DeserTBoB wrote:

> Those who read what I did to my '86 Fifth Avenue may find this
> somewhat interesting. I just took a 678 mile road trip to northern
> Nevada via US 395 in the car, using cruise control, AC about 40% of
> the time, speeds at posted limits not exceeding 65. Average max road
> speed: around 62 MPH.
>
> Vehicle/drive train: '86 M-body, LA roller cam 318, Holly "Carter
> clone" 6280 feedback carb., A-904 trans with lockup converter. Basic
> timing: 7° BTDC @ 630 RPM per California spec. Fuel: 87 average
> octane "regular."
>
> Trip plan: Lv Lancaster CA via north CA 14 to US 395 to the Nevada
> state line at Topaz Lake and return. No local driving at destination
> (just bicycling around the lake), no idling with AC on, no "warm up"
> idling, etc.
>
> Elevation at start and destination: 2580 and 5950 ft above sea level.
> Maximum elevation: Conway Summit, 8130 ft. Route has three major
> 6-8% grades northbound.
>
> Fuel economy going: 25.4 MPG
> " " return: 28.9 MPG
> Average: 27.2 MPG
>
> All CA smog gear is working as per spec., as well, with no
> disconnected EGR or other illegal mods.
>
> The best mileage ever from this vehicle was a trip from Laughlin, NV
> to Barstow, CA: 29.1 MPG, average max speed 55 MPH.
>
> I think it's fixed. Why do newer, smaller models with V6s get worse?
> One can only ponder, but the answer always comes back the same.


Way back when I owned an M-body (83 Gran Fury) it would consistently
turn in about 20-23 mpg highway. They were definitely sleepers when it
came to efficiency. Chrysler always did build the best, even in the dark
dismal days of the 80s.

But it also had a 2.45 rear gear and couldn't get out of its own way
off the line (though the top end was darn near unlimited). My wife's 93
v6 LH would simultaneously out-accelerate the M-body, AND get better
mileage, AND has cleaner exhaust. I still like driving my 60s cars
because a) they really ARE more powerful than modern cars, and b) they
have style. But I'd never argue that they meet the same kinds of
simultaneous performance objectives (power, efficiency, emissions) that
is possible today.