CR question for 1960 389's
 

Was the hi vs low CR in the 60 389's achieved by the machining of the heads or the pistons. I'm assuming it was head machining. Am I wrong?

I know in 61-62 they had a LCR piston,in 63 I believe they made the diff in the head.No clue about 60.Tom

In 1960 they had a slew of CRs, and the lowest compression with the tiny Rochester 2 bbl, it had dished pistons, besides the head modifications. Pontiac used the same 2bbl that the early tri-powers used for the center carb. I believe it's designation was 420 E, meaning economy. The 420 E was only rated at 215 HP with an 8.6 CR. I had a friend that I attended Vo tech with, that had one of these 420 E cars that pulled the heads to do a valve job, and I saw the dished pistons on his car. Pontiac used 3 different compression ratios and 9 different HP ratings in 1960. I owned a 318 HP tri power 1960 Pontiac with 10.75 CR so I saw the highest offered CR, and also saw the lowest CR in the same year.

The table below shows only 2 different head CCs, and the only way to arrive at lower CR was dished pistons.


1960 Pontiac
HP Disp C.R. Ind. Carb Model Head cc Valves Trans
215 389 8.6 1-2 Roch 2GC 71.3 1.88/1.60 Std
215 389 8.6 1-2 Roch 2GC 71.3 1.88/1.60 Std
230 389 8.6 1-2 Roch 2GC 71.3 1.88/1.60 Auto
235 389 8.6 1-4 Cart AFB 71.3 1.88/1.60 Std
281 389 8.6 1-4 Cart AFB 71.3 1.88/1.60 Auto
283 389 10.251-2 Roch 2GC 71.3 1.88/1.60 Auto
303 389 10.251-4 Cart AFB 71.3 1.88/1.60 Auto
318 389 10.753-2 Roch 2GC 66.8 1.88/1.60 All
333 389 10.751-4 Cart AFB 66.8 1.88/1.60 All
348 389 10.753-2 Roch 2GC 66.8 1.88/1.60 All

Thx for the great replies/info. Much appreciated. Did the low CR heads have any external identity features different than the high CR ones. Anyone know?

I assume that they have the codes cast in same as the later heads did. From Wallace Racing the casting numbers (536109) seem to be the same as do the 2 digit code (69)

The 1960 Pontiac Master Parts Catalog lists 2 part numbers for heads (could easily be the same casting numbers). 536794 for "All 3/2 B.C. & T425A" engines and 536794 for all other engines. There are no heads listed in the "Special Engine and Chassis Parts" section.

Same catalog has a good chart of what parts were used in which engines in 1960.

Forgot to translate the "Model Application" info from the Engine Identification Chart into readable English:

Model 21 is Catalina, 23 is Ventura, 24 is Star Chief, 27 is Bonneville Wagon and 28 is all other Bonneville models.

See http://www.pontiacsafari.com/L1Garag...dex.html#Heads.
That should explain it.

See http://www.pontiacsafari.com/L1Early...nes/index.html and scroll down to 1960 for options -- and other information.

After Larry's comment about the 1960 options and my comment

I went back and looked in the "Special Engine and Chassis Parts" section again. The parts are listed alphabetically and I had looked for "head". I should have looked for "cylinder head".

Cylinder head and valve train pkg. Use w/535480 camshaft ....... 989670
I'm guessing this 989670 head and valve train package would include the casting number X 535461 O "Super Duty" head Larry refers to.

Here are the cams listed in the "Special Engine and Chassis Parts" section.