Foxbody Mustang or How I learned to love the mullet.

Well I did it. After the sale of my NB Miata, I was hunting for a new car to fill the hole in my heart and void my bank account. Talked to a good friend of mine who's downsizing his former salvage yard and ended up securing a "well enjoyed" 1984 Mustang. Started life as a Turbo GT, somewhere along the line a 5.0 was tossed in. Car was previously wired by a combination of a toddler and a dull pair of kitchen scissors. 

Point of this post is, I would like advice on what to do to it. Currently the docket is to turn it into a autocross car that can dual purpose as a street car. This is my first foray into carbed bare bones cars so I'll glady take advice. Looking to bring it to the challenge to possibly exhibition run it in May.

p.s if this is the wrong section, please direct your anger to Patrick, love you homie.

Step one:  brace the heck out of that chassis.  Then brace some more.  Then brakes.

Weld-in subframe braces and torque box reinforcements are critical.  Then on to front and rear strut tie bars.  Cage next.

They are wonderful cars with a notoriously weak platform.  If you can stiffen them up, there are enough bolt on upgrades available to keep you busy for a long while.

Brakes should be in there too, and while you're at it I would absolutely upgrade to 5-lugs.  You can do this cheaply with stock replacement parts from later/larger cars.  Upgrade the axles during this step too.  Then you have the choice of literally thousands of wheels.

Finally, figure out what rear end gears you have and evaluate what you'll actually need to give you the performance you want.  For auto-x I would be 3.55 or 3.73 would work well.  4.10s are great for 0-60 but you're shifting a lot and they make the car busy on the highway.

I have a ton of history with these as I have owned many and I spent time as director at Mustangs Unlimited.

The good news is that they are light, so it takes less to be fast!  Let's see some pics in the build section!

Ford was very good at turning a minimum of thin stampings into a structure with a fold here, a crease there.

After a while, this becomes a noodle as all of the metal work hardens around the spot welds.

Just to reiterate: Bracing, and more bracing, then brace some more.

An SN95 front subframe and uprights and steering will transform the car geometry wise, steering feel wise, and brake wise.  You gain better Ackerman, much better wheel bearings, and a better roll center, although there are subframe mods to improve that even further.

In reply to ExcessKuma :

This is not in the wrong section. You'll find GRM is not fanatical about what goes in what section.  If it's radically the wrong section it can easily be moved but won't be done without your knowledge. 

Loweguy5 said:

Step one:  brace the heck out of that chassis.  Then brace some more.  Then brakes.

Weld-in subframe braces and torque box reinforcements are critical.  Then on to front and rear strut tie bars.  Cage next.

They are wonderful cars with a notoriously weak platform.  If you can stiffen them up, there are enough bolt on upgrades available to keep you busy for a long while.

Brakes should be in there too, and while you're at it I would absolutely upgrade to 5-lugs.  You can do this cheaply with stock replacement parts from later/larger cars.  Upgrade the axles during this step too.  Then you have the choice of literally thousands of wheels.

Finally, figure out what rear end gears you have and evaluate what you'll actually need to give you the performance you want.  For auto-x I would be 3.55 or 3.73 would work well.  4.10s are great for 0-60 but you're shifting a lot and they make the car busy on the highway.

I have a ton of history with these as I have owned many and I spent time as director at Mustangs Unlimited.

The good news is that they are light, so it takes less to be fast!  Let's see some pics in the build section!

 

Definitely was looking at the Torque box reinforcement as that seemed to be a common point everyone mentioned to me!

Will look into the brakes later down the line primarily because I don't have a spare set to throw on, in the meantime it'll be just a pad upgrade new fluid and rotors.

I'm going to assume it's running its 3.45 factory rear end, the whole car is a mystery so it's not certain what rear end is in it till I get it going again. Even the 302 in it looks to be pieced together!

Definitely will be seeing this one in the build section as I stumble through Mustang ownership!

Pete. (l33t FS) said:

Ford was very good at turning a minimum of thin stampings into a structure with a fold here, a crease there.

After a while, this becomes a noodle as all of the metal work hardens around the spot welds.

Just to reiterate: Bracing, and more bracing, then brace some more.

An SN95 front subframe and uprights and steering will transform the car geometry wise, steering feel wise, and brake wise.  You gain better Ackerman, much better wheel bearings, and a better roll center, although there are subframe mods to improve that even further.

Going to sound stupid here but the SN95 subframe just bolts on?

In reply to ExcessKuma :

The track width is wider so you will probably need to roll the fenders and maybe modify the lower fender stay, but yes you can bolt a 1994-2004 k-member into any 1979-1993 FOX. You might need to clearance a couple of mounting holes and add some percussive persuasion in a couple of spots. 

You will want to dump the stock rear end for an SN95 rear. It's stronger, 8.8 versus the stock 7.5 in the 1984, and has disc brakes. I am assuming the axle is stock. It may have been swapped for an 8.8. If so, you can swap in the later disc brake parts. Of course, the aftermarket is infinite so you have a metric E36 M3 ton of options. 
 

Good luck. 

In reply to ExcessKuma :

If I'm not mistaken, thar car still has a 7.5" rear end and I thought 2.73 or 3.08 gears.  Convertibles had 3.27s.

Truly the best upgrade is to find an entire 8.8 rear with the gears you want.  There are enough of these that have been wrecked that those are fairly plentiful (Ranger rears are also 8.8 and with 3.73 gears, but are too wide and would require some narrowing and moving of the spring perches to fit it to the car).

Respectfully, if you're going to compete with it at all the brakes need far more than pads.  Even if you stay 4 lug, newer cars can donate the stock parts and offer you much better braking.

I know I'm spending your money, but I've now owned 8 Mustangs from 1979 to 2020 and feel pretty comfortable with their weak points.

Keep in mind that with the torque of a 5.0L, even 2.73 rear gears are not as bad as you might think. My '88 5.0 5 speed LX had 2.73 gears and they were just fine, I daily drove it over 100k miles, took it down the 1/4 a few times, and collected quite a few trophies autocrossing it.

You had to keep a light foot on the throttle all the way through 1st, and even most of the way through 2nd, or the rears would just light up. Fun through the cones, not so much in the rain in traffic. Loved that car. Put an off-road H pipe and Flowmasters on it, I could set off car alarms just idling through a parking garage.     

Loweguy5 said:

In reply to ExcessKuma :

If I'm not mistaken, thar car still has a 7.5" rear end and I thought 2.73 or 3.08 gears.  Convertibles had 3.27s.

Truly the best upgrade is to find an entire 8.8 rear with the gears you want.  There are enough of these that have been wrecked that those are fairly plentiful (Ranger rears are also 8.8 and with 3.73 gears, but are too wide and would require some narrowing and moving of the spring perches to fit it to the car).

Respectfully, if you're going to compete with it at all the brakes need far more than pads.  Even if you stay 4 lug, newer cars can donate the stock parts and offer you much better braking.

I know I'm spending your money, but I've now owned 8 Mustangs from 1979 to 2020 and feel pretty comfortable with their weak points.

Oh trust me, I'm noting your advice, it's just it has quite a bit of work to be done before I can even dream of putting it on a track. Also the talk about the diff reminded me that my buddy had sent me a picture of it and wouldn't you know it, it has an 8.8 diff cover on it.

Difficult to tell because of lens walleyevision, but that appears to be an 8.8.  They had a much more square cover than the 7.5, large gap between the two middle bolts on the sides.

To be sure, you can find a chart that shows the different cover bolt patterns for various rearends. That is the way we traditionally IDed them.

SN 95 suspension front and rear and a 4 valve modular engine.  

In reply to Pete. (l33t FS) :

It's definitely an 8.8, 7.5 were flat on top an bottom 

In reply to ExcessKuma :

That in itself is a win!   It will make for a fun project.

Mustangs are great!  I love my wife's 2011 V6 six speed with some Maximum Motorsports suspension goodies.  It's a blast on the track, and CHEAP . . .

NOHOME said:

SN 95 suspension front and rear and a 4 valve modular engine.  

I say 'no' to the mod engine. A SBF weighs so much less, takes up much less engine bay space and is much easier/cheaper to buy go-fast parts for. I had a track day student with one lightly gutted with a SBF and it was PLENTY fast. I giggled every lap riding shotgun in that thing.

In reply to ddavidv :

I agree. The car will handle better with the small block. Anything you can do to take weight off the front of the car will help. 

ddavidv said:

NOHOME said:

SN 95 suspension front and rear and a 4 valve modular engine.  

I say 'no' to the mod engine. A SBF weighs so much less, takes up much less engine bay space and is much easier/cheaper to buy go-fast parts for. I had a track day student with one lightly gutted with a SBF and it was PLENTY fast. I giggled every lap riding shotgun in that thing.

Just playing the devils advocate, cause why not?:

Do you know for a fact that the Mod engine weights more than a 302? Myself, I am not sure. The Mod engine is aluminum top to bottom compared to the 302's iron block and heads. Longblock to longblock comparison would be interesting.

As for performance parts being easier and cheaper? Pointless when the mod engine starts stock about where the 302 ends up with reasonable upgrades. The 302 is a stone ax from an earlier generation and is not much beyond the buggy whip in development. If you can tune a 302 to run better at 300 hp/torque than a stock mod engine with a stock computer, then you are very good at this game. Quarterhorse is out of business, so digital solutions are harder to source.

The mod engine will rev much higher than the 302 can dream of and also have tuning overhead beyond where the 302 literally breaks in half. Turbo and NO2 perhaps?

Service wise the modular engine is a dream compared to the 302. Dry manifolds and accessories that bolt directly to the block. Ever change the water pump on a 302 after it has been on a while?

If you just want something that fits easy and makes a lot of power for the money, then its pretty hard to not go with a 5.3 Ls. Better stock out of the scrapyard than a 302 could be with any amount of money spent on it and the moon is the limit for power on a budget. Ls comes in aluminum if weight is really an issue.

I have a 302 in the Molvo and can at best describe it as "adequate for the job in a 2700lb car". But in truth the 302 is to the LS what a British sports car would be to the 240Z when it came on the market; a passing of the torch.

Thanks for all the insight on the modular engines but honestly I have 0 plans of sinking more power into it. Engine wise it has a D8/9 block, E7 heads, sounds like maybe a mild cam, Performer 289 Manifold, HEI Distributor, Ford Motorsport headers and a Holley Demon 625 Carb. Internals are unknown till I get a boreoscope inside to see what I'm dealing with. Scouring the forums people were posting similar setups doing mid to high 13's and while this car isn't being set for the strip, I think that's enough power for a beginner street/track toy to really get into Autocross.

I am pretty sure that accessing the headers on a 4v mod engine involves dropping the subframe, as do many other things.

The 4v is LARGE.  It has a deck height something like 3/4" taller than a 302/5.0 engine and it has enormous cylinder heads.  Meanwhile the 5.0 is a lightened version of the 302, which was engineered to use as little iron as possible in the early 60s.  

IIRC the Mod motor weighed about 80-100lb more than a 5.0 despite the aluminum block. 

Remember that aside from the enormous heads, the Mod motor has a deep skirted block design with large crossbolted main caps, and much thicker cylinder bores to handle the compressive stress of the head bolts threading deep into the block vs. threading into the deck.

The whole reason Ford ditched the 5.0's architecture was that it was so flimsy and noodly that they would have had to completely re-engineer it to meet coming emissions standards.

Pete. (l33t FS) said:

I am pretty sure that accessing the headers on a 4v mod engine involves dropping the subframe, as do many other things.

The 4v is LARGE.  It has a deck height something like 3/4" taller than a 302/5.0 engine and it has enormous cylinder heads.  Meanwhile the 5.0 is a lightened version of the 302, which was engineered to use as little iron as possible in the early 60s.  

IIRC the Mod motor weighed about 80-100lb more than a 5.0 despite the aluminum block. 

Remember that aside from the enormous heads, the Mod motor has a deep skirted block design with large crossbolted main caps, and much thicker cylinder bores to handle the compressive stress of the head bolts threading deep into the block vs. threading into the deck.

The whole reason Ford ditched the 5.0's architecture was that it was so flimsy and noodly that they would have had to completely re-engineer it to meet coming emissions standards.

Any idea how much a 5.0 weighs versus an ecoboost 2.3? Seems like the old 5.0.is closer to power levels of that motor.

Don't get me wrong, the Mod motors have advantages, particularly for endurance racing, but it's a heavy engine. I personally prefer the character of the old 5.0, and it really makes a difference in how the car drives. 

While this book is old much of the theory of what to do to make a Fox car handle is in here.

Mustang Performance Handbook 2: Mathis, William R.: 0075478002023: Amazon.com: Books

The are many aftermarket parts that make it a bolt on afairs, such as tubular "K" members.

I road raced a '93 Cobra "R" back in the 90's and used this book as a "what to do" source.

The torque boxes are not that big a deal unless you plan on drag racing it of fitting really wide sticky tires.

You really need to figure out just what class you want to run in auto-x so that you don't over mod the car and put yourself in a class where you won't even be competitive.

The "R" model was very much improved over the street cars. It got all of the chassis re-inforcements that the convertables got. 

Basically what everyone is saying is strip it down to the bare unibody and replace everything.  While you have it stripped down, completely redo/add structural bracing since it has none.  Other than that, not much you need to do to it.  

Honestly, in today's world IMO the Fox is such a poor starting point for an autox car that I wouldn't bother with mods.  Just run it as is and have fun.  

Don't get me wrong, from a cool factor I absolutely love the Foxbody.  From a driving standpoint it's a platform designed 45 years ago and wasn't designed for performance even back then.  Set your expectations extremely low.