Help identifying these heads please?

[Kevster]

Hi,

When I bought my 65, it came with lots of spare bits, including a pair of heads.

These heads appear to have an extra threaded hole next to the spark plug. I thought this must be some sort of smog feature, however, none of the diagrams I've seen show pipes running to each cylinder.

I have tried looking up the head numbers but one appears to have been re-stamped, presumably a replacement and the other I haven't found. 3786591

Maybe it's for the nitrous

[notched]

All I can see is that they are small valve heads. I would need to see more detailed pictures of the combustion chambers and the ends of the heads. What size bolts run along the intake manifold log? Are they all 3/8-16 thread or a mixture of 3/8-16 and 1/4-20?
I looked in my GM Corvair parts book from 1970 and do not have that casting number listed. I also have never seen heads with holes drilled and tapped like that. Smog engines did not utilize modifications like that.

[Wagon Master]

Like stated we need a picture showing the whole combustion chamber.
1. Does it have single or spring with flat damper valve springs?
2. Is the opening where the cylinder jug goes a little over 3.800 or 3.735?

[bbodie52]

3796591 ???


The Clark's Corvair Parts online catalog tech page lists several heads that have a casting number that begins with "379". All are 1961 heads, with the exception of a 1962-63 turbo head. None have a number that matches your 3796591 head. The CORSA technical guide listing also does not list that head casting number. In fact, none of the head casting numbers listed in either table end with "91" as the last two digits.

http://www.corvair.com/user-cgi/catalog ... age=TECH-3


I think this was a special experimental head developed for use on the highly secret Corvair powered lunar rover...

[64powerglide]

Kind of makes one wonder just how much we don't know about these wonderful automobiles!!!

[Kevster]

Great, looks like we have a mystery!

Here is a picture of the chamber.

The second port looks original from the way the fins are cast, unless it was modified very well and a long time ago?

Single valve spring and GM38 cast on the head.

Any advance on a regect from the lunar rover?

[bbodie52]

I think that after a great deal of research the GM engineers concluded that an air cooled engine would not cool sufficiently without air. The same GM engineer was heavily criticized for his $500,000 lawn chair seats, and for installing a rain umbrella upside down to catch lunar rain, instead of deflecting it to keep the astronauts dry.





The engineer was demoted, and later developed the variations in the Corvair steering column, after completing his work on the award winning designs used in the Corvair passenger compartment heater systems.

[Kevster]

The bore for the jugs is 3.741".

The bolt holes along the intake are a mixture of sizes with 3 x 1/4"

[notched]

They look like 64-66 turbo combustion chambers or even 68-69 110 smog heads. The large vacuum tubes on the carb pads makes them non turbo although they could have been drilled. The bore opening is early sized. The mixture of bolt sizes on the intake log is 65 and earlier. I don't really know what to say about how or why those extra holes are they. You might want to look up Bob Helt or Steve Goodman on the other message board as one of those guys might know something about them.
With the open chambers most guys will run away from them as you can never achieve proper squish.

[Kevster]

Thanks for the info Notched.
I gave any thought of using them due to the extra port, I had thought they might be turbo as that was the closest match from the Clark drawings.

Now I just want to know what they are and what the extra port was for!

I'll try the other forum and see what we get.

Thanks

[notched]

I can see the additional casting for the choke coil rod to come through and it does not appear to be drilled. The fact it has this casting leads me to believe the oldest they can be is 1962. The last detail would be whether it has the casting boss for the turbo oil drain. You did not provide a picture of the rocker box. But my opinion is they were some kind of over the counter 62-64 head. The open chamber is definitely like the turbo heads.
I personally would not use them as those chambers are very prone to detonation.

[66vairguy]

Just a wild guess - but I wonder if someone was adding a second spark plug (granted a small one) for use as and aircraft engine. I've seen some creative modifications on Corvair engines in aircraft.

[bbodie52]

Aircraft use, and the desire for increased reliability in continuous operation as opposed to high performance in a competition environment would seem to apply to this type of small valve head application. The use of a secondary spark plug that is physically smaller in size would seem to be an interesting approach that would accomplish the gains of a dual ignition with an easier implementation using available space effectively while avoiding the need to close and eliminate the existing spark plug port.

The pictures below compare this head with another design seen on the Corvair Center...


http://corvaircenter.com/phorum/read.ph ... 087,585091

[my65]

I think that bbodie52 and 66vairguy hit the nail on the head.
Check out this site about Corvair aircraft engines http://sonexbuilders.net/viewtopic.php? ... 8&start=20

[Kevster]

Thanks guys.

It appears to be a 10mm thread, which certainly is an available small spark plug size.

Not many home built planes in the uk and defiantly not many powered by a corvair engine I wouldn't think!
I guess the heads got shipped over as spare parts and once people realised they weren't any use, they have just passed around and ended up in a haul of spares that came with my car.

Mystery solved, thanks guys.
Kev.

[ral1963]

The head number is 3786591, not 3796591 .... 145 cu 98hp engine, used in 1961, and 62&63 on export engines.