Which heads are these?

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Which Heads are These?

110 hp
3
43%
95 hp
4
57%
 
Total votes: 7

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tdsherman325
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Which heads are these?

Unread post by tdsherman325 » Tue Mar 29, 2011 8:35 am

The number is 3880708. According to Clark's, they're 95hp heads, but according to http://www.angelfire.com/ca4/CorvAIRCRA ... mbers.html they're 110hp, and if I look around, I can find a few people selling heads with these numbers as 110 heads. So, which is it?

Thanks,
Terry
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atwistedgrip
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Re: Which heads are these?

Unread post by atwistedgrip » Tue Mar 29, 2011 12:25 pm

Look like low compression heads to me. Not 110.
Gary
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cvair4life
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Re: Which heads are these?

Unread post by cvair4life » Tue Mar 29, 2011 1:44 pm

I don't know what they are but I added a poll for you :) Seems like I got better results from a poll as folks don't have to actually reply
1966 Corsa Coupe

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flat6_musik
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Re: Which heads are these?

Unread post by flat6_musik » Tue Mar 29, 2011 2:36 pm

atwistedgrip wrote:Look like low compression heads to me. Not 110.
I'm kinda inclined to agree with Gary.....110's are supposed to have a full point higher compression, and I don't see anything in that combustion chamber that would "bump" it up from 8.25 to 9.25. Aren't all corvair piston heights the same, pretty much, for the specific year?......and the compression change is in the heads?

Terry, do you have a link to Clark's page?......'cuz that Angelfire link claims it have gotten its info from Clark's.

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65Ragtop
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Re: Which heads are these?

Unread post by 65Ragtop » Tue Mar 29, 2011 5:39 pm

They are 66-67 110 AIR (smog) heads. The 110 engine with these open chamber heads used a pop up dome piston to achieve the higher 9.25:1 CR.
Mike S.
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CARGOIL
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Re: Which heads are these?

Unread post by CARGOIL » Tue Mar 29, 2011 7:49 pm

Good job ragtop. I'm impressed. :tu:

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flat6_musik
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Re: Which heads are these?

Unread post by flat6_musik » Tue Mar 29, 2011 9:23 pm

CARGOIL wrote:Good job ragtop. I'm impressed. :tu:
I know I learned something today! :tu:

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tdsherman325
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Re: Which heads are these?

Unread post by tdsherman325 » Wed Mar 30, 2011 6:09 am

the Clark's catalog page is here: http://www.corvair.com/user-cgi/catalog ... ind_page=1, but, oddly, it lists 3880708 as 110 heads, whereas my paper catalog lists them as 95. I guess the paper catalog is wrong, then?

Thanks, ragtop. I'm impressed as well. So the difference between 95 and 110 smog engines is the pistons and not the heads? if that's the case then I must have the lower compression ratio as I've got aftermarket flat pistons in mine.

Thanks for the poll, cvair4life. I hadn't thought of that.

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65Ragtop
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Re: Which heads are these?

Unread post by 65Ragtop » Wed Mar 30, 2011 9:38 am

I looked up the head numbers in my paper Clarks catalog. I think what they did was group "like" or interchangable heads together to save space. They do say that the listing is incomplete. I also looked up the online version and they got it right there but once again grouped the head numbers to cover 66-69. So basically, the paper catalog is incorrect but only in a "factory original concours show car" kind of way. The 3880708 heads are 66-67 vintage for sure. Just as a note, the aircraft guys tend to get it right as their life depends upon it. ::-):

As an example: There were 2 types of low compression 95 HP heads used between 64 and 67. One on non-AIR engines that had the quench chamber design and another design (yours) used on AIR engines with the open chamber. This open chamber design was also used on 64-66 turbo motors.

It is not uncommon to find aftermarket flat top pistons in AIR 110 engines these days. To my knowledge, there are no longer any aftermarket companies that supply the domed pistons anymore. Best bet if you need them would be NOS stock. Probably not many of those left either. Not a problem though. The CR with flat tops is about 8:1. For a daily driver this works out great with todays variable gasoline quality and mixtures. There are a lot of variables to consider but generally speaking as a base line place to begin, a compression ratio of 8:1 will be well supported by a gasoline with 80-octane or above. Easy to find. A 9.5:1 CR would perform best with a gasoline with 95 octane or above and so on. Good luck finding that around town! :02:
Mike S.
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140Vair
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Re: Which heads are these?

Unread post by 140Vair » Wed Feb 14, 2018 11:41 am

My '68 Monza with the original base, 95HP A.I.R. motor came with the 3880708 heads.
IMG_3855.jpg
I had it out to clean, change lifters, reseal and paint all the tin.

My vote is that they were used for both 110 & 95 engines.
68, Monza, 95, PG #7732, built 3rd wk of 01/68

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bbodie52
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Re: Which heads are these?

Unread post by bbodie52 » Wed Feb 14, 2018 6:13 pm

tdsherman325 wrote:Tue Mar 29, 2011 10:35 am

The number is 3880708. According to Clark's, they're 95hp heads, but according to http://www.angelfire.com/ca4/CorvAIRCRA ... mbers.html they're 110hp, and if I look around, I can find a few people selling heads with these numbers as 110 heads. So, which is it?
ImageImage
:link: http://www.corvair.com/user-cgi/catalog ... age=TECH-3
Image

Image

According to the combustion chamber diagrams on the Clark's Corvair Parts page above, and to the cylinder head casting numbers on that same page, the style and shape of the combustion chamber matches both 150 hp/180 hp turbocharged heads, and 1968-1969 SMOG heads. The casting number you provided (3880708) matches 1968-1969 (SMOG) 95 hp cylinder heads.

According to the Cylinder Head Numbers chart on page Code Numbers 5 in the attached CORSA Corvair Technical Guide 1+2 - Corvair Code Numbers, the casting numbers 3880707 (1966-69) and 3880708 (1966-67) are assigned to a 110 hp 164 CID engine with a 9:1 Compression Ratio. Based on your combustion chambers in your photograph, the shape of the combustion chamber shown, and the casting number you provided, I suspect that the chart in the CORSA reference is in error. The combustion chamber volume shown in your picture would seem to match the low compression ratio (8:1) used on turbocharged and 95 hp SMOG heads.
CORSA Corvair Technical Guide 1+2 - Corvair Code Numbers.PDF
CORSA Corvair Technical Guide 1+2 - Corvair Code Numbers
(1.25 MiB) Downloaded 3 times
:think: :idea: I have a theory... Chevrolet did some strange things to carburetors, camshafts, pistons, and possibly cylinder heads in 1968-1969 to try to make the SMOG pump work better on the hot-running air cooled Corvair engines. It might be possible that the heads shown were fitted to the low Compression Ratio (8:1) 95 hp SMOG engines with flat top pistons AND to 110 hp SMOG engines that needed a 9:1 compression ratio. The 110 hp engines may have used the same heads but were then fitted with DOMED PISTONS to raise the compression ratio. The open combustion chamber shape may have helped to prevent detonation in the SMOG PUMP engines.The reasons for the rare domed pistons may have been lost or confused over the years. :dontknow:
Corvair Underground — Corvair Book, Page B-14 wrote:PISTONS And how to identify them.
The chart to the left shows all pertinent dimensions for Corvair pistons. Essentially there are 4 stock types. Three are different as to dimensions and are listed. The fourth type is a 64-69 design with a “pop-up” face. (Sometimes called “domed” pistons) These were used on 65-69 Corvairs with hemispherical chamber heads for engines listed as 110 hp with smog pumps. The pop-up pistons CANNOT be used with regular 110hp or 140hp heads because of clearance problems.
:link: http://www.corvairunderground.com/2006_catalog.pdf

:guitar: :whoa: So the "hemispherical" combustion chamber heads are found in both 8:1 CR 95 hp SMOG PUMP engines fitted with flat top pistons, and were also used in 110 hp SMOG PUMP engines that had a 9:1 CR when fitted with the domed pistons.
Brad Bodie
Lake Chatuge, North Carolina
Image 1966 Corvair Corsa Convertible

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