Thread: 1980 RPM's
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Old August 31st 04, 01:20 PM
Fred
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<< My car is running at around 3200 which seems a bit high & my gas milage
is terrible. I was thinking it should drop down to around 2200...>>
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What is the stock rear-end gear ratio in that car?

It has always amazed me how people got along with 3.23:1 rears (or
numerically higher) in older musclecars. The engines in these cars (350 CID
and more) produced more than enough torque at 2,000 rpm to keep the car
cruising happily at 65 mph. Having the engines spinning at over 3,000 rpm
at 65 mph is just terrible and totally wasteful.

Shortly after I had purchased a 1976 Trans Am 4-speed (with stock 3.23:1
rear), I immediately swapped in a Richmond 5-speed and 2:56:1 rear end.
This made a HUGE difference... HUGE. Best mod I ever made on any car, ever.
Prior to the trans and rear swap, the 455 was darned near melting down at 75
mph (3,500 rpm+), sucking gas faster than you could imagine. Can't believe
GM sold cars this way, but I guess transmission technology was fairly poor
back then. And then I've seen original GM ads advertising old Buick GS's
and Ram Air GTO's etc with factory 3.73 or 4.11 rear ends (with optional
4.33:1)!!! Pure insanity. This is truly "race-only" stuff. These cars
must have been completely unuseable on the highway. I can't see how a 400+
cube engine could last very long spinning at 4,000 or so rpm with little
load all day long... would surely overheat before long... mileage would
probably be 5 mpg or something, car would be screaming away making loads of
noise and vibration, etc. When GM sold those cars with 4.11:1 rears, I hope
they had warning decals on the dash that read "not for use on highway!!!".

As for your `80 Vette... you may want to consider swapping in milder rear
gears. You will lose a little tug off the line, but your highway experience
will be much more pleasant. What do you have in that car... a 3.55? 3.23?
Maybe swap in a 2.73 or so. If the car was a manual, then you could go the
Richmond 5-speed route which is well worth the fairly high expense. I've
heard of some guys swapping in manual 5-speeds into auto tranny cars... not
too hard if you can get all the manual trans parts (clutch pedal, linkage,
etc) out of a wrecked manual car.

Or... I don't know too much about auto trannies, but aren't there some later
model 4-speed GM auto trannies that might work in your car? If you can get
one with a super low first gear, then you could swap in a 2.56 rear without
losing much tug off the line, etc.


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