Dale Amy
March 1, 2008
Take a look at a Boss block for the modular crowd. With 5.0 liters of displacement while still 4.6-liter deck height, FRPP's new cast-iron Boss 5.0 block (PN M-6010-BOSS50) may be just the ticket for mega-power street and drag 'Stangs. Suggested retail is $2,050.

Horse Sense: A non-Siamese block has water passages in between the cylinder bores. The more rigid Siamese block has nothing but solid metal between the bores.

Lately, the midnight oil has been burning fiercely at Ford Racing Performance Parts, especially in the realm of crate motors and, more to the point, engine blocks. It seems just a short while ago ("It's Good to Be Boss," Jan. '07, p. 104), we were scoping out FRPP's ultra-stout Boss 302 pushrod block, and now we're taking our first look at its modular counterpart, the Boss 5.0.

Displacing-as you likely guessed-an even 5.0 liters, this is much more than a bored 4.6-liter block. In fact, the Boss 5.0 is a new casting that incorporates many strength, cooling, and durability improvements compared to its factory modular counterpart. On a historical side note, it's also among the final series of engine blocks to be poured in FoMoCo's famous Cleve-land casting plant, scheduled to close its doors sometime around the end of 2007.

Despite its eight bigger holes-3.700 inches in diameter versus a 4.6's 3.552-inch bore dimension-the Boss packs about 10 pounds more muscle than the OEM iron casting, most of which can be found in the main web/bulkhead areas. Stiffening this area surrounding and supporting the crankshaft is a huge ingredient in the recipe required to contain the ludicrous amounts of power we're producing these days. That explains the rationale for casting the Boss 5.0 in iron instead of lighter aluminum.

Getting to some cooling detail, note that on the Boss block (below), a cooling passage routes around the front-most head bolt on the passenger side. Contrast this to the passage configuration on the stock block shown here.

Road racers may shun this block in favor of aluminum to get the lighter nose weight-and that's OK because they're normally not running more than 500 hp. As power levels increase beyond that, aluminum blocks have a tendency to develop more flexibility or "walk" in the bottom end, which, among other things, adversely affects piston ring seal. When the rings aren't sealing, power is leaking away, as is durability. "At as low as 500 hp, you'll make more power with an iron-block than an aluminum block because the rings will seal and last longer," says FRPP's Jesse Kershaw. One obvious application we see for the Boss 5.0 is on '03-'04 Terminators, many of which now routinely pound out 700 or more high-boost, rear-wheel ponies. As those bottom ends wear-and they will-the Boss is the ideal replacement, one that also brings along the obvious benefit of additional displacement at a stock 4.6-liter deck height.

Still on the topic of crankcase, the Boss 5.0 main caps are machined so they can easily be drilled for an additional pair of bolts, but it seems the power threshold necessary to require such additional clamping measures is high. How much power can this block handle as issued with its two-bolt caps and cross-bolts? "I think we're talking 1,000-1,100 or more horsepower," Jesse says. "The Sutton drag car is currently making more than 1,000 hp, and they've been running this block all season long. They actually set the EFI Renegade record for e.t. and mph in the NMRA without any issue, and that's with the two-bolt mains." So yes, this is a stout chunk of iron. "For a street car, I think this is the last block you'll ever have to buy."

Stock 4.6-liter main caps, similar to the one on the right, utilize dowel locating pins to speed assembly. Don't confuse these with an extra pair of cap bolts. The Boss main cap on the left is a two-bolt setup that's also cross-bolted like a stock 4.6. It also has machined flats outboard of the main bolts that can easily be drilled should there be a need for four-bolt caps. The folks at Sutton High Performance don't bother with the four-bolt conversion on their EFI Renegade S197.

Aside from its brawn, the Boss 5.0 casting also addresses a slight cooling imbalance evident between the left and right cylinder banks on factory 4.6-liter blocks. Due to coolant routing, a factory modular has better cooling of its driver-side bank than the passenger side. Under extreme conditions, this can impact head-gasket life on the passenger-side bank. The Boss features revised passages that provide a 50/50 coolant split between the banks. Speaking of which, in order to achieve the 3.700-inch bore, the Boss 5.0 is of Siamese-bore design, eliminating the water jackets surrounding the cylinders.

While some might wonder about running Siamese bores on the street, Jesse says, "We've had one of these blocks in Mike Tymensky's street car for more than 30,000 miles, including a trip to Florida and back, so we have a high level of confidence in the block's street application."

FRPP's warehouse has a good supply of Boss 5.0 blocks ready to ship. Cleveland has cast about 1,500 of them, and they're being machined in batches by Roush Industries (see sidebar, The Boss Goes to Finishing School.) If we get a chance to use one for a block-swap tech project, we'll be sure to fill you in on how it does. In the meantime, we give you the details on how this new modular monster earns the honored Boss moniker.

With this clear identification, there is no mistaking a Boss 5.0 block. Yes, it's confusing: FRPP's part number for the block is M-6010-BOSS50, whereas the "6015" on the block indicates a casting or engineering number. This is typical of Ford's numbering protocol.

The Sutton High Performance crew out of Illinois ran a prototype Boss 5.0 iron-block in its e.t. and mph record-setting EFI Renegade S197 during the '07 NMRA season. Previously, they had campaigned both wet- and dry-sleeved 3.700-bore aluminum blocks. Some good reasons for the switch, according to Sutton engine-builder Jerry VanDerLinde, include: "Two different times we actually broke the main webbing out of the aluminum block. No matter which sleeve system we used, they would egg-shape or distort under the power we gave them. We'd then lose compression and power."

But heads-up racers like low weight, right? "The iron-block is 60-70 pounds heavier, but it was more than worth the weight for how much durability we got out of it. The cylinders stayed round all year; the main webbing and the oil pressure were perfect. We've literally had to do no maintenance to the block this year, and we put about 1,240 hp to the crank."

And that's using the two-bolt main caps as issued with the block. Jerry, in fact, opines that this may in fact be stronger than drilling for a four-bolt setup, since that drilling would take structural material from the caps. "The revised cooling system has been a huge improvement to us as well," he says. "There has always been an issue with uneven cooling in the modular motor, and this block addresses that uneven cooling."

Jerry's summation: "If you want to make serious modular-motor power, you absolutely have to use this block."

When the trucks started leaving the Cleveland casting plant bearing palettes of Boss 5.0 blocks headed for FRPP, they made an interim stop at one of Roush Industries many Detroit-area facilities. Here, the as-cast lumps of painted iron are given all the critical machining necessary to turn them into functioning modular foundations. To the uninitiated (like me), this Roush machining line is amazingly automated, with a trio of five-axis Makino A81 machining stations doing all the finish work, served by a computer-commanded conveyor system that methodically moves the blocks from station to station. It's great for consistency, and no back-breaking manual lifting is required.

The main caps are received as clumps of cast iron. At a separate station, they're converted into fully finished, drilled, and tapped caps with precise tolerances. The caps are then bolted to the blocks before the final crank boring is completed.

While we would like to have shown more meaningful photos of this facility, a lot of the procedures are proprietary and some of the ongoing projects are secret, so we were asked to limit ourselves to the task at hand.