More 840 head questions...

[Chevy454]

I recently bought a set of mint 840 heads, and they are currently at the machine shop. Well, I told them to do a basic rebuild on them, and to put the correct for 1969 2.19/1.72 valves in it. Well, they called this morning, and said that they thought the heads originally came with 2.19/1.88 valves, as the area around the seats were uncut and had not been changed. The heads are dated F 7 9 and E 9 9. So, are these late heads, which GM felt were going to be used as service replacements, thus they recieved the 1970 size 1.88 exhaust valve, or... ?

Now, NHRA lists both the 840 and the 291 head as acceptible for use on the '69 L-72, and Colvin's book is unclear about the use of 291 heads (or at least un-clear to me!) in '69. The 291 heads came with the 1.88 exhaust valves, and Colvin said the 840s ceased production around May of '69. So what do we have? Could these be a "combination" 840/291 head? Was the 291 ONLY a service replacement in '69? Were 840s used as service replacements?

I am building this engine for the certified stock class at the Pure Stock drags, so whatever I find needs to backed up with some info.

[Edited by Chevy454 (06-18-2001 at 11:39 AM).]

[GMH454]

Can't help you BUT, you might have answered something that has puzzled me for a long time. Had a 435hp roadster for a while with a factory build date of early July 1969, and you can probably guess that it had one of each head. Never seemed to worry it as it could spin the 10" tyres effortlessly, but it sure had me perplexed. The head dates from memory were about 3 weeks apart. Car had been in Australia since early 1970 and the engine apart from loosing the tripower at some time had not been messed with. I figured that the 291 was a warranty replacement but now......
Terry from the land of OZ

[Chevy454]

Interesting info, GMH. So, it looks like there WERE some 291 heads installed in place of the 840s in '69, and they weren't just "service replacements" for the 840s. I am also assuming that the 840s I have came with the 1.88s so they could be used in conjunction with the 291s? GMH: what size valves were in the heads you are talking about.

The machine shop called again today, and said that the heads have absolutely NOT been touched, and that they came with 2.19/1.88s in them. He said he could put in 1.72s, put they wouldn't flow worth a darn due to the downsizing of the seat. He also mentioned that in his reference books, he ONLY shows the 2.19s being accompanied by 1.88 exhuast valves...the 2.19/1.88s are hi-perf while the 1.72s are low-perf and came with 2.06(?) intakes. My local parts guy (MoParts on here) also checked his books, and they DON'T show a 2.19/1.72 combo.

Any ideas?

[Rowdy Rat]

2.19/1.72 was the high performance valve package for rectangular port closed chamber cast iron heads until the 1970 model year when the 291 head was introduced. I don't know where the machine shop came up with a 1.88 exhaust, but I have never seen anything but a 1.72 in a pre 1969 cast iron head.

Your other question is a bit more difficult to answer. Did Chevy start using 291 heads during late 1969 (1970 model year)? I've never seen them on an original car and I've asked several other people who deal with these cars on a regular basis if they had seen 291s and their answer was "no" as well, but they didn't see a reason why it couldn't happen either... Obviously, you're right at the change over point so it is certainly possible.

Two points to add to the discussion...

I recently had a chance to look at a very low mileage 1969 L-71 Corvette at a show in MO. The car was in the 38,000 VIN range (very late build - it started down the assembly line on December 17, 1969) and had a little over 5,000 miles on the odometer. It had 840 heads although I have no idea what the valve size was.

What heads were used on the 1970 L-78 engines (don't have my resources handy)? What valve size? I had heard that only the LS-6 cars received the big exhaust valves anyway... Is this true or just urban legend?

Regards,

Stan Falenski

[Chevy454]

Stan:

According to CBTN, both the LS-6 and the L-78 used the 291 ehads in 1970.

Here is what CBTN (65-69) says about the 2 sets of heads:

840
<UL TYPE=SQUARE>
* This cylinder head was the first big block head produced with a temperature sending unit boss. Very late 1967 cylinder heads would have the boss, but it would not be drilled and tapped. Production of this head began around May 1967 and ceased around May 1969. This head is identical with #3904391 except for the temperature sending unit boss and two accessory bolt holes added to the end of the head.[/list]
291
<UL TYPE=SQUARE>
* This cylinder head is indentical with #3919840 except that it has a tapered spark plug seat, and an exhaust valve seat redesigned to accept the 1.88 exhaust valve. As with #3964290, #3964291 was produced with both "N" and "peanut" series type spark plug seats. This was the last closed chamber square posrt cast iron head produced. It was produced in both plug designs for service replacement, including 1965 through 1969 model years. This was also used in 1970. [/list]
So, does Colvin mean the 291s were ONLY used as service replacements on '69 cars, or that some cars could have gotten them?

[Rowdy Rat]

I get the impression that Colvin is saying that the 291 head replaced the 840 head in production at X date and also became the service replacement for the 840 when that occurred. From the information on the 840 head, Colvin leads you to believe that this date was around May 1969. If that was the case, you should start seeing 291 heads in cars built July-August 1969 as the stock of 840 heads was depleted. Terry's observations from his own L-71 roadster tends to support that...

Fact is that I haven't seen too many solid lifter 1969 Chevys that were built after July 1969... I know that they're out there, I just haven't seen them. This is definitely something that I plan to research. I did find it odd that the late build Corvette that I looked at still had 840s in mid-December 1969. You would tend to think that any 840 heads left in inventory would have been used long before this. I have e-mails out to a few other people on this topic; perhaps they can shed some light when they reply.

By the way, how goes the buildup for the PSMCDR? As I said before, I'm impressed that you've decided to go with the AMA specs for the certified stock class of this event... I hope that you do well!

Regards,

Stan