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Post Info TOPIC: 68 Powertrain Axle Chart


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68 Powertrain Axle Chart


So today Carl (68_Grande) sent me the copy of the powertrain chart he got with his GM documents. 

To me, the thinking is backwards on axle ratios between the 396 and 427. Why would the 427 need a steeper rear gear than a 396? More power, more torque on a 427 and yet they give it more gear? Why would you want it to run higher RPM on the highway than a 396? The only obvious thing is maybe the 427 had a taller tire? I didn't think it didconfuse

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1966 Strato Chief 2 door, 427 4 speed, 44,000 original miles



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When I purchased the Grande, I thought the car must have a 2.73 rear end. I scraped away paint and grime off the passenger side of the rear axle but could not find the stamping to indicate the gear ratio. Perhaps if I spent some more time or had it up on a hoist I could have did a better job but needless to say, I did this with me on the garage floor and subsequently never did find the stamping.

This fall I got the GM vintage docs and the docs don't make any mention of a rear axle option so I would assume the axle was base equipment.  https://canadianponcho.activeboard.com/t65942818/vintage-services-buildsheet/ The car came the 396, M40 (THM) without AC so by this chart, it would indicate that my car has a 2.56 rear end. I am ok with that because I want a cruiser, not a dragster. Now I know why its so difficult to lay rubber!!

But, as Carl says, when you go down the chart and look at the L36 427, the base axle with a THM 400 is 2.73 and with AC is a 3.07. So, I find that also puzzling as Carl mentions as the 427 has more HP and torque so what would be the rationale for this combination? Is it as simple as here is the biggest engine GM has at the time so with the lower gear ratios, you would be able to feel the power and put a smile on your face??

Puzzling.



-- Edited by 68 Grande on Thursday 7th of November 2019 09:46:53 AM

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I think the 427 was always marketed to be a more performance oriented engine, so GM equipped it as such. GM probably took a shot, and tried to econo down the 396 and sell it as into a strong highway cruiser, hence the 2.56. Still offering the 3.31, such as to market it as a versatile midrange performer. I don't know the numbers, but the 396 probably outsold the 427 two to one, so it was more of their "do-all" kind of motor. They probably would have never dumbed the 427 down with that ratio. Why bother, it would have been outside of it's intended purpose.

Those who wanted a better street pull bought the 427. Optioned with a 2.73, it would have performed better with the 65/50 more HP/TQ than the 396 anyway, good enough if that's what you wanted.

In 69 did they not offer a 2 barrel BB?



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67' Grande Parisienne. Ex Ottawa USSR Embassy car, 67- 68.
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Crazy as it sounds, I bet the 396 outsold the 427 more like 20 to 1. I have documents for a 68 Parsienne 427 4 saying a total of 18 sold.

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1966 Strato Chief 2 door, 427 4 speed, 44,000 original miles



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Yes, 69 396 2 barrel, I think it was 265 horse?

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1966 Strato Chief 2 door, 427 4 speed, 44,000 original miles



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4SPEED427 wrote:

Crazy as it sounds, I bet the 396 outsold the 427 more like 20 to 1. I have documents for a 68 Parsienne 427 4 saying a total of 18 sold.


 I knew two to one would be low, but not that low. Wow!



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Thanks for publishing!

 

The 396 was at the sweet spot where you would have an abundance of torque via the cubes, but manners were also good because of the general performance cam. The 427 came with a hotter cam that put the operating range about 500 rpm higher, the incrementally higher numerical ratio works within that. For people that sought performance then the 427 was the way to go, 10~12 mpg be damned. The 396 would probably be good for about 15 mpg.

 

It is interesting to see the effect that offering optional axle ratios has on axle stocking at the factory. Using the Beaumont as an example, between standard vs. metallic brakes, Positraction vs. open carrier, Oshawa still had to have 20 different axles in stock for the '67 Chevelles & Beaumonts, whereas in the U.S. where you had a choice of ratios and they had to stock 46 different axle assemblies.

 

Mark, the 396 2-barrel was indeed used in 1969. You would have nearly all the same bottom-end torque but on regular fuel. The 2-barrel would be a slug and would run out of steam if you tried to run the car as a drag racer. Still would be real easy to get a lot more out of that choked-down engine with a few customary mods, else it would be good with a tall axle as a highway cruiser.



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The curious thing about that '68 chart is that it shows both the M20 (2.52:1 low) & M21 (2.20:1 low) as being offered. I wonder if they actually offered the M21 in Canada that year? The chart may simply be "borrowed" from an existing U.S. Chevrolet chart and may have included the M21 as a bit of an oversight. I dunno, has anyone seen a documented 1968 Canadian Pontiac with an L36 & M21 as opposed to an M20? The 427 has enough torque that it could pull the taller low gear and then benefit from the resulting closer gear ratio spacing afforded by the taller low.



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67 Chevelle Malibu Sport Coupe, Oshawa-built stocker 250 Powerglide 40,000 mile

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I just read the production numbers on 396 in Canadian Ponchos, but for the life of me can't find it right now. The production was something over 1,300 on 396 in the year I was looking at and we know the top engines the 427, was usually less than 50.



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Bud Lindemann road tested a 69 Impala with the 396 2bbl and it was a real dog



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I once went up against a 69 Parisienne 396 2 barrel with my 69 327 250 2+2 and a blew him away from light to light. Highway would have been another matter.

The owner even said it was a real dog.



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Canadian Poncho wrote:

Bud Lindemann road tested a 69 Impala with the 396 2bbl and it was a real dog


 The shop that I did my apprenticeship at had the contract to service OPP police cruisers. The 1975 Biscaynes had a 454 with a 2 barrel. Talk about a dog. Also duals after the catalytic converter, I dont know what advantage that would be. Those old GM converters were pretty restrictive. 

 

Paul



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I drove one of a '75 Biscayne ghost cars, 454  but with 4bbl, same exhaust configuration.  Top end of 115 mph.  The Dodge Polaris 360 2bbl did better and it had a light bar that caused enough wind drag to take about 10 mph off the top end and it still did 125 mph.  The Biscayne was an embarrassment



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cdnpont wrote:

I once went up against a 69 Parisienne 396 2 barrel with my 69 327 250 2+2 and a blew him away from light to light. Highway would have been another matter.

The owner even said it was a real dog.


 The engine was not designed or intended to drag race, especially in a car with the mass of a Parisienne. Your 350 with 15 less HP had a few hundred pounds less weight , big blocks weigh just under 700 pounds fully dressed but the torque was well suited to station wagon use for example. I've always found small blocks to be more sprightly at launch as well. 



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