what kind of gas mileage out of your car

It seems that no one is concerned about gas mileage. But for a lot of us, gas is part of the free money left over from the weekly expenses. It is a difference between a Sunday afternoon cruise or a drive and set car show, or stay home. So, I have access to a 2003 Suburban with a 5.3 aluminum motor and probably a 4L60 transmission. So mileage is part of my concern, but an LS is an ugly motor to a old skool guy. If I can pick up 5+ mpg [14.5 on highway at 70 mph] then I will spend the money. I have to go to an automatic, and 4L80 is a expensive swap into a non computer car. [400R4 is not capable to handle my torque] I think a lot of people would be interested in gas mileage even if it is a secondary consideration.
66 Lemans convertible w/A/C
BBC 489
HP EFI TPI tunnelram w/2 throttle bodies
10:1 compression
282/288 .510/520 lift comp roller
ported close chamber heads big valves
TKO600 5 speed
3:70 Ford 9"
25.5" tires
8/10 mpg in town[ some? spirited driving ]
14.5 mpg highway @70 mph

So on my current car, a 1966 Chevelle, I went for almost pure mpg. Not for occasional driving vs showing but because it’s my daily driver. Rain or shine.
I still have 325 HP but it’s from a V6. I also run a 6 speed auto where both 5th and 6th are OD.
Driving normal I get between 30-32 mpg. I have had one max mpg run of just under 40 mpg. It will still spin a tire (no posi) and is fun to drive.
I know this isn’t the norm and I love the sound of a warmed over SB or BB. And I agree with you that latervengines are not as “pretty” to look at. That’s why they come with plastic covers for everything. New “coil cover” valve covers help but from the factory they’re pretty blah looking
It was something I thought I try and I’m glad I did. I’m spending way less on fuel than even my LS1 powered 67 conv (since sold).

Transmission gears are your friend, for mileage. I'd try for a 6 or 8 speed transmission. Case in point, the 2015 Tahoe I just ditched had a 6L80E and a 400ishHP 5.3l. All factory, except 4.10 rear gears that I had installed, and a little EFI Live work on my part. It was a 5300lb gigantic wind catching box, but it was fun (not as fun as yours, but I did surprise a lot of folks with it) at lower speeds, averaged 18MPG city, and pulled a best of 23.5MPG on the highway on a trip to Arizona. It would have been even better with 3.73s, because 1st gear was useless with the 4.10s until I put a larger tire on (about 33in diameter vs the factory 31.6) to bring the ratio down to around 3.91. That made it only mostly useless. But, the OEMs are in the habit of gearing them too high to pass the federal mileage test instead of real world mileage (and which goes to show why government mandates do more harm than good) so changing for a lower ratio usually helps all the way around.

For you this would require a Gen4 5.3L, or better yet a 6.2L, with a 6L90E and perhaps 3.23 or 3.42 gears with that tire size. A calculator that takes trans gear, rear gear, tire size and RPM into account would help you decide what the best ratio and tire size would be. Should have similar performance around town, with mileage over 25MPG on the highway.

I'd stay away from the 4L80E if you want better mileage. It's a heavy beast that takes a lot more power to spin than other transmissions. Its purpose is handling high power and heavy loads. The newer 6/8/10 speeds can handle similar loads and are built for better mileage. The 4L80E was really a TH400 with overdrive, and is a design from a time when mileage meant how far it was to the next town.

The biggest difference in fuel economy you will make is with proper gearing. A lot of time, I see people rant and rave about the economy of EFI or LS engines but, in reality, transmission/rear end gearing usually plays a bigger role.

If your TKO 600 is a close ratio, the OD gearing would be close to 1:1. .8 overdrive, 25.5" tires and 3.70 rear is pretty wound out for a 489 BBC at 70mph. I'm sure that big of an engine wouldn't mind a 3.00-3.25 rear end. You would really cut down the number of times that 489 inhales air/fuel per mile just by dialing back the rear end gear for the highway speeds.

I would try changing your rear end gear before ditching your 489/TKO for a 5.3/4L60. By the sound of that setup, I imagine you have a lot of money there. That 489 is probably making amazing torque numbers and I'm sure you would miss that going to a 5.3.

I had a 13 ZL-1 Camaro, around town I would get 16-17mpg and on highway u could fairly easily get 23-25mpg. It was a stock ZL-1. I know the zl-1 has 3.70 rear gears.

2nd generation Camaro, mild 350 sbc build, ~400 HP....Th700r4, 3.42 axle ratio and a gear vendors OD...

I get ~30 mpg highway with the lean cruise mode kicked in on the EFI. I'm doing about 2200 rpm at 85 mph with the lockup engaged on the converter and the double OD from the GV.

Around town its a much different story though... probably 13-14 mpg if I'm driving normally with no lead footing.

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Originally Posted by Jonathonar89

The biggest difference in fuel economy you will make is with proper gearing. A lot of time, I see people rant and rave about the economy of EFI or LS engines but, in reality, transmission/rear end gearing usually plays a bigger role.

If your TKO 600 is a close ratio, the OD gearing would be close to 1:1. .8 overdrive, 25.5" tires and 3.70 rear is pretty wound out for a 489 BBC at 70mph. I'm sure that big of an engine wouldn't mind a 3.00-3.25 rear end. You would really cut down the number of times that 489 inhales air/fuel per mile just by dialing back the rear end gear for the highway speeds.

I would try changing your rear end gear before ditching your 489/TKO for a 5.3/4L60. By the sound of that setup, I imagine you have a lot of money there. That 489 is probably making amazing torque numbers and I'm sure you would miss that going to a 5.3.

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Yeah even before I converterd to EFI, I had swapped in a 700R4 back in 1992... at the time I had an Edelbrock performer package on a 350. Still had the 3.42 axle. On the highway I was getting 21 mpg with the carb.