'91 Mustang build/repair thread! (Foxie).

[Baltothewolf]

I promised this thread a looooong time ago, but I didn't have money or the will-power to put money/time into this car, but now I got my life a lot more straightened out, I'm ready. I'll post pics when I get home later today or tomorrow.

Goals with this car:
My number one goal, is to have a 'Tokyo drift' style sleeper. Basically, a ****ty looking car on the outside, but under the hood is an absolute MONSTER.

Story behind the car: My uncle got this baby from a close family friend at 33,000 miles. The previous owner didn't take care of the interior, but serviced the engine as he was supposed to. My uncle tore the car's interior down to nothing and cleaned it up and made it look nice, and drove it to around 140k miles. His ex-wife took the car in the divorce and TORE it up BAD. In the 50k miles she had it, she only had the oil changed once. I'll post detailed pics soon, but it's pretty bad. The car leaks oil if it sits at an angle (oil pan gasket? Idk). But other then that and the recent smog pump seize, which is a common failure the car is in good mechanical shape.

Stuff that will be done eventually.
Replace windshield (giant crack).
Bouncing speedometer.
Steering wheel. (extremely worn).
Rims are bent. (curb strikes).
Brakes are severely worn.
Low braking power, I think this is related to worn brakes but not sure.
Smog pump seized.
Entire interior replaced (except seats).
New doors (one is bent from a robbery, other is just FUBAR).
Drop down dome light causes fuse to instantly pop.
Both headlights and tail lights need to be replaced.
A/C needs recharged (R-12).
Alignment.
Transmission flush/refill.
Compression check.
Replace master cylinder.


Things done thus far:
Cleaned interior of makup/dirt. Must have gotten 10LBS of makeup off the steering wheel, climate control, door, etc etc.
Power steering pump was making a god awful noise when turning, and the fluid was as thick as mud and black as used oil, so I changed that and it's still making noise, but sounds much better.
Spark plug change.
Replaced headlight/DRL switch, was stuck in the 'on' position.
Cap and rotor change.
MAF sensor cleaning.
Throttle body cleaning (was super bad).
New air filter.
Replaced hatch. Was rusted through at the bottom of the windshield between the windshield and wing. It's red now.
Passenger side exhaust replaced. Had a hole from hitting a speed bump way too hard.
Rear brakes adjusted.
Replaced broken tail light. Was backed into a pole (not me). Caused no damage to bumper.

Immediate mods/repairs that I'll be doing in the next 2 months.
4.10 rear end.
KYB shocks in the rear and springs in the rear and front.
Front struts (unsure what I'm going to go with).
Eldebrock manifold.
70MM throttle body.
CAI/K&N air filter.
Injectors cleaned (I seriously think one is running lean) by mrinjector.us
Electric fan conversion.
Subframe connectors.
Rear control arms.
New 4-lug pony rims.
Power steering pump.
AOD 'hold' Valve body for better AOD trans/launch control.
New speedometer cable.
Stuff that I'll be doing that doesn't cost alot of money in the next few weeks.
Remove interior and give it a good scrubbing to try and save the carpet.
Install and paint new doors. They are currently white.
Install new door panels along with the doors.
Clean up the engine bay.
Change brakes (already have them).

Future mods that I will get done (probably 1-2 years out):
Vortech intercoolerless supercharger.
42LB injectors (might only go 36 we will see).
MSD ignition box.
On the fly Boost controller/timing retard advance/rev limiter box.
Rebuilt AOD transmission.
Transmission temperature/A,F ratio/Boost/Oil temp gauges.

Pics: They are old, but I'll take some sooner or later.

[Baltothewolf]

The other day I went out to the car to figure out if I could convert to manual door locks and to my surprise, yes, I could! The way these doors work is, they have a separate solenoid type system with a corkscrew, that turns and pushes it locked when you lock the car. BOTH of them were seized. I just disconnected them from their mounts and they hang freely now in the door, so I can lock the car with the keys. The car had an alarm system so, I just arm it and don't have to worry about it. Alarm wouldn't arm before I did this fix.

One thing that's bothering me with this car is its mileage. I slam on this car everywhere, but it looks like I'll be getting around 10 mpg this tank, which is a little concerning. About 60 of the 135 miles traveled so far was to work and back, and I just set cruise control on 50mph and cruise to work and back. Can oil thickness make a difference? I'm running 10w-40. Don't get me wrong I do NOT drive this car for mileage, and have raced 3 people this tank, but from what I have read, even with going to the drag strip people still get 15-19 with 3.73 gearing, and I have 2.73 gearing!

[The_Jed]

I think there's a bit of a parabolic curve for the returns realized by taller gearing. Sure, at a steady state lower rpms will usually equal better f.e. but, the effort required to accelerate to that speed or maintain it against aerodynamic drag will be increased with the taller gears.

I think there's a compromise "sweet spot" for gearing that will yield the best overall f.e. while not necessarily the best in any one set of conditions. That being said, something may be wrong. Your car is 800-1,000 lbs lighter than mine and I have no overdrive yet the worst tank f.e. EVER for my car was about 13 mpg and that was with lots of playing in the snow.

You could build on very potent and efficient Fox with junkyard parts! I could write my parts list (I've done TONS of research over the years) if you'd like.

[The_Jed]

Yes, a thinner viscosity oil would reduce parasitic drag a bit, not sure if it would be noticeable. I'd go with a 10w30 during the winter. With the life that engine has had I assume the bearing tolerances have opened up a smidge and I wouldn't want to risk going much thinner than that.

A roller cam retainer plate bearing and roller rockers would also slightly reduce parasitic drag. Lots of little differences can add up to a big difference!

[Baltothewolf]

Originally Posted by The_Jed

I think there's a bit of a parabolic curve for the returns realized by taller gearing. Sure, at a steady state lower rpms will usually equal better f.e. but, the effort required to accelerate to that speed or maintain it against aerodynamic drag will be increased with the taller gears.

I think there's a compromise "sweet spot" for gearing that will yield the best overall f.e. while not necessarily the best in any one set of conditions. That being said, something may be wrong. Your car is 800-1,000 lbs lighter than mine and I have no overdrive yet the worst tank f.e. EVER for my car was about 13 mpg and that was with lots of playing in the snow.

You could build on very potent and efficient Fox with junkyard parts! I could write my parts list (I've done TONS of research over the years) if you'd like.

Yes please, I would appreciate that! As for the oil choice, yea, I went so heavy because I know this engine is old and I don't want a lack of lube anywhere. As for changing it from winter to summer, I have had the car for about 6-7 months now, and have only put about 1500 miles on it. I didn't have the money to replace the spark plugs/wires/cap and rotor, and it was running quite rough so I didn't drive it very much. Right now it's in non-op with no insurance (state farm wants 60$ a month, double what my insight is). Can't afford to insure and work on it. I know 60$ doesn't seem like much, but 60$ is a set of doors (I passed on a couple sets of 2 that were in good condition that I regret) or a smog pump, etc etc.

[The_Jed]

I totally understand, $60 goes a long way for Fox parts!

The ring and pinion from an Exploder or F150 would fit, but not the whole rear end, they use leaf springs.
To have a bolt-in housing swap you'd have to snag one from another Mustang, an '83-'88 T-Bird or Cougar or an '84-'92 Mark VII.
The bare housings width is the same on Mustangs from '86-'98 but the '94-'98 track width is about 1.5" wider due to the ABS ring inboard of the axle flange, as is the Mark VII housing.
The '99-'04 housing is about 1.5" wider than the '86-'98 so the track width is an additional 1.5" wider or 3" total wider than an '86-'93 Fox.
Any of those rear ends would physically bolt right in but would require some re-routing of the brake lines.
The '94-'98 rear end may cause some rubbing of the outer edge of the rear tire on the rear wheel opening and the '99-'04 will most likely cause rubbing.

You could snag a 7.5" rear from a V6 equipped SN95 and kill two birds with one stone; 3.27 or 3.55 gears (I think) and 5 x 4.5" bolt pattern. The newer 7.5's are much stronger than they were back in the '80's.
I had planned to grab the k-member, A-arms and spindles from a '94-'98 V6 to swap into a Fox, cutting and re-welding the motor mount pads for a 1" rearward relocation.

If you use the '99-'04 spindles you'll NEED offset rack bushings since Ford raised the point where the outer tie rod bolts to the spindle, on the spindle it's self. If you don't use them you'll encounter tons of bumpsteer.

SN95 A-arms are 1" longer than those on a Fox so you'll gain about 2" of track width up front as well. You'll also have tons of negative camber, if you don't slap on a set of caster/camber plates to dial some of it out.

[The_Jed]

A lot of people say you'll need a 4 wheel disc specific proportioning valve if you swap from rear drum to rear disc but, when I ditched the TEVES system in favor of a standard master cylinder/booster from a '94 Mustang in my Blue Mark VII I ran it with no proportioning valve at all and I liked it. It was very direct and communicative.

Tubular K-members are really cheap these days. QA-1 makes one that moves the centerline of the front wheels 2" forward (I think) and offers two sets of slots for the motor mounts. That would yield a nice gain in caster and potentially make a decent improvement in weight distribution. Large tires might rub a bit, though. I think it's $250 or so.

If you upgrade to 31 spline axles you could snag the traction lok out of an Exploder.

[The_Jed]

Junkyard speed parts:
The '96-'97 5.0 Exploder (Mountaineer) had GT40 heads with 3 small vertical bars cast into the front. Approximately 62cc combustion chamber, 1.84" intake valves, 1.54" exhaust valves. Any header that fits an E7 head will fit these.

The '97.5-'01 5.0 Exploder (Mountaineer) had GT40P heads with 4 small vertical bars cast into the front. Approximately 58cc combustion chamber, 1.84" intake valves, 1.48" exhaust valves. Your O.E. shorty headers will fit these but, very few aftermarket headers will fit due to the angle of the spark plugs.


5.0 Explorer Intake manifolds(internally identical to the Cobra):









The Fox Mustang uses and internal EGR just like the '96-'97 Exploder. You'll also have to drill and tap the lower intake for your ACT sensor.













The Explorer has a better injector than the Mustang and Mark VII that provides better atomization.

If you want to get really wild the 300 six and '87-'88 T-Bird and Cougar 5.0 have 15 lb/hr injectors as opposed to our 19 lb/hr. I've always wanted to mix and match O.E. parts to create a lean burn Fox.


Our cam has slightly more lift on the intake lobe and more duration on both sets than the Explorer. On top of that the GT40P heads would bump your compression up slightly.

With the Explorer intake(s), GT40P heads and your short block I would expect about 275 hp at the crank with better than stock f.e.
Then add a 2.5" H or X pipe and a free-flowing cat back with some under drive pulleys and 1.7:1 rockers and you'd have one angry Fox!

[Baltothewolf]

All this info, my head is spinning!! I think I'll definitely get the T-Bird rear end, as I want rear disk brakes anyway, and it would save a lot of money just going that route rather than buying a conversion kit. The problem is, did the 83-88 T-Bird have a 3.73 rear end in it? I don't want any taller than 3.73, but I definitely don't want as short as 4.10.

I don't plan on ever going 5-lug. I love the stock pony rims, and don't think I'll ever stray from them.

I plan on going 31 spindle eventually, but not yet.

Is the 96-97 Exploder head a direct bolt on? I remember talking to a lad a while back that was telling me about it being a direct bolt-on.

All these mods will keep the car smog legal right? I live in California and it's the most strict state in the entire United States when it comes to emissions.

[Edit]: Ok so after some reading (And a YouTube video) I see where there would be a big difference porting it. Where can I get this done?

[The_Jed]

I think only the Turbo Coupe had rear discs, not 100% sure though.

The heads will bolt right on. There may be a few hiccups with the EGR system, but it's a bolt-on swap.

I'm not sure but I assume, as long as you retain your emissions equipment you'd still be smog legal.