Olds 350, (does these numbers make sense) WHAT YEAR???

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Pharozen

Greasemonkey
Dec 19, 2012
205
42
28
Triana
Look at the numbers below and hopefully someone can once and for all, verify the YEAR of my olds engine. Does these number make sense to anyone:

395558 2

31r145933

There is the number 7 by the #1 and #8 spark plug.

CFD

409

147

These are all the numbers/characters that I could locate on my engine, in hopes that I can determine the year that my engine was produced.

I'm hoping that it's a 1968.
 

King_V

Master Mechanic
Jul 17, 2013
307
5
18
Sicklerville, NJ
If what I found from here matches up, then given your block number of 31r145933

3 = Oldsmobile
1 = 1971
r = plant of manufacture (though I don't know what R translates to)
145933 = last 6 digits of VIN of the car it came from
 
Oct 14, 2008
8,806
7,746
113
Melville,Saskatchewan
The early heads flow better and have smaller chambers. Your engine will be 8.5 to 1 or probably less if stock. 71-72 had decent small chamber heads with big dish pistons, lowering compression. The casting numbers are the same through 76. Later #8 heads have 10cc larger chambers and need under the valves unshrouded to equal early head flow. Later 3A heads are crack prone and restrictive.
 

Pharozen

Greasemonkey
Dec 19, 2012
205
42
28
Triana
olds307 and 403 said:
The early heads flow better and have smaller chambers. Your engine will be 8.5 to 1 or probably less if stock. 71-72 had decent small chamber heads with big dish pistons, lowering compression. The casting numbers are the same through 76. Later #8 heads have 10cc larger chambers and need under the valves unshrouded to equal early head flow. Later 3A heads are crack prone and restrictive.

What are #5 and #6 heads? How are they different from the #7?

I just read that #7 heads and #6 heads are the best heads to have.

I also read that the advertised cc chambers actually vary. For example, an advertised 64cc for #7 heads may actually be larger than 64.

So I guess, what I'm asking now is; is there really a difference between #6 and #7 heads?
 

King_V

Master Mechanic
Jul 17, 2013
307
5
18
Sicklerville, NJ
The info I've gleaned from here suggests that the #7 and #7A are about the same as 5 and 6 - 64cc chambers.

Note the 1972 7A has the letter A as being smaller than the #7, almost like a subscript. The 7A heads from 1985 upward have the letter A being the same size as the 7, and those are the roller-307 heads with coffee-straw-sized ports....

The #8 head used from 1973-1976 and has 79cc chambers. Compression was maintained by going to flat-top (I think) pistons, whereas the 1971 and 1972 heads had the lower compression by using dished pistons, if I recall correctly. (warning: I may NOT recall corectly!)

The #3A (A the same size as the 3) from 1977-1980 was 75cc.

The 7A of 1972 is supposed to be good for unleaded fuel - hardened valve seats.

I'm not really sure how much difference there is between the #5, #6, and #7 heads. Maybe the earlier ones flow a little better? Not sure... only the one semi-cryptic line in that same webpage that says "Dick Miller claims that #5 heads flow the best bone stock and untouched."
 

1bad79

Royal Smart Person
Dec 3, 2011
1,023
890
113
Allendale mi
All the info above is pretty much right, if you are coming to Michigan any time soon I have a 68 350 with number 5 heads I might consider selling for the right price :D
 
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