Dale Amy
March 1, 2004

Horse Sense:
A stroker crank provides not only greater swept cylinder volume between piston TDC and BDC, but also a longer lever arm for the piston to push on.

Difficult as it may seem to believe, the overhead-cam 4.6 is now in its ninth year of residence under the V-8 Mustang's hood. And, despite a shaky first couple years, the modular has more recently developed a penchant for performance way out of proportion to its dinky displacement. Still, the little cammers can rightfully be accused of being a bit torque deficient, since there's only so much grunt to be found in 281 ci. More displacement would clearly help.

Luckily-especially since many modulars are by now becoming a bit worn and frazzled-bottom-end help is on the way from a variety of sources. Awhile back, we scoped out Livernois Motorsports' big-bore modifications that bump the modular up to 5.0 displacement while maintaining stock 3.5433-inch stroke. This time our attention turns to VT Competition Engine Development, a relatively new company that has taken the opposite approach to achieve that same magical 5.0 liters. VT goes for a minimal 0.020-inch overbore, but bumps stroke up to a healthy 3.75 inches with a forged steel crankshaft of its own design, teamed with your choice of billet or forged steel rods, and forged pistons in compression ratios for either blown or nonboosted applications. VT offers its stroker either in kit form or as an assembled short-block (with the buyer's choice of iron or aluminum block).

VT also offers a long-block, for that matter. Since bigger displacement also demands a similar increase in air supply to fill its enlarged lungs, VT has ported PI heads on the option list, and has developed a couple different SOHC cam grinds for naturally aspirated applications, as well as one blower-friendly grind. Based on our dyno testing, you should plan on heads-or at least cams-with any stroker swap, as the deeper breathing cylinders demand more than the stock head/cam package can provide.

We'll give details on all these components in our photo captions, but we figured the best way to see how it all works was to visit VT's impressive Lansing, Michigan, facilities (see sidebar VT, Phone Home) and compare them back-to-back with factory counterparts on the company's SuperFlow SF-901 engine dyno. We can't show you any of the machining steps because VT had assembled our subject short-block prior to our arrival. We first dyno'd the VT 5.0 short-block (with 11:1 pistons intended for natural aspiration) topped by stock PI heads and cams, after which we bolted on VT's Stage II PI heads and the more aggressive of the company's duo of naturally aspirated bumpsticks. Boy, does the combination work, producing peaks of 351 hp and 361 lb-ft. These numbers then shot up to 376 hp and 385 lb-ft with the substitution of an Accufab throttle body. So much for the modular's lack of torque! Full details of the power curve can be found in our dyno side-bar (but you've already looked there anyway, right?).

VT, Phone Home
Not far from the East Lansing campus of Michigan State Univer-sity sits the strikingly modern and uncharacteristically sanitary home of VT Competition Engine Development, a firm some readers may be rightfully unfamiliar with. It all began a couple years ago when life-long car guy Lance Thompson decided he wanted to get involved in the auto-motive performance aftermarket, so he got out his checkbook and began investing in the equipment and personnel to make it happen in first-class fashion. Our guess is the checks were fairly big. The result is a shop that has the bright and spotless appearance of a well-funded Winston Cup outfit, and it is filled with the latest in engine building and testing machinery, the latter including both a SuperFlow SF-901 engine dyno and an in-floor Dynojet. Of course, it helps that the guys Lance hired to operate these pricey toys have years of experience and know what they're doing.

As its rather lengthy name suggests, engine building is a primary focus of the company-not only on the Ford modular side, but also with the fast and furious import crowd. As sort of middle ground between those two markets, VT is also giving serious consideration to a Focus engine program that will address the Zetec's factory rod and piston weaknesses under big boost. The company has a tuner on board, whose job it is to make all these projects run once they're assembled.

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On the modular side, VT has concentrated so far on the Two-Valves, but we wouldn't be surprised to see some DOHC cam grinds in the dyno cell in upcoming months. VT may not have been around for long, but if its first efforts give any indication, the company should have a bright future.

On the Dyno
4.6 w/Stock PI Heads and CamsVT 5.0 w/stock PI Heads and CamsGain or (Loss)VT 5.0 w/Stage II VT Heads and CamsCumulative Gain or (Loss)VT 5.0, Heads, Cams, and Accufab Throttle BodyCumulative Gain (or Loss)
RPMTRQHPTRQHPTRQHPTRQHPTRQHPTRQHPTRQHP
3,400274.2177.5341.0220.8 66.8 43.3314.1203.439.925.9329.6213.4 55.4 35.9
3,500282.6188.3340.3226.8 57.7 38.5311.3207.528.719.2330.4220.2 47.8 31.9
3,600284.5195.0339.1232.4 54.6 37.4314.8215.830.320.8342.8235.0 58.3 40.0
3,700290.6204.7343.3241.8 52.7 37.1330.8233.040.228.3353.1248.8 62.5 44.1
3,800296.2214.3326.3236.1 30.1 21.8341.3246.945.132.6369.9267.7 73.7 53.4
3,900303.0225.0320.9238.3 17.9 13.3356.7264.953.739.9381.1283.0 78.1 58.0
4,000298.2227.1303.0230.7 4.8 3.6361.4275.363.248.2384.8293.1 86.6 66.0
4,100293.2228.9301.7235.5 8.5 6.6358.9280.165.751.2384.9300.5 91.7 71.6
4,200306.3245.0296.7237.3 (9.6) (7.7)353.0282.346.737.3380.6304.3 74.3 59.3
4,300306.2250.7286.5234.6(19.7)(16.1)344.9282.438.731.7381.2312.1 75.0 61.4
4,400301.2252.4285.7239.4(15.5)(13.0)346.4290.245.237.8381.5319.6 80.3 67.2
4,500301.3258.2273.0233.9(28.3)(24.3)355.5304.654.246.4377.2323.2 75.9 65.0
4,600299.6262.4268.0234.7(31.6)(27.7)353.3309.453.747.0378.2331.3 78.6 68.9
4,700300.5268.9263.8236.1(36.7)(32.8)353.9316.753.447.8374.1334.8 73.6 65.9
4,800296.9271.4256.5234.4(40.4)(37.0)352.3322.055.450.6376.0343.6 79.1 72.2
4,900292.5272.9253.9236.9(38.6)(36.0)352.4328.859.955.9371.4346.5 78.9 73.6
5,000289.7275.8251.9239.8(37.8)(36.0)353.3336.463.660.6377.8359.7 88.1 83.9
5,100282.0273.8245.2238.1(36.8)(35.7)350.5340.468.566.6378.6367.7 96.6 93.9
5,200276.3273.5245.3242.8(31.0)(30.7)344.1340.767.867.2369.3365.6 93.0 92.1
5,300272.2274.6241.0243.2(31.2)(31.4)342.6345.770.471.1368.9372.3 96.7 97.7
5,400261.0268.4241.6248.4(19.4)(20.0)337.4347.076.478.6365.6375.9104.6107.5
5,500250.4262.2235.9247.1(14.5)(15.1)332.1347.881.785.6354.9371.7104.5109.5
5,600n/an/a226.9241.9n/an/a327.5349.2n/an/a345.2368.1n/an/a
5,700n/an/a221.6240.5n/an/a320.0347.3n/an/a335.2363.8n/an/a
5,800n/an/a204.2225.6n/an/a318.3351.5n/an/a329.0363.3n/an/a
5,900n/an/a202.0226.9n/an/a309.9348.2n/an/a322.1361.9n/an/a
6,000n/an/a190.2217.3n/an/a303.5346.8n/an/a314.9359.7n/an/a

All testing was done using Hooker long-tube headers, a stock Bullitt intake, 24-lb/hr injectors, and a Pro-M 90mm mass-air.A stock throttle body was used in all cases except where noted.

As you can see, substituting the VT 5.0 stroker short-block beneath stock (PI) heads and cams had an immediate and healthy effect on both bottom end torque (up by 66 lb-ft at 3,400 rpm) and horsepower (a 43hp gain at 3,400), yet top-end power and torque were way off. Since air/fuel ratios looked fine on the dyno's wideband oxygen sensor, the most logical explanation is that insufficient air was finding its way to the enlarged cylinders once the revs picked up-a problem we would attribute mostly to the factory cams. We had, after all, added both cylinder volume and higher compression.

Bolting on VT's Stage II heads and cams took care of that little problem with gusto, providing peak-to-peak gains of 75.7 hp and 55.1 lb-ft of torque over the stock 4.6. Even better, at 5,500 rpm the gains were a whopping 85.6 hp and 81.7 lb-ft. Almost as an afterthought, we then bolted on a freer-breathing throttle body, thereby removing one more obstruction from the engine's airway, and showing the importance of getting rid of all induction corks. With its lungs now properly filled with every breath, the stroker now produced 109.5 more horsepower, and 104.5 more lb-ft of torque at 5,500 rpm than did the stock SOHC-increases of nearly 42 percent. Not bad for a mere 0.4 liters (21 ci) of displacement increase.

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