Stolen Goods hasn't seen the road for some time. That's about to change.
Stolen Goods, our '93 Cobra project has created quite a stir in the Mustang community. Our almost unreal find of an SVT machine had a mere 1,300 miles on the clock, but the drivetrain was missing and we had to rebuild it and give it a new life. In the past few months, we got the car off blocks, and it's rolling again. Now it's time to get the heart of the snake beating-and since late-model Cobra Mustangs were essentially factory hot rods, we went back to the factory to find a suitable powerplant.
A Cobra By Today's Standards
In bringing Stolen Goods back from hibernation, we wanted to achieve a performance level greater than that of the original '93 Cobra-or the R model, for that matter. When it comes to exceeding the factory engine output, that may be one of the easiest things to accomplish. Though the '93 Cobra and Cobra R powerplants were rated at a mild 235 hp, the same GT-40 components that SVT bolted on the engine were known to produce closer to 270 in independent tests. But even the latter mark is easily surpassed given the bountiful aftermarket of go-fast products.
If you look to 1995, the 351-powered Cobra R was still rated at only 300 hp. You have to move on to 2001 for more power, when the modular-powered Cobra R model's 5.4L, DOHC powerplant thumped out 385 hp and 385 lb-ft of torque. That's a stout number, but one we think Stolen Goods can eclipse, all while keeping the engine civilized and maintaining the broad torque curve 5.0L Mustangs are famous for.
From the beginning of this project, we never planned to do anything overly radical to our resident '93 Cobra, as we wanted a reliable and rock-solid platform to provide plenty of hours of high-performance fun without a lot of maintenance. Therefore we opted to go the naturally aspirated route with the engine. No blower belts to deal with, no trick fuel system needed, and no intercoolers or nitrous bottles to worry about, just raw horsepower and torque, all of the time. With that decision made, there were two ways to build the motor. We could design a high-revving 306, a stroked 302, or go with a big small-block Windsor.
To end up with a nice balance for open track, autocross, street, and strip driving, we set a goal of 400-425 flywheel horsepower. Another stipulation your author made was that Stolen Goods would have to make do with a 3.27, or at most, a 3.55 gear to keep the revs down on the highways. That pretty much ruled out the high-rev idea since the engine would spend far more time in the low and mid-rpm range. We also wanted to keep the stock hood, and while we've seen 351s fit under one, it usually came with great effort and mods to other items like the K-member to achieve this. So the Windsor was out.
Going with an 8.2-inch deck-height block would be the ideal choice, and since your author spends more time striving for deadlines than he does building engines, we turned to the Ford Racing Performance Parts catalog in search of an assembled short-block.
Ford Racing Performance Parts' new Boss block (PN M-6010-BOSS302) retails for $1,759 and f
Part number M-6009-C347 is a 347ci stroker short-block assembly that uses a Sportsman two-bolt main block along with forged pistons, connecting rods, and crankshaft. That seemed like a pretty good choice, and it might be for many of our readers. We contacted Jesse Kershaw of FRPP to get his opinion and talked with him about our engine's intended use. That's when he offered us one of FRPP's new Boss engine blocks.
The Boss is Back
The new Boss block (PN M-6010-BOSS302) was designed with input from Ford's NASCAR engineers and from information gained during Ford's involvement in the ASA racing series. The Boss is set to be the basis for all of FRPP's crate engines in the near future, and it will be available as a bare or assembled short-block as well. At the time we went to print, assembled block production was still in its infancy. In fact, we received one of the first 150 blocks produced.
Its major features include four-bolt splayed caps on the number 2, 3, and 4 main crankshaft journals, screw-in, O-ringed freeze plugs and oil galley plugs, 11/42-inch main cap and head bolts, and a diesel-grade, nodular-iron casting that can be bored and stroked out to 363 ci. It is 16 pounds lighter than the R302 block it replaces and retails about $240 cheaper at $1,759.
Since we're not professional engine builders, we contacted Tom Naegele at D.S.S. Racing in St. Charles, Illinois, about constructing our snake's short-block. D.S.S. had assembled the 331ci Super Bullet bottom end in our project ProCharged Pony a few years ago, and the engine has handled everything we've thrown at it, so we knew it would be up to the task of building Stolen Goods' powerplant.
Naegele's plans for the Boss block includes using D.S.S. Racing's brand-new horizontal machining center to perform its CNC Level 20 blueprinting, giving us a state-of-the-art hunk of iron to use as the basis of our buildup. He also gave us his take on FRPP's new offering and expounded on some of its features as well as what D.S.S. plans to do to the new hunk of iron.
The new Boss 302 block weighs about 32 pounds heavier than a Sportsman block, yet it's 16
Splayed main caps on journals 2, 3, and 4 will help keep the bottom end together under sev
The Boss 302 utilizes common OD cam bearings or conversion bearings for use with most off-
Screw-in freeze plugs and oil-galley plugs increase the strength of the block walls. These
Naegele's Take on the Legend Reborn
"For all practical purposes, FRPP's new Boss block is the R302 replacement," Naegele says. "Features include a four-bolt block similar to the R302 block. Main bolts are 351W 1/2-inch fasteners (R302 are 7/16), and in order to do this they had to move them outboard. This required FRPP to provide a new oil pump pickup due to space limitations. Keep in mind that there are no 302 blocks out there with 1/2-inch mains. We're going to install different main studs that are a little longer so that we can use the D.S.S. main support system.
"The head bolt holes are 1/2-inch pieces, like 351W and R302 blocks, but they're slightly deeper for better gasket retention and a lesser chance of ripping out threads. To utilize the extra length, you'll need different fasteners.
"The Boss' cylinders measure roughly 3.990 inches. The undersized bore needs to be finished bored and honed, just like the R block. The Boss' thick cylinders offer a comfortable 4.125-inch overbore capability-the R302 was stretched at 4.125 and often required sonic checking. It was more of a 4.100 piece.
"The new Boss block uses common outside diameter (OD) cam bearings or conversion bearings for use with most off-the-shelf cams. The R302 block was the first to come out with common OD bearings (Dart blocks use them also), and from a manufacturing standpoint, it's easier to bore the cam bearing holes all the same size. Stock cam journals, however, are all different sizes. Most cam companies sell common OD cams through special order, but FRPP came up with conversion bearings to facilitate the use of common off-the-shelf 302/351W grinds. The conversion bearings are a bit expensive, though the cost has come down some from when they first came out.
"Another feature that FRPP added to the Boss block is its improved front and rear lifter-galley oiling feeds. The R block just oils the lifter galley from the rear and can starve the front lifters of lubrication. The Boss went the way of the Dart block, as it feeds the front and rear lifter galleys. In blocks with only rear oil feeds, FRPP noticed scuffing of the front lifter bores in some endurance applications. For the average Mustang enthusiast, this is not much of a concern, but it does add performance and value to the package.
"In the lifter valley, the Boss has finish align-honed mains and lifter bores-R blocks must be align-honed, as the bores are small out of the box. The Boss' big lifter bosses allow machining for offset or bigger lifters.
"One feature the Boss block shares with early Boss blocks are screw-in freeze plugs and oil galley plugs. The R block has screw-in galley plugs for oil but press-in plugs for the water. Dart blocks use press-in freeze plugs as well, unless machined by the builder for the screw-in type pieces.
The R302 block has screw-in galley plugs for oil but press-in plugs for the water. Dart bl
"When you drop a stroker crankshaft in a stock 5.0 or R302 block, you need to machine the block for counter weight clearance, but FRPP has provided ample room with the Boss, and it has also done a nice job of cleaning up the crank case casting. Normally you could expect an hour to an hour-and-a-half of grinding on an R302 block to fit the crank.
"The Boss has a shorter cylinder length, which makes rod bolt clearancing of the cylinders obsolete, but it may limit the amount of stroke and compression height you can run. The bigger you go on stroke, the more the piston protrudes out of the bottom of the cylinder. The Boss cylinders are approximately 0.400-inch shorter in length than a stock or R block.
"The deck heights on the Boss are 0.010-inch tall and will need to be equalized and decked just like the R block. This is fairly common among aftermarket blocks. The Boss features siamesed cylinders, and when FRPP was designing the block, the people in the NASCAR and endurance racing arenas that they talked with said the siamese design could overheat the head gaskets, so FRPP provided the Boss block with siamese cross-over coolant bleed holes to help remove trapped steam from trouble areas.
"In order to make the new Boss readily accepted by early Mustang and Ford enthusiasts, FRPP included a boss and tapped hole for the clutch cross-shaft from early '60s/'70s cars. This wasn't present on either the R block or the A4, which put a lot of people out when it came to building good motors for old cars with manual transmissions.
"Unlike most of the competition, the Boss block has a provision for the use of the factory dipstick, rather than requiring one to purchase a special oil pan-mounted one.
"The three center main caps are four-bolt and, more importantly, splayed. Splayed caps help keep main-cap walk under control, as they tie the cap laterally on an angle, which secures the cap, minimizing the sliding on the parting surfaces. Front and rear are still two-bolt pieces. The D.S.S. main support system that we'll use in this build will keep them from walking, and it also allows the use of a full-length billet-aluminum multilevel scraper/windage tray. Aluminum deadens the harmonics that make main caps walk. It does need longer main fasteners, and the main support comes with all of the necessary ARP custom hardware.
"The Boss block's big-bore nature is a win/win situation. While you can take it out to 363 ci (basically a 347 with a 4.125 bore size), this offers challenges when it comes to street-car longevity. The best engine combination is a result of the best compromise of all aspects of the engine, including rod ratio (rod length divided by stroke) and piston-ring placement. Engines that have poor rod ratios and use short piston designs tend to have the pistons rock in the bores, which causes excessive wear and added friction at a higher rpm. For racers, seasonal maintenance (rings and bearings) is not an issue, but it's not something someone with a street car is going to want to do. The short pistons also usually end up having the wristpins in the oil ring, and that can lead to oil control trouble if the proper ring package is not used.
FRPP added a boss and tapped hole for the clutch cross-shaft from early '60s/'70s cars. Th
"This is why many engine builders recommend the 331ci stroker assembly for street cars. The common 331 comes from a 3.250-inch stroke, a 4.030-inch bore size, and a 5.315-inch connecting rod. This combination results in a 1.250-inch compression height, which provides proper spacing for the piston rings. It is far superior than the 1.090-inch height found in common 347ci motors. The better rod ratio and taller piston results in better ring placement and spacing. Subsequently the piston rocks less in the bore and promotes greater ring-and-piston life. The taller piston prevents the wristpin from intersecting the oil ring and a better 1.63 rod ratio is achieved.
"The common 347ci engine, with its 3.400 stroke, 5.4-inch rod, 4.030 bore, and 1.090 compression height (the distance from the wristpin center to the top of the piston) makes for the same inefficient piston/ring/rod ratio design and results in a 1.58 rod ratio just like the 363.
"With the Boss block's big-bore capability, we can obtain the 347 ci along with a 1.63 rod ratio. Using a 3.250-inch stroke, a 5.315-inch connect-ing rod, and a 4.125-inch piston, we arrive at 347 ci with the 1.63 rod ratio-a 347 done the right way.
Having consulted with engineers from its NASCAR teams, FRPP opted for siamese bores and pr
Cylinder-head bolt holes are 1/2-inch diameter and extra deep, which should provide plenty
One feature that FRPP added to the Boss block is its improved front and rear lifter-galley
The Boss has finish align-honed lifter bores-R blocks must be align-honed, as the bores ar
D.S.S. Block Blueprinting
"People often toss around the term blueprinting, but few understand it," Naegele continues. "Our new horizontal machining center was purchased because of the need and desire to CNC blueprint a block more accurately than was previously possible. Blueprinting is remachining the critical dimensions and geometry to correct it based on factory specs.
"The crankshaft main centerline is pretty much ground zero, and cylinders should be 90 degrees apart and equidistant from the crank and camshaft centerlines-each bank should be 45 degrees from the centerline. Another important part of blueprinting is ensuring the deck surfaces are perpendicular to the cylinder bore, which should be directly located over the crankshaft and parallel to the 90-degree centerline.
"From the factory, OEMs just need blocks to have similar compression between cylinders. The closer you get to a perfectly machined product, the better it will run and the longer it will last. Because of the slack in factory tolerances, compression from bank to bank will be different. D.S.S. has seen a minimum of 0.005 inch difference, and as bad as 0.025. The OEM engines just need to run and last through the warranty period; however, setting deck height and ensuring it is equidistant from the crank centerline is extremely important to get the most out of your motor.
"Many places use the Sunnen CV616 or CK10, as they're the industry standards and are designed to hone 0.030 over without boring the cylinder. If you do not bore the cylinder and then hone it, you are not correcting the cylinder; you're just averaging the wear and not straightening out the cylinder. You are also moving the cylinder over in the direction of wear. It'll run fine, but that's the difference between average and truly blueprinted.
"Honing cylinders with torque plates is also an important part of blueprinting. A lot of CNC equipment fixtures off the oil-pan rail, which is how Ford machines its blocks, but it's not the main bore and not a good reference point. The fixture that D.S.S. manufactured to do its CNC work is the only one of its kind, and it allows us to blueprint off of the mains instead of the oil-pan rail.
"Oddly enough most aftermarket automotive CNC and conventional machines mimic the same OEM set up off of the oil pan rail. Also, most bore off of the OEM cylinder and true the decks using a bubble level. For Joe Average, that's OK, but it should be perpendicular. Most boring machines go off of the deck surface, so if it isn't perpen-dicular, then cylinder bores won't be exactly 90 degrees from the crank.
Since the new Boss 302 block uses larger 1/2-inch main-cap bolts, a different oil-pump pic
"All of Level 10 and 20 CNC blocks are blueprinted off of the mains, something D.S.S. has been doing for the last five years. We invested heavily in this method, and though it's more profitable to do it the old-fashioned way, this is the right way to do it. Holding a block rigid enough to machine within a tenth or two vertically off of the main centerline is not easy (or cheap), but the countless hours of CAD design and machining paid off. This is by far the most accurate, rigid block fixture and machine we have ever seen.
"Why is that so important? Here's an example. Camshafts are ground with lobes 90 degrees apart, but what if your block was 89 or 91 degrees? What if your compression ratio was three or four tenths of a point different side to side or even front to back? Of course it will run, but it won't be optimized, and in a high-performance application, getting the most from what you have is of the utmost importance. Our Level 20 CNC blueprinting on the Boss block also includes the required lifter boss relieving so the factor lifter retaining hardware can be used.
"Twenty-five years of racing and honing thousands of blocks has taught us plenty about the importance of ring seal and cylinder prep. The three-step honing process we developed is done on all of our Level 10 and 20 blocks. These steps are pivotal to our customers' success."
Large and In Charge
Thanks to FRPP and D.S.S. Racing, Stolen Goods is in good hands. Our new Boss 347 should give us plenty of go-fast grunt to make mincemeat of the '93 R model, among others. Next month, we plan to have the short-block complete and detail the rotating assembly, along with some of the long-block parts like the heads, cam, and intake manifold. See you then.
This graphic shows the main centerline and the engine's 90-degree V configuration. It's im
D.S.S. Racing's new three-axis horizontal machining center is a state-of-the-art piece of
Here is our Boss 302 block mounted in the D.S.S. fixture. As you can see from the picture,
We'll take the rough 3.99-inch cylinders out to a finished 4.125 bore size. This, combined
The new Boss 302 block is getting its lifter valley machined for the factory lifter retain