The Stovebolt Site Forums The Shop Area Engine Shop 235/261 Cylinder head differences

I have searched on this forum as well other places and can't really find any good information about the critical differences between a 235 head and a 261 head. I know there were several different styles of head made for the 235s, but I believe only one casting for the 261s. What I am really looking for is combustion chamber volume differences. Anyone have this information?

I'm pretty sure you have to remove 1/8" from a 261 head to match the volume of the smallest chamber head which is casting #848. Removing that much creates valve train complications so a head swap is the easiest. More info here.

Thanks for that info Curt, however I was a little bit confused about the list of casting numbers - are those ALL 261 heads or are some of them from a 235 engine?

If the idea is to put the head on a 261, the 848 fits perfectly with no mods except for the steam holes that need to be drilled in the proper place. My engine shop already knew how to do this, so I don't have any information on how do machine these heads. I am under the understanding that there is no difference in volume using the 848. I have this setup myself.

The 848 head has the smallest chamber volume, the 850 head is slightly larger and much more common - from what I have read. Both engines that I have have the 850 head on them, however one of the engines appears to be a 235. The other one is definitely a 261.

If there is no difference in the "volume" when using the high compression 235 head compared to the lower compression 261 head, how do you think the 235 with a high compression "848" head achieves that high compression?

There was a post a while ago about drilling the additional coolant passages on the "848" head at an angle. Maybe someone will post info on this? I think the drilling information might have come from the Inliners International discussion board?

Inliners site has a very good write up on the steam holes search engines>261 steam hole question by poster Curt B #5628
Inliners Post

Yeah CurtB posted pics and a descriptive detail of how to do it. Its more involved than just placing a 261 gasket on the 235 head and drilling the holes. One row of steam holes has to be drilled at an angle of they wont penetrate the water jacket in the head.

The 848 is used in most of the how-to's on this subject because they are the most prevalent. Out of 6 random 235's I have in stock, 4 of them have the 848. Not that they are the best, they are just more available.

Since this is a very necessary procedure (proper steam hole placement), its just prudent unless you own a machine shop to just take it to the engine shop and have them do it. If your engine shop has no idea what you are talking about, you have your first clue as to the need to change engine shops. If you all lived in Central Kansas, no problem. Jims http://www.jimsmotormachine.net/ in Galva, KS knows exactly what to do.

I agree that they are the most prevelant but disagree about them not being the best especially on a 261 due to the benefit of reduced chamber volume and of course more compression. Info on drilling the head.

We should expect that the "848" high compression head is the most common high-pressure 235 head: it was made for over 75% of the high pressure 235 years.