Horse Sense: Ed Hohenberg is the main manat Wolf Performance Engineering [www.wolfperformance.com], whichprovides high-performance and mechanical engineering (yeah, realengineering) services. While Ed is obviously a pretty sharp guy, he'salso an experienced racer who's had success racing a Fox Mustang in NHRAStock Eliminator. He's also an experienced tuner that sells bothDiabloSport and SCT products.--Ed.
The '03-'04 SVT Cobras are amazing cars. Not only do they excel in allmanners of vehicle dynamics (acceleration, braking, and cornering), butwhen you aren't leg-pressing the stop-and-go pedals, they're alsocompletely sedate for day-to-day driving. What's even more amazing ishow easy and economical it is to add significantly more horsepower tothese cars--like another 100 hp--which we did one day last summer for lessthan $1,200.
Our recipe was the tried-and-tested combination of after-cat exhaust,low-restriction air intake, smaller supercharger pulley, and performanceflash tuner. In the end, we picked up almost 90 rear-wheel horsepower(equating to roughly 105 hp at the flywheel, using the standardSuperFlow dyno correction for driveline efficiency). What you reallyfeel when you squeeze the go-pedal, however, is the torque--we picked upan amazing (there's that word again) 120 lb-ft at the wheels (more than140 lb-ft at the engine).
Other than the exhaust system...
Other than the exhaust system (not shown), here's more than 100 hp justwaiting to be installed. Parts include a K&N FIPK air intake, a2.80-inch pulley and corresponding belt, the two flash tuners we tried,and new copper spark plugs (recommended when running additional boost).
But there's more than just the before-and-after. In order to provide ourreaders the best data to use as smart shoppers, we systematicallychassis-dyno-tested each modification, so you can see which made themost horsepower per dollar. To make sure the dyno data weren'tflash-in-the-pan flukes, all comparison dyno runs were done on the sameday, and were run twice for each mod (hot-lapped for the second run toensure fair test comparisons--for example the engine, tires, gear oil,and such were warmed up). Several engine parameters were also loggedduring the dyno testing, again to ensure maximum consistency between theruns. In the end, the better of the two back-to-back runs was taken forcomparison data, but typically the difference was less than 2 hp betweenthe two runs.
The first step was to baseline our Cobra, and this particular '04 snakedidn't disappoint. Stone stock and with just over 2,000 miles on theodometer, our Cobra laid down 381.5 hp to the rear wheels at 6,000 rpm,revealing the factory's 390hp flywheel rating was a bit conservative. Onan inertia chassis dyno (we used the SuperFlow at Motion Performance inWinnipeg), these cars are typically in the 360-380 rear-wheel-horsepowerrange, so evidently we ended up with a strong one. One thing to noteabout the stock dyno run is the air/fuel ratio goes really rich beyond6,000 rpm. This is likely due to the exhaust catalyst monitor in thestock tune, which, when it senses the cats might be getting too hot,dumps extra fuel into the engine to cool them back down.
Tune Time
Up first on the stone-stock...
Up first on the stone-stock Cobra was the DiabloSport Predator flashtuner. From the comfort of our passenger seat, we simply plugged theunit into the OBD-II port, then followed the on-screen prompts toeffortlessly add the new tune.
A performance tune was our first modification on the stock Terminator.While the '04 EEC V will still take a chip, we stepped up to the latestand greatest flash tuners--the DiabloSport Predator and the new SCTXcalibrator 2. Both tuners can be found for around $400 by a smartshopper and are loaded with many other features, in addition to theperformance tunes.
Installing the tunes was as easy as plugging the units into the OBD-IIport under the dash, then following the on-screen prompts. The SCT tunerhad three tunes installed for differing fuel-octane numbers (we wererunning 94-octane pump gas), while the Predator had a 91-octane tune, ageneric "performance tune," and a "pulley tune," the latter tworequiring 93-octane fuels. We chose the 93-octane tune for the SCT, andthe Predator "performance tune" for the stock Cobra. Then it was dynotime to see how the tunes performed.
After dyno testing with the...
After dyno testing with the Predator tune we flashed the stock tune backin, then tried the SCT Xcalibrator 2 tune. Adding the tune was astraightforward deal, although the process was a bit quicker with theXcalibrator 2.
While both the SCT and Predator tunes made more torque and horsepower,both also ran the A/F richer than stock, which was already quite rich.In hindsight we realized the reflashing process would clear any "learnedcorrections" in the EEC, so the gains we saw on the dyno from the flashtuners may have actually been greater had we cleared the stock EEC oflearned corrections for the baseline run. The EEC had previously learnedto lean itself out--hence the leaner A/F ratio for the stock baseline,which would make more power than a richer baseline.
The Predator performance tune made the previous high-rpm rich situationeven richer and, as a result, gained only a few peak horsepower overstock, even though rear-wheel torque was up by 10 lb-ft until the A/Fwent rich. This doesn't sound like much, but when we installed the samePredator performance tune with the after-cat exhaust and cold-air-intakeupgrades later, horsepower gains were much more dramatic over the stocktune. With the SCT tune, torque improved all across the board, and thepeak power was also up significantly, likely due to the A/F being leanerand more stable at the higher rpm range, as compared with the stock orPredator tunes.
For all dyno testing, we monitored...
For all dyno testing, we monitored and datalogged several engine-controlparameters, such as engine temperatures, rpm, spark advance, mass airvoltage, throttle position, and fuel pressure, using an SCT Raptorhigh-speed datalogger and our trusty laptop.
While the Diablo tune still went rich at the top end due to the catalystprotection programming, SCT disabled the catalyst temperature models intheir tune, resulting in a consistent A/F ratio at high rpm. Of course,if you choose to drive at 6,000 rpm all day long at WOT, you'll likelydamage your cats from overheating, but for short blasts they'll be fine.In the end, the SCT strategy worked for maximum horsepower, to the tuneof 16 peak rear-wheel horsepower over stock, with a stout 28 lb-ft gainin peak rear-wheel torque.
Flash Tuner on stock Cobra--cost per rear-wheel horsepower: $25
The Pipes
First on our list of mods...
First on our list of mods was to replace the stock after-cat system.Here's why: The tailpipe outlets fake you into thinking the stockexhaust is bigger than it actually is. In fact, the stock tailpipes areonly 2.25 inches in diameter and full of crimped bends that furtherreduce the flow potential.
Next up was the exhaust install. The original mufflers did a great jobsilencing the factory-blown Cobra down to acceptable EPA noise levels,but at a significant restriction to flow. Similarly, the factorytailpipes with their crimped bends and only 21/4-inch diameters alsodidn't do the best job flowing the exhaust out the back.
The cure was a MagnaFlow after-cat exhaust system for the Cobra. Thesmart-shopping cost for the kit is around $500. Installation is simpleand straightforward, without the need for specialty tools assuming theaverage hot-rodder installs all the parts used in our combination ontheir own. Installation costs aren't included in our calculations. Butwe weren't up to crawling around under the car for an afternoon, so wetook the car and kit to Keystone Ford/Mustangs by Matt, where the techsused their lift for a more comfortable install. Rick Clemenson fromKeystone Ford did the after-cat installation on our Cobra, while we gotin his way taking pictures or stood around doing nothing.
We replaced the stock after-cat...
We replaced the stock after-cat with this system from MagnaFlow. Noticethe real 2.5-inch pipes, and smooth mandrel bends everywhere. The shinyfinish was also a welcome change from our rusty-looking stock pipes.
The stock after-cat system is attached at the muffler-extension-pipeflanges connecting to the H-pipe, has two rubber hangers per side, andbolts onto hangers for each exhaust extension. To remove it, undo theextension hanger bolts at the rear, the flange connectors up front, thenlube and pry the after-cat out of the rubber hangers to remove eachmuffler/tailpipe assembly. Each side is one complete welded assembly.Possibly the best thing about the IRS system on these Cobras is the easewith which the after-cat can be replaced, as the tailpipes do not haveto snake up and over the axle--they go below everything so they just dropout.
To install the new system,...
To install the new system, Rick first (loosely) mounted up the front extension pipes and mufflers for both sides
Installation of the new after-cat is only slightly more difficult, sinceeach side now consists of many individual parts. Reading theinstallation instructions is always a good idea, but even macho he-mantypes who refuse to read should be able to get it right the first time.After scanning the instructions, Rick mounted the muffler-extensionpipes loosely, slip-fit the mufflers, hung the tailpipes on the factoryrubber hangers, slipped the system together on each side, then alignedit all and tightened the U-clamps holding everything together. Last, thetailpipe extensions were slipped on, aligned, then clamped tight andbolted up with the factory hangers.
 The tailpipes were then installed...  The tailpipes were then installed on the factory rubber hangers, and the entire system slipped together. At that point the mufflers, tailpipes and front extension pipes could all be aligned, as Rick shows here. Once aligned, the new stainless steel U-clamps were installed and tightened up. Caution here, as the stainless fasteners will not take the same torque as regular steel ones; unfortunately we found out the hard way. |  Finally, the chrome exhaust...  Finally, the chrome exhaust extensions were slid into place, aligned, and tightened up. |  With the huge 3.5-inch outlets,...  With the huge 3.5-inch outlets, we can no longer pass off our Cobra as stock! |
Just the looks and sound of the new after-cat were worth the money, buthow well would it actually perform--how much real horsepower versuspsychological horsepower? Back on the dyno at Motion Performance,MagnaFlow did not disappoint. On the otherwise completely stockTerminator, the after-cat alone picked up over 30 hp at the wheels, withanother 21 lb-ft of torque--all that while still having a respectablymellow exhaust note (i.e., your neighbors aren't going to hate you).
After-cat exhaust on stock Cobra--cost per rear-wheel horsepower: $16