Modular FAQ

1.I recently installed an off-road h-pipe on my car and now I get a Check Engine light, what wrong with my car?
2.I want to change to bigger injectors, is there anything else I need to buy?
3.I swapped gears, what size speedo gear do I need to buy?
4.What is the biggest size slick I can run on my car without cutting?
5.What size rim do I need for skinnies, and do I need spacers too?
6.What are pulleys and why do they make horsepower?
7.Why do I need an aftermarket shifter?
8.What is the difference between progressive and specific rate springs?
9.I want to replace my t-45 transmission with something stronger, what options do I have?
10.What is the difference between shorty and long tube headers? Which should I buy?
11.Is a cat back worth the money? How much HP will I gain?
12.What are lower control arms and why should I replace my stock ones?
13.What does the quad shock do, and should I buy new ones when I change my regular shocks?
14.Can I install gears myself?
15.I want to run 12s NA on my Cobra, what mods should I get to achieve this goal?
16.When I owned a 5.0, the best free mods included bumping timing to 14 degrees, the mod motors don't have distributors though. How can I advance my timing?
17.At what point do I need an ignition system like the MSD or Jacobs boxes?

Q: I recently installed an off-road h-pipe on my car and now I get a Check Engine light, what wrong with my car?
A: The stock catalytic h-pipe comes with 4-6 converters from the factory. There are 4 o2 sensors that tell the computer if the cats are doing their job, The first set looks at emissions and then compares to the rear set. When you run an off-road pipe the readings never change so the computer senses something is wrong and trips the "Check Engine" light. There are several ways to fix this problem. First you can go with a set of MIL eliminators. These plug into your rear o2 sensors and basically fool the computer into thinking everything is OK. Option 2 is a custom burned chip. The chip can be programmed to turn off the rear o2 sensors among other things. This will also remove the light. Keep in mind with either modification, power must be disconnected for them to work. You can also make a set of your own with a few bucks of parts from Radio shack.

Q: I want to change to bigger injectors, is there anything else I need to buy?
A: When you decide to change injectors to a 42# or smaller injector you also have to have your mass air meter recalibrated to work with the injectors. On a Pro-M this requires sending it in for re-calibration. On a C&L is requires a sample tube change. Anything larger than 42# FRPP/Bosch injectors or 50# MSD injectors will require an injector driver and/or a stand alone computer.

Q: I swapped gears, what size speedo gear do I need to buy?
A: On gear ratios 4:10 and below for 5 speed cars and 3:73 and below for AODE cars you can change speedo gear to compensate for the new gears. 4:10 and 3:73 gears require a white 28 tooth speedo gear. This will get you within 5 percent of true speed. 3:55 gears require a yellow 26 tooth speedo gear. With higher gears you can use a speedo calibrator/compensator. This will plug into the tranny and will give you a much more accurate speed.

Q: What is the biggest size slick I can run on my car without cutting?
A: On the 94 and up Mustangs you can run a 15x10 rim with 5.5 BS and clear the brakes and wheel wells. The biggest slick for those rims would be a 28x11.5x15. This will barely clear the wheel wells. Most NA racers run 26in tires due to the shorter heights. Power adder cars are better suited to the 28in tire.

Q: What size rim do I need for skinnies, and do I need spacers too?
A: On a GT you can run a single 7/16 spacer and a 15x3.5 in front skinny. The Cobra is a lot more involved. You need to run 2 spacers and put longer studs on for the skinnies to clear the calipers. There have been some questions regarding this mod being legal and safe for certain racing groups but it does allow you to keep your Cobra brakes and run skinnies.

Q: What are pulleys and why do they make horsepower?
A: Underdrive pulleys do exactly what the term implies, they slow down the speed at which the accessories drive. They accomplish this by using different size pulleys on the crank, water pump, and alternator. The alternator and water pump are run a slower speeds while the crank spins more freely. Think of switching gears in your 10 speed bicycle from the big gear in front and the little gear in back to the little gear in front and big gear in back. This slows down the tire and makes it easier for you to turn the pedals. This allows the engine to rev up much more freely and is usually good for 8-10 horsepower.

Q: Why do I need an aftermarket shifter?
A: The T-45 transmission used in the 96 and up Mustangs is on the weak side and the sloppy stock shifter doesn't help matters any. A good aftermarket shifter will add life to your stock trans. They feature positive stop bolts that will prevent you from breaking a shift fork on a good hard shift. They also use better materials to give the shifter a much firmer feel.

Q: What is the difference between progressive and specific rate springs?
A: Progressive rate springs have a variable spring rate. What this means is that the spring gets firmer as it gets compressed. The harder you push into a corner the stiffer the spring becomes. A specific rate springs features the same rate all the time, it does not matter what pressure is applied on the springs. Progressive rate springs tend to have better characteristics on the street where as a specific rate springs shines on the track.

Q: I want to replace my t-45 transmission with something stronger, what options do I have?
A: There are several options for replacement transmissions for the T-45. The most popular is a swap to a 5-speed Tremec Trans. You will need the following to do this: Tremec 3550 trans, Lakewood modular bellhousing, Tremec specific shifter, and a drive shaft yoke from a 5.0 car since the 3550 was designed as a T-5 replacement. If you choose the stronger Tremec TKO trans you will also need a TKO specific clutch though the TKO comes with its own driveshaft yoke. Another option is the Tremec T-56 6 speed conversion. The 6 speed is becoming more popular because the extra overdrive gear allows for more aggressive rear gearing while keeping highway RPM at a minimum. You will need the following for the T-56 conversion: Tremec Mustang specific T-56 trans with bellhousing and a Pro 5.0 six-speed shifter. You will also have to have your driveshaft shortened one inch. The stock 4.6 yoke will work since the trans was designed for mod motor use. You will also have to slightly modify the trans mounts or order one from Energy Suspension. These are the most common swaps although some more serious racecars have gone to LenTech automatics or C4 automatic trannies.

Q: What is the difference between shorty and long tube headers? Which should I buy?
A: Both shorty and long-tube headers are available for GTs and Cobras. Short tube headers make more power than stock manifolds but less than a long tube header will. The short tubes are the same size as the stock manifolds so you can use the rest of your existing exhaust system. Longtube headers make more torque and power but installation is much more involved. The headers extend down to the transmission and require a specific short matching h pipe. If you can, get the longtubes they will increase your torque and HP more than shorties will but they cost more.

Q: Is a cat back worth the money? How much HP will I gain?
Cat back exhaust systems are usually better engineered and fit and look better than stock parts. However they rarely make more power than a simple muffler swap on stock pipes unless you are running a power adder car and are considering a 3in exhaust system. HP gain is 2-5 hp on average.

Q: What are lower control arms and why should I replace my stock ones?
A: Lower control arms are one of the parts that connect the rear of the car to the chassis itself. Their main duty is to keep the rear from swaying and plant the tires. Aftermarket arms such as Hotchkis, Steeda, Megabite, and others use better bushings and stronger materials to plant the rear tires during straight-line acceleration and cornering.

Q: What does the quad shock do, and should I buy new ones when I change my regular shocks?
A: Ford began installing quad shocks years ago to stop the rear from hopping during hard acceleration. Just about all the major suspension companies offer a replacement quad shock. Many racers simply remove the quad shocks because their aftermarket control arms do such a good job of controlling axle hop. Home Install tip from Rich Nagle: when swapping quad shocks the visible top nut will not turn. This nut is welded to the frame. Reach under and you can remove the bolt from the rear.

Q: Can I install gears myself?
A: Yes you can if you are mechanically inclined and have a good selection of tools. Check out our own James Adkins' tech article on gear installation. If you are not comfortable doing it yourself, get it done professionally.

Q: I want to run 12s NA on my Cobra, what mods should I get to achieve this goal?
A: This greatly depends on your use of the car. It's a popular belief that a well driven Cobra will go high 12's with 4:56 gears, slicks, and a shifter. This will set up will not last a long time due to the extreme pressure on the stock rear parts when launching on slicks. There are a lot of combos that will get an NA cobra into the 12's but they all require steep gears (4:30+) and sticky tires. An aftermarket shifter, pulleys, and an offroad pipe should immediately follow gears. After that its an aftermarket mass air meter, timing adjuster, and then a chip of some kind. This will result in a solid mid 12 sec car on drag slicks or cheaters and a high 12 sec car on radials.

Q: When I owned a 5.0, the best free mods included bumping timing to 14 degrees, the mod motors don't have distributors though. How can I advance my timing?
A: This is as simple as a call to Steeda. They sell a timing adjuster that fits on the crank of both GTs and Cobras. You simply loosen the 2 setscrews and turn it to the proper setting on the indexed trigger.

Q: At what point do I need an ignition system like the MSD or Jacobs boxes?
A: Most people do not run an aftermarket ignition unless they run a power adder of some kind or a hard-core NA race car. The ignition provides additional spark for a hotter burn in the cylinder. This will usually result in more power, especially in a power adder car. With a power adder there is more pressure in the cylinders so the added spark is a good idea to avoid spark blowout. You can also add other accessories such as a 2-step which are a great help for a drag car. The 2-step limits engine RPM while holding down an interior mounted switch. This is perfect for consistent rpm launches at the track.

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