Mustang Performance - Plan For Ponies, Part I

Have you ever wondered what you could do with a stock Mustang’s performance? We think about this when we’re muscling onto a freeway, wondering where the factory-rated 225 hp is. Truth is, those factory horsepower ratings were mostly Madison Avenue hoopla. They don’t mean much in the real world where tires become intimate with the asphalt. Horsepower really doesn’t carry much weight in the relative scheme of things. Torque is what should mean the most in your pursuit of power.

Torque is what really matters when it’s time to step on the gas. Take a ’65 Mustang with a 225hp, 289 4V, for example. Father Ford tells us that the 289 4V engine makes 225 hp at 4,400 rpm. So what? The 305 lb-ft of torque that comes in around 3,200 rpm is what pulls weight with us. Wide-open throttle is where our engine does its best work. Punch the accelerator, hear the secondaries open, and feel the pressure at your backside. Maximum backside pressure (acceleration) should come on board around 3,200 rpm. The mill begins to go to sleep beyond 4,000 rpm.

The more aggressive sibling, the 271hp 289 Hi-Po, achieves maximum torque and horsepower in the 6,000-rpm range because that’s where it’s designed to make its power. It’s a racing engine by nature. Ford did this with a more aggressive camshaft profile using the same valve, the same port, and the same carburetor sizing. This means you can turn any Ford small-block into a Hi-Po with the correct camshaft profile. Summing it up, the camshaft determines an engine’s personality more than any other modification. But we are getting ahead of ourselves.

Our readers ask us how they can step up power without losing the stock appearance. That’s an easier question to answer than you might think. We decided to answer this question with a chassis dyno and good old-fashioned engine tuning. We contacted Jerry Choate of West Coast Classic Mustang for a subject vehicle—his father-in-law’s ’65 Mustang GT hardtop. Then we called Mike Morgan Motorsports in North Hollywood, California, for answers on improving power. House expert Derek Real offered guidance in this area. When we picked up the Mustang GT from West Coast Classic Mustang’s new location in Reseda, California, the car was running poorly. Low-end torque was nonexistent, leaning on the throttle was disappointing, and the rebuilt 289 didn’t accelerate smartly as you would expect with a gentle throttle tip-in. There was also a lean surge and lackluster performance.

Creating power boils down to knowing how to plan for it. A few of us put the cart before the horse (so to speak), thinking that quick-and-dirty bolt-ons are the answer. Your first priority should be a solid foundation. On the day of our first round of dyno tests, it was hot and miserable in the San Fernando Valley, with the mercury around 95 degrees and a relative humidity of 60-70 percent. Warm temperatures adversely affect power, as well as our attitudes. Engines struggle to make power when the mercury rises—they prefer cool, dry air because it enables them to make more power via thermal expansion. Cool air is dense, in that it rapidly expands inside an engine, which makes more power. Hot air isn’t as effective because most of the expansion has already occurred outside the combustion chamber.

The Basics
First, you should have a healthy engine with good compression, low oil consumption, quiet bearings and piston skirts, spec’d camlobes, and a fresh timing set. These are necessary basics for performance. Without them, no amount of engine tuning will make a difference.

Run a compression check on a warm engine. All eight bores should yield uniform compression readings. The norm for a 289 4V engine, for example, is 120-160 psi per cylinder. At a warm idle, manifold vacuum should read around 22 inches. Anything below 18 inches of vacuum in a stock engine isn’t healthy. Low manifold vacuum doesn’t always mean bad piston rings, a wiped camshaft, or burned valves. However, it can mean incorrect ignition timing or air/fuel mixture, a faulty vacuum advance, or an intake manifold vacuum leak. Manifold leakage is detected with a bouncing vacuum gauge needle, depending on the nature of the leak. A wiped camlobe or poorly adjusted rocker arms can also cause needle fluctuation. The process of elimination will solve these problems. With a healthy engine in tow, we’re ready for tuning on the chassis dyno. Mike Morgan Motorsports has a Dyno Jet 248 that enables us to see firsthand how much power our Mustang can produce at the drive wheels.

Dyno Might!
It’s one thing to talk the talk, but it’s another to walk the walk. A quick blast on the dyno eliminates all doubt. Derek Real and Raymond Rivera positioned our Mustang GT on the dyno, safely tied everything down, and went to work. Real saddled up behind the wheel while Rivera manned the computer keyboard. We’re about to find out how much power the Mustang generates in a poor state of tune and why. We have a dead-stock 289 4V V-8 with an Autolite 4100 carburetor and a single-point distributor with an inoperative vacuum advance.

Real slips the C4 into Drive, gently accelerating through First, Second, and then Drive. At approximately 60-mph dyno speed, he mashes the accelerator, kicking the C4 into Second (passing gear). The 289 screams, followed by an upshift into Drive at 4,400 rpm. If our Mustang had been on the highway, it would be accelerating through 100 mph. At 117 mph and 4,600 rpm, Real comes off the gas and brings the rear wheels to a stop. The maximum horsepower is 128.4 at 4,100 rpm and torque is 193.9 lb-ft at 3,400 rpm—our baseline.

When it comes to an engine’s state of tune, there’s a lot to consider in the classic Ford camp. The Autolite 4100 is an outstanding carburetor. Its simple design and trouble-free performance make it a favorite with Ford enthusiasts, who would rather have it than an equivalent Holley 1850. Our Autolite 4100 is a 480-cfm four-barrel. We learned during our first dyno pull that the fuel/air mixture is decidedly lean, which hurts torque. This was apparent as engine rpm increased. The mixture grew leaner—and so did torque. This tells us that carburetor jetting is too lean due to jet size or perhaps obstructed passages.

The stock ignition system demonstrates the need for improvement also. Worn distributor bushings, point bounce, and an inoperative vacuum advance are factors. Worn distributor bushings and shaft cause the shaft to wander, changing the dwell angle and point gap—which makes for inconsistent performance.

For Dyno Run No. 2, we decided to swap in a Pertronix Ignitor ignition module. The Ignitor eliminates ignition points and condenser in old distributors, making them virtually maintenance-free. The Ignitor also improves cold starting and ignition performance throughout the range. You can feel a noticeable difference behind the wheel.

We decided to see if there would be a noticeable difference in power with the Ignitor installed. We gained horsepower (up 2.7 to 131.1) and torque (up 1.1 lb-ft). These gains won’t make the record books, but they show us what’s possible.

Look at what happens when we remove the air cleaner prior to dyno run No. 3. Not only do we have a restrictive, hot-air tube, air-cleaner housing, but a dirty air filter to boot. We gain 2 hp yet lose torque—less than 1 lb-ft. The changes we’ve made aren’t much to write home about. We upgraded to a Pertronix Ignitor module and gained a modest amount of power. We also gained reliability and fuel efficiency and learned that the Ignitor changes the spark curve. When you install the Ignitor on a small-block Ford, this changes the initial spark timing. With points, initial timing was 13 degrees BTDC (before top-dead center). With the Ignitor, timing retards to 6 degrees BTDC, which hurts power. Admittedly, we didn’t allow for the spark retard, which adversely affected our results, nor did we gain the power we’d hoped for with the Ignitor. That’s our fault, not Pertronix’s. Had we bumped the timing ahead by 7 degrees initial advance, we would have likely seen a gain of 5-6 hp and 10 lb-ft of torque.

With all the buzz about spark plugs, we decided to see how a new set of spark plugs would affect performance. We screwed in a set of Bosch plugs (though we recommend Autolite or Motorcraft platinum tips) to see what—if any—gains would be achieved from such a simple swap on Dyno Run No. 4.

Much to our surprise, we lost horsepower yet gained torque with a spark plug change. Peak horsepower comes in lower this time at around 131.3. Torque is up modestly at 196.7. This isn’t always a reflection on spark plugs themselves, but changing atmospheric conditions during the spark plug change.

As you can see, the changes we made didn’t witness much of a difference in performance at wide-open throttle. Upgrading to the Pertronix Ignitor and removing the air cleaner netted the greatest gain at nearly 5 hp at wide-open throttle. With these changes, torque is up nearly 3 lb-ft.

On an average, we’ve gained 4 hp and 5 lb-ft of torque. Although these numbers fail to impress, they show us what’s possible with simple engine tuning and better components. Modest improvements and tuning can net between 5 and 10 hp on a stock engine.

If we could repeat this baseline test, then for starters, we would have rebuilt and rejetted the stock 4100 carburetor. And we would have made adjustments to the vacuum advance as well, which wasn’t working at all. Improving the fuel/air mixture (richer mixture) and recurving the vacuum advance (improved initial advance) would have netted more horsepower from the stock 289.

Overall, we didn’t make that big of a difference in torque or horspower, but did prove one thing: minor tuning can make a difference. Just by upgrading the Petronix Ignitor, removing the stock air cleanser, and changing the spark plugs we managed to gain 4hp and 5lb-ft of torque. Not bad for a few hours work. But what can you do if you want more power fron your vintage small block? That’s the question we’ll address next month with some help from the folks at Edelbrock.