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Stealth Stang Exhaust Modification - Yo, Exhale!
It Is Time To Dump The Clogged Stock Exhaust Junk And Go With Parts That Offer More Flow
Last month, we embarked on a mission to start adding horsepower to a new project vehicle at the MM&FF stables. The car has been dubbed the Silver Stealth Stang and belongs to our esteemed colleague, Ken Miele. For those who don't recognize his name, Miele is the contributor responsible for the tech column called Yo, Ken!. We added an assortment of induction pieces to help the 160,000-mile Two-Valve engine inhale easier. The upgrades didn't break the bank nor did they require special training to install. This month, our goal was to help the engine exhale better in the form of shorty headers, an x-pipe system, high-flow cats, and an after-cat exhaust system.
The Silver Stealth Stang began its project car life in the Dec. '08 issue when we added a complete Hotchkis suspension system. It helped the car handle the New Jersey roads nicely. Last month, we headed to Radical Racing where the gang installed a JLT cold air kit, a TFS 70mm throttle body, and a TFS upper plenum. Radical Racing proprietor Craig Radovich, cut a custom tune using DiabloSport CMR software and loaded it into the car with a Predator. Power went from a paltry 215 rwhp up to 225 rwhp, but the mid-range gains were enormous; at one point we calculated a rise in horsepower by about 32 rwhp.
On track, we were a little disappointed with the initial results thanks largely to the car being hot and the weather abnormally warm. The car had run 14.31 at 96 mph, a number we thought should have been in the teens. Miele did redeem himself and showed up to one of MM&FF's track days after the story went to print, where he knocked off a stellar 13.98 at 97 mph. The difference was much cooler weather, an iced intake, and an outstanding 2.00 60-foot time-that has never been duplicated. On average, we figure our original estimate of 14s should be expected for the mods. We want to put a lot of emphasis on track testing with the Silver Stealth Stang, because a lot of mods work better in the real world than solely in the dyno-testing world. Radovich is also a big proponent of track testing to go along with dyno results for that very reason, too. He says it best-you don't live on a chassis dyno, the real test is on the track.
With the car running consistently, it was time to make some more changes. This time we would open up the exhaust to help the engine kick out the extra air it had been ingesting thanks to the new induction components. Due to the mild nature of the engine, we decided to grab a set of shorty headers from Ford Racing. Complementing the shorty headers is a Bassani x-pipe and after-cat exhaust system. The stock pipes feature three cats per side and huge mufflers; the Bassani components are made of 2½-inch pipes and have a pair of high-flow catalytic converters. Topping it all off, the Bassani exhaust pieces are stainless steel, meaning they will outlive the car by being resistant to rust.
Once again, we relied on Radical Racing to handle the installation in its Atco, New Jersey-based shop. We arrived promptly at 9 a.m. and the Radical crew (Mitch and Lee) was ready to tear into our 160,000-or-so mile hot rod. The severe mileage meant they were contending with rusty nuts and bolts. Surprisingly, the shop prefers to drop out the K-member and front suspension in order to swap headers. According to Radovich, it's just easier, and since there is such high-mileage on the odometer, he was expecting some of the exhaust manifold studs would break off in the head. That would require drilling out the remnants, tapping the hole, and installing a Helicoil. We raised an eyebrow about dropping the K-member assembly due to time and effort, but the guys just laughed at Miele and I. Shockingly, they had the engine supported and the K-member removed in 39 minutes. The exhaust was buzzed off, and just as Radovich had expected, a rusty header stud broke. Luckily, it was just one stud, and it took longer to fix that than to install the headers, x-pipe system, and after-cat exhaust.
Shortly after lunch break, the car was fired up and sounded really good. The Two-Valve was throaty at idle, but not excessive. The Bassani mufflers aren't terribly loud during regular driving, and Miele has reported back that there isn't the dreaded drone at highway cruising speeds either. On the dyno, the car sounded so much better and healthier-as did the horsepower and torque results. There is no doubt that adding exhaust on a high-mileage Mustang is worth power, the exhaust flow from the high-flow cats versus the six factory units (which were probably half-clogged) is worth the swap alone. Radical Racing's DynoJet chassis dyno showed nice peak gains, 9 rwhp and an outstanding torque increase of 29 rwtq.
Our gains at peak horsepower might not be up to snuff for some, but you cannot deny that the additional peak torque is super-impressive. Increases in peaks are glamorous and great for bragging rights, but in our world of track testing, the average power is what makes cars run quicker. One look at the graphs tell us that on track, the Silver Stealth Stang should pick up considerably. As we pour over the data, the graph shows it picked up 22 rwhp in the mid-range and as much as 40 rwtq. Comparing the two graphs, the mid range gains are not just an up and down trend. The baseline and after-exhaust lines stay far apart from 3,000 rpm through nearly 5,000 rpm. Those kinds of gains are sure to show up on the dragstrip, which is precisely where we headed after the chassis dyno testing. Radical Racing is a mere one mile away from Atco Raceway, the site of our initial testing.
Earlier in this article, we mentioned that Miele had driven the car to a best of a 13.98 with a sick 2.00 60-foot. The unfortunate part of that heroic pass was that the weather was abnormal and Miele has yet to even get close to that short-time again. The car's engine was also iced down for the 13-second run. Our follow-up times for the exhaust upgrades were done on a warmer day, and the Predator showed a 210-degree water temperature, similar warm engine conditions to our baseline runs and post-intake upgrades. Stock, Miele ran 14.43 at 95 mph, and then followed it with a 14.31 at 96.8 mph. Miele delivered a new-best time of a 13.97 at 97 mph, with a 2.07 60-foot, with the new exhaust enhancements. It puts our overall gains at .46 seconds better than stock, and .31 seconds quicker than the parts from stage two of the build.
Like all good enthusiasts, we possess great bench racing skills and put them to work on this car. If Miele could repeat the 2.00 short-time, then 13.80s wouldn't be out of the question for the Silver Stealth Stang. That leads us into the next slew of problems as we try to go quicker and faster with a high-mileage, budget built Two-Valve Mustang. Why can't we do it? The answer is simple. The car has trouble leaving the starting line and that is directly attributed to the tight torque converter that comes from the factory. We don't know the exact stall speed, but an educated guess is that it is around 2,000-rpm. The rear gear also needs to be numerically larger. Right now, Miele runs a 3.73:1 gear with the 285/40-18 Nitto 555 tires. That tire checks in at nearly 27 inches, and was cutting down on our rear gear.
We are not ones to leave something alone, and just knowing we can go even faster had us scheming and planning for our next set of mods. Next month, we will take advantage of our newfound horsepower. It doesn't do any good if we can't get the car out of the gate quickly and get into that broad powerband that our dyno sheets show. That means we must get a looser torque converter and jump the gear ratio to 4.10:1. Also helping reduce rotating weight and drivetrain vibration will be the addition of an Axle Exchange aluminum driveshaft.
For now, Silver Stealth Stang has a little bite to go along with its newfound bark. Now we just need to help the Stang get out of its own way.