5.0 Mustang & Super FordsHow To Engine
DOHC Ford Modular Engine - What a (Big) Bore
How Big And Wild Can You Go With Today's Modular Technology?
If you're thinking that a big-bore modular Ford small-block is just what you want for your high-performance Mustang, make sure you hook up with a machine shop outfitted with the right equipment to handle the specific hardware this engine demands. Check out the modular specialists in this magazine and talk to folks who have completed similar projects.
Everywhere you look, the modular Mustang takeover is in full swing. Ford is offering the hot-test Mustangs ever with the GT, the Mach 1, and the Cobra; our magazine is full of ads offering cool parts for your new Mod-'Stang; and modular-powered Mustangs are legitimate threats in heads-up Ford drag racing.
It would seem that everything is perfect in the modular performance arena. But the bulk of parts sold to modular racers are basic ones-shifters, cold-air kits, suspension components, and bolt-on power adders. Hard-core fanatics of the modular Ford are longing for the aftermarket to develop proven stroker kits, ported heads and intake packages, and-perhaps most of all-reliable valvetrain and camshaft gear that can take the ravages of big modular power without puking all over the starting line.
Andrew Cluck of Columbus, Ohio, approached us with an interesting story idea. He wanted to share his trials and tribulations of designing and building a big-bore modular DOHC engine to help educate anyone else facing the same daunting task. A reformed street racer with 13 speeding tickets on his résumé, Andy knows a thing or 13 about fast cars. His bolt-on '98 Cobra had run 12.30s at more than 110 mph with the stock exhaust manifolds and no computer tuning, so he was off to a good start. Having driven 450-rwhp cars before, he set that as his goal for a wild-street-car combination.
Not wanting to go the blower route or rely on nitrous during those "special" moments, Andy decided that a naturally aspirated version of the Four-Valve motor that the car came with could be just what he needed to scratch that itch. Once he began looking around, he realized that modular bore-and-stroker kits were coming onto the market, so he thought he'd add that into the project as well. When all the details were listed on paper, Andy had planned out a 5.3 naturally aspirated combination that would reliably crank out 450 rwhp on pump gas, with the strength to take a 200hp shot of spray if the opportunity arose. With the right suspension and supporting gear in place, the car would have the potential to run in the nine-second zone while still having the quality reliability of a commuter car. But where to begin?
When you're talking DOHC modular Ford small-blocks, you begin with those massive cylinder heads that are just dripping with high-rpm potential. Andy was nice enough to share his personal notes on all the different versions of these cylinder heads that are available to the hot rodder.
B Heads ('93-'97 Lincoln Mark VIII, pre-'99 Lincoln Continental, '96-'98 Cobra): These swirl-port castings were the first production Ford DOHC heads. With generously sized twin intake ports, square primary and round secondary, these heads do their best work after 8,000 rpm. Their best use seems to be on power-adder motors. It's probably not the way to go for a streetable, naturally aspirated motor.
C Heads ('99-'01 Cobra, '99 Lincoln Continental): Also known as tumble-ports, these heads feature a single-intake port with a smaller cross-sectional area that boosts airflow velocity. This allows for substantial increases in midrange torque production and superior horsepower production (compared to B heads) under 8,000 rpm. They also feature the same small exhaust ports as B and Navigator heads.
Navigator Heads ('99-present): These 5.4 DOHC heads feature essentially the same intake port design as C heads, but they have a much larger intake port volume than 4.6 castings. Despite the fact they have the same small exhaust port as B/C heads, the extra intake port volume could be beneficial in helping fill a motor of greater displacement. Expect slightly better midrange torque and sub-8,000-rpm horsepower production than even C heads. The larger intake port size, however, leaves a sparse selection of intakes from which to choose.
FR500 Heads (Ford Racing Performance Parts): These high-flow after-market heads feature a modified C head intake port (raised roof) capable of flowing 330-cfm-plus (at 0.500 inch lift) on the intake side (with a Stage II port). But, with the same small standard exhaust port as most other DOHC heads, you will still have to remove a decent amount of material from the exhaust ports. Port entrance shape/size remains identical to C heads, so finding an intake isn't hard. The heads are capable of producing power beyond 8,000 rpm, unlike earlier versions of the tumble-port castings.
'03 DOHC Heads ('03 Aviator, Marauder, Cobra, Mach 1, Australian Boss 260/290): Featuring the same ultra-high-flowing intake port as FR500 heads, but combining it with a newly designed larger and more rectangular exhaust port, these may be the best all-around DOHC Ford heads yet. For those with a forced-induction street motor, they are without question the best heads available. As with the FR500s, they should produce great power even beyond 8,000 rpm, regardless of application.
Andy had this to say about his final choice of cylinder head. "The decision to use Navigator heads for the 5.3 featured in this story was a fairly simple one. The combination of a tumble-port intake design and slightly more intake port volume than a regular C head seemed like a winning combination for an 8,000-rpm naturally aspirated motor of larger-than-normal dimensions. If I could do it over, I would use '03 DOHC heads without question. The reason is that there is a much broader selection of intakes to use with the '03 DOHC heads than with Navigator (5.4) heads on a 4.6 block. The larger 5.4 heads don't leave a lot of room in the valley for the lower portion of an intake to sit, essentially requiring the use of either an ultrashort runner (highly modified) '99-'01 Cobra intake or a custom sheetmetal unit."
For a $1,500 investment (plus an existing aluminum modular block), you can turn any 4.6 modular block rebuild into a big-bore 5.0. John and Mike Tymensky of Modular Performance can bore and resleeve any Ford modular aluminum block to big-bore specs (3.55-inch bore to 3.70-inch). Downtime is typically only three to four weeks. Besides netting an additional 24 ci, the major advantage of going big bore is that the valves unshroud themselves from the heads and cylinder walls-allowing for increased airflow at all lifts. More specifically, increasing the bore size from 3.55 inches (stock) to 3.70 inches (big bore) will allow the same DOHC head to flow approximately 20-30 cfm more than it would have on a stock-bore motor. When enhanced with precision porting from Fox Lake Power Products, the airflow gains only improve-and remember, ported DOHC heads already flow 290 to 330 cfm (intake; at 0.500 inch lift) on a 3.55-inch bore.
With properly matched components, there are substantial torque gains to be had from idle to redline. A modular 5.0 can have the low- and midrange of a stout pushrod 5.0 (302 ci), and the high-rpm pull that only an uncorked/ unrestricted Four-Valve can provide. Naturally aspirated, and on pump gas, expect 375-430 hp and 330-360 lb-ft of torque at the rear wheels from an optimized (ported stock heads, aftermarket cams, ported intake, exhaust, and so on) big-bore motor. It truly is the naturally aspirated Cobra motor that should have been-just imagine if Ford had given us 5.0 (4- by 3-inch) dimensions.
"I don't have much experience with modular strokers," Andy says. "But from what I've learned from experts like James Hensler and the Tymensky family, you really need cams and headwork to get any naturally aspirated gains at all. If you're really stuck on stroke, and you need to stay naturally aspirated, start with an iron-block 5.4 (3.55x4.165) and save yourself a ton of headaches, hassles, and cash. Used 5.4 blocks (cannot be big-bored), perfect for rebuilds, can be found for under $200 at junkyards across the country."
For those looking for something truly unique, there are a few modular big-bore and stroker kits floating around. Using a custom stroke (3.75-inch) forged steel crank, longer-than-stock forged connecting rods, and custom short-skirted JE pistons, Houston Performance's 324ci modular big-bore stroker package is one such kit that's presently available. Gains over a big-bore alone are speculative at this point, but one could conservatively estimate a mild horsepower gain and an even more moderate bump in torque. It should be pointed out that in the case of a big-bore stroker, the extra stroke is fully exploited via the opened bore unlike in a stroker alone. Expect 430-500 hp/ 380-420 lb-ft of torque at the wheels out of a naturally aspirated, pump-gas, big-bore modular. A running example that we know of is rated at 448 hp/382 lb-ft on pump gas. Stroker kits (crank, rods, pistons) range in price from $2,500 to $4,500 depending on the quality of componentry.
ModCamPonents [(941) 729-2608] and several other companies recently began manufacturing billet camshafts for DOHC motors. Until last year, all aftermarket DOHC cams were reground stock Ford cams-no one in the aftermarket could locate billet cam blanks to grind. ModCamPonents has also released a set of modular DOHC adjustable cam gears. The adjustable gears are designed to work with the ModCamPonents cams-you can't run one without the other. Together, they allow an engine builder to vary cam timing 360 degrees in intervals of 2 degrees. The custom valves we're using are +1mm intake and +2mm exhaust, and they are also longer than stock. The valves feature a single-groove keeper designed to work with the new dual-valvespring kit.
"[After much searching]...I sourced the final dual spring kit (third try) from Al Papitto of Vero Beach, Florida. These springs have been tested in the ranks of Pro Stock motorcycle racing and are capable of 0.560-plus-inch lift and 13,500 rpm. The new valvetrain required machining of the cam towers to clear the larger springs and also necessitated custom valves-requiring more head disassembly/reassembly. Since I would have to use new custom valves anyway, I decided they might as well be optimized-we went with +1mm intake and +2mm exhaust sizing, and yet another valve job.
"My advice to anyone thinking of building a high-performance modular motor is to be prepared for the realization that there is no such thing as compromise-the 5.3 is a great example. My buildup began with the intent of utilizing a regular big-bore, as when we began, the big-bore stroker kits hadn't yet been released. My initial thinking on the matter was that the additional stroke would help make a high-strung motor a little more streetable via the extra torque it would have to generate-and, of course, the more displacement, the better. Though the motor is a substantial 43 ci larger than a stock Cobra motor, 324 ci is still ultimately only 324 ci. Without the aid of pressurized air, a naturally aspirated motor of modest dimensions has no choice but to rev to unnaturally high engine speeds to make real power.
"For a street motor, you'd be smart to cap it at 8,000 rpm (which is tame compared to the revs the aluminum-rodded 4.6/5.0 race motors are turning). And, in order to make power that high, specialized components such as dual valvesprings with titanium locks and retainers; a quality forged or better rotating assembly; higher-compression pistons requiring better fuel; big-lift, big-duration cams that kill low/midrange power; and one heck of an engine builder become necessary. While good at making high rpm power, a motor with hogged-out ports, big cams, and short intake runners will also undoubtedly not be a low-rpm stump puller.
"So, my moderately sized big bore/ stroker may not be as torquey as I would have initially hoped, but I have learned to live with the rationale that I like horse- power more anyway...I'd like to thank the following people for their help/ advice/guidance in this project: James Hensler, John and Mike Tymensky, Al Papitto, Jason Fowler, Ben Dorn, John Mihovetz, Joe Lynch, Lindsey Druien, and Tony Meyers."
In The End
While Andy's project engine con-tinues to be assembled, there are two successful examples of the big-bore modulars. Chris LaFear is running around the streets of Michigan with his '01 Cobra convertible packing a 305-inch version of this Hensler mod mill. The engine made an impressive 374 rwhp and 361 rwtq utilizing a ported (stock runner length) stock '01 Cobra intake, Fox Lake Stage II ported '01 Cobra heads, an FR500 valvetrain kit, a Modular Performance big-bore block, 10.5:1 custom Diamond pistons, Eagle H-beam rods, and BBK long-tube headers. With a high-winding, naturally aspirated DOHC under the hood, the 'vert is a blast to drive, Chris reports.
Dennis Sharp has been going through all the same paths that led Andy to his current combination. But Dennis' Houston Performance big-bore short-block is topped off with all FR500 Ford goodies including the heads, the correct FR500 intake, and other FR500-specific pieces. So far, he's cracked 420 rwhp at only 7,500 rpm (limited by the FR500 computer that resides in the car). He's looking for solid 11-second performance from his naturally aspirated '97 Cobra.
That's the long and short of pioneering modular motor building. It's promising that "average" guys are attempting these projects. As for cost, the basic big-bore package will run you around $7,500-a really nice starting point for a serious street car. A tricked-out, big-bore, stroker mod motor such as Andy's is in the neighborhood of $15,000. You're probably thinking you can build one heck of a 5.0 Windsor motor for that much coin-and you're right. But the pushrod stuff has been out for more than 40 years. Give the mod guys some time, and those big, beau-tiful heads and four cams are going to start paying off. Good luck with your modular combination.