Mustang Three-Valve Stroker - Supersize It
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.
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.
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.
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.
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.
Both Livernois stroker packages share a custom Manley H-beam rod in 5.850-inch length, but for those seeking the absolute ultimate in strength-and price-a billet I-beam rod is optional. According to Mike, Ford's factory rod is the weakest link in an S197 modular's OEM bottom end. Unless extreme detonation is the culprit, the factory rod will almost invariably fail before a piston. Of course, once a rod lets go, short-block disaster soon follows.
Once again, these Manley rods aren't off-the-shelf pieces. For instance, at the piston-pin end, the rods are narrower than usual because the Mahle tool-steel piston pin is shorter than most but beefier in wall thickness. The narrower rod end allows the piston's pin bosses to come further inboard for greater pin support and overall rigidity.
We mentioned that Livernois offers two Three-Valve stroker short-blocks, with the principal difference between them being their piston designs. These pistons are likely the most research-intensive components in the whole project and are made by Mahle to Livernois' specs. They also benefit from constant updates and improvements filtering down from Mahle's world-wide participation in motorsports. All are phosphate-coated to prevent galling or microwelding in the pin-bore and ring-groove areas. All wear Mahle's patented Grafal skirt coating, which acts as a cushion against piston rock-over and also provides a tighter piston/cylinder fit for quieter operation. The most apparent difference between the two levels of piston is in the depth of the top ring land.
A (Mahle) ring package itself is common to both piston designs, though the customer has the option of switching out the plasma/moly top ring in favor of stainless steel, while the second ring can be changed to a race-oriented, hooked-groove (Napier) style. The entire ring package is designed for maximum oil control, as oil getting through into the combustion chamber is a prime cause of detonation.
When it comes to dish volume for compression ratio, Livernois offers several options. While it's accepted that forced induction demands a lower static compression than natural aspiration, Livernois also draws a distinction between the various types of forced induction. The biggest dish/lowest compression is reserved for positive-displacement superchargers and turbos, which develop boost almost off-idle. However, because centrifugal blowers don't really pitch in until higher up on the tach, Livernois suggests a higher-compression piston to generate power and efficiency down low. The specific compression ratio is usually determined after consultation with the customer on his specific combo/application.
As of this writing, the standard Livernois Three-Valve stroker short-block is priced at $3,995, while the extreme-boost version goes for $4,195 (plus a $1,000 core charge in the absence of a customer-supplied block). While there are probably less expensive modular strokers available, Mike explains why the Livernois versions are worth their asking prices: "First off is the amount of custom labor that goes into them as far as block prep work, machine-prep time, final assembly practices, and quality control procedures. We use a lot of higher-end race-engine building procedures that are adapted down to a more general build, which simply takes us a lot more time. Also, we don't just purchase an off-the-shelf rotating assembly, stick it in a block and call it a stroker short-block. We go through an almost OEM-level of testing to come up with the parts that go in our short-blocks. We've purchased off-the-shelf parts and tested them, and they've failed at different power levels for different reasons, so we went about designing our own parts with different manufacturers."
We at 5.0&SF have little doubt that Livernois is crafting some stout strokers, and we know the welcome bump in displacement will certainly swell the modular power curve-in particular, adding some much needed torque at lower revs. At the moment, we can't tell you exactly how much additional horsepower and torque they'll produce over a stock 4.6. Like anything else, the block-to-block power delta will depend upon the overall combination.
That said, one of the high-boost short-blocks being assembled during our visit is destined to end up under the hood of Livernois' in-house Whipple-blown '07 GT. We plan to feature that car in an upcoming issue, and we'll include Livernois' dyno documentation of all the stuff the company is installing on that project, short-block included. When we know, you'll know.
If a short-block's good, then a long-block's better, right? If you're planning a whopping power adder, you may as well bolt on some heads capable of keeping up with the flow. Livernois has the S197 market covered with three stages of CNC-machined Three-Valve heads. We discussed the company's initial Three-Valve head offering in great detail a while back ("Triple Threat," May '06, p. 210), but the range has expanded since then to three stages:
Stage 1 uses the same port/chamber CNC program we outlined in our earlier article, but it now retains stock valves (and valve job), springs, and guides. These or Stage 2 are great for normally aspirated or relatively low-boost applications.
Stage 2 excavates larger ports via its revised CNC program and brings along a valve job with revised angles for better flow. Stock valves are utilized, though reground to match the valve seats, and are teamed with upgraded springs and bronze guides.
Stage 3 is treated to the CNC program with an even larger port volume. It dispenses with the stock valves for stainless steel intake valves and high-temp Inconel versions on the exhaust side, both 1mm larger than factory (the valve job is modified accordingly). These are the breathers you want for those megaboost applications.

Photo Gallery: Mustang Three-Valve Stroker - High-Power 'Stang Engine - 5.0 Mustang & Super Fords Magazine



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