What's the minimum head thickness that can be used? How do I tell the difference between a 2wd and 4wd head? Are there any cr differences between the two (I'm using a 200 block)? And how do I choose pistons and rods to get the right cr (I'm after long rods and short pistons)?

Dan

 

138.68 min according to the book(but lots are below this)
2 wd has a bracket/casting above the exhaust ports for a turbo hanger and the coolent temp sensor for the dash is at the front next to this (on a 4x4 its at the back near the ecu temp sensor (the blue one))
the 4x4 has a slightly less cr than the 2wd
the heads are interchangeable without touching the bottom end
spacers are req if fitting 4x4 cams in a 2wd head

steve

 

Thanks Steve much appreciated

Would a 138.3 head be scrap or still useable if it was freshly skimmed to this thickness?

 

I believe there are heads fitted that are 137.XX
the issue when over skimmed is the exhaust seat falling out, the area around there is extremely thin when overskimmed
it's a case of take your chance..

steve

 

The minimum thickness is 138.x MM (can't remember the last figure), if you head over to the "Tech essay" room, there is a article by Stu, as to why this is.

The reason is when they are skimmed below this, you start loosing material around the valve seats.

Martin

 

138.68mm

 

you can have stakes put in the valve seats to make them usable below 138mm

 

The problem is the piston to valve clearence with std crown heights, at 138 you are way off the valve seats falling out .