Hey guys here's one for you:

They made the 512 block for some time in the later part of 1968, when did they unofficially start making the 291 head that was meant to go with it, and did any make it on any copo 512 blocks?

According to 'Chevrolet By The Numbers' 512 block (427&454) was released October 1968 and used thru 1971. The 291 heads (396,402,427&454) were 1969 and 1970 only. Since the COPO engines were just ordinary 427/425 engines in a non RPO application, yes, they could have and would have been used together.

Our COPO Chevelle was one of the last built and it has 840 heads. I think you will find that the COPO Chevelle engines were built several months before the cars were so the 291 heads would be unlikely. The Camaros were built on into the fall so they could be a different situation.

COPO's had 840's according to copo.com!

Im fairly certain Copos could have come with 291 heads. I have a copo chevelle built 07C [july third week 1969].I also have a set of June 9 and 10 69 291 squareports[f99 and f109].That tells me the 291s were made well over a month before my car was and most certainly they could have made it on copos . Ive personally seen one original copo with a 291 AND an 840 head,both were dated within a few weeks and were late may early june dated on a july build car.

I have a 840 head dated F-2-9 and have seen a 291 head with a date of F-2-9. Could they have been making them at the same time?

Al: I have an F 7 9 840 currently on our Camaro, and have a F 10 9 291 head on the shelf...do you know what kind of spark plug seat the F-2-9 291 head had or what it's valve sizes were? And which valve size is your F-2-9 840 cast for?

the 840 has the 2.19 1.74 valves with the large spark plug..the 291 ( I sold to sully ) had the same I think with the peanut plug.

ALbert

The engine in our Chevelle is stamped T0402MQ and this car was one of the last COPO Chevelles built. Everything in the engine would be manufactured in March or earlier. I don't think there were any 291 heads on the market in this time frame.

Sounds about right, Keith...I've *heard* of a pair of 291s on an original COPO Camaro and 1 840 and 1 291 on an L71 'Vette...

Well a lot of conjecture on this one, lets add some facts and see where it goes:

Most of the COPOs did receive the 840, mostly because there were so many 840s when the 291 officially in the books was available and unofficially available. Most believe that the 291 was available in June of 1969, but in fact since the the 512 came out in late 1968 the head that was designed for it was most likely available as well, but not used becasue there were so many 840's and the COPO engine was a 425 HP engine not a 450 HP.

Some of the accounts of 291 and 840s used on one engine would have to have the 840 exauste valve ground to match the 291 because that was the only difference between the two heads. The peanut spark plug came later.

I have a pair of K 20 8 291 heads sitting on my 512 block, so my belief is that they did make some 291s as far back as they made 512's or close to it, but they did not necessarily make it on the COPO or other cars at that time as a loose rule of thumb.

Also I thought that during the late 68 or early 69 there was a strike, that would probably nessitate using available stockpiles (840's) to continue production.

Ed C does say the 840 head, but my feeling is that some did get the 291, with a .520 .520 lift L72 camshaft the difference in the exauste valve really wouldn't have made much difference in HP, coupled with stock exauste manifolds the over exausting of the engine probably would be nulified, hence nill difference in HP, probably, others may disagree.

Any other opinions

Also I thought the exauste valve was 1.72 not 1.74 on the 840 head?
291 were 1.88