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Intake Manifold, Carburetor Combination, and Ignition System Upgrade - 4 Barrels Of 5.0L Fun Part 2
Our '85 Capri Gets An Intake Manifold And Carburetor Combination, Along With A New Ignition System.
Last month we started a short build series on an '85 Mercury Capri; this month we're continuing with an intake manifold and ignition system swap. To bring you up to speed, we took what was essentially a stock 5.0L Capri and updated the brakes and rear axle with later-model Fox-body components.
As purchased, the Capri ran a sluggish 15.44 at 89.79 mph. After a few tweaks and the addition of Weld Racing Draglite wheels and Toyo drag tires, we chopped at the elapsed time tree until it read 14.26 at 94.10 mph. In this issue, we weren't lucky enough to make such impressive headway in reducing our quarter-mile elapsed times. For the most part, the faster you go, the harder it is to improve.
Coming right off the track with our impressive 14.26 performance, we popped the hood and bolted on a Holley 600-cfm carburetor, which was part of the Summit Racing Value Pack that we ordered. We felt that the 750-cfm Edelbrock piece that was on the car was simply too large for a little 302ci engine, and wanted to see what a more appropriately sized fuel mixer would do. To that end, we then installed the Holley, along with a 1-inch spacer that we needed to make the carburetor clear the stock intake manifold.
Out of the box, the Holley produced a 14.33/93.94-mph run with a 1.94 60-foot time. Our next pass started with a 1.93-second short time, followed by a 14.14 e.t. at 94.96 mph. We made another pass after that, which resulted in a 14.37 at 93.79 mph (1.98 60-foot). We expected a bit more improvement in elapsed time from the carburetor, but mph did pick up slightly, so there may be something else hindering the progress.
At this point, we felt brave and tried to perform a trackside intake manifold swap, but our efforts were thwarted upon start up as we sprung a leak at the back of the intake manifold. We didn't have another set of gaskets, and more importantly, the track was about to close, so the intake test had to wait for another day. Best laid plans and so on and so forth.
The leak turned out to be nothing more than a lack of proper cleaning at the cylinder head's rear water port. So we reinstalled the Weiand Street Warrior dual-plane intake manifold, along with the Holley 600, and headed back to the track. We also took the time to wire in our new Performance Distributors ignition system so we could easily perform a trackside swap of the ignition components.
Seeing that the spark plug wires were still original, we thought it was time to update the ignition components. At some point, someone had changed the spark plugs, but everything else was as Ford built it. Performance Distributors delivered a set of its hot Livewires, billet aluminum wire looms, an Inferno 2 ignition coil, and a Dyna-Mod to replace the factory Duraspark setup.
Our first run of the evening netted a 14.48 at 95.98 mph, this despite a wimpy 2.15-second short time. Our driver, George "The Greek" Xenos launched the Capri at 3,000 rpm and shifted at 4,700 rpm, just like we had at our previous test session. His second pass of the evening started with a slightly quicker 1.98 60-foot time, which translated into a 14.30 at 95.80 mph.
The Greek reported that the car was still accelerating hard at 4,700, so we raised the shift point to 5,000 for the next run. The higher shift point was the ticket as the Merc responded with a 14.12 at 96.32 mph, even with a slow 2.00 short time. Feeling there was a bit more in the car before we moved on to the ignition system, we made another hit and a quicker 1.96 60-foot time netted our first 13-second pass-a 13.98 at 97.05 mph. We opted to raise the shift point on the next pass and ran a 14.06 at 96.95 mph with a 1.96-second 60-foot time.
Truthfully, we expected a bit more from the intake manifold and carburetor combination, and while we did pick up 2 mph, we're thinking a jetting change may be in order. Unfortunately we didn't have any with us, so we moved on to the Performance Distributors Firepower ignition system. Lucky for the Greek, he got to play crew chief and driver while we took the photos.
The factory plug wires were disposed of quickly, and we ditched the spark plugs as well. PD specified wider plug gaps (0.050 to 0.055-inch) with its Inferno 2 coil and Livewires, so we opened up a fresh set of Autolite 25s, gapped them to 0.052, and screwed them in. We also plugged in the Dyna-Mod and coil connections. The 5.0L immediately sounded better and revved faster upon start up, but would this translate to quicker elapsed times on the track?
Pulling out of the burnout box and up to the line, Xenos pulled the engine rpm to 3,500 and let the clutch out. The first 60 feet passed in a scant 1.91 seconds and he shifted each gear at 5,200 rpm. The Capri tripped the top-end lights in 13.98 seconds at 97.05 mph. That's the first time we saw a 97-mph trap speed, and we wouldn't dip below that the rest of the evening. On the next run, the 60-foot rose to 1.95 seconds, and the quarter-mile time followed at 14.04 seconds at 97.03 mph. We followed this with three 14.0s, and a hard 4,000-rpm launch netted a 1.88 60-foot time, along with a 13.94 at 97.09 mph.
While the mods this time around did not make a significant leap in performance as on our first outing, they have put us solidly in the high-13 to low-14-second range at 97 mph-a 0.2-second reduction in elapsed time and 2 more mph. We'll get ourselves a box of jets for the next time out at the track and see if that might wake things up a bit. We also have a complete true-dual exhaust system that we're going to bolt up to replace the factory Y-pipe, headers and 2.25-inch exhaust. In addition, we've picked out a pair of high-performance cylinder heads and a hot camshaft to get our carbureted 5.0L thumping.