The Stovebolt Site Forums The Shop Area Engine Shop 1960 a better block ?

Is there any benefit using a 1960 261 block over a 1956-57 block ?

Are they all 261 blocks?

What year truck do you want to use it in?
Front motor mounts might be different (but, easily adapted, usually).

The 1958 and later blocks will allow full-flow oil filtration (and, if already set-up/selected for full-flow oil filtration, you will need to use full-flow filtration).

Other people will add-to and correct/clarify.

1960 & later blocks don't have case pads near front of block on sides mounts used in Task force trucks.

It's going in my 52 truck.

I have a 1960 261 in my 1954 Suburban. I cannot remember (from 1972) if I had to drill holes in the front plate for the front motor mount (similar/same as needed on your 1952 truck.

Compression ratio increased a little in later 261s (1960 compared to 1955/56), but I do now know when or why.

I think the ratio was increased only due to the 848 head being used was it not? I have a chance to get three 261 full engines from a guy. I already have a 56-57 261 block cleaned up and checked for cracks for a rebuild but if the 60's blocks are better i could always take this opportunity to change over before the machine work is done. Having a fully filtered oil system is not a priority to me. (or should it be ?)

The 261 did not use an 848 235 head from the factory.

You can use a 56-62 3836848 on any 261, but you have to drill 6 holes in the head to match up to the 6 additional coolant passages used on all 261s. Those 6 holes should be in the correct location and at a specific angle (someone posted the drilling angle for the extra coolant passages on the head - maybe someone will post a link to the thread).

Some people have speculated on how/why the compression ratio changed in later 261s - maybe someone will post information and documentation?

The full-flow filter is nice, but it might not a "selling point" in choosing between 261 year-engines. There is however the "cool factor" of having an original full-flow system with original canister. This 261 full-flow oil filtration system was the first GM factory full-flow oil filtration system (GMC did not have a 6-cylinder full-flow oil filtration system during these years).

oops my bad then.........should have looked at the casting web page for the head info first before posting.

Would the 848 head still then have a smaller chamber then what would have been used on 850 head?

sorry my post window was open and i never saw your updated post.

wolffcub,

My guess is the same as your guess - smaller combustion chamber in later 261 heads?

I have a '54 & a '59 261, both have 3836850 cast heads.

Yep, the 261 head codes (supposedly) were:

3703570, 3836850 - 1954 to 1962

They might have changed the castings in later years - we are guessing?

They may have decreased the "deck height" by shaving the base of the head (or, the deck/top of the block)?

Let's hope we get posts with better explanations/speculations for the increased compression ratio

Here you go....the holes to add on an 848 head for a 261

http://i140.photobucket.com/albums/r19/LutherParris/1950%20Chevy%20Coupe/Enginepictures011.jpg

http://i140.photobucket.com/albums/r19/LutherParris/1950%20Chevy%20Coupe/Enginepictures010.jpg

I'll have to check my notes for the angle but from memory it seems it was 12 or 13 degrees. That is so the hole you drill hit in the water passage. without the angle there is a chance on a couple holes that you hit the side of the water passage and not the center where it will flow good.

...this is from memory guys. I don't have my notes handy.

Cut-away view of 261 head
You can see why only one of the holes needs to be at an angle to clear the casting.

The 56-57 261 block i got last summer for my rebuild ended up having a crack in it but i was lucky to find another one. The head on the 261 that i got was a 848 head and it already has the steam holes in it. The guy selling the three 60's 261 blocks told me on the phone today that one of the blocks he just happened to have in his garage had a 848 head on it. I will know for sure tomorrow as he was also selling a 235 and im wondering if he was looking at that block and not the 261.

This statement may confuse and does not apply to Canadians. Up here (in Alberta anyways) there is an abundance of 1955-1962 Pontiac cars which came with a 261. They all have 848 heads (drilled by GM of Canada), hydraulic lifters, bypass filtering, and a fiber timing gear and are far easier to come across than a full flow version from a truck. So far I have not found any GM of Canada documentation to support this however.

I wanted to find out definitely what was up with the "steam holes" and so cut up a head to investigate this as well as port shape and possible alterations. I see Pre 68 Dave now has that picture in his album as does Deve and who knows who else by now. The full album of the cut up head can be seen here.

So i might have stumbled up upon some nice engine finds. Want one curt?

I now have a '61 261 with the 848 head (Rochester Monojet carb) and I can't tell any difference in performance over what I had with a '53 235 (Carter W1 carb).

Maybe my 261 isn't tuned up right?

And all the people i have talked to they all claim it a very noticeable difference when going into a 261.

Wally,

What year/engine Rochester one barrel carburetor?

Tim,

I'm 550 miles distant from my '48 until the middle of May. I'll try to remember when I get back to it.