The Stovebolt Site Forums The Shop Area Engine Shop Which head is best?

I have two Chevy 235 heads, both of which have been rebuilt. One has a casting number of 3835913; the other number is 3836848. The info found so far shows that the 5913 is a 86.2cc head while the other is a 79.1cc. I am not familiar with the cc ratings on heads and need to know which would be better on the engine I plan to use. The engine has a casting number of 3769716 and an engine number (stamped into the smooth area behind the distributor mounting hole) of F0707B. I'm cheating a bit here since I have a 41 Chevy 2 door sedan rather than a truck, but this site is the best I've found for info on stovebolt engines.

848 is the head of choice as lower cc the higher compression and more power. However is the average driver I wouldn't think you could tell the difference. Just keep the other as a back up!
Best of luck

3769716 is a 1958-1963 high-oil-pressure engine block

3835913 high-pressure engine head was used from 54-55st.
The most common higher-compression high-oil-pressure engine's head is the "848" head (56-63).

The 913 head can be milled .090" to get the same compression ratio as an 848 head, but a few other modifications need to be done, like recessing the intake valves the same distance, shimming under the rocker arm stands, and adding lash caps between the exhaust valve stems and the rocker arms. None of that is particularly difficult, but the parts-swappers of today usually don't have the technical ability to do such things. If it's not a bolt-on swap they claim "That's impossible!" Too bad!
Jerry

"I have two Chevy 235 heads, both of which have been rebuilt. "

If the 848 head is good, it is the head you should use.

Definitely, highest compression ratio without using special pistons is very tough to do with these engines.

One other thing to consider, the 5913 head uses a smaller port for the water temp sender then the later 848 head so if that is a consideration. As for the 848 head, that head entered service in 56. I have one dated September 55 for the 56 production. The 56-57 motors had a compression ratio of 8:1 where most of the literature that I have seen suggests that the 58 and up motors had a 8.5 CR. Quite a few years ago when Tom Langdon was still working (pre retirement) at GM, he looked up the chamber volumes of the head casting numbers for me which I posted some years back on the inliners site. At the time, the 848 head was spec'd at 79.1 cc. That being said, I have never measured the chambers from a 56-57 head and say a 59 head to see if the bump in reported compression was combustion chamber driven or something else.

combustion chamber driven or something else

Good point

Thanks loads fellas!! Lots of good advice here!! It'll be a while before the work gets done, but the results will be posted here.

Might the higher compression in the 1958-1963 235s be due to the use of the higher lift “261” camshaft as standard equipment in those engines?

while on the subject,
does anyone know how the corvette heads compare to 3836848?
early head is 3836066 or 3838066, one of those numbers is a typo but i don't know which
and the later head is 3836241

I do not know the answer, but, a search does show the 3836241 235 head as being the high compression Corvette 235 head used in 1954/55.

If anyone has that casting number head, please post the date casting code.

Here is/was one at a good price.

I have nothing empirical on this but my feeling is that quite a few of the parts for the 53-54 corvette motor (and 55 for the few 55 6 cylinders that were built) were standard production items. So while there may have been differences in the casting numbers, the parts were similar to the parts already in use. I rebuilt a 54 vette motor a number of years ago and I did not see any outward differences in the block and head. Looked like a standard powerglide block from the era, and the standard head from a power glide motor. springs, keepers, push rods, rods, pistons, bearings, crank all standard design items. The 54 cam had similar specifications as the 261 truck motor, not sure if 53 used the same specifications, my gut says no as the 261 did not start production until 54. There were some differences of course, special valve cover for 53, intake with the carter yh carbs, split exhaust manifold, ignition shielding, a few things, but overall I think chevy was trying to keep the production costs to a minimim by using as much off the shelf stuff as possible. So the long winded answer is that no, I don't think there is anything unusual about the vette head, except the price, lol.

Compression ratio, as i understand it, is a basic math problem. It is the comparison of the volume of the combustion chamber, with the volume of the cylinder from BDC to TDC. This would be considered a static comparison, with no involvement with any moving parts (such as the camshaft design).
Where it can get squirrelly is when one engine is set up with TDC ending up shy of the top of the cylinder, while another engine is set up with TDC closer to the top of the cylinder. The additional volume above the piston which does not reach the top of the cylinder should then be considered as part of the combustion chamber volume.
For a 235 to go from 8.0 to 8.5, there would need to be a considerable reduction in the volume of the area above the top of the piston and the top of the deck at TDC and a reduction of the combustion chamber of the head.
0.5 is a lot of gain.
I have had a head milled .090 and it left little if any quench volume on the head near the intake valve. I can't imagine that this would aid in the swirl characteristics of this head, and it would likely shroud the intake valve even if it were recessed into the head (to avoid contact between valve and piston).
Having said that, one will not know this until one puts it on the dyno. Parts in motion often defy the "logic" of static parts diagrams and engineer's preconceived notions.
Look at an old Harley engine. On paper, it should not run. Put it on the street and hang on!
Carl

I have long wondered why GM designed the combustion chambers as they did. Performance wise and economy wise it's not the strong point of the engine. Was it that the science was not well developed? By the 30s there were both hemispherical and wedge designs on aircraft and racing engines. Was it cost? How does the sort of bath tub design end up cheaper? Was it an accommodation to low octane or poor volatility gasoline? A look at engine designs shown in my old Thomson Products manual shows that GM was the only user of OHV designs on American cars in the thirties and GMC, Mack and Cummins the only truck engines. One can see why Wayne came up with a 12-port head for Chevrolet in the fifties. Too bad GM didn't buy that design from them. The engine still had a 10 lifespan at that time. Anyone know if the Wayne head was a wedge design?

I also note that GMC 228 & 248 engines in the mid thirties had very radical cams -- like over 300 degrees duration. What was that about? Maybe an attempt to limit cylinder pressures at low RPM to prevent detonation? I doubt the engines were ever called on to run over 4,000RPM or so. By the late thirties they were back to more conventional valve timing. All the while compression ratios were like 6.75:1.

the wayne head was more or less a hemispherical combustion chamber. but the valves followed the same layout, as it used the same cam.

The odd looking Chevrolet chamber was copied by Toyota, and both Mercedes (L4, L6) and Jaguar (V12) produced a similar chamber.
The original Chevrolet goals were intake swirl, knock suppression by quench, and high turbulence. A "pure" hemi sounds like a good idea (first used before WW1) but it has compression ratio problems (tall heavy dome needed for high CR), bad quench, very heavy and complex valve gear, and high cylinder head weight.

W/r/t: "GMC 228 & 248 engines in the mid thirties had very radical cams -- like over 300 degrees duration"
Never saw that, source is?

The OEM GMC chambers follow 2 basic shapes, either open and roughly hemispherical (more "bowl" shaped) with no quench area (circular gasket outline), or more elliptical with quench at two opposed closed surfaces flush with the gasket.
However, "hemispherical" usually means that the valves are separately angled to the bore axis (the "stem angle", which may be equal intake vs. exhaust, or slightly different) and to each other (the "included angle", equal to the sum of both stem angles). In older engines the stems are frequently 45° to the bore, making the included angle 90°. This includes H-D OHV engines 1926-83, Chrysler-Dodge-DeSoto hemi 1951-58, Triumph and BSA motorcycle, Jaguar XK-E, etc.
By comparison, all 4 of the OEM GMC head types (hemi or closed, big or small port) have vertical and parallel valves.
The Wayne GMC head sat flush on the block (not wedge or hemi), with parallel valves but they appear to be angled to the bore.
Photo: http://tinyurl.com/y2t38sor
Quench is possible depending on piston design. The intake and exhaust valves are arranged like the stock GMC head, so it can use a stock cam, many other heads have alternate valve positions and require special cams. There are other GMC heads with open chambers like OEM but 12 port: Fisher for example.

The first commercially successful wedge engines were the 1949 Cadillac and Oldsmobile V8.