Compression question for 1960 engines
 

Does the difference in compression between the economy engines and the 10.25 comp engines lie in the heads or the pistons? Thx for any replies / input.

RA

I think the 62s had dished pistons,not sure before then.Tom

In the high comp motors it was always done with the heads and head gasket thickness as you can clearly see when you look at a factory parts book!

Other wise the factory would have had to have a incredible mind boggling number of different piston fitted service replacements blocks to make and keep in stock for shipment!

For example , in 1970 in terms of the 400 motors that where not RA4s there where 3 different compression ratios for these motors, yet there was only the 479879 service replacement block listed for all 400s including the RAIII motor.
From 72 to 74 there was only one 400 cid service replacement block listed in the parts book.

Only on the mid 70s did this change somewhat when the factory began to add a chamfer to the top OD of some of the pistons to lower the compression yet even more then what the already big chamber heads did.

In 1961 the 8.6 cr pistons were dished. The others were flat top.
Have to find my 1960 book to see if it is the same.


:)

The oldest listing in my parts book goes from 65 down to 59 and it says all the pistons for the 389 where the same.

To my knowledge there was only one head available on 60 production (non SD) 389s, the 536109.

I do not think I have ever taken apart a 8.6 cr engine.
Though having looked at the Parts books in the dealership I agree that the 389 engine
was offered with those pistons in some application.

Great info.

Tom V.

Thx 4 all the replies. Hoping that the heads were the same.

In 1960 if I recall right there was a head that was only used on the tripower motors and the 425A motors.

Wait, I think the different head was only used with the #7 solid cam, so it would have been a SD head ?

All following info from 1960 Master Parts Catalog.

If you are asking specifically about 1960 (not 1960s) there were two heads offered. Any with 3x2 carbs and T425A engines used head part # (not casting number) 536794. All other 1960 engines used head part # 536793.

Then under "special engine and chassis parts" is a listing for "cylinder head and valve train package (use with 535480 camshaft)".

Here is a chart of 1960 engines. Reading across the top, notice comments about cylinder heads, cams, throttle bores, pistons, etc.

Hope this helps.

The first year I see diff heads for 389 pass car engines was 1963 for dif CRs.All years before that down to 1959 used the same heads.FWIW,Tom

The chart makes one wonder how the heck big the dish was in the export motor's, no?

I had a friend that owned a 1960 Catalina 2 door sedan, 3 speed stick, with the E engine in 1970. This was easily identifiable by removing the air cleaner and noticing the 2 bbl carb was the small version, the same size carb used in the center carb on tri power cars through 1965, when they went to the large center carb for one year, 1966.

This was in my final year of high school, and at Vo Tech, that he pulled the cylinder heads off to do a valve job. I can recall that, yes, the pistons were dished on that Tempest 425 E engine, (Pontiac used the Tempest designation on engines before it became a car model of the compact series in 1961) to arrive at the lower compression ratio for regular fuel. Hope that answers the question the OP asked............;)

Per Pete McCarthy's book: all 1960 production engines used 536109 head castings (there were also 535461 castings for SD heads sold over the counter.) However, heads on 10.75:1 high compression production engines had an 'X' stamped just above and left of the casting number. 425A Trophy heads with HD valve springs had an 'O' stamped above and right of the casting number.

This method was used from 1958 through 1962.

Wow! Thx for all the great info. Got my question answered and then some!
RA

In 1956 Buicks 322 had 3 different pistons for their pent roof chamber heads. One for stick shift Specials., another for Dynaflow Specials and the third for The Century, Super and Roadmaster. All had different height domes.

I am failing to see what 1956 Buick motors have to do with 1960 Pontiac motors.

"Does the difference in compression between the economy engines and the 10.25 comp engines lie in the heads or the pistons? Thx for any replies / input."

I guess I misread the question.

Here you go, it IS the pistons. I've had my hands on these back in the day. Driven a 303 HP 389 where the guy put in the dished pistons and it was tough to tell much of a difference in performance. You might get away with 89 with these guys...maybe..

https://www.ebay.com/itm/25491660366...UAAOSwUuFW10Hm

The School me on 389's guy might be interested in these as well.

pression
 

The 64 326 low compression engine used 389 heads. :old: