Muscle Mustangs & Fast Fords
The Four-Valve Swap Power Struggle Upgrade
When You Need 9-Second Muscle And Your Two-Valve Engine Can't Hack It, Swap It Out For A Four-Valve.
As much as Ford's modular engine family was maligned when it debuted, we have seen the performance envelope for modular-powered Ford street cars ripped open in recent times. Big horsepower and streetability now go hand in hand, but at some point, there is a limit. We found that limit when we met up with Bob Watson of Jacksonville, Florida.
MM&FF has known Bob since 2002, when he hauled his Mustang to our Bullitt Mustang shootout. He took First place running 11.95. Not a bad lap given that it was his daily driver at the time. The Bullitt would in fact remain his daily driver for four more years, logging some 92,000 miles on the clock. The dependability of the supercharged Stang was simply awesome.
Over the years, Bob sought to increase the Bullitt's performance at the track by adding a speed part here and there, and before long, everything from the intake to the oil pan had been modified. However, the more he pushed it, the more unreliable the engine became. Three different short-blocks all produced a number of issues, not the least of which were leaky head gaskets. The big-bore, wet-sleeve, stroker engine that Bob was running is suspected to be the cause. Head gasket swaps are not exactly the easiest job to do on a modular engine, step one being "remove the engine."
When it was running well, the 5.0L big-bore Two-Valve pounded out some 600 rwhp, but Bob, like most of us, was looking for a bit more power--enough, in fact, to get him into the 9-second zone, which he wasn't all that far away from having run with a best e.t. of 10.01 on a 40-degree, mineshaft-like day in Gainesville. The car normally ran 10-teens and 10.20s in the Florida heat and humidity. Bob conferred with a number of people regarding his options to get reliability and make the additional power needed to run 9s consistently. He chose to swap in a Four-Valve modular 4.6L engine.
Over the next few issues, we're going to show you what's involved in swapping a Two-Valve engine for a Four-Valve 4.6L powerplant. With our subject vehicle already highly modified, there are quite a few changes that need to be made that are specific to this Bullitt Mustang, and we'll be sure to cover those, as well. At the conclusion, we'll offer track results along with a reliability assessment.
For this month's installment, we expand on the theory of the project a bit, detail the engine specifications, and show you some of the parts that are needed for the build.
The Pros and Cons of the Four-Valve Swap
The Four-Valve upgrade decision was solidified after consulting some highly respected modular motor experts. Al Papitto of Boss 330 Racing (Vero Beach, Florida) and Kris Starnes of Starnes Racing Heads (Hastings, Florida) assert that the Four-Valve chamber configuration is far superior to the Two-Valve chamber. The four valves are distributed evenly around the cylinder, with the spark plug centrally located allows for much better combustion (flame spread) and less possibility of detonation in a forced-induction motor. The extra two valves per cylinder allow much better flow to the cylinder, and the smaller valves have less mass, allowing lower spring rates that provide power at a much higher rpm range.
These advantages really add up in horsepower production. Papitto was convinced that the sleeved block caused most of the head gasket failures, but he was also very emphatic that the Two-Valve arrangement could still cause detonation and additional head gasket problems at the power level the car had attained. That was the final nail in the Two-Valve motor's coffin. Head gaskets were not going to be a routine maintenance item on the new mill.
There is, of course, a downside to the Four-Valve decision, too; namely, the funding to replace a significant number of components that are required for the conversion. Our subject vehicle incurred more costs than a basic Four-Valve-to-Two-Valve swap in that many of its engine components, the Vortech supercharger system in particular, are specific to the Two-Valve Bullitt Mustang. This required obtaining even more parts that are specific to the Four-Valve Mach 1 or Cobra modular engines.
Since we have high expectations (i.e., high power output and reliability) for this build, we didn't scrimp on the short-block. Al Papitto worked his magic on the engine to accomplish our goals. He started with a standard-stroke crank and a 0.030-inch overbore on the cylinders because he believes the stroker combinations for modular motors present too many compromises, including less than desirable rod ratios and ring configurations.
With the decision to go with a standard stroke, we considered our block options. It would have been easy and cheap to go with a new steel block, but aluminum offers an approximate 70-pound weight reduction directly over the front wheels. That being said, we called around and were able to acquire a Teksid aluminum block from Darrin Burch of BC Automotive.
We hoped to reuse the rotating assembly from the Two-Valve engine, but Papitto noticed some feathering of the balancer keyway. Since it was marginal, we decided to replace it with a new Kellogg forged-steel unit. The Oliver billet connecting rods were reused, but the pistons are new pieces from CP Pistons. Given the combustion chamber in the heads and the 9cc dish in the pistons, the compression worked out to a rather high (for a supercharged application) 9.5:1. This was to maintain good throttle response.
The CP pistons were fitted with a Mahle ring package, and the 4.6L block received a Boss 330 Racing-spec Melling oil pump. Considered by many to be a weak point in these motors developing high rpm, Papitto worked with Melling to develop a reliable oil-pump design.
The pivotal piece of hardware in this upgrade is, of course, the cylinder heads. There have actually been several different editions of quad-valve heads produced for the modular motors. The first was the "B" casting cylinder head that was attached to the Lincoln Mark VIIIs and SVT Cobras until 1998. In 1999, Ford released the "C" casting Tumble Port head, which lasted until 2001. Ford Racing Performance Parts released the FR500 four-valve head in 2002, which featured better low and mid-lift flow numbers than the Tumble Port design. The FR500 heads, with some slight updates, eventually became the U231 casting used on the '03-'04 SVT Terminator Cobras.
If your lottery ticket comes through--and your luck continues to allow you to locate a set--the best choice of all is the '00 Cobra R heads. These are extremely rare, though, and an easier way to get a set is to find a pair of Ford GT or Shelby GT500 heads, as these are very similar to the Cobra R casting. All of these heads present various issues when it comes to intake manifolds, but that's another story altogether. The Terminator heads are considered the best cost-effective heads, and in the end, we chose to use a set of late-production Terminator heads. Early Terminator heads only had three or four threads for the spark plugs. Ford later went to nine threads to cure a spark-plug blowout issue.
The cylinder heads were sourced from Darrin Burch at BC Automotive, and shipped directly to Kris Starnes of Kris Starnes Racing Heads, in Hastings, Florida. Starnes has been providing some fast Mustang enthusiasts with his ported cylinder heads, and he came highly recommended by Papitto. Starnes worked over the Bullitt's Two-Valve heads that allowed it to run 10.01 seconds in the quarter-mile. The porting job on the Four-Valve heads was beautiful both aesthetically and, as you'll see later, functionally.
Kris first worked the exterior of the upper plenum and removed all the extraneous stuff that wouldn't be used. He then port-matched the throttle body opening to mate up with the BBK twin 65mm unit that we're reusing. We also had to remove an Allen-head plug on the gasket aside of the throttle body to allow routing of the idle air, as the Bullitt intake doesn't utilize this port. Next, the inside of the upper manifold was ported to smooth flow and increase the intake volume as much as possible. After streamlining it, Starnes dropped the upper plenum off to Bruce Birkett of Palatka, Florida, who applied a liquid-like, silver finish.
The lower manifold of our intake setup is a huge departure from the standard Cobra intake manifold. Starnes converted the long-runner manifold to a short-and-straight runner design by applying a lot of machine work and epoxy. The bottom portion of the runners were removed and the areas filled with epoxy. This transforms the intake to allow a straight flow of air from the plenum area directly to the intake runners.
Starnes does not recommend this configuration on all applications, as it is particularly suited to high-rpm, forced-induction motors. The shorter runners will kill port velocity, and both torque and driveability will suffer on a naturally aspirated street car, or even a low-boost-level blower or turbo setup. Keep in mind that the sort of powerband change that a short-runner intake provides may require different gearing or, as in our case, a higher stall speed for our torque converter.
With the removal of the runners in the intake rework, we lost considerable plenum volume. Starnes supplied us with a fix for that in the form of a 1-inch aluminum spacer that he offers on a custom basis.
Two great sources that we contacted for a number of parts were the Mach 1 Registry and Liberty Ford. Searching the boards at www.mach1registry.com netted numerous items, such as the water crossover tube, timing cover, thermostat housing, and the cam and coil covers. Randy Stinchcomb at Liberty Ford opened up the replacement parts catalog and got us the Four-Valve's oil and transmission dipstick tubes, as well as the throttle cable and bracket.
In our next installment, we'll drop the new bullet in the chamber and set our sights on a dragstrip and 9-second timeslips. Check out the captions to see the dirt on this Four-Valve buildup and be sure to check back as we put it to the test.
Papitto picked out his own Comp Cams camshaft profile just for this engine combination. Comp's XE266BH-116 grind offers a split duration of 230/232 at 0.050, and a valve lift of 0.475-inch on the intake and 0.450-inch on the exhaust. The four bumpsticks went in with custom springs and titanium retainers to give us the right combination of valve force and high-rpm capabilities. The Comp camshafts offer extreme performance and great driveability, too. The car has just enough of a lope that people in the know will notice it, but it's tame enough that most people won't have a clue to the car's actual capabilities.
Other hardware exclusively required for the Four-Valve (which we've largely covered in the captions) include: headers, valve covers, a water-crossover tube, a thermostat housing, water hoses, a front timing cover, timing gears, timing chains and tensioners, additional lifters/followers, a throttle cable and bracket, oil and transmission dipsticks, a Mach 1 wiring harness (modifying a GT harness is possible), 4-V coil packs, an alternator bracket (we were able to use the Bullitt alternator but you'll need a 4-V alternator if you're converting anything but a Bullitt), fuel rails and associated tubing/connectors, and, last but not least, new mounting brackets and hardware to remount the Vortech T-trim and parts to modify the Vortech aftercooler to a Mach 1/'01 Cobra configuration. If dealing with an automatic, you'll more than likely require a higher stall-speed converter, too.