389 question...
 

I was wondering what the differences were between the YS and the YR or WG engines are other than the HP rating.

I understand that some of the engine codes are different due to the type of transmission the car came with I was just wondering what the factor was that made them have different HP ratings... I was it the heads and cam?

If anyone knows I would appreciate the help. Thanks!!

65 an 66 models
WG 421, 338 hp, 4bbl, manual shift, 10.5 CR
YS 389, 335 hp, 4bbl, auto, 10.75 CR
YR 389, 360 HP 3X2bbl, auto, 10.75 CR

On the 65-66 389 engines, all the blocks were the same. The HP difference came, as you noted, with the use of different heads and camshafts. All the blocks have the same casting #'s and are interchangeable. The only difference is the stamping of 'YS', 'YR', 'WS' or whatever.