Just curious, in your experience, what is the most fuel-efficient V-8 equipped vehicle you've ever observed ? (in terms of highway mpg)

My 93 vette gets 26-28, which is the best I've ever observed for a 350

 

LS bases 6 speeds get 30mpg

 

My ~375 rwhp 94 LT1 M6/4.10's gets 26-28 mph on the highway.
My 650 hp 01 Twin Turbo LS1 M6/3.42 gets 30 mph/highway.

 

84 6.2l Diesel, 34mpg. (in a fiero)

 

I'm going the wrong way. 84 406. 3/4 gallon of race gas/quarter mile run.

 

I can get 30 mpg with my LT4, if I am on the interstate with cruise set at 70.

But overall average (city/highway/some spirited), it's in the 21-24 range.

Still much better than my pickup or the new Camaro SS we bought.

 

just picked up a 67 C-20 4x4 with a 327 & 4-speed behind it. Truck only weighs about 3900 which is just 700 more than the vette, problem is the axle ratios in the C-20 are 4.55:1. Trying to figure out which ring & pinions to get for it. 4th gear is 1:1. Tires are 30.5" dia so @ 60mph current rpms are 3012, a set of 3.08's would knock rpm @ 60mph down to 2038 but I have no experience in choosing axle ratios... yet !! I'd like it to get 22mpg on the hiway.

 

I average around 20, but if it's just highway I usually get between 27-28

 

I have an Isuzu Vehicross for a winter/2nd ride. It's got 4:30 gears and is full-time 4x4. There is constant debate on their forum about how to improve MPG. BTW, on my Isuzu, 4th has a .75 ratio.

Because of the need to swap out 2 diffs for a gear change, no one does that. OTOH, there is room for bigger tires and people have gone from the stock 29.5" size up to 33's. In no case has anyone ever reported appreciable gains. The same hold true for converting to manual front hubs and turning off the electronics of the 4x4 sensing system. (IOW, people have converted to 2WD w/o much change.)

The only thing that's ever helped is converting from auto to stick. And, a handful have done so.

VX's (Vehicross) get between 15-19mpg with a fairly well designed dual-overhead cam V6 motor. They also weight about 2tons.

The moral is it VERY hard to improve on what the factory gave you. You can spend more money trying to improve what you got than the savings you'll recover. If I were you (and really serious about trying), I'd convert to a stick with an OD. Maybe a ZF!!!

That said, I've seen reports of up to 33mpg for a V8. Mostly, that's with direct injection engines. My 89 was actually measured at 30mpg with it's ZF6. Since I converted to a 383, I've yet to drive it out on the road far enough to see what happened. My guess is I dropped about 10% -- which is what city driving seems to have done (with the conversion). Probably not too surprising since I increase CI's 10%.

 

When I first got my '92 it got 30 highway.

Since I've done my mods it has gone down some but honestly I have never driven a tank of pure highway miles in 10 years. I'm always at couple hundred miles of highway and the rest in town which makes that number fall real fast, usually low to mid 20's.

If I was to run all highway I see no reason why I couldn't get 26-28 out of it.

 

Its a stick. I'm seriously considering going with 3.08's on both front and rear, that will cut rpm's down by 1/3 and fuel consumption is directly proportional to rpm. And an RV cam for hi torque up to about 3500 rpm. Its got an sm420 with a creeper gear, the taller diff gears might help to make that a more useful gear for non-hauling applications.

 

That would be my '88 Vette; 30-31 highway and mid 20s around town...

 

Sounds like a neat truck
Pics?

Youll need to build that 327 for torque 3.08s/tall tire/3900 lbs will struggle to gain speed. Yes at cruise better mpg but..think you get it. Im wondering if lugging that thing at 2k may be counterproductive to mileage.
Or not

A cam in the low 2teens 1/5/8 header and a performer intake would wake it up. Elgin and Erson (still around) made a killer cam for this trying to remember the grind on it. Isky makes some good stuff too.

 

I have no idea, when the gauge gets low i fill the tank.

 

Wife gets 18ish commuting in town, 31+ on long trips. 2004 LS1 auto coupe
I had an 88 that got 16ish commuting around town and mid 20's on long trips
The 92 gets around 6 at the road course

 

Came with factory dual exhaust, plus being a 67, its emissions exempt so that leaves lots of options open. I have a spare set of our LT-1 aluminum heads I've worked a little - can plug up the big holes on the deck face of the head, ... pondering whether anybody makes a carb manifold for our LT-1 reverse-cooling engines that's got the right angles / locations of manifold bolt holes so I don't have to fill & drill - it'd be nice to just plug the deck holes and slap those on there. Years back Crane made grind 967601 which was a blueprint cam for the 350HP 327. But, even a profile akin to the stock grind from our LT-1's I might choose, b/c it was engineered for all around perf & economy and my 93 vette puts 310 ft lbs to the wheels, which isn't all that bad in the grand scheme of things & it gets good mileage. Dang, whats our diff ratio in the 93 ? I was thinking its like 2.59:1, maybe I need to go look it up again...

 

Without a ZF, 30 on the hwy seems impossible. mid-20's around town, I know is impossible.

Lessen you're holding some secret water-vapor, injection/electric hybrid secret you never let on about.

OK...maybe you let is coast downhill when you measure.

 

My 99 got 33.6 @ 65 driving it home from Kansas City, MO. After a few mods it easily got 36.6 @ 65 if driven carefully and could get 40 @ 55:

http://www.youtube.com/watch?v=uQialnqMFxs

 

I'll be the first to raise the flag.

That "instant" mpg reading your showing means absolutely nothing over the course of a tank of fuel.

Hell, I can get upwards of 60 mpg in LT4 using the "instant" reading.

Fill your tank up, and drive until almost empty. Then fill again, recording the gallons used and miles traveled.
Divide the total miles traveld by the gallons of fuel used.
My guess is it will be nowhere near 40 mpg, or even 36.6.

 

Yup ..that's not real world.