The Stovebolt Site Forums The Shop Area Engine Shop Pros Cons of an "850" Cylinder Head

I have come across a complete '57 235. The Head is an 3836850 casting number. I'm not familiar with this head or combustion chamber. Has anyone had experience with one of these?

Craig - The "850" head is actually a 1956-62 "261" head according to my casting code info. The details about the '57 261's head can be found in the 1957 Chevrolet Truck Data PDF.

Dan, I was aware of that as it crosses in my books. I'm just wondering if it is worth chasing as much as a "848". I looking for compression rating and measurements.

The seller claims it's on a '57 235.

Craig - The only thing I could quickly find on the "850" 261 head was that it's introduction in '56 upped the 261's rated compression ratio to 7.8 to 1. Not sure how that affects it's use or compression ratio on a 235???

The combustion chamber is pretty similar to the "848", the valve size is the same. I may just take a chance on the entire engine, the price is cheap enough to make it worth the risk.

I'll let you know..

Cool

If I find something more on the head differences, I'll post what I find in case it may help in future plans for the engine.

261 head (and gasket) has coolant passages drilled between cylinders 1 -2, 3-4 & 5-6.

The 850 head will bolt onto any 235 from 1954-62 as well as the 261. It will have a very slightly lower compression ratio than an 848, but it's still a good head. It can be milled to raise the compression ratio to the same as an 848 as long as the intake valves are recessed the same distance as the head is milled. The six coolant spray holes between the cylinder pairs will have no ill effects on a 235 block- - - -they just won't flow any coolant because the 235 block isn't drilled for them.

I'm not concerned with the coolant passages, it's currently mounted on a 235. Externally the head looks the same as an "848", not sure about the oiling to the rockers, though I imagine it is the same.

A slight compression loss is not really an issue, the head will more than likely be resurfaced while being rebuilt.

One of the 261 engines I have stashed away has its original 850 head. When I build up that one, I'll probably mill it to match the combustion chamber volume of the 848. A little bit of a compression bump and a Melling CCS-1 camshaft gives a noticeable gain in low end torque, without the problem of a lumpy idle and erratic manifold vacuum.
Jerry

I'm running the CCS-1 cam in my 261, 848 head, coolant passage drill, 261 valve train, springs, exhaust valve rotator with stainless exhaust valves.
Runs strong, smooth idle.

A "261" with .060 over 265 Chevy V8 pistons, and a 4 1/4" stroke will have 291 cubic inches. That 850 head probably won't need to be milled if I build the engine like that. Those extra 30 cubic inches will give it plenty of compression.
Jerry

I have the same set up on an "848" head for a .060 over 235 I'm building. It uses NOS 1.940 intake valves from a '53 235, milled .040.

Manley makes a duplicate of that 1.940 intake, one that's designed to fit a custom cylinder head fora big block Chevy V8. The only difference in dimensions is the location of the keeper groove, which can be added by a quick, simple plunge cut with a parting tool on a lathe. The part number is 11583-1. Get ready for some sticker shock- - - - -they're E$$$$PENSIVE!
Jerry