308 head milling

Chris Smith

Curious how much to mill a cast iron 54 308 head to gain a half point of compression. Also what is the most I can safely have milled off for maximum compression. 

Browniepetersen

Chris, in my never to be humble opinion milling the head is not the best way to go if you are looking for increased performance.  The head is two inches thick (give or take--those I have measured never have been two inches.)  I have been told that you can mill up to .200 on the head.  I have also been told .100.  At best, the added compression is not much.  I milled a head .130, installed it, and at start-up it blew a hole from the water jacket and filled the engine with water/antifreeze.  I have also been told that you can hone out the recesses.  It becomes the same issue.  If it is power you want, machining, intake/exhaust valves and modifying the cam is the best way to go.  Perhaps Randy will chime in and give some particulars--there have been a lot of posts on building a 7X engine and also an engine with maximum -power. 

LHudson

A option that has not been discussed is cc ing the head. The head we used on the engine we rebuilt, my son spent a lot of time cc ing the head. The head was cut but don't remember how much. There was a lot of varence in the volumes of the chambers. The time spent doing the cc ing was well worth it.  Might be a option.  L Hud

Chris Smith

Is a 262 head worth the time and expense? 

RichardD

Certainly when someone does valve reliefs the compression ratio is dropped. How do you get the ratio back up ? Mill the head/special piston head?  Oxymoron?? If you can't do more than clean up the head surface and no one makes special topped pistons, why would anyone relieve?

Just curious~~

Ol racer

FYI
There is a fine line between Relief & Compression Loss on a Flathead....Relieving to 7X depth greatly improves breathing when installing larger valves, performance Cams, etc. Compression is brought back by block modifying. However, these Mod's are not really necessary for a Street Motor

An easy Mod is to install a 262 Head raising the compression while not choking the Mtr like a 232 head would since true 7x Mtr's used a 'Spl Modified' 232 Head) .. Installing a 262 Head on a 308 has been done for Yrs.
 
Regarding milling, probably safely.060 (Although ive gone more then Flycut the Exh Chambers
 then 'side gapped' the plugs... ...

maasfhcenturylinknet

In January i sold my '54 hudson coupe to a friend in Florida.  Rebuilt engine-relieved- 372-254 cam, slightly larger valves .050 -262 head-popped pistons up out of block .012 and 200 lbs of compression.  Drove it to florida on 91 gas and now over 7000 miles no problems.  Good power

DavidC

Pay attention to these thickness numbers.  Hudson recommended replacing head if milled thinner than 1.94, others have had success down to 1.92-1.90.  I did not know about this with my rebuild, head milled to 1.89.  The machine shop was nice enough to mill the topside ribs down a bit as well, making them real pretty.  Unfortunately this weakened the head and I developed a linear crack to the water jacket-goodbye head.  New one is already milled, 1.94, the top untouched.  Working well so far.