4.2 high output,,build input needed - JeepForum.com
LinkBack Thread Tools
post #1 of 2 Old 09-09-2009, 08:23 AM Thread Starter
Registered User
Join Date: Nov 2006
Location: u.s.
Posts: 375
4.2 high output,,build input needed

i figured i'd ask you cj guys as you will know more about the 258's.....when i replace my yj motor (92 242) in the future..i dont want to go stroker..so would it be better to just do a usual 4.0,,or get a 258, and put the 4.0 or better cam,and 4.0 head/intake etc on a 258 short block.

So,,,,i know a lot of you have done the 4.0 head swap,,but a cam,efi also,,and if so,,is the longer strok and few more cubic inches noticable over a stock 4.0 h.o............thanks

xjandyj is offline  
Sponsored Links
post #2 of 2 Old 09-09-2009, 09:45 AM
Registered User
1983 CJ7 
Join Date: May 2009
Location: Texas Hill Country
Posts: 6,742
Cubic inches are always better as long as you can feed them. Heads are almost always the bottle neck and unfortunately are usually left alone. If you know how or can sub it to a competent machine shop I'd definitely go with the 4.0 head and have the valve bowls blended paying attention to the short-turn radius (where the port floor rolls down into the valve seat) and the long side radius along the intake valve for improved swirl. Depending on fit, you may want to match the ports to the intake.

If you can then find a cam with a fairly short duration but as much lift as possible and hopefully ground on something tighter than a 110 LCA, pair that up with a correctly done exhaust, re-curve the centrifugal advance on the dizzy and use a CDI ignition you'll probably be a pretty happy Jeeper. Does anyone make high-ratio rocker arms for the 4.0 head?

You weren't specific about your intended use or power range for the new engine, though.
swatson454 is online now  

Quick Reply

Register Now

In order to be able to post messages on the JeepForum.com 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
Are the input/output gears interchangeable in the D300? 243 Jeep CJ Forum 2 03-28-2009 05:42 PM
High 5 Build Thread... 1Rustycj5 Jeep CJ Forum 7 03-22-2009 10:28 PM
high output alternator Old Yeller Jeep CJ Forum 2 07-25-2007 11:14 AM
High Output Head on 258 I6 Worth it?? qwert98 Jeep CJ Forum 7 05-07-2007 06:35 PM
SOA input needed CJfreak Jeep CJ Forum 1 07-04-2006 10:48 AM

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