235 or 261? Stovebolt Engine Numbers ID Help

I've heard lots of 235's had the captains bars. Enough so that I wouldn't count on that as a reliable way to ID engines. The numbers are really the only sure way to know.

 

measuring the bore is another good way.

 

I did end up plugging them before I found out what I had. But I didn't run it. I won't run it until I have proper oil flow, obviously, lol. I was going to run without a filter, but now I'm looking for something cool to run. I'll probably have to run a Mr. Gasket type remote filter or a simple rubber oil rated line from one port to the other for now until I can find something cool to replace it.

Tell me more about the 848 head. I understand it raisess the compression when used with the 261 block. But what else makes it more desireable for performance? And is there a way to tell for sure if it's just a regular replacement head or a vette piece?

And thanks everybody for all the help. The posts in this thread and my other oil filter thread for sure kept me from blowing up my engine on the assumption it was a 235.

 

the 848 head compression thing is more hype than anything else. you are dealing with a 7.5 or 7.75:1 compression truck motor. The most its going to raise the compression is .25 or .50 if you are lucky. they only make 200 hp.

all the 18 bolt heads work and for all practical purposes it doesnt make a nickels worth of difference in all practicality.

 

Don't they have different combustion chambers? Won't this affect performance? I ask because I thought I read something to that efect a while back or maybe it was the difference between the 235 head and 261 head, can't remember (maybe on the '55 Hot Rod 261 article, Soup That Chevy). And thanks.

 

In theory, yes it will affect performance. But its not enough to make a big difference. Especially if you dont have the trans, gears and tires correct. You can go the extra mile to get the 5 extra horses out of it and then kill what you just did with a poor ignition or an automatic trans.

The last few horses are really expensive and hard to get out of these inlines.

 

Does yours have the second set on the opposite side as described on the site at the link?? "The 261 has two pairs of parallel raised 3/4 inch long bars cast in the block. This is not seen on a 235 except 1954. (This is apparently not accurate) One pair is above the starter and the second pair is at the top middle of the left side of the block very close to the head. See photos below. The one exception is the early 261 produced in 1954 to mid 1955. It has only one "Captain Bar" above the starter but keeps the pair on the left side." Just wondering.

 

Sounds like you have an engine just about like the one we are gonna "Test Mule" our intake on. 261 with a 848 head.

Kevin
Ooltewah Speed Shop

 

Lower the compression? I don't think so. Frank McGurk once said that you'd have to mill a 261 head .125" to get the same gain as milling the "848" head .030"

There's lots of info on these heads on the net. I just dug this one up.
Tom Langdon, before he retired from GM spec'd out the following:
3703570 95.5cc combustion area
3836850 86.2cc
3835913 86.2cc
3836848 79.1cc

Your 848 head was not original equipment on any of the 235 Corvettes (it was first produced in '56) but became the only replacement head available to them thus a lot of the old 'Vettes have the 848 head on them.

 

Yeah, I meant raise the compression. Oops. I fixed my post above, lol. The McGurk milling info was in the '55 Hot Rod article Soup That Chevy. I didn't know the combustion chamber info. Thanks a bunch.

 

Dyce did a head for me a few years ago and he cc'd it. I dont know what his numbers were, but it wasnt real close to the advertised numbers. Maybe he will chime in and tell us what he remembers.

 

I'm curious to hear too. In the '55 Hot Rod article, the compression was much lower than advertised on the 261 they tested and so power was also down from factory specs.

 

I've got one, captains bars and all, never overbored, only small ridge in cylinders, good oil pressure, 110-120 compression except #6 which has a bad valve, the good 848 head, complete w/ carburetor (I just rebuilt it with TOMCO kit), fuel pump (new), original steel vacuum and fuel lines, generator (works fine), starter (rebuilt), water pump (new), etc. - make me an offer! Gotta come to Florida to get it but that is not all bad, eh?

 

Here is a good artical about the 261 http://www.oldchevytrucks.com/Tips/261_six.htm