Muscle Mustangs & Fast Fords
1985 Mercury Capri 5.0 Dual Exhaust System Part 3
A Dual Exhaust Uncorks Our Capri, And Some Track Tricks Get This 5.0L Moving More Quickly.
Although the late-model Mustang movement didn't really take off until the fuel-injected 5.0L Mustangs started taking out Brand X cars left and right, Ford's carbureted 5.0L Mustang and Mercury Capris were plenty fast given similar mods. We've so far proven this with our project ercury Capri, and this month we continue to chop at the elapsed-time clock with a dual-exhaust setup, a few changes to our track procedure, and a couple of mechanical modifications.
In the last few issues of MM&FF, we've been modifying this '85 Merc with bolt-on parts, including an intake manifold and carburetor from Summit Racing Equipment, Performance Distributors ignition system, and lightweight Weld Racing wheels with Toyo Proxes slicks. The modifications have allowed us to take this once-sluggish 15.6-second ride to a quick 13.92 at 97 mph. Shaving a second and a half off our elapsed times and adding some 8 mph has been a lot of fun, and this month we aim to improve on our success further.
Since we opened up the intake tract with the Weiand Street Warrior manifold and a more appropriately sized Holley 600-cfm carburetor, it was time to uncork the exhaust system, which up until now was utilizing the factory two-into-one-into-two arrangement. It's amazing to us that the car still had this on it when we picked it up, but it's time for it to go in favor of a true dual exhaust system.
While we could have gone the shorty header route, we decided to optimize the combination by going with long-tube headers. Summit Racing provided us with a pair of Flowtech 15/8-inch headers that wear a nice ceramic coating. The high-temperature ceramic coating will help keep heat inside the header tubes, which helps speed up the exhaust gas' exit, not to mention that it keeps the headers looking nice for years to come. With long-tube headers comes the need for a shorter H- or X-midpipe. Going for the deeper, more muscular sound, we opted for Flowtech's H-pipe sans catalytic converters. It's an aluminized steel piece that features the same three-bolt flanges that the header collectors have.
Looking to keep a cap on excessive noise, we called the folks at Dynomax for the back half of our system. Having used Dynomax's Ultraflo Welded mufflers, flow tubes, and tailpipes on project Stolen Goods a while back, we knew the Dynomax parts would fit well, provide the proper stainless steel tailpipe look we were after, and give our 5.0L a healthy sound without being obnoxious. This time we opted for the Ultraflo stainless steel mufflers, and to be perfectly honest, they sound exactly like the Welded series mufflers. In the staging lanes at the track, the Capri is quite quiet, and even in the burnout box, it's rather docile sounding, but at any rpm, it sounds great and no doubt has improved the exhaust flow. Summit Racing carries the Ultraflo SS exhaust system, and it also provided us with a new double-hump transmission crossmember from Ford Racing Performance Parts.
A couple of late nights in the barn, along with the help of MM&FF subcontractors George Xenos and Brian Bohnsack, had the Capri up and running in time for our track rental at Gainesville Raceway in Gainesville, Florida. We arrived with carburetor jets in hand, and a thirst for quicker elapsed times. Before we took to the track, we had to take care of a leaky freeze plug and used a rubber plug from the local parts store. These things have a bolt that goes through the middle and you can tighten it up in the hole so it doesn't blow out under the pressure. It is a great temporary fix, and we'll be replacing all of the freeze plugs here shortly.
After dealing with the leak, we headed to the burnout box and proceeded to heat up the Toyo Proxes 26x9 drag slicks. We've got about 60 passes on these and we're just now getting to the end of their life. They've always been very consistent and have provided us with plenty of traction for achieving maximum at the track. With a 3,500 rpm launch and 5,200 rpm shifts, Xenos piloted the Capri to a best ever 13.64 at 99.40 mph. Our short time had dropped to 1.87 seconds, while mph picked up by 2.5 and we lopped off 0.2 second from our elapsed time.
With the improved intake and exhaust flow, we opted to try a higher rpm shift point on the next run. Unfortunately, we experienced valve float at about 5,800 rpm, resulting in a 13.74 e.t. at 98.52 mph (1.87 60-foot). On the next pass, we upped the launch rpm while bringing the shift point back to 5,200. We crossed the stripe in an identical 13.74 seconds, but at 99.08 mph-this despite a slower 1.90-second short time.
Up until now, we've been taking it relatively easy on the launch so we could get more consistent results that would provide a better understanding of how the performance parts performed. On the next pass, launch rpm was raised to 4,500, which resulted in a slower 1.90 short time but a quicker 13.62 at 100.08 mph. Since we experienced a bit of tire spin at the hit, we pulled back the launch rpm to 4,200 for the next run. We spun again (1.93 60-foot) but turned in a 13.66 at 99.82 mph.
At the behest of Editor Smith, we dropped the tire pressure to 12 psi and hung the tach needle at 5,000 rpm before dropping the hammer. Our 60-foot time dropped as well to 1.87 seconds, and the Capri tripped the clocks in 13.63 seconds at 99.97 mph. With the Toyos now digging in hard, we left the line at 5,500 on the next run. The Capri charged to a best-ever 60-foot time of 1.79 seconds, and went through the traps in 13.55 seconds at 99.46 mph. Editor Smith proposed airing up the front runners to reduce rolling resistance, while your author suggested pulling off the accessory belt.
With only minutes to the end of our track rental, we bumped the front runners to 50 psi, and yanked the serpentine belt. (Note: Keep in mind that with the belt removed, the water pump will not turn. You can only make one run in this trim and the belt must be quickly reinstalled to prevent overheating the engine.)
Xenos heated the slicks with a Second-gear burnout and staged the Capri. With the water pump sitting idle and no air blowing across the radiator, things would get hot rather quickly, especially considering we were more or less hot-lapping the car. Xenos let the clutch out at 5,500 rpm and powershifted each gear at 5,200. The clocks lit up with an impressive result-a 13.31 at 102 mph. This despite a slower 1.86-second 60-foot time.
While we can certainly chalk up some of the performance to the addition of the exhaust system, we also made great gains by taking advantage of our track time and tested different shift points, launch points, and tire pressures. We also had a feeling that the factory clutch fan was robbing a bit of power, and we're still running the factory pulleys and serpentine belt.
Having reached, more or less, the maximum launch and shift rpm points, we'll be watching for the weak links to show. Things like the factory driveshaft, T-5 transmission, and 28-spline differential are all at risk, and even more so after next month's round of mods where we will be looking to add another 50-100 hp with a high-flowing set of aluminum cylinder heads and a hot camshaft. With the extra power, some suspension mods are in order, and we plan to follow up the head and cam test with those, as well as some power saving bolt-ons. We'll be heading back to the track to see what the parts have to offer, and we'll bring you all of the details on how to get your carbureted 5.0L to achieve maximum.