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Project Ford Focus ZX3: Part 2

Adding pulleys and a flywheel

Dave Coleman
Jul 18, 2002
0110_33zoom+ford_focus_zx3_coupe+rear_left Photo 1/18   |   Project Ford Focus ZX3: Part 2

Project Focus is turning out to be remarkably easy. In hindsight, this might seem predictable, considering the near constant praise of its nimble chassis, handsome body and, well... willing, if not eager, engine. But it is that engine that had us worried. Judging by its specs alone, Ford's Zetec engine is quite the underachiever. With 2.0 liters of displacement, dual overhead cams, and four valves per cylinder on its resume, one has to wonder why it only makes 130 hp.

A close look at the engine, however, will send any performance enthusiast into fits of replacement anxiety. The intake manifold is a tortured, long runner mess seemingly designed to prevent horsepower. The throttle body is tiny and half shrouded in an effort to improve the Focus' crawling-through-traffic performance. The catalytic converter is nestled next to the engine and fed through a bizzare, convoluted, pinched exhaust manifold. The intake ports are straight and well positioned, but far too small for serious horsepower. The flywheel seems to weigh 30 lbs. And the cams, based solely on how the engine responds underfoot, seem ground for hauling groceries. It makes you want to replace everything. And that's exactly what we plan to do.

2017 Ford Focus
$16,775 Base Model (MSRP) 18/25 MPG Fuel Economy

In our last installment (May, '01) we managed to wake the groggy Zetec with the standard, simple bolt-ons (intake, header, exhaust and adjustable cam gears) and realized an impressive 13-hp gain in peak power. Even better, venturing to the right side of the tach, which had previously been wasted effort, was, after our work, actually worth the trip. We saw a full 24-hp gain right before the rev limiter stopped the fun. Not bad for a weekend's worth of work, but there is still a lot left to do.

Unorthodox Pulley
An underdrive pulley is a standard, no-brainer upgrade. It doesn't matter what kind of engine you have, what else you have done to it, or what order you do the modifications in, an underdrive crank pulley will, almost without fail, be good for 3 to 5 hp. The principle is simple. All the engine-driven accessories (water pump, alternator, power steering pump, etc.) take a certain amount of power to drive, and all of them will take slightly less power if they are driven more slowly. Since all these accessories are driven off the crank pulley, changing the size of the crank pulley is an easy way to slow everything.

The stock crank pulley is 5.2 inches in diameter, so for every rotation, it moves 16.3 inches of belt. (Get it? 16.3 inches is the circumference of the pulley, and since the belt wraps around the outside of the pulley, that's how much the belt gets moved.) The Unorthodox Racing pulley we installed is only 4.15 inches, so for the same revolution, only 13 inches of belt get yanked through. With the belt moving more slowly, all the accessories move more slowly, and less power is lost to the accessories.

In addition to the change in size, the Unorthodox pulley saves a bit of weight. The stock pulley is a hefty cast iron piece with an integral harmonic damper and weighs in at 3.2 lbs. The billet aluminum Unorthodox piece has been cross drilled to the edge of existence, resulting in a net weight just more than half a pound. Some will argue that this weight is worth as much or more than the slower-moving accessories, but physics makes a pretty strong argument against that. In "Technobabble" last month, I revisited the topic of rotational inertia and how it affects performance. Out of that discussion popped a formula to estimate the effect the rotating mass on a flywheel will have on the acceleration of the car as a whole.

With only the slightest hand waving, we can use that formula for the crank pulley as well. Since rotational inertia is proportional to the square of the radius of the rotating object, it should be obvious early on that something small like a crank pulley will have dramatically less rotational inertia than something big like a flywheel. If you plug in the stock pulley radius (2.6 in.), weight (3.2 lbs), the gear ratio in first gear (3.667:1) the final-drive gear ratio (3.82:1) and the radius of a stock 195/60-15 tire (12.1 in.), the formula predicts the equivalent of another 14.5 lbs from the rotaional inertia of the pulley. That drops to 4.9 lbs in second gear, and gets even less significant as you continue to shift. The weight savings is a very nice bonus, but it isn't where the power (3 to 4 hp across the powerband, just like clockwork) is coming from.

FocusSport Flywheel
Spending time with the Focus has brought some driveability issues to the front of the "things that annoy us" list. Near the top of that list is the sluggish response of the engine when between gears. On the one-two shift, for example, the engine has a tendency to hang on to revs, instead of slowing to where it can match the speed in the next gear. The result is an annoying, Driver's Ed lurch into the next gear. The opposite is true on downshifts, where a quick blip of the throttle should be sufficient to match revs for a lower gear, but the Focus requires a whole leg full of throttle to spin the engine up.

These are actually separate issues caused by separate things. The engine refuses to settle quickly because the idle control valve opens and intentionally holds revs up. This is an emissions control strategy that only seems to exist on American cars. Besides clumsy shifting, this also virtually eliminates engine braking, which adds an uneccesary level of difficulty to driving tasks as diverse as controlling the cornering attitude at the limit and trying to maintain a constant following distance in traffic. Why are American manufacturers the only ones with this problem? It probably has to do with the dominance of automatic transmissions in Detroit; they don't have engine braking either.

The sluggish blip is mostly the fault of an intentionally half-shrouded throttle body that lets very little air past in the first quarter of the throttle's travel. This very progressive throttle is an attempt to prevent the drivetrain from bouncing around on its mounts while crawling through traffic. It works, but for enthusiastic drivers, the throttle response is annoyingly slow.

We managed to dramatically improve both without addressing either cause. Instead, we replaced the massive 21.5-lb flywheel with an Aluminum FocusSport flywheel weighing only 9 lbs. The flywheel is actually a surprisingly complex piece. Besides giving the engine enough inertia to keep spinning at idle and to damp out the individual power strokes, it also has to act as a friction surface for the clutch, and, in the case of the Focus, as a toothed wheel for the crank position sensor.

The ECU monitors engine speed with a Hall-effect sensor that can sense a piece of ferrous metal passing. In many cases, these crank sensors are simply wheels with a series of square teeth cut in them, but on the Focus a series of recesses are drilled into the back of the flywheel and the metal left between each hole is what triggers the sensor. Of course, Hall effect sensors can't see aluminum passing, so with FocusSport's aluminum flywheel, the holes (or more precisely, the metal between the holes) had to be replaced with a series of steel pegs. It's a little more complicated than your average flywheel, but the sensor continues to work perfectly.

Play with the same effective weight formula that we tried on the crank pulley (only now with a radius of 5.5 inches), and you can see that in first gear, swapping to the FocusSport flywheel is like removing over 260 lbs from the car. No surprise, then, that it feels much more lively in first gear. In second, the effect is only about 95 lbs, and by third it's less than 50, but the real benefit of the lighter flywheel isn't the acceleration, it's the dramatic improvement in driveability. Blip the throttle now and it actually revs, upshift quickly and you no longer have Driver's Ed flashbacks. In short, it feels like a normal engine.

In the near future, we plan to tackle the original causes of these problems with a new throttle body and some sort of carefully engineered obstruction to the idle control circuit, but until then, we're quite happy with the flywheel solution.

FocusSport Header
Headers for the Focus fit into two categories. Those that strive for legality by staying completely on top of the very close-mounted catalytic converter, and those that eschew morality altogether and eliminate the catalytic converter. The shorty headers, like the JBA header we installed last time, have limited potential for power gains, since their runners aren't long enough for proper exhaust scavenging. We were reasonably happy with the mid-range power gains we saw on with the JBA header, but we were really curious to see what a proper header could do for the Focus. On the other hand, we really aren't happy running without a catalytic converter. A good catalytic converter does such a good job cleaning the exhaust and sacrifices very little power on a naturally-aspirated engine. What we really wanted was a long-runner header with an underfloor cat, so we begged until FocusSport made one for us.

First we installed the standard FocusSport race header (well, again, we just begged and FocusSport did the work) and tested it. Where the JBA street header made all its gains before 5000 rpm, the race header had the same low-end gains and added another 6.8 hp on the top end. FocusSport's Randy Robles reports seeing more than twice that gain on the shop's Focus, but its car was equipped with some fairly radical camshafts and aggressive port work, and was being compared against a stock exhaust manifold. We did try adjusting the cam timing, just to make sure the header hadn't changed the ideal cam timing, but we found no additional gains.

While the header's power gains were quite impressive, the removal of the catalytic converter also made things way too loud. The 1320 Motorsports exhaust has only one muffler, and without that big cat in the way, the exhaust note went from pleasant to deafening.

Poking around under the car, we noticed a lot of surplus room where the downpipe passed between the front crossmember and the bottom of the car. A little cutting and welding later, a small catalytic converter was filling the space. Back on the dyno, we honestly hoped to prove that the catalytic converter made no difference in power. Unfortunately, it did knock a few ponies off the chart. In its worst moments, the cat knocked off 2.7 hp and 4 lb-ft of torque. Not ideal, but worth the clear conscience.

More to Come
There is so much left to do it boggles the mind. We have intake manifolds, camshafts, throttle bodies and chips already in the works, and that's just under the hood. We've been tinkering with the suspension too; we'll have some good news on that front soon.

(310) 484-2322

Thirteen Twenty Motorsports
({{{760}}}) 736-4467

JBA Headers
(619) 229-7797
Short Header

(714) 630-6353
Long Header, Flywheel

Unorthodox Racing
(516) 253-4909
Underdrive Pulley
By Dave Coleman
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