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Ford Mustang Pro Bullet Short Block Engine - Mods For The Masses
D.S.S. Expands Its 4.6 Short-Block Lineup With Strong, Affordable Offerings For Street And Track
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.
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.
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."
Tom says another way of looking at this quality issue is, "Cobra engines [the '03 version] have forged aftermarket rods in them. That tells you what you need to know if Ford is writing a check to another company... and this is with a 6-psi blower."
Bad as their reputation is, the connecting rods can be addressed with better bolts in the stock rod for naturally aspirated engines; power adders are best handled with a forged aftermarket rod.
Third on the must-improve list is the oiling. There are no worries as far as the oil galleys are concerned, but the combination of high rpm and parsimonious oil-pan capacities means an enthusiastically driven, modular V-8 will pump most of its oil to somewhere far from the oil-pump pickup. Spun rod bearings are the result.
Modular engines also use powdered-metal oil-pump gears in their gerotor oil pumps. We've heard of these gears breaking, but Tom says he's not had that problem. In his experience, the issue is simply a lack of oil capacity and flow volume at elevated engine speeds. This is rarely an issue, with brief outbursts in First and Second gear, but any modular revving to 6,800 rpm should have more oil-pump and pan capacity. It's simple physics driven by rpm, according to Tom. "If 302s went this high, they'd need [a pan and pump] too."
D.S.S. offers Canton 7-quart oil pans in either drag- or road-race configuration, along with Ford Racing Performance Parts oil pumps to address modular oiling. They also have a windage tray, which helps at higher rpm for those constantly revving their 4.6s.
The Pro Bullet Short-Block
As Tom puts it, D.S.S. has applied the same technology to its 4.6 Bullet short-blocks as it did to its popular 306 Bullet short-blocks. This has resulted in a notably more robust "stock" short-block at affordable prices-one cured of the modular weaknesses mentioned earlier. D.S.S. hopes these newly low prices will reduce the apprehension many have felt about working with the modular engine family.
D.S.S. Pro Bullet short-blocks are available in four varieties:
|4.6 Romeo Mod||$1,799.95|
|4.6 Windsor Mod||$2,199.95|
|4.6 Windsor Pro Mod||$2,999.95|
|4.6 Windsor Super Mod||$3,999.95|
These prices include the basic short-block, which is the block, crankshaft, connecting rods, pistons, pins, and rings. The oil pump, pan, front cover, water pump, flywheel, and windage tray are not included.
The headlining Windsor Super Mod has been available for some time, but the other short-blocks are new offerings. All are outright purchases; there is no core charge on any of these engines in their Two-Valve, iron-block GT applications. We're not covering the aluminum Cobra versions in this article, but they exist and are priced nearly the same, but they require the core short-block to be returned to D.S.S.
Note also the use of Romeo and Windsor names. This differentiates the block style, which differs in the way the main caps are crossbolted. D.S.S. says the Windsor block's peg and slot system is a little better than the Romeo's all-bolt version, and that accounts for some of the price jump from a Romeo to a Windsor.
Perhaps most exciting due to its wide application and reasonable pricing is the $1,799 Romeo Mod. D.S.S. builds these using seasoned-core Romeo blocks-that's a fancy way of saying a used 4.6 Mustang GT block that has taken its final thermal set. Likewise, a used crankshaft is prepped and balanced "to race specs," which is plus or minus 1 gram. The connecting rods are stockers fitted with high-strength SPS bolts, the pistons are forged, the rings are moly, and the tri-metal bearings are from Federal-Mogul. This short-block is aimed at the replacement and street-performance market where it will give reliable service in naturally aspirated form up to 7,000 rpm. The Romeo Mod may not have the sex appeal of its more extensively prepped siblings, but it's all the foundation many street-driven GT engines need. Given the low price and freedom from piston or rod breakage in less-than-power-adder service, this combination ought to prove highly popular.
For those ready to step up $400, there's the Windsor Mod. What it adds is a new Windsor block with the peg and slot main-bearing crossbolt fea-ture. D.S.S. buys these service blocks new from Ford, then machines them as necessary to arrive at perfectly flat decks; chamfered holes; and other basic, prepped block features.
To match the stronger block, a new crankshaft is used in the Windsor Mod and higher short-blocks. It is balanced to better-than-new Ford, or race specs. The rods are factory units with SPS bolts, and the forged pistons, rings, and bearings follow the Romeo Pro Bullet practice as well. The result is plenty of engine for the drive-it-like-you-hate-it, naturally aspirated crowd.
Forced induction means the stock connecting rods cannot be used, and for that sort of work, D.S.S. will step you up $800 to the $2,995 Windsor Pro Mod short-block. It too uses a new Ford Windsor service block, along with a new forged eight-bolt Cobra crankshaft and beefy D.S.S. 4340 H-beam connecting rods with ARP 2000 bolts, as detailed in the photos and captions. Furthermore, ARP main bearing studs are substituted for the stock main bolts, and the bearing package is stepped up to harder-shelled, severe-duty units. This engine will take care of all streetable boost and nitrous levels and just about any track-only tune-up as well.
Finally, D.S.S. offers the all-singing, all-dancing $3,999 Windsor Super Mod short-block as the ultimate expression of what the stock-block modular engine can take. As with the Windsor Pro Mod just described, this is an all-forged assembly with studs, heavy-duty bearings, and all the rest. What the extra $1,000 buys is a slew of D.S.S.' blueprinting trickery that's worth 30-40 hp.
As this edge-on view of the H-beam (left) and stock rod (right) shows, shape and visual mass don't suggest why the stock connecting rods are weak. The concern is how they are made-the powdered metal process. It's inexpensive and easy for Ford to build, but it yields a marginal-strength connecting rod. Run with forced induction and the stock rods often fail in midbeam!
Another issue with Ford's modular connecting rods is the cracked-cap design. This closeup of the parting line between rod and rod cap shows the design's characteristic uneven edge. This edge makes the rod unrebuildable in the conventional sense. Standard overhaul practice is to bore the rod's big end and use oversize bearings, but that is not acceptable for performance work. It's typically better to simply toss the rod and start over with something stronger. D.S.S. has found 400 hp as the limit for the stock rod and good bolts. Above that, an aftermarket rod is a must.
Hypereutectic pistons are the modular's number-one weakness. D.S.S. uses only these stout forged replacements with one of two dishes-10 cc or 18 cc-for the GT engine. Juggling the piston dish and cylinder heads (the dividing line is 1999) gives a workable range of compression ratios of typically 9.2:1, 9.8:1, and 10.8:1. Pre-'99 modulars used the 10cc dish; substituting later heads with that shallow dish gives the 10.8:1 compression, which is great for naturally aspirated engines. Forced induction engines need the 18cc dish, which can drop to 8.4:1.
What we have here are the so-called "Romeo" main bearing caps. The Windsor cap uses the barrel-like devices on the side bolts. D.S.S. says these allow more preloading of the side-bolt fasteners, and thus a bit more block and main-bearing strength.
Naturally, D.S.S. has a way to get even more strength out of the modular bottom end-its $299 MSS, or Main Support System. The MSS is a 31/44-inch-thick, 6061 T6 aluminum main stud girdle. The idea, according to D.S.S., is to dampen harmonic vibrations in the block and caps to prolong block, bearing, and especially crankshaft life (modular blocks aren't as fragile as 302s, but the cranks benefit from all the stability they can get). The MSS also allows fitment of D.S.S.' $109 windage tray (not pictured), which really helps keep the oil from roping around the crank at high, 4.6-rpm levels. That frees up horsepower and lessens oil aeration.
Machine work is where D.S.S. calls home. Here a modular block receives a 0.015-inch boring perpendicular to its already squared decks. Ultimately this will be a 0.020-inch overbored Super Pro Mod block; the final 0.005 inch of cylinder wall material will be honed out. For the Super Pro Mod short-blocks, D.S.S. uses standard 0.020-inch and 0.030-inch overbores in modular blocks. Romeo engines receive a 0.020-inch cleanup pass, the Pro mod and Windsor Pro Mod use standard bores because they are built using new blocks, and the high-zoot Super Mod engines are 0.020-0.030 inch overbored depending on the desired result. Exactly what bore size to use on such engines depends on the valve package and other tuning parameters, says D.S.S. The company's recently introduced line of forged 4.6 and 5.4 pistons has eliminated piston availa-bility as a major factor in boring decisions.
D.S.S. can really lay into its bag of machining tricks on its Super Pro Mod short-block. One of these is achieving the best-possible ring seal via cylinder honing. Derived from its Pro Stock drag experience where increasing vacuum on the intake stroke is key, D.S.S.' honing specifications require a three-step process. All honing is done with aluminum torque plates, submicron-filtered honing oil, fresh deglazed stones, and plenty of experience. Three different grits and three dif-ferent honing speeds are used. If all this sounds a bit over the top, D.S.S. simply replies that it works.
Machining the cylinder block decks parallel to the main bearing bores and equidistant from the crank centerline is the first step of squaring a block and is one of D.S.S.' Super Pro Mod blueprinting techniques. D.S.S. uses a diamond-impregnated cutter called a CBN tool bit along with attention to the feed rates and speeds to assure the desired finish. The idea is to get just the right roughness on the deck to work with the head gasket for maximum gasket retention but minimum-depth leak paths.
As expected, all D.S.S. short-blocks are carefully inspected at assembly time to ensure proper functioning and engine longevity. Here the oil clearance is being measured by finding the diameter of the main bearing bore and subtracting the crankshaft journal diameter from it.
All D.S.S. 4.6 short-blocks are electronically balanced to racing tolerances of plus or minus 1 gram. Unlike 5.0s, 4.6s are neutral-balanced, meaning there is no counterweight cast into the flywheel or balancer. This makes swapping dampers and flywheels simple, not to mention providing a more stable crankshaft at high rpm.