Re: Weird 12-bolt ratios
Posted by Cam Milne on 3/14/2018, 8:34 pm, in reply to "Weird 12-bolt ratios"
There were optional ratios available in 1969, usually an economy, performance and special choices were offered. The specific ratios (std & optional) were really dictated by engine / transmission combination. |
Now I know that you are asking about a Canadian Pontiac (1 of those Chevy-Pontiac hybrids). Traditionally the Canadian cars usually only offered the standard ratio for a given engine / trans combo, but around 1969 they began to freely offer different ratios as options. My personal belief is that GM was really starting to take advantage of the Auto Pact, sending U.S. cars into Canada & also Canadian cars into the U.S. (to keep the Cdn / US import / export numbers in check). That opened up production at the Canadian plants to the U.S. market in a major way, and they could now justify offering more ratios for the broader market. I mean if you were in charge of production planning at the Canadian plant & only sold in the Canadian market, that market is small and it would not be economically viable to offer too may variations (they sold, what, in the order of 13 427 4-speed Canadian Pontiac full-size in the Canadian market in 1969?) I think for 1969 they brought in 6 or 7 L72-powered full size Chevrolets imported from the U.S.
For instance look at what happens to stocking when you offer just the standard ratios on the 1967 Canadian Chevelles. Between Positraction or open, metallic brakes or asbestos shoes you have to stock 20 different axle assemblies to satisfy production requirements. In the U.S. on the '67 Chevelles they offered a range of ratios for a given drivetrain combo and therefore had to stock 46 different axle assemblies. See how that works?
The 2.29:1 ratio was RPO GT2 & was only offered optionally on big block cars (396 & 427s) with Hydramatics.
The 2.56:1 ratio was RPO GT1 & was standard with the 396 & LS1 427 with the TH400. It was optional on all others when running a Hydramatic combined with engines ranging from the 250 six through the L48 350
The 3.55:1 ratio was RPO G96 & was offered with all engines optionally, though there were specific engine / transmission combos offering it.