14 MPG?

[Ron Dame]

I bought my '80 (350/TH400) not expecting it to be an economy car, but even after a full tune and a carb kit, I'm getting only 14 MPG mixed driving, though largely highway miles. I was hoping  more around 18 in mixed, so I am wondering is it typical, or do I need to some more sleuthing?

Thanks!

[Gunslinger]

That's a smog era engine with a 3-speed automatic...excellent transmission it is...but that's probably about what you can expect from the combination.  Without knowing the rear axle ratio you might be able to squeeze out 16mpg if the car is tuned on a computerized machine.  Changing the transmission to an automatic overdrive such as a 200R4 or 700R4 will help drop the rpms and improve mileage.  

[pantera928]

4 hours ago, Gunslinger said:

That's a smog era engine with a 3-speed automatic...excellent transmission it is...but that's probably about what you can expect from the combination.  Without knowing the rear axle ratio you might be able to squeeze out 16mpg if the car is tuned on a computerized machine.  Changing the transmission to an automatic overdrive such as a 200R4 or 700R4 will help drop the rpms and improve mileage.  

That is about right. I have a 1980 also. I have thought about putting a 200-4R in mine as i believe that the mounts line right up with the ones used by the TH400

[wildfelr]

RQB3263/81/305 ..... WITH 700R4 OD and 2.72 rear gear I get 20MPG  on a good day .....love it

[Ron Dame]

OK, so as far as tune, I apparently am OK, so I won't look for problems. As I'd like an LSD, I might swap to a lower numerical ratio at the same time as I'm not a speed freak, but I'm not a granny either.

[Gunslinger]

You could always replace the TH400 with a 5- or 6-speed Tremec.  Performance and economy!  It would take a while to recover the conversion costs but it would be a great swap.

[wildfelr]

RQB3263/81/305    ALSO...i cammed up the 305 for the torque needed to operate in  OD.... ALSO completely depolluted ...installed real true dual exhaust .... removed any and all computers and installed a non electric q-jet carb and dual electric cooling fans ..... ALSO I seldom use the A/C   keep up the good work .....BILL