What kind of mileage can I get?

[finaltable]

I was offered a promotion at my job last week; the downside being that I will be commuting about 70 miles round trip each day. Last time I faced a commute I bought myself a Mk III. It appears that it is time for another. I don't care about going fast; I like the look of the car, the confident push of rear wheel drive and the targa roof. I know cars can be modded for power, I am curious to know if the car can be tuned to be more efficient. I have access to a mechanic (my uncle) who will be happy to help install anything I need, even a 2JZ engine swap if that would help. I am open to any suggestion that still makes the car look and sound professional, e.g. no stripped interiors or fart cannon exhausts. This to be a touring car, not a street racer.

Thanks

[Busted Knuckles]

The most efficient you'll get is keeping it in factory tune. I get 19 mpg with my 1988 N/A 7M-GE during in-town commute (25 miles a day, stop-n-go), and have gotten 27 mpg highway travel on road trips. The only thing different I've done is an exhaust upgrade, but still have the factory cat and factory intake system on it.

The engine is so peppy, I barely use the gas pedal to maintain the normal 70 mph highway speeds here around Atlanta. I keep having to be mindful of the speed, because this car hits 90 mph real quick, and GA has a new super-speeder law and aggressive cops.

[finaltable]

Small world: When I was commuting previously I was driving from Athens to Atlanta, working in the Jimmy Carter/Peachtree Industrial area. 55 miles each way, though it took about 1:45 because of rush hour traffic. Nothing helped me relax after a long day quite like taking the top off and cruising 316 with the stereo turned up and the blue skies above me.

[Green7mgte]

youd find on ebay stupid things like magnetic fuel line clips that are suppose to increase your mpg.. doubt it actually does anything.

[907mge]

I can think of a few things:

Manual trans.

Best ratio rear diff you can get to keep the rpms down at highway speeds.

Lowering the car will help reduce drag by moving the wheel up towards the car reducing exposed tire.

Actual Cold air intake, not one sucking hot engine air.

Less restrictive exhaust if you keep your foot off the pedal.

Tires with low rolling resistance and lighter wheels.

[cre]

A larger diameter exhaust can make fuel economy worse... You run a serious risk of reducing the effectiveness of the cylinder scavenging that factory exhausts are usually tuned for.

You can get better economy from a well tuned aftermarket engine management system... even better if you tune it to control a modified EGR system which is modified (reduced cylinder displacement ).. EGR FTW!!!

Over inflating your tires, not to the point of distortion, but a few extra psi. Narrower tires would help in a number of ways: rolling resistance, wind resistance, weight.

A 3.73:1 differential (only in '89 and newer 7M-GTE equipped MKIIIs).

Lightweight drive shaft... I'd recommend still getting a two piece given the amount of mileage you'll be putting it through but you can get a lighter two piece fabricated and one that accepts a more common center carrier bearing.

The factory intake is cold air... just leave it alone.

Run a W58 (manual) transmission from a N/A... much lighter than the R154 and shifts smoother too.

Reduce rotating mass as much as possible; lighter flywheel, lighter wheels, driveshaft, smaller alternator, lightweight aluminum flex fan (don't forget that you need to use the correct fan clutch with it too).

Run the LOWEST octane gas you can without any pinging. Lower octane fuel has more kinetic energy. It has more power per unit than higher octane... BUT it's a balance; If you go too low you'll get pinging and the ECU with pull spark advance costing you power in a different way.

Lay off the boost.

Remove any spoiler from the car, including the factory one. They all increase the drag coefficient of the car. smaller whale tails may actually serve to reduce it but unless you can find actual wind tunnel test results, the odds are that it was just made for looks and isn't going to help anything else... it's either just more weight or it's more weight AND more drag.

Driver at speeds under 60MPH. Resistance to motion increases almost exponentially with the object's speed; It doesn't matter if you're not gunning it, 65MPH is going to cost you a lot more than 60MPH.

The aftermarket EMS (and running the right octane) is going to net you the biggest gains; If you keep a functional EGR system (stock or beefed up) you may run as lean as 16.1:1 during smooth cruise conditions and the engine will still idle smoothly at about 15.1:1.

The best engine to do all of this on is a 1JZ-GTE, IMO... Although, I've seen about 28MPG (IIRC) on a 7M-GE with most of these mods. I was stupefied by the gains. It was on a VERY long, two way road trip... two tanks of gas to compare results with... no city driving at all though.


Back to the exhaust thing; Replacing the cat, resonator and muffler with more free flowing / high flow components is GOOD. The stock resonator and muffler are baffled and HEAVY!

[907mge]

Do you think the under cover would help with drag? And is it even possible to still get one? Personally untill my friend said about it I didn't know there was one.

http://www.cygnusx1.net/Supra/Librar...spx?F=5102&P=1

[cre]

Yes, you can still get them. They also help the cooling system as air is better directed... the same for the fan shroud. The more efficient you cool the car the more efficiently the engine runs. An additional undercover(s) to cover more of the transmission tunnel and rear subframe along with some air dams in front of the wheels will also help.