Here's one that will puzzle you, Its puzzled me and friends that know thier casting numbers for BBC Heads. Now I have a set of 3964291 Heads, They are Rectangular port Closed Chambered Heads and have a 109 CC, 2.19/1.88 Valves. This information comes from Mortec.com, Chervolet By the Numbers and a few other books I have. I have a set and they are very nice and are indeed closed chambered heads. Now for the Kicker, I just picked up another set of these 291's, But they are OPEN Chambered. Yes they are identicle casting with an OPEN Chamber, They are not modified to an open chamber, They are stock or some did one hell of a job making thse apear like a stock open chamber (Very Very unlikely). The Date codes are I 9 9 and I 12 9 and the castings once again are 3964291. Can anyone shed some light on these heads I have? I know chevy did a lot of weird things, But this one takes the cake, Open and Closed chambered heads with same casting numbers?

Someone did a good job of modifying the chambers. 291s came with std or small spark plugs but those were the only differences ever made.

If you have an email address you can clearly see that these have Not been modified at all. I can send you a picture, These are identicle to the 990's chamber and would be ruined (Not enough Iron on these to make an open chamber) if they removed these closed chamber to make it an open chamber. You have to see these to see what I'm talking about

One other thing, I checked a set of 291's that I have and ARE Closed chambered and where the spark plugs meets the Head (The seat) its Flat on the Closed Chambered head and these 291's that are Open Chambered the seat is tappered. Now I compared them to the 990's and they appear Identicle to the 990's I can understand a casting mistake, But to not only cast the wrong casting number in the the head and be a few years off on the Date Code would be highley unlikely. The 990's came out in 1971, The 026 also came out in 1971 Only. So they would have a 2 Digit Date code for the Year, Mine only have a 9, 1969, They are September and would make them correct for the Famouse LS6 Chevelle. Anyone else care to comment, Come on Guys, This has got to be an interesting one to you.

well post some pics or PM me and i will post them for you!

Daniel

I will shoot a picture to you if you give me an email address, I don't know how to post a picture otherwise I would, Thanks

Send it to any one that replied and they will post for you if you wish. We are all curious about this anomaly :confused:

I see the heads are on Ebay now. The chambers are polished looking

I tend to think they have been opened up by someone to an open chamber.
They made two versions of the '291' head. One took the taper seat spark plug, while the other took a gasketed spark plug.

I don't think the casting foundry would make that kind of "mistake" (cast it as an open chamber when all the others are closed chamber).
You say there isn't enough material to grind out, but that seems to be the only real answer.
Just my .02 worth.
Rick

Hi Rick.
Do you happen to have the Ebay listing #? I would like to see the picture.

The Ebay item number for the heads is: 160024789088

Rick

From what the machine shop tells me and from what 2 other Chevy "Guru" Friends of mine say that they would be ruined if they tried to open them up as much as they have been opened. They are all identicle chambers, They are not converted chambers, They are indeed factory chambers, Only modifications were the Intake Valve enlargement and polishing of the chamber only. Wierd one huh?

Is it possible the casting numbers are not legit?

I know I have friend racing class stock cars, that can weld casting numbers from an approved head onto an unapproved head so that it will pass and allow him better flow.

I do alot of welding and I can guarantee you that these are not welded. The casting would be smoothed out where the casting number would be placed. If anyone is near Burbank Area and would like to see these for yourself You are more than welcome to check them out. They are legit open chambered heads, Not modified one bit other than the Valve enlargement and smoothing of the bowels

The 840 head can't be opened up to make them a true open chamber (you must modify the open chamber piston to make it fit) but I'm not sure about the 291. the valves are unshrouded quite a bit compared to the 840 and there just might have enough meat in them to gring to open chamber specs. The chambers look funny for a factory head maybe someone can post a picture of a 990 chamber I don't have any around that aren't modifyed.

i have a buddy who bought a set of 291's at a estate sale that has crane stamped on them. someone from another board said back in the day crane and a few other companys worked these heads and resold them. think they are feb 69 castings one day apart.guy bought them bare for 70.00 !

I emailed the guy who came out with the BBC Casting Book from MSA-1 Here's what he had to say about them:
I don't have an answer. I wish I knew what went on at Tonawanda. Every once in a while something weird shows up that is unexplainable. If the chambers were not ground from CC to OC by a shop then possible an old top cast form was used with a OC bottom cast form, but I'm guessing now.




Mark Allen

Well, Either way they are a Very Nice set of heads and I'm sure who ever buys them will be very happy with them. Aluminum is the route I'm taking with my build up otherwise I would use these.

maybe they are a set of one off heads. experimental. that left the factory when they weren't suposed to. kinda like that olds f85 convert that was on barret jackson.

Who knows, Maybe??? I've researched them and asked around and no one seems to kknow for sure, Just a lot of opinions. Like I said either way they are a very nice set and I'm sure someone will get some good use out of them