MPG daily driver swap in 59 Mercury

**Kevin Whitten** · 09-16-2018, 06:38 AM

Got a 59 Mercury Monterey weighs 4000 lbs and has a 291 diff. Wanting a high MPG LS configuration.
I was thinking of 5.3 with a 460E but also wondering if a 6.0 with 460e would do better considering the weight and high
291 diff. Also I could use help with choice of exhaust and other things i can eliminate or add to get premium gas mileage.
The old girl will look good, ease down the highway, and hopefully get 20? maybe more? Thanks for your time i dont know much and need help.

***SMWS6TA*** · 09-17-2018, 07:17 AM

what size rear?

5.3's are stout engines but the 6.0 has better options over the 5.3. MPG is based on a tons of factors besides GR.

Engine specs, Tire size, tune, transmission, rear end as well as weight of the car. 20 mpg is not far off or hard to achieve.

F bodies are around 3600 lbs while most Silverado's average 6300-7500lbs depending on model and year. Most 5.3's in those trucks avg 16-18 mpg. While most f-bodies avg 18-24 mpg some better depending on how the driver drove.

Please, please, please.......make a thread on your build. It would be an awesome build to follow here.

**pajeff02** · 09-17-2018, 02:53 PM

4,000 lbs is nothing for a 5.3 -- they are a stout engine. Problem with the 4L60E is the jump from 2nd to 3rd -- just too widely spaced. What size wheels/tires will you be running? If you are going "donk" size then the 2.91 differential is going to suck at everything but getting good mileage.

**Kevin Whitten** · 09-17-2018, 06:11 PM

No donkin going on. Stock is 14" wheel but if I switch to 16" with low profile I can keep the same diameter. So maybe a 6 speed would tighten things up? I dont want a total dog just a balanced ride with MPG as the realistic goal. Also wondering about a 5.7 combo. Thanks for your time and input. This thing is gonna happen, I am trying plan the work then work the plan....oh and i dont know much except that i have had 2 death threats so far from Fordies.

**Kevin Whitten** · 09-17-2018, 06:18 PM

Thanks man,
its got a 9" rear at 2.91. I am keeping the same overall wheel diameter just changing the rim and tires a little. I really appreciate your encouragement on doing this and will for sure keep a thread record going. this is not a popular car by any means but the first time i saw it i loved it. Its just got a coolness that deserves to be rolling. Im getting old and it fits me good. Worthless to most but still valid and not done yet.

**pajeff02** · 09-18-2018, 02:59 AM

I love oddball cars -- would take a Monterey over a Mustang or Camaro any day of the week. You can run some calculations with your rear end ratio and tire diameter to determine cruising rpm and such. You would also have to factor in the OD on the 4L60E. With smaller diameter tires (ie. non-donks) the 2.91 rear may be just fine, especially with your goal of having something that gets decent mileage. Between the 5.3 and the 5.7 you are honestly only talking around a 40 hp difference in stock configuration. Both engines respond well to headers and some simple bolt on mods to up the output. Jump up to a 6.0 and now there is a serious difference, especially in torque which is what it take to move old iron. Remember to factor in your fuel system modifications -- unless you are switching over to a carb, you'll need 58 psi at the rail with all of these engines.