Wayne Cook
June 1, 1999
Photos By: emap usa Archives

Step By Step

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A car like this GT350 will ride pretty hard for everyday street use. However, it will cut a nasty apex at Road America.
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These JBA headers will make a big difference in the way your engine pulls...
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...particularly when combined with the Borla universal exhaust kit.
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This Weiand Stealth intake topped with...
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...the Holley 600-cfm carb with vacuum secondaries makes a perfect intake combination for a 289, 302, or 351W.
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This Tremec five-speed transmission offers the best of all worlds for your early model drivetrain.
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Under the car, a set of gas shocks like these KYBs will get you started on the road to great handling.
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Here’s a good-size front sway bar for an early Mustang. If you compare this bar to a stocker, you’ll see how much thicker the replacement is.

Stock or modified--his is one of those great philosophical questions that Rodin's Thinker ponders as he sits with his chin on his fist. He's got a '65 Mustang, and he can't quite decide whether to make performance upgrades or to leave his steed stock. He wonders what way to go if he does choose to make modifications. What represents a good compromise for his car?

We appreciate his predicament. We've been there too. It isn't easy trying to second-guess engineers who have a lifetime of training and multimillion-dollar test facilities at their disposal. However, we must remember that these engineers have to average everything they do to appeal to the broadest range of potential customers. They know Mom needs to get the groceries and the dry cleaning. Along with that, she expects to be able to do so in reasonable if not complete comfort and safety. These engineers can't tailor Mom's car to meet the specific needs of an enthusiast also.

Normally, Mom doesn't run in the 12s or go honking at Elkhart Lake or Laguna Seca on weekends. She doesn't want the idle of a Super Stock 427 or the ride of a GT350R.

Engineers do a pretty good job creating cars that do most things well. For them, balance is the key with respect to the application. Balance should be the key to any project application as well. Great performance comes when all components work well together. When mechanical things work in harmony, you'll see the checkered flag. It's not any one component that gets the job done, it's components working together as though they were made for each other.

To leave something stock or to go with a modification requires a lot of consideration. Your application will dictate some of your parameters, but so will cost, appearance, safety, practicality, and more. To examine the pros and cons of stock versus modified, we need to choose an example and an application. To stay in sync with many of our readers, we're not going to choose something we want to run in the 12s or place First on the road course. We will try something real-world, just like the average enthusiast who wants decent performance.

Let's say we have a '65 Mustang. It's an A-code 289 four-speed with front disc brakes. Our car is not a rare K-code Hi-Po convertible with a bench seat, so upgrades or modifications won't affect its value as a collectible--we'll leave that factor out of this equation. We don't advocate that you make changes to a car that has tremendous inherent value as a good collector's example. Our car is stone stock, and we want the car to hold its own at the go light, corner tight on a winding mountain road, and still offer Mom something she can use to fetch the groceries. We are also limited by a budget of around $3,000. Sound like a tall order? It is.

It is fortunate that we are starting with a Mustang, because most of what we need is already built right in. In stock trim, it has sprightly acceleration and great balance, but it's soft in the corners with a lot of body roll. The car stops fairly well. The brakes are the original stock units. Let's look under the hood first. In this area, there are a lot of approaches in the quest for additional horsepower. Due to our limited budget, exotic stuff like turbos or superchargers are out.

An A-code 289 is good for 225 hp, which is a good starting figure. The stock engine is quiet, runs smoothly, and delivers good performance. If we want to improve our acceleration, a few well thought-out modifications are in order. One of the first things to look at in a stock A-code engine is the factory-equipped single exhaust. The A-code engine has a four-barrel carb, so the single exhaust system is really holding us back. To begin with, we want to install a dual exhaust system. One option is going with the K-style Hi-Po factory iron manifolds in front of a dual exhaust system. Check with California Pony Cars for exact reproductions of the 289 High Performance exhaust manifolds. This will help add some ponies. The advantage to using cast-iron manifolds is that they're quiet. Since a dual exhaust setup with cast-iron manifolds can be had on a stock Mustang, here's a modification we can live with.

It used to be that long-tube headers were our only choice. With these, you hear every ping and tick, so the underhood noise level is considerable. A modern set of shorty headers is a good way to go, because the thick steel of the tube wall makes them almost as quiet as stock manifolds. Automotive Engineered Products offers JBA shorty headers, as do several manufacturers. These are a good choice. You'll get the best of both worlds, because headers will improve exhaust flow over the cast-iron manifolds a good deal.

Back everything up with 2-1/2-inch pipe and a pair of good low-restriction mufflers, and you'll have a free-breathing exhaust system. Check with Borla for a great high-performance system.

In a stock versus modified context, we suggest going with the header-dual exhaust system, because you have the potential to gain a lot yet lose nothing. Up top on the mill is an Autolite 4100 4V carburetor on a cast-iron intake manifold. The Autolite four-barrel is a great little carb that's easy to work on. Rated at 490 cfm and equipped with vacuum secondaries, it is up to the task on a stock 289 engine.

Now that the exhaust has been opened up, think about providing more cfm capacity on the intake side. A Holley 600-cfm carb with vacuum secondaries is a solid choice here. Now we have a little reserve on the top end, but not so much that the mill is overcarbureted.

While in the neighborhood, it's a good idea to exchange the iron intake with an aftermarket piece. Many kinds are available; Weiand and Edelbrock are good choices. A dual-plane manifold will work best for our application. Not only will this aid engine breathing, it will spare a good amount of weight off the front wheels. Every little bit helps. Take a rattle can and paint the manifold to match the engine color if you want to retain a stock-looking appearance. Top off that new carb with an open-element Hi-Po air cleaner. These are available at Larry's Thunderbird & Mustang Parts, and along with everything else, you're going to notice a big improvement in acceleration.

In the toss-up between stock and modified, subtle performance mods win in our book. All these things can be done to a Mustang, with very little lost in the tradeoff.

What's the gain? The gain is a real-world improvement of between 25 and 40 hp. That's a lot of power, and those are conservative numbers. Add 40 ponies, and we end up with a 265hp engine. This much horsepower in a 2,980-pound car will have us lookin' pretty good at the traffic light.

Going one step further for acceleration improvement could involve changing those stock 2.80:1 or 3.00:1 rear cogs to something in the area of 3.50:1. Acceleration will greatly improve with this move. In our stock versus modified quandary, however, there is a bigger tradeoff. Going to a deeper gear in the rearend dramatically affects highway cruising ability. You'll be pushing the revs to maintain that 65-mph speed. It's a tough call to choose between heroic stoplight performance and cruising ability. At Mustang & Fords, we say don't choose. Have your cake and eat it too.

How, you may ask, is this possible? Simply latch on to a T5 or Tremec five-speed manual transmission. Ford Motorsport can set you up, or if you're trying to save some money, check with Autumn Fleet Sales for a good used unit. California Pony Cars can help out with a complete conversion kit that includes the crossmember, bellhousing, and everything else needed for a slick conversion.

If you replace the four-speed transmission with a five-speed, you'll have more than your cake--you'll have a seven-course meal. Not only can you keep that 3.50:1 rearend, you'll enjoy even better performance at the go light, because the five-speed has a lower First gear than your old Top Loader four-speed. But the real benefit is impressive highway cruising ability. In Fifth gear, your mill will be loafing when you break the speed limit, even with the lower gears out back. In our opinion, the 1:1 final drive ratio found on older cars is their biggest shortcoming. When you add overdrive to a '65 Mustang, you won't believe the difference.

With the overdrive transmission, the disadvantage of the lower rearend gear is eliminated. Do the rearend change and the tranny swap at the same time, and your car will still look stock. Nobody will know about the expanded capability of the car except you. In this category, we vote modified again.

Now that we're doing better at the stoplight, what about that mountain road? Getting a '65 Mustang to corner adroitly is easier than you think. A couple of changes and additions underneath can make your rig surprisingly agile. Assuming the car can be aligned, start with a good set of shocks like those from KYB. They seem to have just the right amount of resistance and will help firm up the ride.

Next on your list should be a heavier front antiroll bar. Check with Performance Suspension Technology for a complete selection of suspension-related goodies. A thicker than stock bar will go a long way toward minimizing body roll. On that twisting mountain road, the difference will be apparent. The car will corner closer to level, and you won't feel like you're going to roll off the edge of the road. Go one step further and install a rear sway bar, and you'll notice an even greater difference.

If we check our wisdom again with respect to stock versus modified, we feel modified wins again. The reason here is that there's everything to be gained and virtually nothing lost. With these mods, your Ford's handling and ride will improve substantially. There is nothing lost because the car still looks stock. As a last step, make sure the car has the best tires you can afford. Try for the largest size that will fit properly on the wheel, because the largest possible contact patch is desirable. Choose a 60- or 50-series tire to keep the sidewall height to a minimum. These two factors in tire selection will help handling a lot. Check with your local BFGoodrich dealer for help in determining your tire needs.

In the final analysis, you can get away with all these modifications and still have a stock-looking car. However, the car will corner tighter, accelerate quicker, have better cruising ability, and achieve far better fuel economy. You will have a far safer car that's happy in the fast lane. In truth, we get the best of both worlds. Call it restomod.