Matt Rawlins
March 1, 2000
Contributers: Matt Rawlins

Rev It Up

Q: I recently traded my '95 GT for a '92 LX 5.0 with 87,000 miles. It has the usual bolt-ons: a 75mm mass air meter, a 65mm throttle body, pulleys, 3.73s, an MSD ignition, and a full exhaust. It retains the stock clutch and tranny. The car was running great until something strange happened.

I launched hard with five people in the car, spinning the tires through First gear. When I shifted into Second, the rpm shot up well into the redline as if the throttle was matted. Even with my foot off the accelerator I could not engage any gear. The shifter just sat in Neutral while the car revved upward to the redline on its own. I stopped immediately and shut off the engine. After a few moments I started the engine back up and the car ran and shifted fine, but the rpm needle sat inactive beyond the 7,000-rpm mark. Then, after a minute of driving, the needle awoke and returned to normal operation. Since then, the car and the tach have been normal but I would like to know what the heck happened and if I should be concerned.

Rob Ticchio
Springfield, MO

A: After speaking with some local Mustang experts and dealerships in the Southern California area, the consensus seemed to be that the problem could well have been a sticky accelerator cable and a dirty throttle plate. Both of these could easily have caused your accelerator pedal to become stuck, especially after a hard launch. Our suggestion to you is to thoroughly clean out your throttle body and grease the throttle linkage as well. A car with more than 87,000 miles is bound to be in need of some cleaning in these areas. If after cleaning both of these the problem reappears, by all means take it in to your nearest Mustang shop or dealership and let the pros have a look at the car. We don't think it should be a problem again though.

How Much?

Q: I own an '88 GT and recently had the engine overhauled in favor of a dealer-remanufactured 302. It was strapped with all the regular bolt-ons, including a Cobra intake, a 70mm throttle body, a Crane fuel pressure regulator, a '90 mass air computer, pulleys, short-tube headers, an H-pipe, and an after-cat exhaust. How much power do you think this combo is making? What roller rocker arms are best for this setup? And what size tires can I safely go with on 16-inch rims (Cobra R) without rubbing?

Jose Carrera
Fort Walton Beach, FL

A: Your tire fitment problem doesn't have to be a problem, although we don't know if you meant to say 17-inch Cobra R wheels instead of 16-inch. We don't know of any company that makes 16-inch Cobra R wheels, but in case you do, the answer to your question would be to fit a set of 245/50-16s all the way around. This size will give you the best traction and avoiding any rubbing. Of course, if you meant to say 17-inch wheels, then you could safely step up to 255/40 in front and 275/40 in the back.

As for your rocker arms, your main problem is clearance. With your cam, 1.7 arms are a better choice to get some additional lift, assuming that piston/valve clearance is OK. Another thing to consider is your cylinder head plan. If you plan to swap in an aftermarket cam, 1.6 arms will suit you the best. Horsepower for your basically stock engine with bolt-ons should be around 235-240 hp.

Rebuild vs. Replace

Q: Many of us love our Fox-body Mustangs and wouldn't trade even for a newer SN-95 or the cartoon-like '99s. I'm committed to running my '89 forever, replacing what it needs and rebuilding my 5.0 when the time comes. The problem is, when is that time? And which is best--replacing or rebuilding? My '89 LX convertible is mostly stock with the exception of a few add-ons like headers, an air filter, mufflers, subframe connectors, and 16-inch wheels. It has racked up an impressive 132,000 miles without any problems, not even any oil burning.

I'm a diehard subscriber and read every issue cover to cover. I would love to see a story on engine rebuilding, mainly for the bottom end, crank, pistons, and cam. But if I were to rebuild or replace the 302, what would be the way to go?

Stuart Schoen
Marina Del Rey, CA

A: Whenever the question of replacing or rebuilding comes up, it's always a good idea to replace worn-out parts whenever possible and if the budget allows. Your '89 with 132,000 miles sounds like a strong runner still and may only need to be freshened up a little to get it to feel like new again.

On the other hand, it depends on whether you plan on doing more mods to the engine as time passes. If you do, we'd suggest you save your pennies and purchase a new short-block with a stronger bottom end. You can never go wrong with a sturdy bottom end. You usually can tell that it's time for a rebuild when the car starts to show signs of leaks, loss of power, burning oil (as you mentioned) and repeated trips to the shop. Other than that, it all depends on how hard the car has been driven by you or the previous owners.

For the Masses

Q: I recently purchased an '88 GT which had been in a crash. Since then, I've had the car repaired and it looks like new again. It's time for the engine mods to begin, but I'm wondering whether or not I should convert the speed density to mass air. The mods I plan on installing are a Cobra intake, a cam, heads, a blower, and the other usual bolt-ons. If it's a must that I convert, which kit should I get?

Jason Hayes
Bean Station, TN

A: Mass air is king when it comes to turning your 302 into a stronger engine with intakes, cams, heads and blowers. Speed-density Mustangs have been known to accommodate modest modifications, but when it comes down to changing your cam and intake configurations drastically, as with the mods you mentioned, driveability will suffer greatly with the speed density. And we're assuming that you actually want to drive your 'Stang after all the money has gone into it for the upgrades, right? You don't want to put in all this time and effort just to look at the car. By converting to Ford Racing's mass air kit for around $500, you open up an unlimited amount of possibilities in increasing your power. The Ford conversion kit comes with everything you need including a new computer(EEC-IV), a mass air meter and sensor calibrated for stock injectors, a wire harness, and all necessary hoses and brackets. Pro-M [(248) 399-9223] and Interactive Systems and Technologies [(770) 720-1259] also offer conversion kits with larger-than-stock mass air sensors.

Shake, Rattle and Roll

Q: I own an '89 GT with a five-speed. Lately, when I shift from First to Second, my whole shifter starts shaking. I took the driveshaft out figuring it was probably the cause and that it may be twisted or out of sorts. I then ran the car without the driveshaft and ran the shifter through the gears--no shaking. So I guess it's the driveshaft that needs to be replaced, but if it still shakes after I replace the driveshaft, what do you think the problem could be? I also would like to know what computer chips you like for the most horsepower. I want to buy one but don't know which is best for my GT.

Cory Brandes
St. Peters, MO

A: We asked a technician at Denny's Driveshafts, an aftermarket company specializing in drivetrain parts, about your car's problem. He said it was likely that since you removed the driveshaft and ran through the gears without any vibration or noticeable shaking, you probably solved the problem right there. Your stock driveshaft could have gotten old and out of round at some point, so it's probably a good idea anyway to replace it with a stronger, lighter, and beefier aluminum unit.

Your computer chip answer depends on what you want to eventually get from your '89 GT. Do you just want a mild, streetable car that is driven daily, or do you want to eventually put in a new set of heads, an intake, and maybe a supercharger? These are the kinds of questions you have to ask yourself before spending a few hundred bucks on a chip. The reason for this is because when you buy a chip from any manufacturer, they'll want to know how modified your car is so they can accurately match it with the right chip. Different engine combinations require different fuel and timing curves. Just because your buddy's '93 LX runs one company's chip doesn't necessarily mean that it will be the right choice for your engine combination. Decide what your final goal will be with your GT and then call up the different chip companies (Hypertech, Kenne Bell, Superchips, and so on) and ask them what they recommend.

We Have Ignition

Q: I have a '93 LX 5.0 five-speed with the following parts: a K&N air filter, pulleys, a Flowmaster exhaust, 3.55 gears, and 14 degrees initial timing. I want to add an MSD ignition box, but I don't know which one to use. Can I use the 6A (without the soft-touch rev limiter) because the factory computer has a rev limiter built in? Or do I need the 6AL with the soft-touch rev control? I would also like to bore out my stock mass air meter about 5mm. Can this be done without any problems?

Phil Mahoney
Chicago, IL

A: The factory EEC-IV computer does have a built-in rev limiter which the factory has preset to limit the fuel delivery to the injectors at around 6,250 rpm. This in turn controls the engine speed but it isn't the best way to do it because it creates a lean condition on the engine at a dangerous time. Basically, Ford was trying to stop severe engine damage with this system, unlike the MSD ignition (with the soft-touch control) which works by eliminating spark to the cylinder and then firing that cylinder every other cycle. This method is a much better way to fight over-revving because it keeps the fuel pumping, causing a rich condition rather than starving the engine of fuel.

As for which one to go with, we suggest the 6AL because it is the better unit. We would definitely stay away from boring your mass air, and advise against it. Put simply, boring the mass air meter doesn't always net good results. Chances are it will create a hunting and surging problem even without bigger injectors. Mass air meters that have come straight from the companies sometimes aren't perfect and those are created with precise machinery. You're better off with an aftermarket meter which has been calibrated for your injector size.

False Judgment

Q: I own a '90 GT convertible with an AOD tranny. I've added an off-road pipe, Flowmasters, an air filter, and a short belt. Is it true that convertibles are toned down from the factory? I've heard from various people that GT convertibles have about 25 hp less than regular GTs. If this is true, what can I do to get this power back? Also, how can I improve my AOD?

William Rosen
Bethesda, MD

A: We’re sorry to hear you’ve been given such bad information. It’s completely false that Ford lessened the horsepower output for the drop-tops over the regular GTs. All 5.0 models were given the exact same V-8 engine which puts out 225 hp. Your car, however, may feel slower than a GT or LX because it’s considerably heavier. The convertibles were the heaviest 5.0s, and what makes it even slower is its AOD. To improve the tranny, install a set of 3.73 gears and an AOD shift-improvement kit from Art Carr, Level 10, or Baumann Engineering. That should put you up to speed with the lighter pack.