Shooting for 30 mpg with my '92 Mark VII.
 

<---My fuel log indicates the low end of my average MPG when driving to and from work. The best I've seen for a tank was 17.7 mpg, according to my tripminder and miles driven/gallons used. I'm hoping I'll be able to raise my tank average to 30 mpg or more. I'm going to attack my mpg goal from multiple angles.

First and foremost the car needs a transmission since overdrive slips,reverse and the other forward gears are fine, though. The t/v cable popped loose on the previous owner and o.d. was toast before he could get it to a shop. So for now I'm driving with a 1:1 trans gear @ 60% lockup (according to the web). A new trans would be .67:1 o.d. with 100% mechanical lockup. While I'm saving up for a transmission I plan to make a few small, cheap improvements.

There are two routes I can take to work; one that is about 8 miles long and is 50% highway (55 mph limit), and one that is 13 miles long and is about 70% highway (70 mph limit).

My car is basically a long wheelbase, heavy Fox Mustang with an air suspension that uses longer A-arms and longer rear control arms.

From what I've been able to find, the stock AFR for a '92 5.0 Fox falls between 11.8:1 and 12.2:1. Lots of room for improvement there.

My car weighs 3,800 lbs, lots of room for improvement there too.

My car's Cd is .38. I think I may be able to reduce that a bit.

Here's the plan:

Lower the Cd without losing the original character of the car (no boat tail), reduce the curb weight, reduce parasitic drag on the engine, and increase the efficiency of the engine.

Aero:
Remove side mirrors (if legal) and install interior mirrors.
Install a grill block and possibly hood vents
Install an air dam
Possibly install rear skirts, not sold on this idea though.
May install a small spoiler, if needed

Parasitic drag:
Remove smog pump and hoses
Underdrive pulleys
Junkyard electric fan
A/C delete? (not sure on this one)
Thinnest possible synthetic fluids

Engine Efficiency (Mechanical):
Transmission (of course)
1996-2000 5.0 Explorer cam
1998-2000 5.0 Explorer intake with injectors
Roller rocker arms (still debating 1.7:1 vs 1.6:1)
Adjustable fuel pressure regulator (try to tune for 14:1 AFR)
larger, lower restriction exhaust
Narrower L.R.R. tires.

Weight Reduction:
The smog and A/C deletes will net a pretty big reduction
Mustang manual front seats (potential 60 lb loss here)


The overall goal is to have my cake and eat it too. :)
Progress will be slow :turtle:

A/C won't reduce much paracitic drag when not running. It will drop about 25lbs or more from the front end though. Maybe look into a manual steering box too if you don't do a lot of 3pt turns and parallel parking. Air dam and E-fan will help a bunch and should be some of the easier mods to do especially if the car shares more than just suspension with the Fox cars.

What are you looking for out of this car, that the Impreza doesn't cut it at?

The Impreza is the winter beater, this car is the nice 3 season cruiser.

@Spacemanspi: I had considered picking up a manual rack or de-power the o.e. rack but, even after the weight reduction it will still be a 3,600 or 3,700 lb car.

Also it goes back to the character of the car; if it were a Fox Mustang I'd have no troule slapping a manual rack on it and manual brakes for that matter. That's one of the niceties I'll wind up keeping on this car.

My fox weights just under 3k lbs with the spare tire, back seat and rear carpet removed (all back in now) and it's still almost impossible to steer without the p/s pump.

Lotta weight over the nose on these Foxes! :)

I just saw a MkVII on the road today, which is pretty rare around suburban Detroit these days! Good luck on your mods and F.E. progress.

A 'less restrictive' exhaust will not help mpg. The whole idea is to run at low rpm. Not conducive for larger exhaust. Also a less restrictive system would only show a small benefit at wot wide open throttle. How often are you there??????
I had the exact same car 15 yrs ago!
Loved the ride! I did get 28mpg on a 1700 mile trip to Dallas from Sacramento. The trick was to coast engine on down hills and drive 64mph. I did not do any mods.

I would never delete a/c. It's a luxury car. Lose the spare tire.
Also consider changing the rear axle ratio. I bet the lcs (basicly the hotrod edition had a different ratio than the base model.
Or go with a taller tire. The trick is to lower the rpm at cruise.

@Mcrews:
Yep, it's an LSC.
I have considered swapping to a 3.08 or 2.73 rear gear but I think that as much as it may help my highway mpg, it would hurt my city mpg. Not 100% sure, but it's definitely something I'll keep in mind.

I crunched some numbers last night at work:
O.E. tire = 225/60-16 (83.66" circumference)
first l.r.r. tire I found was 215/65-16 (84.83" circumference)

If I stick with the AOD gearset I'll have 2.40 1st, 1.47 2nd, 1.00 3rd and 67 O.D.
With my o.e. tires that would be 1,651 rpm at 55 mph and 2,101 rpm at 70 mph
With the l.r.r. tires it would be 1,628 rpm at 55 mph and 2,072 rpm at 70 mph.

If I use a 4R70W gearset I'll have 2.84 1st, 1.55 2nd, 1.00 3rd and .70 O.D.
o.e. tires = 1,725 rpm at 55 mph and 2,195 at 70 mph
l.r.r. tires = 1,701 rpm at 55 mph and 2,165 rpm at 70 mph

^with 3.55 gears.

I'm leaning toward the 4R70W gears since the deeper first gear would make it easier to get the car moving, at just under two tons it has a lot of inertia!

Hey, you made it to within 2 mpg of my goal with no mods! Maybe there is hope! :)

More @ Mcrews:

True I rarely ever go to wot but I am a racer at heart (even though I haven't raced in over 10 years...) and even though the mods I have planned are aimed at fuel economy, there is still a bit of overlap into motorsports functionality, particularly the aero. I'm still kicking around the idea of hitting a few autocrosses and possibly an open road race as well.

Basically I want to reduce drag, increase efficiency and, if possible, increase torque output while moving the peak lower in the rev range, hence the exploder cam and intake. I may try to improve the weight distribution a tad while I'm at it, but nothing radical. I want the car to look stock or close to it.

I'll be tinkering with a few aero mods over the next two weeks since I'll be off work.

5 speed swaps are very common on those cars. But if you wanna stay auto, the 4R gears and 3.08 or 2.73 rear would probably make the most sense. Adjust the air ride sensors to drop the car as low as it will go.

Nice Turbo Coupe!
Is there a thread on it or do you have any more pics?

I used to auto cross a 79 rx7.
As I got older and had a daughter I got out of the racing mode. I still like to compete... Now I just compete w the scangauge!!!

I put taller tires 5% on my q45 w 340hp. Never even noticed at start! It really depends on how much hwy driving you do. I did 70% hwy so it paid off for me!

Is your engine carbureted or fuel injected? That makes a HUGE difference. If EFI, you could use an O2 sensor to get the A/F ratio closer to stoichiometric. If not, add it.
I agree with your philosophy regarding increasing the FE, but trying to keep some level of why you own the car in the first place.
Good luck!

It's injected, the same engine as a '92 Mustang except mine is speed density controlled and a Mustang would be mass air.

I thought the engine was the 5 liter gt motor?

Just read on wiki that all Mark vii had the same engine....

You thought right, it is the 5.0 GT engine. :)

All Mark VII engines were close to the same...well except the BMW sourced Diesel. I nearly bought one of those, kind of wish I would have. A diesel Mark VII + T5 + 2.73 rear gears = high mpg! :)

There were a few changes up to late m.y. 1987 then from '88-'92 they were all the same, regardless of submodel. I had an '87 LSC with true flat top pistons (no valve reliefs) and E6 heads. It made slightly less power than my '92; 200 hp and 285 lb/ft vs 225 hp and 300 lb/ft, respectively.

Before '87 they had the lo-po version of the s.e.f.i. fuel injection system. And before THAT they had a central throttle body similar to GM's TBI. I'm not sure of the specs on either of those.

That Q45 is one slick car!

I'd love to get my grubby little paws on one of those or an LS400.

I've been doing quite a bit of research on afr tuning and achieving stoichiometric combustion. I still have a LOT to learn.

Today I removed the o.e. mudflaps then slapped together an air dam out of some leftover bits from a work shelf kit.
Baby steps... :)

Thank you!! 270000 trouble free miles! Am going to get an 05-06 last yr, in 2014!

Stoichiometry is the job of the closed-loop part of the EFI. Some years ago was the last published comparison of aftermarket ignition systems on the 5.0 you have, the MSD showed the most torque at all RPM, and the best idle. When you begin completely burning all the fuel, not as much will need to be injected for any given throttle opening. You'll still need x amount of air for your cruise RPM, however.
And for that, you don't have that much more drag than a 'stang, and you may already know this, but yours came with 3.27:1 axle gears and 225/60R16 tires, while the 'stang had 2.73:1 with 225/55R16s, so that's known good, but many '83-'86 F150s had 2.47:1 rear axle gears you can swap into your rear axle if you want to try even less RPM.
If you do come across a set of those, I'm curious which of the 3 possible tooth counts Ford went with. ( 42/17 or 47/19 or 37/15. I suspect the latter, but the old 9-inch used the first )

Mine *should* have 3.27 gears, according to the diff tag, but it has 3.55 gears. I've crunched the numbers dozens of times and I always get within .05 of 3.55:1.
My first Mark VII should have had 3.27's but it had 3.73's.
Interesting tidbit about the truck gears, I did not know that!

It was my first car and I haven't had it in a few years now. Sold it to my friend as a parts car (it was pretty well done for) for his autocross bird

https://scontent-b-lga.xx.fbcdn.net/...58636304_o.jpg

:eek:

I've read all about that car!!!
Unreal fabrication ability.

It's a small wor... internet! :)

The Q45 had been on several websites and forums. When I sold the Q, several people who called said they were very familiar w it from the internet. Kinda took me by surprise.

I took it for a drive and it seemed to have more wnd noise at the side mirrors and windshield. I'll do some back to back tests with it installed and uninstalled when I get the chance to see if the noise was all in my head.

I hope you take this as helpful rather than contentious, but calculations mean nothing. The AOD is notorious for incomplete lockup, especially in third. The reason diff covers never came with drain plugs is so you'd have to pop the cover and visually inspect everything, which is a fine way to confirm the tooth counts stamped into the perimeter of the ring gear. Many people never change the diff lube, yet get away with it for decades and several hundred thousand miles. But the cover gasket is $3, and 2 quarts of synthetic 75W90 are $8, so there's really no excuse for not knowing what's in there. And even if there is a magnet in there, it likely needs cleaned off. Plus your Traction-Lock diff probably needs rebuilt, so this makes it easy to confirm. Ford offers new clutches for it at maybe $35-ish.
Or get the complete rear assembly from a '94-'98 'stang GT auto with the 2.73:1 already loaded and set up correctly for no whine, then do the above to that before swapping it in. That's under $ 200 all total. The glitch is that the 'stangs that came with 2.73:1 used a different output shaft in their AODs, with more teeth, than 'stangs with 3.27:1, so you'll need a little correction box, those are $62 from PATC.

I disagree about calculations being meaningless but agree about the diff oil. Also, if the diff tag has any credible info on it at all, mine was a peg leg from day one. I've already put my feelers out for a diff on grm.

Hit the highway today with my makeshift air dam and while hitting 70 mph took very little throttle before, it seemed a tad easier, nearly effortless. Even though I'd hardly call it empirical data, the instant mpg readout on my tripminder read 1-2 mpg higher than it usually does along that particular stretch of highway and my average mpg over the past 600 miles went up by .2 mpg so it's safe to say my car likes it!

The front of the car also felt more planted at speed.

Got any pics of the new air dam?

Oh, it's ugly. I haven't taken any pics of it yet.
I'll see about getting some tomorrow.

Using a formula found on this site it looks like 2,000 rpm would yield 1,000 ft/min piston speed, which I gather is the low end of the sweet spot.

With 225/60 tires and the 4r70 gear set that would put me at about 63 mph.

With the same tires and the aod gears I'd be at around 66 mph.

With 4r70 gears and a 2.73 ring and pinion that would be almost 83 mph.

I'm sure it's just another bit of data to be taken into account when trying to dial in the best compromises in all aspects of f.e. for an ecomod set up and not THE deciding factor but that seems to indicate the 3.55's may not be so bad after all.