talk with who ever you are getting the pistons from and make sure the have valve reliefes in the top which most do. You dont need a new head to run the higher compression but its a good idea to clean the heads up with a valve job and have the valve springs checked. You will what the head milled to make sure its strait and at the same time have the machine shop measure the cc size so you can get the proper size piston for the compression that your after. Also check your cam for wear. To many people run old cams without checking for worn spots on the lobs and end up with poor performance. For what the cost its a good idea to replace it.
After all you dont want to do this again at 60k-100k do you.
eltj is offline  
post #4 of 4 Old 01-14-2002, 09:32 AM Thread Starter
Registered User
Join Date: Oct 2001
Location: Portland OR
Posts: 60
Thanks! Your right, I don't want to have to do this again!

2000 Cherokee 4.0 4X4, K&N
88xj is offline  

Quick Reply

Register Now

In order to be able to post messages on the forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.

User Name:
Please enter a password for your user account. Note that passwords are case-sensitive.


Confirm Password:
Email Address
Please enter a valid e-mail address for yourself.

Email Address:


Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page

Similar Threads
Thread Thread Starter Jeep Forums Replies Last Post
0 Compression #7 and #8 HO4.7 splash56 Engines & Drivetrain 4 08-05-2009 07:48 AM
Compression #'s BIG1RED9 Engines & Drivetrain 5 10-23-2006 11:56 PM
compression (PSI) Wagoneer Man Engines & Drivetrain 0 12-27-2005 09:04 PM
Compression, How low is to low ?? 97powerstroke Engines & Drivetrain 3 06-27-2005 07:15 PM
Compression Anyone? Raven18940 Engines & Drivetrain 4 05-20-2004 07:33 PM

Posting Rules  
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are On
Refbacks are On

For the best viewing experience please update your browser to Google Chrome