Looking for some help i just got My 1991 mustang 5.0 And need more power where do i start? I already did headers bbk xpipe And flowmasters i am on a budget but would like to make it faster any help on what to do Next? I have been hearing abt gears but dont know how they Work or what they are i am New but realy want to learn any advice helps! Thanks
New To Mustangs But Love Speed
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Gears dont give you horsepower per se, but they do change how your csr puts the power to the ground. The gears people talk about are your rear gears in you differential. I believe you have 2.73s stock (100% sure somebody will correct me if i am wrong). Upping the gear ratio gets you off the line faster but does hurt your top end. Most people go 3.73 on manuals ans 4.10s on automatic. 4.10s on a manual will make your rpms higher at cruise so worse gas mileage. My car isnt my daily so i am going to put 4.10s MAYBE 4.56s but idk about that because going that high is usually track only use. Gears are youre best bang for the buck mod. Theyre a little difficult to install yourself. I work 95 hours a week so i have my mechanic do my work anyways. After gears i would do an intske manifold. Other than that, you would be suprised how far a set of new plugs and wires will get you, especially if the ones you have are old
Welcome to Stangnet... 
Not all of us know how to fix everything, but some of us know how to fix some things
with excellence!
Some things to consider from someone who has been driving and fixing 5.0 Mustangs for 20+ years...
If you are in California or some other state with strict emissions laws, part of the deal should be that the owner takes the car and has it emissions tested. If it passes, you buy the car and pay for the emissions test cost, if any. If it does not pass, walk away from the deal. For a mechanically inexperienced owner, emissions related problems can be difficult and expensive to fix.
Keep in mind that states with strict emissions laws may make the go faster goals more difficult to reach. Some parts are OK to replace with aftermarket parts and others aren't. Check carefully before you get out your wallet and buy something you can't use in the area where you live.
If you want to do the fix up & power up thing, make sure that you have some other
form of reliable daily driver. That way the stang can sit while your wallet and hands
take a rest from the last project that didn't quite get finished on that 3 day weekend.
Things always cost more and take longer the first time you do them. Having some
other working vehicle makes life easier since it isn't the big crush to get it running
for the Monday morning drive to work or class.
Plan on spending some money on tools it you don't already have them. The stang
has both metric and American fasteners, so you really need two sets of wrenches.
A timing light, digital voltmeter, vacuum gauge, compression tester, fuel pressure
test gauge and fuel line coupler tools are some of the test & tuning tools you'll need.
Visit the pawn shops and sometimes you can find a deal on tools & test equipment
if you stick to well known name brands.
A sheltered work area is almost a must, someplace that you can leave the car in
pieces without upsetting anyone. Some guys here have changed a transmission in
the parking lot of their apartment in a rainstorm, but they will tell you it wasn't fun.
Depending on where you live, a warm dry garage is a nice place to do the winter
projects that stangs tend to become.
EFI (Electronic Fuel Injection) Computer - every stang after 85 has or had one:
don't let it intimidate you. The computer based EFI systems are not hard to fix
and most of the time they tell you what's wrong with the engine. Here's a book
that will get you started with how the Ford electronic engine control or "computer" works.
Ford Fuel Injection & Electronic Engine Control 1988-1993 by James Probst:
ISBN 0-8376-0301-3.
It's about $35-$45 from Borders.com see http://www.amazon.com/ . Select
books and then select search. Use the ISBN number (without dashes or spaces)
to do a search
Use the ISBN number and your local library can get you a loaner copy for free.
Only thing is you are limited to keeping the book for two weeks. It is very good,
and I found it to be very helpful.
For lots of great ideas and tech notes on upgrades and repairs, be sure to check
out http://forums.stangnet.com/showthread.php?t=643651 “Useful Technical Thread Index” sticky at the top of the 5.0 Tech forum.
Things that break often:
T5 5 speed manual transmission (syncros go bad, mostly 3rd gear)
TFI Module (Thin Film Ignition module - mounts on the distributor)
Electric door locks (see the link in my sig for a cheap & easy fix)
O2 sensors(oxygen sensors) They are good for about 60,000 miles and start to go
down hill after that.
TPS Sensor (Throttle Position Sensor) causes flaky problems with idle & acceleration.
Fog lights They overheat the wiring and cause the headlights to flicker. The fix is
cheap and simple if you can do electrical stuff.
Harmonic Balancer – they separate between the hub and outer ring. A harmonic
balancer puller is a must have to change it. You can rent or borrow a puller from
most of the larger auto parts stores.
Things that are very durable:
Engine - as long as it hasn't been abused, it will run good for 150,000-200,000
miles without an overhaul
Rear axle other than an occasional case of worn clutches in the traction lock,
they almost never have problems.
Computer - believe it or not, the computers seldom have problems of their own.
Most of the problems are with the sensors and the wiring.
Suspension – the front and rear suspension has very few problems if the car hasn’t
been wrecked or seen a lot of drag strip runs. The drag strip runs tend to distort and
tear the mount points for the rear axle control arms. Revving the engine up to 4000
RPM and dumping the clutch with slicks or drag radials tends to break things.
Things that don’t break often but are hard to fix:
Water pump mount bolts – they corrode and shear off when you try to change the
water pump.
Rear oil seal on the engine – lots of parts to remove to get to a $20 seal.
Power steering pump – the pumps are noisy and the pulley requires some special
tools to remove and install. If you have the tools, they are easy to do. Again, the
larger auto parts stores will rent or loan the tools for the pulley.
Power Steering rack - it is hard to get the toe in set so that you can drive the car
to the shop to get it properly aligned.
Starter – the top bolt is hard to get a socket on if you don’t have the right combination
of socket, universal joint and extensions.
Everything considered, 5.0 Mustangs are not hard to work on. They just require
some patience and though before you get started.
Still want more performance and on a budget? do the junkyard upgrade...
Gears - 87-88 T-Bird Turbo Coupe rear axle - disc brakes and 3.55 or 3.73 gears in one package for $125-$300. Add another $100-$200 or so to complete the brake upgrade.
94-95 Mustang GT MAF - $40-$100. It is 70 MM instead of the stock 55 MM on regular stangs built prior to 94. It uses a slip on duct on the side that goes to the throttle body and a 4 bolt flange on the other. You need a flange adapter to fit the stock slip on air ducting that goes to the air box. Wiring plugs right in with no changes. *1 *2
95-97 Ford Explorer intake manifold & throttle body $150-$300. The intake manifold flows 220 CFM +, much better than stock. Throttle body is 65 MM, bigger than the 60 MM on stock stangs. I got a 96 with EGR passages that match the stock setup, so my smog gear works just like factory. You’ll need a 65 MM EGR spacer & new gaskets for $65-$90 so you have a place to mount the EGR & throttle linkage.
3G alternator from 94-95 Mustangs or other Ford. $20-$120. A must have to make the electrical system work like it should or if you have an electric fan. You’ll need a 4 gauge power wire and a 125-135 amp fuse to go with it about $15- $30.
Lincoln MK VIII electric fan -$40-$160. Free up some HP by not having to drive the stock fan. The 3G alternator upgrade is a must have prerequisite before you do the MK VIII fan. You won’t have enough electrical power if you don’t do the 3G upgrade.
Aluminum driveshaft: (courtesy of shawn13) It needs to be from a 92-93-94 Aerostar AWD. It measures 45 ½” center of the front U-joint to center of the rear U-joint. You will need the U-joint, part #PUJ353 from NAPA. The Canadian NAPA pat number is 1-0134BF. It should bolt right up after the U-joint swap.
Note: This driveshaft is not an exact duplicate of the Ford Racing part. It is 3” in diameter while the Ford Racing part is 3.5” in diameter. There is no guarantee that the balance will be any better than the stock part.
Use a piece of string and wrap it around the driveshaft. Make a mark on the string where the ends overlap. Measure the length of the string:
On the 3" AeroStar driveshaft the string will be 9.42" or about 9 7/16" long.
On the Ford Racing 3.5" driveshaft the string will be 10.99" or about 11" long
*1.) Metal flange adapter http://www.kustomz.com/components.html Buy the TR70 for $40. Or spend some time on eBay looking for one that may fit.
*2.) MAF & sensor interchange
The 94-95 Mustang 5.0 MAF & sensor is also found on:
1995-94 Mustang 3.8L F2VF-12B579-A2A,
1994-92 Crown Victoria 4.6L F2VF-12B579-A2A,
1995-94 Mustang, Mustang Cobra 5.0L F2VF-12B579-A2A,
1994-92 Town Car 4.6L F2VF-12B579-A2A,
1994-92 Grand Marquis 4.6L F2VF-12B579-A2A,
Evidently the –A1A, -A2A, AA, etc. on the end of the part number is a minor variant that did not change the operating specs. You should be able to ignore it and have everything work good.
Not all of us know how to fix everything, but some of us know how to fix some things
with excellence!
Some things to consider from someone who has been driving and fixing 5.0 Mustangs for 20+ years...
If you are in California or some other state with strict emissions laws, part of the deal should be that the owner takes the car and has it emissions tested. If it passes, you buy the car and pay for the emissions test cost, if any. If it does not pass, walk away from the deal. For a mechanically inexperienced owner, emissions related problems can be difficult and expensive to fix.
Keep in mind that states with strict emissions laws may make the go faster goals more difficult to reach. Some parts are OK to replace with aftermarket parts and others aren't. Check carefully before you get out your wallet and buy something you can't use in the area where you live.
If you want to do the fix up & power up thing, make sure that you have some other
form of reliable daily driver. That way the stang can sit while your wallet and hands
take a rest from the last project that didn't quite get finished on that 3 day weekend.
Things always cost more and take longer the first time you do them. Having some
other working vehicle makes life easier since it isn't the big crush to get it running
for the Monday morning drive to work or class.
Plan on spending some money on tools it you don't already have them. The stang
has both metric and American fasteners, so you really need two sets of wrenches.
A timing light, digital voltmeter, vacuum gauge, compression tester, fuel pressure
test gauge and fuel line coupler tools are some of the test & tuning tools you'll need.
Visit the pawn shops and sometimes you can find a deal on tools & test equipment
if you stick to well known name brands.
A sheltered work area is almost a must, someplace that you can leave the car in
pieces without upsetting anyone. Some guys here have changed a transmission in
the parking lot of their apartment in a rainstorm, but they will tell you it wasn't fun.
Depending on where you live, a warm dry garage is a nice place to do the winter
projects that stangs tend to become.
EFI (Electronic Fuel Injection) Computer - every stang after 85 has or had one:
don't let it intimidate you. The computer based EFI systems are not hard to fix
and most of the time they tell you what's wrong with the engine. Here's a book
that will get you started with how the Ford electronic engine control or "computer" works.
Ford Fuel Injection & Electronic Engine Control 1988-1993 by James Probst:
ISBN 0-8376-0301-3.
It's about $35-$45 from Borders.com see http://www.amazon.com/ . Select
books and then select search. Use the ISBN number (without dashes or spaces)
to do a search
Use the ISBN number and your local library can get you a loaner copy for free.
Only thing is you are limited to keeping the book for two weeks. It is very good,
and I found it to be very helpful.
For lots of great ideas and tech notes on upgrades and repairs, be sure to check
out http://forums.stangnet.com/showthread.php?t=643651 “Useful Technical Thread Index” sticky at the top of the 5.0 Tech forum.
Things that break often:
T5 5 speed manual transmission (syncros go bad, mostly 3rd gear)
TFI Module (Thin Film Ignition module - mounts on the distributor)
Electric door locks (see the link in my sig for a cheap & easy fix)
O2 sensors(oxygen sensors) They are good for about 60,000 miles and start to go
down hill after that.
TPS Sensor (Throttle Position Sensor) causes flaky problems with idle & acceleration.
Fog lights They overheat the wiring and cause the headlights to flicker. The fix is
cheap and simple if you can do electrical stuff.
Harmonic Balancer – they separate between the hub and outer ring. A harmonic
balancer puller is a must have to change it. You can rent or borrow a puller from
most of the larger auto parts stores.
Things that are very durable:
Engine - as long as it hasn't been abused, it will run good for 150,000-200,000
miles without an overhaul
Rear axle other than an occasional case of worn clutches in the traction lock,
they almost never have problems.
Computer - believe it or not, the computers seldom have problems of their own.
Most of the problems are with the sensors and the wiring.
Suspension – the front and rear suspension has very few problems if the car hasn’t
been wrecked or seen a lot of drag strip runs. The drag strip runs tend to distort and
tear the mount points for the rear axle control arms. Revving the engine up to 4000
RPM and dumping the clutch with slicks or drag radials tends to break things.
Things that don’t break often but are hard to fix:
Water pump mount bolts – they corrode and shear off when you try to change the
water pump.
Rear oil seal on the engine – lots of parts to remove to get to a $20 seal.
Power steering pump – the pumps are noisy and the pulley requires some special
tools to remove and install. If you have the tools, they are easy to do. Again, the
larger auto parts stores will rent or loan the tools for the pulley.
Power Steering rack - it is hard to get the toe in set so that you can drive the car
to the shop to get it properly aligned.
Starter – the top bolt is hard to get a socket on if you don’t have the right combination
of socket, universal joint and extensions.
Everything considered, 5.0 Mustangs are not hard to work on. They just require
some patience and though before you get started.
Still want more performance and on a budget? do the junkyard upgrade...
Gears - 87-88 T-Bird Turbo Coupe rear axle - disc brakes and 3.55 or 3.73 gears in one package for $125-$300. Add another $100-$200 or so to complete the brake upgrade.
94-95 Mustang GT MAF - $40-$100. It is 70 MM instead of the stock 55 MM on regular stangs built prior to 94. It uses a slip on duct on the side that goes to the throttle body and a 4 bolt flange on the other. You need a flange adapter to fit the stock slip on air ducting that goes to the air box. Wiring plugs right in with no changes. *1 *2
95-97 Ford Explorer intake manifold & throttle body $150-$300. The intake manifold flows 220 CFM +, much better than stock. Throttle body is 65 MM, bigger than the 60 MM on stock stangs. I got a 96 with EGR passages that match the stock setup, so my smog gear works just like factory. You’ll need a 65 MM EGR spacer & new gaskets for $65-$90 so you have a place to mount the EGR & throttle linkage.
3G alternator from 94-95 Mustangs or other Ford. $20-$120. A must have to make the electrical system work like it should or if you have an electric fan. You’ll need a 4 gauge power wire and a 125-135 amp fuse to go with it about $15- $30.
Lincoln MK VIII electric fan -$40-$160. Free up some HP by not having to drive the stock fan. The 3G alternator upgrade is a must have prerequisite before you do the MK VIII fan. You won’t have enough electrical power if you don’t do the 3G upgrade.
Aluminum driveshaft: (courtesy of shawn13) It needs to be from a 92-93-94 Aerostar AWD. It measures 45 ½” center of the front U-joint to center of the rear U-joint. You will need the U-joint, part #PUJ353 from NAPA. The Canadian NAPA pat number is 1-0134BF. It should bolt right up after the U-joint swap.
Note: This driveshaft is not an exact duplicate of the Ford Racing part. It is 3” in diameter while the Ford Racing part is 3.5” in diameter. There is no guarantee that the balance will be any better than the stock part.
Use a piece of string and wrap it around the driveshaft. Make a mark on the string where the ends overlap. Measure the length of the string:
On the 3" AeroStar driveshaft the string will be 9.42" or about 9 7/16" long.
On the Ford Racing 3.5" driveshaft the string will be 10.99" or about 11" long
*1.) Metal flange adapter http://www.kustomz.com/components.html Buy the TR70 for $40. Or spend some time on eBay looking for one that may fit.
*2.) MAF & sensor interchange
The 94-95 Mustang 5.0 MAF & sensor is also found on:
1995-94 Mustang 3.8L F2VF-12B579-A2A,
1994-92 Crown Victoria 4.6L F2VF-12B579-A2A,
1995-94 Mustang, Mustang Cobra 5.0L F2VF-12B579-A2A,
1994-92 Town Car 4.6L F2VF-12B579-A2A,
1994-92 Grand Marquis 4.6L F2VF-12B579-A2A,
Evidently the –A1A, -A2A, AA, etc. on the end of the part number is a minor variant that did not change the operating specs. You should be able to ignore it and have everything work good.
SteedaGT9150
Advanced Member
search dude, and 3.73 would be fine. 3.55 better if youre gonna be doing any power adders
Sent from my rooted, rommed Galaxy Nexus....
Sent from my rooted, rommed Galaxy Nexus....
Mintsick
10 Year Member
I will second the vote for 3.55's, I couldn't imagine running 3.73's daily in a street machine with the T5.
with 3.55 you'll likely stay in your cars powerband a bit longer and shift a bit less. Ive had em in a few previous cars and wouldnt have it any other way
Sent from my rooted, rommed Galaxy Nexus....
Sent from my rooted, rommed Galaxy Nexus....
Late model restoration sells gears, i use them for pretty much all of my mustamg wants snd needs. I am in texas so if i order them early in the morning itll be at my house that night or early the next day......free shipping. My friends lx had 4.10s, that thing would rip your head off from a stand. Gears are one of those topics that not many people will agree on. I for one say 3.73s are good for DD but i love 4.10s. It kills your top speed, but honestly how many times do you go over 130 on the street? In my town everyone does the stop light to stop light "races" but to each his own. Btw my phone has a huge crack in the screen soooo sorry for the typos
I did have 4.10's on my last car also, but it was not a daily driver. I def recommend something else for a daily driver, especially if it sees highway duty.
Sent from my rooted, rommed Galaxy Nexus....
Sent from my rooted, rommed Galaxy Nexus....
Michael Meadows
New Member
- Mar 24, 2016
- 1
- 0
- 1
I'm in the process of having 3:73s put in my 94 GT so what kinda top speed will it roughly still have n do you know what it's be with the 4:10s?
7upstang91
10 Year Member
Blast from the past here.
Stockish 94 GT with 3.73, you won't have any top speed. I think the car would be out of gear around 135mph.
Stockish 94 GT with 3.73, you won't have any top speed. I think the car would be out of gear around 135mph.
Your mechanic can get the gears and do install - just be sure he is good at swapping gears in the differential. Most are...
Google Tremec gear calculator and you'll see. What different rear gears with your trans and tire size will do as far as rpm and speed...
Google Tremec gear calculator and you'll see. What different rear gears with your trans and tire size will do as far as rpm and speed...
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