Horse Sense:
After talking to D.S.S., we realized we've been running our open-track project car with the pin pulled on the grenade. After all, if the rpm drops below 5,000 or so, we downshift, and the engine has a totally stock bottom end. D.S.S. says road-racing 4.6s die horrible deaths the instant the oil level drops below 5 quarts, and the right thing to do is add a 7-quart oil pan and a high-volume pump.
Pushrods are not going the way of the flathead, but a sign of the times changing is the lowering prices on modular engine bits. Until recently a fiscal quagmire, the modular V-8 replacement and performance market is picking up rpm and apparently some economies of scale. Key examples are the three new Pro Bullet 4.6 GT short-blocks from D.S.S. This Chicago-based engine shop has been turning out the racy Super Pro Bullet at nearly $4,000 for some time, but it has now introduced $1,800-$3,000 Pro Bullet short-blocks for the rest of us.
As with the Super Pro Mod, the Pro Mod 4.6 short-blocks address the modular engine's limp-wristed piston and connecting-rod bolt issues, but they save on some of the finer machining points or unnecessary-at-this-level new parts to keep costs down. With a wide range of compression ratios available, the Pro Mod 4.6 short-blocks are ready to handle all the usual forced-induction systems, as well as spirited, naturally aspirated rpm for the street and street/strip crowd.
But before we dive into the D.S.S. engine program, a few words about the way Ford builds modulars will help.
Price breakthrough is the...
Price breakthrough is the big news with D.S.S.' newest additions to its 4.6 short-block lineup. The company's newest entry-level 4.6 Romeo Mod short-block is only $1,799, yet it offers forged pistons and good rod bolts-enough to handle all the fun street power the majority of late-model owners are seeking. And if it's more you want, D.S.S. now has three more fully prepped short-blocks for seriously supercharged power.
Romeos And Windsors
If Ford would only build one version of an engine... But then, it wouldn't be Ford, would it? We're not talking about the well-known differences between the Cobra 4.6 engine-with its aluminum block, eight-bolt flywheel, and Four-Valve head-and the GT's iron block, six-bolt crankshaft flange and SOHC Two-Valve head. We're referring to the subtle differences in front cover bolt patterns and crankshaft availability among what we all thought were identical 4.6 Two-Valve GT engines.
Ford builds modular engines in two plants-Romeo, Michigan (where modular V-8 production began in 1991), and Windsor, Ontario, Canada. Apparently there have been small differences in the 4.6 engines depending on which plant built them, so engine shops such as D.S.S. have come to refer to 4.6 Two-Valve engines as either "Romeos" or "Windsors." Precisely what these differences are, and what engines they'll show up on, has evaded iron-clad explanation so far (even from the best-placed Ford sources), but in D.S.S.' experience, there are such things as eight-bolt crankshafts in 4.6 Two-Valve engines.
The Stuff That Breaks
Modular Two-Valve engines used in the Mustang GT have three known weak points. As Tom Naegele of D.S.S. points out, what "makes our phone ring" are broken pistons. Left stock, the lightly built hypereutectic Ford GT piston-and the Cobra piston for that matter-are OK. But the first time any meaningful power increase is realized, or detonation breaks loose, the pistons fail. According to Tom, the pistons break in the ring land, between the top and second ring; or occasionally the top of the piston breaks off the upper ring land.
"Usually it won't burn a big hole in the top; it'll just break the ring land," Tom says. Then that cylinder will show 30-40 psi during a compression test. Typically the engine will still run, but poorly.
Ford's modular engine crankshafts...
Ford's modular engine crankshafts are well-engineered designs that D.S.S. has found capable of supporting hot-rod power levels. Three cranks are available from Ford: the forged eight-bolt Cobra and the cast eight-bolt and cast six-bolt GT cranks. D.S.S. uses the Cobra crank in its up-market Pro Mod and Super Pro Mod short-blocks, and it uses the cast eight-bolt in the Windsor Mod. The Romeo Mod, as shown here, employs a cast six-bolt crank.
Don't think these failures are exclusive to goofed-up or over-eager blower and nitrous applications either. Modular pistons are weak enough to commonly fail in not-rodded naturally aspirated applications too. It all shows just how close to the limit modern computer modeling allows Ford to build its stuff these days.
Obviously, the cure for these weak pistons is a forging, so D.S.S. has developed a line of such pistons for its 4.6 engines.
The second modular failure point is the connecting rod and rod-bolt assembly. This failure is a power-adder phenomena Tom noted, so don't expect it with natural aspiration and the stock rev limit. The simply too-weak rod bolts often snap with rpm. Under even moderate forced-induction boost, the spindly, powdered-metal connecting rods fail in midbeam. Clearly, these are signs of weak connecting rods, enough so that Ford engineers honest enough to speak their minds have confided the stock modular GT connecting rods "suck."