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Apr 26th, 2026 | | AD Chevy Trucks  Over 6,000 pictures Brad Allen has an awesome collection of Chevrolet factory pictures that he has set up from film strips. Check them out!
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| | | | Joined: Jun 2022 Posts: 557 'Bolter | | 'Bolter Joined: Jun 2022 Posts: 557 | At a local 2 bit car show Saturday and an old buddy showed up with a 55 2nd 235 all matching engine #s. The question was and is... what is the difference between the 55 5913 head and the 56 848 head other than the temp sender change? All I could tell him was something changed to jack up the CR.
What about it, Jerry?
~~ Jethro 1954 3100Back to LifeIn the Dity Gallery1951 3100 (gone) / 1956 4400 (still in the neighborhood) / 1957 6400 with dump body (retired) / 1959 3100 panel (in the woods junked) / 1978 Custom Deluxe K10 / 1993 S-10 4.3 / 2004 Chevy Crew Cab / 1945 John Deere H / 1952 John Deere B / 1966 John Deere 2510 / 1967 John Deere 1020 | | | | | Joined: Feb 2004 Posts: 29,820 Kettle Custodian (pot stirrer) | | Kettle Custodian (pot stirrer) Joined: Feb 2004 Posts: 29,820 | The 848 head was cast with a smaller combustion chamber to increase the compression ratio. The earlier head can be milled .090" to get the same compression as the 848, but a few other modifications have to be made along the way. The intake valves need to be recessed into the head the same distance as the milling job to prevent piston/valve interference, and also to protect the edges of the valves from the flame front across the surface of the head. Then the rocker arm stands have to be shimmed up the same distance to keep the pushrod length and geometry correct, and a lash cap needs to be added on top of the exhaust valves to keep that geometry right. It's not a terribly difficult project, but attention to detail is important. As the 848's get harder to find, I believe the old school head milling procedure will get popular again.
Edit: It would also be possible to just shorten that tall intake valve stem the same amount the valve is recessed, but if you choose to do that, run a lash cap to avoid the possibility of getting into a "soft" area of the stem and promoting rapid wear. Be sure to account for the thickness of the lash cap when you shorten the valve.
Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
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There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
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| | | | | Joined: Dec 2017 Posts: 1,652 'Bolter | | 'Bolter Joined: Dec 2017 Posts: 1,652 | The 5913 head has a combustion chamber volume of 86.2 cc or so, the 848 head has a chamber volume of 79.1 cc.
Mike
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