Mustang Three-Valve Stroker - Supersize It

Owners of megapower S197 GTs in search of important internal insurance would do well to take a close look at Livernois Motorsports' stroker short-block combos for the Three-Valve modular. These combine the instant power and torque benefit of increased displacement with the longer-term benefit of being able to shrug off way more of a horsepower hit than a factory bottom end.

Horse Sense: Factory S197 aluminum block castings have such wickedly sharp edges and casting flash that factory line workers are issued special gloves to handle them.

It didn't take long for the power merchants of the aftermarket to send forth an army of performance enhancements for the S197 GT's Three-Valve modular, with positive-displacement and centrifugal superchargers, along with turbos, leading the charge (pun intended). As of late, with the benefit of intercooling, as well as the increasing finesse and sophistication of tuning solutions, we're also seeing ever-higher levels of boost. Where just a while back 10 psi was considered impressive, now 15, 20, or even 30 pounds of boost are threatening to become the norm, with correspondingly nutty increases in horsepower and torque. It's now possible to attain 800, 1,000, or more pressurized ponies.

Of course, all this boost means huge increases in cylinder pressures, and an enormous strain is being put on factory reciprocating and rotating assemblies-stuff that was engineered for 350 or 400 ponies at most. Then there's the separate matter of the modular's relatively puny 281ci displacement.

In one fell swoop, Livernois Motorsports has addressed both bottom-end strength and the need for increased swept cylinder volume with its Three-Valve stroker packages, so we ambled over to the company's Dearborn Heights, Michigan, headquarters for a closer look. Livernois is certainly not alone in building modular strokers, but after hearing of the depth of R&D and witnessing the attention to detail that go into these stout short-blocks, we came away duly impressed.

Livernois' Three-Valve strokers begin with a production S197 aluminum block, unless a customer has another preference. Livernois' supervisor of engine development, Mike Schropp, considers these light but strong blocks to be sturdy enough to contain upward of 1,500 hp once the company's simple-but-labor- intensive modifications are performed.

Truthfully, Livernois will build a custom short-block to suit virtually any customer's needs, but the company offers two "regular" S197 stroker packages on its Web site-one built to handle ludicrous levels of boost and horsepower (up to 29 psi or 1,000 hp) and yet another for those approaching the internal-combustion insanity of 30-plus psi or 1,500 hp.

What separates Livernois from many other purveyors of stroker combos is the level of research and testing, along with the resulting specification of custom reciprocating and rotating hardware. The company doesn't throw together unrelated, off-the-shelf components. Let's take a closer look.

The Block

Though others can be substituted, Livernois bases its Three-Valve modular stroker assemblies on the S197's factory aluminum block, having found its four-bolt bottom end to be rigid and durable, provided certain measures are taken to address the possibility of stress risers. Those measures include deburring and radiusing any and all of the factory block's sharp edges or corners-and there are many of them-in the pan rail, main web/bulkhead, and other areas. Why? These sharp edges or corners are stress focal points and can fall victim to cracks, and ultimately, structural failures that will reverberate directly through your wallet.

With beefy four-bolt caps and minimum 17mm thickness in the main web areas, we can see why these blocks are regarded as sturdy and stable in the main bore area. Notice the razor-sharp edges. The surfaces of this stock casting are liberally sprinkled with flesh-shredding edges, angles, and casting flash. Such sharpness is known to cause stress risers-concentration points destined to lead to cracks and other nasty stuff...

This hand grinding continues in the oil passages, specifically within the inlets from the oil pump and the oil-filter adapter, as well as in the main-bearing area. The idea here is to radius sharp corners to improve flow. Front and rear press-in oil-galley plugs are removed, and their holes are drilled and tapped for screw-in pipe plugs to ensure the integrity of galley seals.

The factory cylinder-bore diameter remains essentially untouched, save for a 0.002-inch honing to establish the surface pattern desired for the new ring package. The blocks are then align-bored, but not until certain engine accessories, including an oil pump and starter motor, are temporarily bolted on. This accounts for the small but significant distortion of the block caused by torquing these accessories in place. The idea is to make the main bore utterly true in "as-installed" conditions, whereas the factory, for reasons of cost effectiveness, simply aligns the crank bore with only the main caps attached.

Crankshaft

Livernois' stroker cranks are forged by Kellogg-the same source Ford turned to for the Cobra and GT 500. The stroke is 3.750 inches (stock: 3.5433), for a resulting displacement of about 298 ci or just under 4.9 liters. These are custom forgings to Livernois' specs, with a unique crank for each of the two available piston options. Mike Schropp, Livernois' supervisor of engine development, says: "We gave Kellogg specs for different counterweight designs, with thicknesses and bobweight changes that work better with the entire package, versus just taking an off-the-shelf crank and trying to make the rod and piston work around it." In other words, compromises in the reciprocating hardware were avoided by going to the trouble of having new crank profiles created.

...which is why Livernois invests much hand-labor time in smoothing and radiusing these edges, as can be seen here. This rounding of sharp edges is performed not just inside the crankcase area, but everywhere on the block: top, bottom, front, and rear. Notice also that the factory main-cap bolts are abandoned in favor of ARP studs.

Because these are aluminum blocks with iron liners, no attempt is made to additionally increase displacement by boring the cylinders. A honing to provide the desired bore surface for the Livernois ring package enlarges the jugs by a mere 0.002 inch (to 3.554).

With bobweight profiles and dimensions forged to Livernois' specification by Kellogg, the 3.750-inch-stroke forged cranks provide 298 ci. While it no doubt would have been cheaper to utilize an off-the-shelf stroker crank, Livernois obviously felt it worth the expenditure to customize the crank around what it feels are the best combinations of rod and piston.