Looking to get better mileage from a '90 Supra
 

I've never cared about going fast, the only thing that matters to me is that my car be safe and be something I enjoy driving. I took a job that requires me to drive 550+ miles per week (95% is hwy miles) so I decided if I am going to be in the car that much I am going to drive something I like. In high school a friend had a new 1987 Toyota Supra I always liked so I bought one. I would like to start out by saying I have ZERO interest in driving a performance car. I drive this car because it looks good, it has a Targa roof for nice days and is a solid cruiser. Rice burners are constantly challenging me and I just wave and let them cruise by. I'm a 36 year old professional, not a teenager and racing in my daily driver holds little interest.

I used to drive as fast as I could because I hated spending so much time on the road. Then I started tracking my MPG and discovered I was getting about 19. I made a commitment to driving the speed limit and my mpg shot up to 26! I save a tank every other week just by adding 20 minutes to my daily commute.

Now I am looking for ways to go even higher.

First, I found out the car has a 4.3 rear end. It's a pretty heavy car for a two seater (3700 lbs) and the non-turbo version I have doesn't accelerate well off the line without the higher ratio. I have learned, however, that a 3.9 and a 3.73 rear end were available (the 3.9 was standard in the turbo) although the 3.73 is pretty rare. My first step will be to get a lower ratio rear end. The stock tires are 225/45VR16s, when I have to replace the rears I'll get 225/50s.

That is what I have thought of so far, I am ready to listen to almost any other suggestions. The only things I won't consider are things that mess with the appearance or interior.

All of those changes will likely improve highway fuel efficiency and get you well into the thirties, but imo, you'll have to go even taller to reach peak thermal efficiency at a reasonable cruise, which should get ya into the forties to fifties. I'm not sure about the W series transmissions, but I do know that some longitudinal trans setups allow fifth to be swapped out for a higher ratio provided the one doing the swap is handy and has access to a machine shop. I encourage you to change rear end/tire ratios in order to get yer hands dirty and and see what taller OD ratios do on the highway, but, ya may want to consider finding another W-58 trans and doing a fifth gear swap with the second or third gear set from another W-5x, since this will allow you to put on smaller tires and have even better acceleration for 1-4, with 5 being an ultra-tall gear suitable for cruising at ~55-65mph/50mpg.

It all sounds alot like my situation...
I got a job far away and needed to commute weekly. My trusty workhorse Civic Aerodeck wasn't the highway cruiser I needed to keep me awake so I got me a Honda Prelude (gen 4) for much the same reasons you mention. Now I'm on the hunt for better FE. Time is money for me so I need to go as fast as legally possible (can't afford losing the license). Going fast means that aerodynamics is the priority. The first thing I tried was tucking in the side mirrors while driving on the highway. That alone did 5-6%!
I can't mess with the transmission but instead I got me some new oversize wheels. I bought new lightweight rims with better aerodynamics and fitted slightly narrower tyres with 5% larger circumference. This has brought down rpm proportionally. I'm only on my second tank since the switch but this seems to have given me another 5%. Another thing you can do easily is to increase tyre pressure to the max value printed on the tyres (usually 45 - 52 psi). This has more effect for lower speeds but since it improves road holding and wear etc. it's a no-brainer.

I have realized that without real-time FE-information, it is hopeless to quantify improvements so I'm about to get the SuperMID instrument. I have a long list of experiments and improvements to do so this will be invaluable. For us with older cars (non ODBII), the SuperMID seems to be the best option.

These forums are full of information so spend a week or two reading all posts a year or two back and you will be pretty educated.

I have an 87 Supra Turbo (450hp). If I don't get on the gas, I can get 28-29mpg in that car. Not too bad, esp for a car that makes that much HP and weights 3800 lbs.

I never broke into the 30s. I ended up getting a civic vx getting over 50mpg.
I still have the supra - it's more of a fun weekend car...

Gary

gary, you must have one hell of a garage for the 7 cars you have.