Steve Baur
Former Editor, Modified Mustangs & Fords
May 13, 2010
Photos By: Justin Cesler

In the last few issues of MM&FF, we've been modifying an '85 5.0L Mercury Capri with bolt-on parts from Summit Racing Equipment, Performance Distributors, Holley, Weiand, Dynomax and Weld Racing. The modifications have allowed us to take this once-sluggish 15.6-second ride to a mercurial 13.31 at 102 mph. This month, we aim to improve on this accomplishment with the addition of high-performance cylinder heads and a hot camshaft.

We've never bothered to dyno-test our Capri simply because we're having too much fun at the dragstrip with it. Not everyone can afford dyno time either, and it's much more reasonable to pay $20 at the local test-and-tune to see if your modifications have made a change for the better, not to mention that cars are meant to be driven and we'd rather talk about an adventure to the track.

To recap the present state of our mighty Mercury, we started with a mostly stock 5.0L Capri, its only modifications being an Edelbrock 750-cfm carburetor, 3.73 gears, and a pair of Flowmaster mufflers. We spent the first track session learning what the car responded best to with regard to shift and launch rpm. We then added lightweight Weld Draglite wheels and Toyo Proxes 26x9-inch slicks and skinnies, and we bumped the timing. With these changes, we whittled the quarter-mile time down from a 15.44 to a 14.26, picking up about 5 mph in the process.

We followed up with a Holley 600-cfm carburetor and Weiand intake manifold combination from Summit Racing Equipment, as well as an exhaust system from Summit and Dynomax. Performance Distributors also sent us its Firepower ignition system to give the old lump a healthy tuneup. These enhancements allowed us to chop at the clocks some more, which put the Capri's best lap at 13.55 at 99 mph. We did make a "hero run" with the serpentine belt removed and went 13.31, but we couldn't hot lap it in that trim. The 13.55 is a more accurate representation of what it can do. The 13.31, however, does hint that there is more power to unlock from the 5.0L, and we'll address that next month.

This month, though, we promised to bolt on a set of high-performance cylinder heads and a hot camshaft, and we did just that. We went to Tri State Cylinder Head and ordered a pair of its Flo Tek 5.0X aluminum cylinder heads designed for pedestal-mount rocker arms. The 5.0X heads feature 180cc intake runners, 1.94-inch intake/1.54-inch exhaust valves, 58cc combustion chambers, and valvesprings good for cams with 0.550-inch lift. They also feature hardened locks and retainers, manganese/bronze valveguides, and phosphor/bronze exhaust guides, as well as a five-angle valve job.

You can get the 5.0X heads in a stud-and-guideplate version, but in either case, the retail price is the same-a smoking $798 for the pair. That kind of savings leaves you cash for other speed parts, like the Ford Racing Performance Parts 1.6:1 aluminum roller rocker arms (PN M-6564-BS51) and Trick Flow Specialties 6.25-inch hardened pushrods (PN 21406250), which are a 5/16-inch-diameter rod made from 4130 chromoly. During the installation, we realized that we needed to shim the rocker arms to obtain the correct lifter preload, and we used the 0.060-inch shims from Ford Racing Performance Parts' shim kit (PN M-6529-A302).

For our camshaft selection, we had a myriad of choices, even with the limitation of the stock piston valve reliefs. When it came down to ordering one, we went with a Ford Racing Performance Parts B303 camshaft. The venerable M-6250-B303 camshaft offers 224 degrees of duration at 0.050 on both the intake and exhaust (284/284 advertised), and 0.480-inch of valve lift. It's a great cam for the average street car as it offers a great burbling idle sound and an increased rev range to 6,000 rpm. Best of all, it's just $195 through Summit Racing Equipment, which provided us with the cam, rocker arms, and the pushrods for this buildup.

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At our last track outing, we came to realize we had a leaky freeze plug. With a brown watery substance residing in the radiator, we knew the other freeze plugs couldn't be far behind in rotting away in the block. This problem combined with the fact that we were going to install a new clutch from American Muscle, led us to the conclusion that pulling the entire engine and transmission was the best course of action. Once you have the cylinder heads and the transmission out of the car, there are just the two motor mount bolts and the engine comes right out.

We took this opportunity to clean the engine compartment using some Gunk engine degreaser and a power washer. We also gave the potent little 5.0L a fresh coat of high-temperature black enamel after installing the new freeze plugs that we picked up from the local auto parts store.

In order to put the engine back together, we called Cometic Gasket and ordered its Streetpro top-end gasket kit (PN Pro1016T), which retails for $315.95, as well as the Cometic's conversion kit (PN Pro1015B), which sells for $134.95. The top-end kit includes the intake manifold, exhaust manifold, EGR, valve cover, carburetor, and thermostat housing gaskets in addition to several others. It also includes Cometic's MLS (multilayer-steel) head gasket set. The conversion kit includes the timing cover, oil pan, rear main, and water pump gaskets.

These premium gasket sets from Cometic obviously don't quite fall in with our extremely frugal budget for this project, but we took this opportunity to try the gaskets, and we're happy to report they work great on our 5.0L application. After screwing the new Flo Tek 5.0X heads on the Cometic MLS gaskets using a set of ARP head bolts from Summit Racing Equipment, it was time to bolt up the new clutch and flywheel from American Muscle.

We knew the heads and camshaft modifications were going to add a lot of power to the combination, and while we didn't really have any clutch problems at the track thus far, we'd be asking for trouble once the engine went back in with the hot parts. To that end, we called up Americanmuscle.com, which steered us towards Ram Clutch's HDX series clutch kit.

The Ram HDX clutch kit (PN 34000; $184.99) features a diaphragm-style pressure plate, 10-spline clutch disc, alignment tool, and throwout bearing. It's a 10.5-inch-diameter design for '86-and-later cars, but we opted to upgrade the factory 10-inch clutch and flywheel setup from '85 using this clutch kit and Ram's billet steel 10.5-inch flywheel (PN 34012). This flywheel uses the 50-ounce balance for the 5.0L engine, it's SFI-certified, and retails for $269.99.

Ram says the HDX clutch is good for 450 hp, which is far more than we'll be making, but considering the track abuse it will receive, it probably can benefit from some padding in the numbers. We managed to put a couple of hundred miles on the clutch before letting the hammer drop-Ram recommends a minimum of 500 miles for proper break-in. As long as you don't have any deadlines looming, it should be pretty easy to accomplish that before your start banging gears. Amercianmuscle.com makes it easy to shop for your Mustang as it has a great website with parts grouped by model year.

With the Capri up and running with the Flo Tek 5.0X heads and the B303 cam, we put as many break-in miles as we could before heading to the local quarter-mile to see what it would do. We've been having some transmission troubles with the Capri lately, so things weren't looking good, and some frigid weather-for Florida at least-didn't help the traction situation.

Previously, we had Capri crew chief George Xenos turning the wrenches and banging the gears while we took the pictures, but Xenos decided it was time to earn a real living and went back to full-time work, so we had to find another wheelman. We found two in Rob Baldwin and Chris Crosby, both of whom had pitched in on the project at one time or another. Baldwin got the nod for his proper powershifting performance of former project car Little Juiced Coupe at the track, so we kept the rookie Crosby on reserve for later.

With the ambient temperature down around 40 degrees, there wasn't much hope for the VHT traction compound that was put down on the starting line. Still, we were armed with Toyo's Proxes slicks and a poor man's suspension that really transferred some weight.

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Having previously launched the car at 5,500 rpm, we thought it wise to back the launch rpm down a bit to compensate for the cold track. Baldwin held the throttle at 4,500 rpm and popped the clutch on the third amber. The tires spun badly and when he dialed up Second gear, Baldwin was put on "shift waiting." Once he found Second gear, he pulled the engine up to 5,800 rpm (a feat that wasn't possible before the new heads due to valve float) and shifted the remaining gears to cross the finish line in 15.47 seconds at 104.35 mph. The heinous 3.19-second 60-foot time told the whole story. Baldwin's second pass was much better.

Dropping the launch rpm to 3,000, the Capri spun slightly but moved out to a 1.92 short time. Three gear changes later, the clocks lit up with a 12.89 at 107.99 mph. It was going to be a challenge to get the Capri to leave hard without spinning, so on the next pass, we lowered the tire pressure from 15 psi to 13 psi. We also opted to rev the engine a little higher on this next run, and a 3,000-rpm launch followed by 6,200 rpm shifts turned a 1.88 60-foot time into a 12.74 at 107.88 mph. Baldwin reported that the car didn't feel like it pulled that high, so for run number four, we backed shift points down to 6,000.

At this point, we handed the keys to the rookie, Chris Crosby, who runs low 12s with his naturally aspirated heads/cam/intake Fox-body coupe. Crosby specified 12 psi of air in the tires and attempted a 4,000-rpm launch, to which the Capri responded with bad wheel spin. Crosby aborted the run and wheeled around for another go. This time, a 3,000-rpm launch resulted in mild wheel spin and a 1.88-second short time, followed by a 12.80 run at 107.97 mph.

Crosby followed this up with a final run of 12.61 seconds at 108.74 mph-a better 1.82 60-foot time surely helped. With a lot more air flowing through the engine and cold dense air being sucked down the carburetor, we thought it was time to try a jet change, which is something we have wanted to do for a while now, but couldn't until Holley set us up with a complete jet kit.

For run seven, Baldwin jumped back in the hot seat after swapping out the Holley's 65 jets for a set of 70s. We opted to make a big change in the sizing to see a good change one way or another. As it turns out, that plan didn't exactly work. Baldwin let the clutch fly at 3,500 rpm and the Capri responded with a 1.88-second 60-foot time. It crossed the stripe in 12.84 seconds at 107.53 mph. At the driver's request, we ditched the paper air filter element and air cleaner, and headed back to the starting line.

The staging lanes closed at this point, so this would be our last run. Baldwin took a risk and left the line at 4,500 rpm. The first 60 feet passed by in just 1.75 seconds-our best time of the night. The timing lights lit up with a 12.54 at 108.72 mph. That's a full second off our previous best e.t., and a gain of nearly 9 mph. The Capri is definitely making some steam thanks to the Flo Tek cylinder heads and the B303 cam. Not bad for budget parts.

As triumphant as the last run was, it was also the scariest looking. The car hadn't made a straight pass all night, and Baldwin went near the center line twice. The Capri wanted to launch left every time and unloaded rear tires pretty good at every shift, so we think we have some suspension work ahead of us. With the help of Lakewood Industries and Moroso, that's our plan for next month. We're also going to finally drop the front antiroll bar (yes, it's still on there), as well as maybe add a few more ponies with a couple of small bolt-ons that we've passed by. Are 11-second e.t.'s possible for our Capri? Come back next month and find out.

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