I found this FAQ on the SC

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General Questions:
What does MN12 refer to?
MN12 is the chassis code for the Thunderbird platform. This platform was
used for all 89+ Thunderbirds and Cougars. It is often debated exactly what
the letters and number mean, but we believe MN12 stands for “Mid-specialty”,
North America Project #12”. The MN12 is a rear wheel drive platform with
independent rear suspension. The ’93 to ’98 Lincoln Mark VIII is technically
not an MN12 chassis as it had its own name of FN10, but there are many
similarities between the MN12 and FN10 platforms.
How many Super Coupes and XR7's were produced?
Copy the current chart and place here
Are there any special models of Thunderbird or Cougar that used the
supercharged 3.8L?
In 1990 the SC was offered in a 35th anniversary edition. This special edition
vehicle was painted black with titanium lower body cladding and a blue stripe
that wrapped around the sides and rear of the car. The wheels were standard
SC wheels with a black powder coated finish and polished silver outside lip.
The bird in the wheel center cap was also silver. Each fender received unique
“35th Anniversary” badges as well. The interior featured black and silver
leather seating surfaces with blue piping. The silver leather was actually a
suede material that was quite different from leather usually found on car seats.
The 35th edition was mechanically identical to all other ’90 Super Coupes and
did not have any engine, transmission or suspension enhancements. This model
was available with both automatic and manual transmissions. There is much
more detailed information regarding the ’90 Anniversary models in several of
the back issues of the Chargin’ Thunder (LINK) newsletters. They are worth
purchasing if you want more information.
What colors were the SC and XR7's offered in?
Bill, if memory serves me correctly, you have a list of 13-15 colors
right? If you go to www.rpm.fi/comm/tbird/tb_paint.htm you will find an
incomplete list of colors offered from 89-94.
Can I decode my VIN and door tag sticker?
www.rpm.fi/comm/tbird/tb_vcl.htm This is an EXCELLENT decoder from
Thunderbird Country’s website.
Are there any notorious problems that I should know about this car?
Probably the biggest and most well known problem to affect SC/XR7 owners is
that of blowing head gaskets. When the 3.8L V6 was being upgraded and
beefed up for use in the SC/XR7, the cylinder heads were altered. They used
smaller coolant passages so that more metal could be put into the head thus
making it stronger. This restriction of coolant flow allows the heads to run
hotter than usual. The SC/XR7 also uses a unique lower intake that creates a
restriction in flow of coolant through the rear of the heads. Given the fact that
most SC/XR7’s make anywhere from 11-12psi stock and up to 15psi modified,
this can really put a lot of stress on the cylinder heads thus causing the gaskets
to blow out.
How you look at this situation will depend on how bad you feel about it. It is
an annoyance that some SC/XR7’s don’t make it to 100,000 miles without
blowing head gaskets, but there is an optimistic way to view this. If cylinder
head pressures get too high, there needs to be a way to relieve this pressure. It
is relatively inexpensive to replace a couple gaskets as opposed to rebuilding an
engine. Therefore, most people view the head gasket as a safety valve. It
would be better to blow out this low cost item rather than bend a rod or cause
greater internal damage because the pressure had nowhere to go.
Many of the head gasket failures that occur on the 3.8L motor are the result of
improper changes the owner makes or because of poor maintenance. Other
questions within the FAQ section clearly show that installing a smaller
supercharger pulley will definitely increase your chance of blowing the head
gaskets if the car still has its stock exhaust system. Secondly, engine coolant
should be changed every two years to keep electrolysis at bay. Because of
dissimilar metals between the cylinder head (aluminum) and the engine block
(cast iron), the coolant will actually begin to attack gaskets if it is not changed
on a regular basis.
Can I beat my buddy’s Mustang?
This one comes up all the time. This answer assumes both the Mustang and
the SC/XR7 are stock. When either car is modified, that car can have a huge
advantage and win handily. Most of the time the Mustang in question is a Fox
body 87-93 5.0L. Throughout these years the Mustang made 225HP and
300ft-lbs of torque. That is exactly 15 more HP than the 89-93 SC/XR7, but
15ft-lbs of torque less. So, for comparative purposes, both motors have
approximately the same power output, but they make it differently. The
SC/XR7 will excel in races from 0-60mph whereas the 5.0L will excel in races
from 60+mph. Consider the fact that the Mustang GT weighs 500lbs less than
the SC/XR7 and Mustang LX’s weigh even less, it can be a tough challenge.
Sometimes the SC/XR7’s beat the 5.0L, but I would say more times than not
the Mustang will have the advantage. Keep your races short and sweet and off
the highway and you’ll do much better.
One exception to the “highway” suggestion is in regards to top speed. Even a
stock SC can easily exceed 140 to 145 mph. When driving at these speeds
aerodynamics play a big part in the performance of your vehicle. Hands down
the SC and XR7 have smoother aerodynamics and a lower coefficient of drag
than a Fox body Mustang. We don’t encourage this type of behavior, but you
will outrun a Mustang, in almost all cases, in a top speed contest.
The 94-95 5.0L engines made slightly less power at 215HP and 285ft-lbs of
torque and were found in the last year of the Fox body and the first years of the
SN95 body. These cars might be a bit easier to handle in stock trim. Also
consider the fact that automatic transmissions won’t put as much power to the
ground than manuals. But there is no sense in fooling yourself, Mustangs lay
down quicker times in stock trim. The cars are a close match though and driver
ability can make a big difference on who wins.
The 94-95 Super Coupe flat out makes more HP and Torque than any fuel
injected Mustang GT up to 1998. So, with only weight differences to worry
about, the 94-95 SC has a much better chance of winning more times than not
in a race.
What is the difference between speed shifting and power shifting?
These are two types of shifting that can only be used with manual
transmissions. Speed shifting is the less aggressive form. You simply shift as
fast as you can while still fully depressing the clutch and letting off the gas in
between shifts. This is hard enough on the transmission and is usually only
used when racing.
Power shifting is very hard on the transmission, but is used only when racing
and when you want to extract every bit of performance from your car. You
shift as fast as you can while only depressing the clutch far enough to get it to
disengage somewhat. It may not be fully disengaged, but just enough to get to
the next gear. Additionally, you keep your right foot planted on the gas pedal.
When using this method you much shift very quickly, as your rpms will climb
about 500 in between shifts. Over time you will definitely break your
transmission by doing this, but if you want to go faster on occasions this will do
it. You can notice as much as a .3 second improvement on your ¼ mile times
with this method.
At what RPM should I shift my stock SC/XR7 when racing?
The 3.8 liter SC V6 engine makes a huge amount of low-end torque. In stock
form, it will generate over 300 ft-lb of torque from approximately 2000 to 4000
rpm. Horsepower output rises gradually with RPM and peaks out around 4400
to 4500 rpm. After this point, the horsepower starts to fall off fairly quickly
due to the insufficient flow capability of the stock cylinder heads and fairly
restrictive exhaust system. Therefore, it really is useless to rev your car more
than 5000 to 5200 rpm. Although the 3.8 liter SC engine will continue to rev
easily (but loudly) past 5500 rpm, the car will not generate faster quarter mile
times by flogging the engine at these higher speeds. Shift at approximately 5000
rpm for optimum power output.
When one has modified the 3.8 liter SC V6 with larger induction and exhaust
components, the horsepower will peak approximately 300 to 400 rpm higher.
Therefore, on a modified SC, you may find that the car still makes power up to
5300 and 5400 rpm. To accurately identify where your optimum shift point
should be, consider getting your car tested on a rear wheel chassis dyno. The
information obtained will be extremely helpful to you, as you will see where
peak HP and Torque are generated.
Technical Questions:
How quick is my SC/XR7?
AOD equipped SC’s and XR7’s in stock form typically run mid 15’s. I have
witnessed these cars run anywhere from 15.2 to 16.0, but on average I would
say they are in the mid 15’s. M5R2 equipped 89-93 SC’s and 89-90 XR7’s
typically ran mid to low 15’s. I have rarely seen one of these cars run any
slower than 15.6 stock. 94-95 SC’s, being the fastest production MN12, are
low 15 second cars.
Also remember that times vary upon ambient temperature, elevation, wind,
traction, driver skill and how hard the car was driven. A cool day really is
beneficial to these cars.
How fast is my SC/XR7?
Stock 89-95 M5R2 equipped SC’s and 89-90 XR7’s run anywhere from 140-
145 mph. Stock AOD and 4R70W equipped SC’s and XR7’s can approach
135-140 mph, but become rev limited around that speed.
How much horsepower does my car have?
The 89-93 SC’s and 89-90 XR7’s made 210HP at 4400rpm and 315ft-lbs of
torque at 2600rpm. The 94-95 SC’s made 230HP @ 4500rpm and 330ft-lbs of
torque at 2500rpm
Why do the 1994 and 1995 Super Coupes have more power?
The biggest change to the 94-95 SC’s was that it received the upgraded 3rd
generation Eaton M90 supercharger with epoxy coated rotors. The coating
made the rotors more thermally stable, therefore, Eaton could reduce the
clearances between the rotors and the case for reduced pumping losses. These
superchargers are much more efficient than the older ones, thus allowing it to
realize higher power outputs. They are so efficient that Ford actually used a
larger pulley compared to the ’89 to ’93 model year superchargers. Despite the
larger pulley, they still flow more air than the early model superchargers. Some
other changes to the motor include higher flowing 36lb/hour injectors, different
cam profile and the debut of the electronically controlled automatic transmission
(4R70W). The were a host of other changes for the 94-95 3.8L that are listed
in much more detail here (link to the article)
What type of supercharger do I have?
The supercharger used on all SC/XR7’s are manufactured by Eaton
Corporation. The specific style of supercharger is called a “roots style”. The
other very popular style of supercharger is called a “centrifugal” supercharger.
This is the type that resembles a turbocharger. The Eaton “roots style”
supercharger we use is labeled an M90. It displaces 90 cubic inches (1.5 liters)
and is rated to spin at a maximum rpm of 14,500. These are very durable
superchargers and have a life expectancy way in excess of 100,000 miles.
What is a rev limiter and do I have one?
A rev limiter is designed to keep you from over revving your engine. All SC’s
and XR7’s with the 3.8L supercharged engine redline at 5000 rpm. Those cars
equipped with the manual transmission do not rev limit until 6200 rpm though.
The 4R70W equipped cars rev limit at approximately 5500 rpm. This means
that in both applications, you would be able to rev your car higher than the
designed red line. But once you hit the rev limiter the EEC will cut spark to the
engine so that your rpms do not go any higher.
What is a speed limiter and do I have one?
A speed limiter is a governor that is designed to keep you from accelerating past
a designated speed. This is achieved by programming the EEC to cut off spark
and fuel to the engine after reaching the pre-programmed speed. There were
never any speed limiter placed on any year SC or XR7 with the manual
transmission. Some of the 89-93 SC’s and XR7’s with the AOD were speed
limited at or just under 130 mph, but not all have this limiter. All 94-95 SC’s
with the 4R70W were supposed to be speed limited at 125mph.
Why do we have rev limiters and speed limiters?
All 4R70W SC’s have rev limiters because the 12 inch torque converter starts
to balloon around 5400 rpm. If it balloons enough, the trust washer could eject.
Therefore, the rev limiter keeps drivetrain speeds down.
The speed limiters are present in the 4R70W SC’s because the driveshaft starts
to bend near its critical speed which can depend on rear gear ratios and tire
sizes. The critical speed is when the driveshaft starts whipping in the middle
rather than spinning on its true centerline. This bending creates a vibration or
frequency. The frequency can cause the tailshaft housing to fail. The rear
bushing also gets much hotter and can spin thus dropping the driveshaft at high
speeds. The M5R2 equipped SC’s and XR7’s don’t have this problem because
the driveshaft is shorter and the tailshaft housing doesn’t see as much
frequency. --- compliments of A-Train
How do I remove the speed limiter and/or rev limiter?
This can only be done through the EEC. Several vendors can make a custom
chip that will remove both of these limiters. Usually this is only pursued when
power output has been raised significantly to the point where stock parameters
are no longer compatible with motor configuration though.
What kind of gas mileage should I be getting?
Gas mileage for all stock 89-95 Super Coupes and 89-90 XR7’s should be
anywhere from 17-19 mpg in the city and 23-25 mpg on the highway. Driving
technique as well as level of modifications to your car will change fuel
How much boost should I be making?
Stock SC’s and XR7’s made 11-12psi of boost on average. Some have
reported slightly higher boost levels. Things that can unintentionally affect
boost levels include replacing old exhaust systems and air filters. This may help
explain why several stock SC’s/XR7’s notice different levels. If your particular
car is making approximately 14 to 15 psi of boost, then it likely has had a
smaller aftermarket supercharger pulley installed in place of your stock pulley.
If your car is making substantially less than 12 psi, then you may have a
vacuum leak or some other malfunction.
What are overdrive pulleys?
An overdrive pulley is the pulley that drives the supercharger. The aftermarket
offers two popular sizes of overdrive pulleys that are smaller in diameter than
the stock pulley. The idea is that if the overdrive pulley is smaller, the
crankshaft can spin it faster (via the supercharger belt). One pulley size is
called the 5% pulley or “SVO” pulley. It spins the supercharger approximately
5% faster which will result in an additional 2psi of boost. You should expect a
gain of 10HP, but at the expense of reduced supercharger longevity and an
increased risk of blowing a head gasket.
The other pulley available is called the 10% pulley. There are several
manufacturers of this pulley and as you can tell from the name, it will drive the
supercharger 10% faster. These pulleys offer up to a 3psi increase in boost,
which is noticed by a gain of 15-20HP. This pulley is not recommended for
engines with high miles or ones that are not mechanically sound. The risk of
head gasket failure is dramatically higher with a 10% pulley and this is typically
a $1200 repair job. DO NOT install one of these on your car without first
knowing the risks. If your car has been modified with a substantially improved
exhaust system, then the risk of head gasket failure is minimized. The use of
headers and an exhaust system with larger diameter pipe is highly
Will overdrive pulleys hurt my engine?
Overdrive pulleys can make your supercharger go out faster and put more
stress on your engine. These pulleys can make the supercharger spin up to
15,000 and 16,000 rpm, which is higher than the factory rating of 14,500 rpm.
But, many superchargers live at 15,500 rpm on daily driven SC/XR7’s. Even
Eaton Corp. has admitted that 1000rpm over the factory rating, while not
suggested, will not ensure the death of your supercharger. It is a fact that
overdriving will shorten the life of the supercharger, but these superchargers are
very stout and can take more abuse at higher power levels.
Overdrive pulleys will add more boost though, and this increase in boost
translates into higher cylinder head pressures and temperatures. “Boost” should
really be thought of as “back pressure” within your engine. Higher back
pressure can make your 3.8L more susceptible to blowing a head gasket. That
is why you should always upgrade your exhaust to a higher flowing aftermarket
headers, down tubes, and a larger diameter cat-back system before installing an
overdrive pulley.
What size fuel injectors do I have?
The 89-93 SC and 89-90 XR7 use 30 lb/hour fuel injectors. These injectors
have a red top to them. The 94-95 SC uses 36 lb/hour fuel injectors. These
have a dark blue top color. The two are easily distinguishable.
What size fuel injectors can I use?
30 lb/hour (stock, 36 lb/hour, 38 lb/hour, and 42 lb/hour. Some have
experimented with 50 lb/hour, but this size definitely requires EEC calibration
and should be used for engines with much higher power levels.
How much power can I add to the motor before upgrading injectors?
The rule of thumb for the 89-93 SC and XR7 is not to go past 300 crank HP
without upgrading fuel injectors. The next highest step, 36lb/hour injectors,
should be used up to 350HP. 38lb/hour injectors can be used up to 375HP.
42lb/hour injectors should be used for 375+HP.
What size fuel pump do I have?
The 89-93 SC and 89-90 XR7 had a 108 liter/hour fuel pump from the factory.
The 94/95 has a 128 liter/hour pump.
How much power can I add before upgrading the fuel pump?
This is debatable, but after installing a few air flow enhancing devices such as a
larger MAFS, Throttle body, smaller supercharger pulley, or headers/down
tubes/cat-back, I would say it is time to consider going with a larger capacity
fuel pump. More air into the engine necessitates more fuel.
Fuel pumps do not last forever either and a good rule of thumb is to change
them out after 100,000 miles. As many SCs/XR7s are now ten years old or
older, your car likely has surpassed this mileage mark. Why replace your
original fuel pump with an equivalent from your Ford dealer when there are
larger capacity pumps available at very reasonable prices compared to you will
pay your dealership? The most popular pumps to upgrade to are the 190 lph
and 255lph units. Having the extra capacity for future upgrades is always a
good idea. Don’t forget to change your fuel filter every few years too. These
are often overlooked and when they become clogged, make your fuel pump
work harder and fail sooner. Be proactive, not dumb-active!
What transmission do I have?
All 5 speed Super Coupes and XR7’s used the M5R2 Mazda transmission.
This transmission was chosen in favor over the Mustang T5, because it was
supposed to better handle the higher torque output of the 3.8L. This
transmission stayed the same from 89-93 and in 94-95 received a less
aggressive 1st, 2nd, and 3rd, gear ratio.
All automatic Super Coupes and XR7’s from 89-93 used the Ford AOD
transmission. In 94-95 all automatic Super Coupes received the new 4R70W
electronically controlled automatic transmission.
What does 4R70W and M5R2 stand for?
In 4R70W the 4 means “four gears”, R means “rear wheel drive”, 70 is a
reference figure for torque handling ability, but has no hard numbers attached to
it, and W means “wide ratio”.
In M5R2 the M means “Mazda”, 5 means “5 gears”, R means “rear wheel
drive” and 2 is rumored to stand for “Second Revision”.
How can I improve the shifting of my M5R2 transmission?
There is really no good way to improve the shifting of your M5R2. There are
upgrades and modifications that you can perform that will make slight
improvements, but there is no real cure-all for the notchy shifting M5R2. This
transmission was offered in some Mazda trucks as well as Ford Broncos and
F150’s, therefore, it was never intended to provide a slick feel when shifting,
but rather it was supposed to be tougher than some of the other transmissions
on the market.
Attention to transmission fluid will go a long way. Make sure your fluid is
topped off and use a synthetic type fluid. Redline MTL and GM Synchromesh
are both excellent brands of fluid to use. Some have had good results with
these fluid and others have not. The factory calls for Automatic transmission
fluid (ATF) Mercon 5 to be used in the M5R2 however. ATF is thinner than
Manual transmission fluid and can make shifting through the gearbox easier in
colder temperatures. If you want to keep it up to factory specifications you
should use ATF. Good fresh fluid can provide slight improvements, but do not
expect fluid alone to make a night and day difference in the shifting. The
M5R2 holds 3 qts./ 6 oz.’s and make sure to include a 4oz bottle of Ford
Friction Modifier with the fluid of choice.
It has also been rumored that upgrading the stock blocker rings from fiber to
brass will improve shifting. I do not believe this to be true though. The brass
blocker rings found in newer style F150’s will be more durable than the stock
SC rings, but it will not cure the stiffness in shifting. If it does help, the
improvement is minimal. The brass rings are stronger though and might be an
option from a durability standpoint.
Finally, B&M offers a Ripper shifter, part number 45058, and it is cataloged for
the 1989-1995 T-Bird SC and the 1989-1990 Mercury Cougar XR-7. It is
composed of aircraft quality materials, such as the 6061 T-6 billet Aluminum
base and 303 stainless billet stick and is backed by the lifetime Ripper warranty.
This shifter will not reduce the stiffness in the shifting. Considering it features
a 25% reduction in throw length it will actually reduce your leverage possibly
making it a bit harder to shift. However, the shifter does offer more precise
shift feel and brings the gears closer together. Fifth gear is no longer so far
away with this shifter. The Ripper also features shifter stops which will allow
the shifter itself to absorb the impact of hard shifts. This feature is not found in
the stock shifter. While it may not reduce stiffness in shifting, it is a quality
piece that offers other benefits.
What are the part numbers for the upgraded brass blocker rings for the M5R2?
1st, 2nd, and 4th Gear- F1TZ-7107-A
3rd Gear- F1TZ-7107-H
5th Gear- F1TZ-7107-D
Reverse- F1TZ-7107-G
Was there a difference between the M5R2 manual transmission in any years of
the SC and XR7?
Yes, the M5R2 did change. In 89-93 the M5R2 had the following gear ratios:
1st Gear- 3.75
2nd Gear- 2.32
3rd Gear- 1.43
4th Gear- 1.00
5th Gear- .75
Reverse- 3.26
In 94-95 the M5R2 received some different gear ratios. This transmission had
the following ratios:
1st Gear- 3.42
2nd Gear- 2.16
3rd Gear- 1.34
4th Gear- 1.00
5th Gear- .75
Reverse- 3.26
What is the difference between the AOD and the 4R70W?
The major differences between these transmissions are that the 4R70W is an
electronically controlled version of the AOD and the 4R70W received upgraded
“wide ratio” gearing for 1st and 2nd gear.
The AOD has the following gear ratios:
1st- 2.40
2nd- 1.47
3rd- 1.00
Overdrive- .67
The 4R70W has the following gear ratios:
1st- 2.84
2nd- 1.55
3rd- 1.00
Overdrive- .70
What is my rear end ratio?
All 5 speed SC’s and XR7’s came standard with a 2.73:1 ratio ring and pinion
gear. Most automatic equipped SC’s and XR7’s came with 3.27:1 gears. The
XR7 standard gear ratio for automatic cars was actually 3.08:1, but I’m sure the
vast majority of them were equipped with the optional 3.27s.
What size gears should I upgrade to?
On average, most will suggest that the SC’s and XR7’s with the M5R2
transmission should upgrade to 3.27 and those with the AOD(E)/4R70W should
upgrade to 3.73. I would like to suggest however, that the 3.27 final drive ratio
be used for all 89-93 SC’s and XR7’s with the M5R2, while the 94-95 SC’s
with the M5R2 upgrade to either a 3.27 or a 3.55 final drive ratio.
Since the 94-95 style M5R2 has less aggressive 1st, 2nd, and 3rd gear ratios than
the previous model M5R2, this means that it won’t respond as well to the same
final drive gear when it is backed behind either transmission. The differences
are negligible, but they are noteworthy. Most find the 3.27 gearing to be
suitable for any year 5 speed SC or XR7, but you should be informed of the
With the automatic SC’s and XR7’s, a 3.73:1 final drive is suggested because
you will still have a decent top end when 3rd gear is near the redline. When
racing at the drag strip or just opening the car up on the highway it is never a
good idea to do wide open throttle (WOT) shifts into overdrive. With a 4.10:1
ratio or higher, your car might pull harder, but you will find yourself running out
of gear quickly unless you shift into overdrive.
Why can Fox body Mustangs with the T5 manual transmission use higher final
drive gear ratios than we can?
The T5 transmission found in all manual Fox body Mustangs actually has much
less aggressive ratios than the ratios found in both versions of the M5R2. The
T5 ratios are as follows:
1st Gear- 3.35
2nd Gear- 1.94
3rd Gear- 1.34
4th Gear- 1.00
5th Gear- .063
If you compare these ratios to the 89-93 M5R2 you will see that the M5R2 has
much more aggressive 1st and 2nd gears. Since the first 3 gears of the M5R2
are larger, then naturally you won’t need as big of a final drive gear as a
Mustang needs.
You may also note that the 94-95 M5R2, while possessing more aggressive
ratios, did tame down over time in comparison to the T5. The newer revised
ratios became smaller in the first three gears than the earlier models. In fact,
the new 1st and 2nd gear is not much bigger than the 1st and 2nd gear found in a
T5. The 94-95 M5R2 also shares the exact same 3rd and 4th gear as a T5.
Still, it does have more aggressive ratios and needs less final drive to match the
performance gains that T5 equipped Mustangs will realize with higher rear end
How much will it cost to upgrade the ring and pinion gears in my rear end?
Typically, the cost of the gears themselves is approx. $180 to $200. Depending
upon the general overall condition and mileage of your rear end, you may
consider doing a complete rebuild of your rear differential. Assuming you just
wish to change the gears themselves, you can save some money by removing
and replacing the gear housing yourself. If this is done, typically a shop will
charge $125 to $175 just to change your gears out. If they also remove the
housing, expect another two hours of labor at a cost of approx. $50/hour.
Remember that EVERY time you remove and replace a half shaft into your
8.8” rear housing, the axle seals should be changed to prevent leaking.
How can I tell if I’ve blown a head gasket?
There are different ways a head gasket can blow. The gasket can break around
a coolant passage thus allowing coolant to enter one or more of the combustion
chambers. When you burn coolant, you will notice white smoke/steam coming
from your tailpipes. The break can be bad enough so that coolant drips out of
your tailpipes, or it can be subtle enough to notice just a slight difference in the
appearance of the exhaust fumes. Additionally, some head gaskets can break in
between cylinders, which will not be as easy to diagnose. In both cases, if your
head gasket is blown, you might notice a loss of power, rough idle, and/or
engine knock when under boost.
How much will a head gasket replacement cost?
On average it seems like SC/XR7 owners pay $1000-$1200. Some higher,
some lower. In order to change the headgaskets you need to remove the entire
intake tract, supercharger system, intercooler, intercooler tubing, and
upper/lower intakes. This all adds up in labor that you would usually not be
paying on another car with natural aspiration.
What does the EGR valve do?
This valve recirculates a small amount of exhaust gas into the engine through
the intake manifold. This lowers the combustion chamber temperatures to
minimize the emission of Nitrogen Oxides at part throttle. Because EGR causes
some loss of power, the EEC changes the fuel and spark curves to compensate.
What year Super Coupes had the EGR valve?
The ’89 and ’90 5-speed and AOD cars as well as all the ’94 and ’95 cars had
EGR. There may be a few exceptions to this rule, but this information is
generally accepted as true.
What is the widest tire I can fit on my stock 16 inch rims?
The widest tire that is recommended for the stock 16 X 7 inch SC or XR7
wheels is a 255 50 16. These tires are approximately 10 inches. Most people
have not experience any interference with these tires on suspension pieces,
however, most will agree that you should not go wider. 245 50 is not quite as
wide as a 255, but will offer a very aggressive stance and is also a very popular
upgrade for those that don’t want to risk it with a 255 50. Follow this link to a
tire height calculator. This calculator will tell you different specification of
different tire sizes in relation to your stock tire size (225 60 16)
As an aside to this question, be aware that the overall diameter of the stock 225
60 16s is 26.6 inches. If you decide to go with the 255 50 16 size be aware
that they have a diameter of 26.0 inches and the 245 50 16s are even shorter
yet at only 25.6 inches tall. By going to a shorter tire, the gap between the
wheel lip and the top of your tire grows dramatically and can actually make
your car look like a four-wheel-drive truck. If your car is equipped with
lowering springs, this will address the large gap that will be created, but I’m sure
most people will agree that your car will look quite funny with such a large
fender lip gap.
Will Cobra R’s or other Mustang rims fit my car?
The MN12 chassis utilizes an unusual bolt pattern of 5 X 4.25 inches.
Mustangs utilize a more common bolt pattern of 5 X 4.5 inches. So a Mustang
wheel will not fit a SC or XR7. The only way to make those wheels fit would
be to convert your bolt pattern to a 5 X 4.5 inch pattern. But by doing this,
you will not be able to use your SC or XR7 wheels.
If you want the look of a Cobra R there are several aftermarket venders that
offer exact replicas of the Cobra R wheel and offer them in the 5 X 4.25 bolt
pattern. Dante Design and Pacer are the two most popular brands. You can
get Dante wheels from Super Coupe Performance or from Performance Wheel
Outlet, but be warned that Performance Wheel Outlet does not have a good
reputation for smooth business transactions.
Custom Wheels Market also offers Dante Design Ford Motorsport wheels in
the 5 X 4.25 bolt pattern. Their website is www.wheelsmarket.com. They have
been in business for 10 years, have a 100% clean history with the BBB, and
would like to offer their services to the club.
I want to run Nitrous Oxide (N2O) in my car. What do I need to know about
doing this?
Nitrous is VERY effective on any car, and especially so on the SC/XR7.
Forced induction cars benefit from N2O injection especially since it also cools
down the superheated air resulting in increased boost pressure. It is first useful
to understand how Nitrous Oxide works though.
The Nitrous Oxide is composed of two nitrogen molecules and one oxygen
molecule. When N2O is injected in the intake manifold it changes from a liquid
state to a gas state thus reducing the temperature by –127 F. This makes the
air in the manifold much denser. During the compression stroke, when the
temperature reaches 595 F, the N2O breaks up into nitrogen and oxygen. The
nitrogen cushions the combustion so it won't be too violent and the oxygen does
what it's supposed to do which is burn more fuel. If you were to inject pure
oxygen into your motor your head would be sitting where MIR was? The key
is to feed the motor enough fuel to keep from going into a lean condition, which
is where problems occur.
There are two types of systems available. One is called a “Dry” system. This
works by injecting pure N20 into the combustion chambers. You are required
to use an adjustable fuel pressure regulator to increase fuel pressure before
hitting the button. Since your car is already running rich, once you inject the
N20 you will have enough added fuel to compensate for the added oxygen.
The other type of system is called a “Wet” system. This type does not require
an upgraded fuel system or any messing with the fuel pressure. It works by
injecting a mixture of N20 and fuel simultaneously into the combustion
Both systems allow you to increase the amounts of gained HP by changing jet
sizes. Typically smaller 50-75 HP jets are recommended considering the high
amount of stress the motor is already under though. Both systems have
advantages and disadvantages, but have both been used on the supercharged
3.8 liter motor with success. For more details, we would like to defer to a very
comprehensive article written in the March 2000 Chargin’ Thunder (LINK).
This article answers in-depth the “How”, “Why”, “What”, and “Where”
questions regarding NOS usage.
What are the torque specifications on the supercharger and associated parts?
Supercharger retaining bolts (8mm)- 20-30 nm 15-20 lb-ft
Supercharger retaining bolts (12mm)- 70-95 nm 52-70 lb-ft
Supercharger outlet adapter bolts/studs- 20-30 nm 15-22 lb-ft
Throttle body assembly retaining nuts- 20-30 nm 15-22 lb-ft
Intake elbow bolts- 8-13 nm 6-9 lb-ft
Intercooler tube retaining nuts- 20-30 nm 15-22 lb-ft
Intercooler outlet tube to bracket bolt- 40-55 nm 30-40 lb-ft
Supercharger adapter collar nut- 200 nm 148 lb-ft
Intercooler outlet tube bracket (to block) studfully
seat, then 2-10 nm 17-88 lb-in
Intercooler outlet tube bracket (to block) bolt- 70-95 nm 52-70 lb-ft
Intercooler outlet tube bracket (to block) nut- 20-30 nm 15-22 lb-ft
Intercooler retaining (to radiator airboot) screw and washer assembly-
4-6 nm 3-5 lb-ft
Common Problems:
Why is my oil filter so hard to remove?
If you own an SC or XR7 with average mileage for its year, the chances are
very good that your motor mounts are pretty worn out. Stock motor mounts
on these cars are hydraulic or liquid filled. These motor mounts help quell
chassis vibration better than the traditional solid rubber motor mount, however,
they are also weaker. When they start to break, the engine will begin to sit
lower and lower in the engine compartment which will cause the oil filter to
press against the frame rail and power steering lines harder and harder. If your
SC or XR7 is in this condition then you should invest in a new set of mounts
ASAP. Either the stock replacement or solid rubber mounts will work fine.
Now that I have headers my 02 sensors won’t reach. How do I fix this?
This is a common problem when buying aftermarket headers. All aftermarket
headers have much longer primary tubes than the stock manifolds. This means
that the collectors sit much farther downstream than the stock manifolds, thus
usually moving the position for the O2 sensors further away. The stock O2
sensors are 8.5 inches long, and usually the only way to make them fit is to cut
and spice them so that they are longer. However, you can purchase
replacement 3-wire O2 sensors from Bosch that are longer. #13942-8.5” is the
part number for the stock sensor. #13950-13” are 13 inches long and #13953-
16.5” are 16.5 inches long. With Kooks/SCP short tube headers the 16 inch
sensors fit very well.
Why do my headlights flicker?
This could be a couple things. One problem stems from the “Multi-function
switch” on your steering column. This is the lever that controls your high/low
beams, windshield washer, wipers, and flashers. There are approximately 20
wires that run into this switch and it is not unusual for some of them to burn out
over time thus causing your headlights to flicker on and off. You can either
purchase a new replacement part from Ford or get one out of a similar year
Taurus (probably other models too) at the local salvage yard.
Another common problem is for the actual headlight switch to go bad. This is
the switch in the dashboard that you pull out to turn your headlights on. Since
the foglight switch is wired in with the headlight switch this can place more load
than necessary on the headlight switch. To solve this you should replace your
headlight switch if it has gone bad. Additionally, you can rewire your foglights
so that you can turn them on without the headlights being on. Follow this link
for a “How-to” on rewiring the foglights.
Why does my heater blow out cool air intermittently?
This can either be a bad heater core or just something as simple as having low
coolant. When the coolant runs low it can affect the heater core by not
supplying a constant source of heat. Always make sure the coolant is topped
off first.
How do I fix the peeling black tape on my doors?
Most older SC’s have a problem with the tape material on the doors cracking
and peeling over the years. The best way to fix this is to order the factory
replacement tape from Ford. The part number is E9SZ6320000A9G.
What are the best spark plugs and wires to use?
Ford Motorcraft factory replacement double platinum plugs (AWSF 34PP) are
the most reliable to use. Others have had success with different brands, but the
factory plugs seem to receive the most praise. Spark plug wires, however,
should be upgraded aftermarket equipment. Magnecor is preferred and some
claim success with Jacobs. Both offer superior wires for SC/XR7 applications.
How can I prevent wheel hop?
The best way to prevent wheel hop is to purchase a set of rear air bags for one
or both of the rear coil springs. When inflated, the increased force helps plant
the wheels to the ground with more force. This causes the wheels to resist
hopping until reaching a higher rpm.
Front polyurethane differential bushings also help keep the rear end housing
from jumping around. Others have suggested that in addition to the bags and
bushings, a larger diameter rear sway bar has helped with hop. These
modifications will not cure wheel hop, but will help to greatly reduce it.
How can I make my car run cooler?
First of all, don’t always believe what your dash gage is saying is true. Factory
gages are notorious for being inaccurate. Verify the coolant temperature by an
external gauge if possible. The SC radiator, because it shares space with the
intercooler, is by space restriction not as large as it probably should be. If your
car has not had its coolant changed every two or three years, then there is a
very good possibility that your radiator is partially clogged. Flushing/cleaning
may help, or replacement may be necessary. Replacing the stock radiator with a
thicker aftermarket Griffin unit will likely help dramatically. Your radiator hoses
may also have a blockage inside them. The lower hose is especially prone to
clogging because it has a wound metal spring inside it. Deposits have been
known to gradually attach to this spring and over time restrict flow substantially.
Hoses should be replaced every five years. Use a good name brand of coolant
of your preference (I recommend Prestone) and add some brand of "water
wetter" product. This will aid in the heat transfer capability of the coolant and
help to keep your cooling system cleaner. You may want to replace your stock
197-degree thermostat with a 180-degree unit. Also there are several
commercially available programmable or variable ways to make your radiator
fan come on at a lower temperature.


could u not have just posted a link to this or what

Tim Moore

This is the new "Longest thread" all by itself. But it does have a lot of usefull information. Virgil i think we should all print this post for our future reference


Re: Complete Idiot's Guide to SC History (!)

"Totally" agree, Tim...! After all, this is better than
half the bullshit, half-truths we read much of the
budweiser time we spend on this site....lol !
As Ernie would cliche us: 'know what-a mean?' (!)

PS-1: I keep a case of canned coke by my terminal,
lol!!! But tease my son, that I'm proud of him, that
"somebody" in the family is a loyal Budweiser Man:
He is it!(!) Must be those tshirted babes that
got his commitment...lol!

PS-2: Hey, Jeremy: Thanks for all that great info!!!
I bet your typing skills have taken a paradigm shift
upwards and skywards...lol! Peace!


Re: Complete Idiot's Guide to SC History (!)

not typing!!

It's called copy and paste :rollin:


Re: Complete Idiot's Guide to SC History (!)

Darn, here I wanted him to get all this credit...!
OK, Jeremy, let's save the Oscar for some other

Active non member

Re: Complete Idiot's Guide to SC History (!)

I am only here to give positive and uselfull info and suggestions.


Registered User
General questions:

Nice job detailing the components of the SC. I have compiled similar info from various sources, but your info is very helpful.




Registered User
Any help would be appreciated

I am new to the Super Coupe scene. I own a 1989 Red Supercoupe with 118,000 miles. It is totally stock and I was wondering what upgrades should be done first. I would love to hit the 300 to 350 hp range.



Registered User
good info

Im a nu B but Im so glad to read all the info on this post. I relley needed the torque spec. My sc has griffen colling and better headders and a pulley. I dint think ill go with the NOS it,s fast alerddy


Registered User
just one more Q. if you please

ok head gasket ,why are the holes so small on the gasket as comparied to the ports on the block and the head? is it me or sould'nt the holes in the gasket at least resemble the ports in the block and head or am i clueless .maybe thats why it gets so hot ? or can you cut the holes biger or in the same shape as the ones in the block and head?
by the way greate job on the fyi post if they dont like it dont read it thanks again im replaceing the head gasget in mine in a couple of days and i can't beleive the last one held as long as it did they must not have taken the head completly off ? jk


Registered User
1990 XR7 SC V6 TO 302 V8 conversion

Just blew v6 and wanted to replace with 302 V8.
Have M5R2 Mazda transmission and was told this would
not bolt up. Is this true? If so, what are my options?