Ask any older hot rodder about exhaust cutouts or dumps. In the old days, lakes racers would drive to the track and uncork the exhaust with a simple three-bolt cap so they could go faster. Most hot rodders still believe they need to drop the exhaust from their cars to go fast. As wives' tales go, this one is doing a good job of hanging on. But with the coming of '90s power technology, cutouts should soon be as desirable as a pair of Stromberg 97 carburetors.
Borla Performance is at the leading edge of this technology. It's no longer necessary to hassle with unbolting the exhaust system in the name of going faster or quicker. As an example of Borla's contribution, Hurley Blakeney pushed his Ken Duttweiler-built, 380ci, small-block-Ford-powered AA/Altered Turbo Thunderbird down the Heartland Park NHRA strip at an astounding 6.99 at 203.29 mph, and has since run a 6.75! While that makes Blakeney's thundering T-Bird the first Competition Eliminator doorslammer to both run in the 6's and exceed 200 mph, the best part is he did it running a pair of Borla XR-1 mufflers.
It used to be that the thought of mufflers on race cars would have been as attractive as a stripped head bolt, but today's political and social climate demands that many race tracks put a muzzle on excessive noise. This is where the XR-1 was born. In fact, Borla has created a quiet revolution with its Collector muffler, designed for dragsters and doorslammers with precious little room for mufflers under the chassis.
While mufflers don't create horsepower, a poorly designed exhaust system can cost power. That's an accepted fact. But what is less known is the boundary where mufflers begin to cost horsepower. One place where muffler technology is certainly being tested is the Fastest Street Car competition, where these cars are required to run a fully muffled exhaust.
To clear the air, Borla suggested a test. Nitrous Oxide Systems (NOS) bolted a nitrous-assisted 540ci big-block Chevy onto Ken Duttweiler's Stuska dyno for the test. The test would involve first baselining the engine without mufflers, then bolting on a couple of different Borla mufflers to evaluate engine performance.
This 540ci Rat motor is a development engine used by NOS to test new products, but it is no slouch when it comes to making power. The cast-iron tall-deck Bow-Tie block starts out with a large-by-huge 4.50x4.25-inch bore and stroke, and uses a Callies 4340 steel crank and Bill Miller aluminum rods. Since this was intended as a nitrous engine, Childs & Albert supplied stainless-steel rings to seal the Venolia 14:1 forged pistons. The mechanical-roller Crower cam has a dual-pattern design with more exhaust duration to properly scavenge the cylinders, especially for nitrous, with 320/330 degrees duration and .760/.780-inch lift.
The Brodix-cast Pontiac Pro Stock aluminum heads are an important key to the power this "little" big-block makes. The titanium valves are pushed around by Jesel 1.75 rockers, while the Hogan sheetmetal intake is topped off with a pair of Brad Urban's Carburetor Shop 1050-cfm Dominator carburetors. Ignition is handled by a complete MSD-7 system, while Hooker supplied the 2 1/4-inch primary headers fitted with 4 1/2-inch collectors.
The go-faster part of this combination is a complete NOS Pro Shot Fogger system fitted with four solenoids and eight Fogger nozzles. NOS also employed the new Fogger-2 nozzles, which are an update of the original Fogger design. The system with the new nozzles was originally jetted for a 250hp increase, but the new nozzles helped the system create more than 400 additional horsepower over the engine's normally aspirated power. We're talkin' a thumpin' 900 horsepower at 6900 rpm. Squirting the nitrous into this rascal skyrocketed the power to an earthshaking peak of 1365 horsepower at 6500 rpm. This motor could certainly test the mettle of any muffler.
Making this kind of power alone would be a great story, but then Duttweiler, with assistance from Bill Floyd and Jay Jones, installed a pair of Borla's Vacuum Wave Collector mufflers, which were later switched for Borla's latest-generation 4 1/2-inch Shoot-Out Series race muffler. The dyno test was run as an acceleration-rate test, which is similar to the way an engine performs in the car.
While the power numbers moved around between the baseline test and the two subsequent muffler-equipped tests, the Depac data-acquisition system installed on Duttweiler's dyno gave a simplified bottom-line evaluation in the form of average horsepower between 4500 and 6800 rpm. The power for the baseline open-header test averaged 740 horsepower, as did the collector muffler and the new 4 1/2-inch Shoot-Out muffler. Often, specific rpm points can be used to "prove" or "disprove" the ability of a part to work, but even at the peak of 900 horsepower, the numbers varied by less than 10 horsepower between all three tests, or roughly one percent. The key here is that the average power remained the same.
The next big test was to evaluate the effect on power at the nitrous-assisted level of around 1300 horsepower. At this time, Duttweiler changed the test procedure to make it easier to collect the data and to lessen the time the engine was under load on nitrous. The new test would load the engine at only 6500 rpm.
NOS brought more than just its engine to this test, however. NOS's engineer Karl Staggemeier also configured the test cell with a complete nitrous-flow data recorder so that the actual amount of nitrous flow in pounds per hour could be recorded.
Duttweiler leaned on the Rat motor first with the open headers, then with the collector mufflers, and finally with the Shoot-Out mufflers. Power jumped to well over 1300 horsepower in all three tests, but an unexpected variable made a clear-cut evaluation of the mufflers' performance a little difficult.
In each of the two muffled tests, nitrous flow decreased slightly, creating an independent variable. It's intuitive that if nitrous flow decreases, there's a solid chance that power will also decrease. Given this, the power differences between all three tests are not that great.
The baseline pull with open headers generated 1337 horsepower, while the test with the 4 1/2-inch Shoot-Out Series muffler cranked out a close 1320 horsepower, and the collector muffler test established 1303 horsepower. Each of these horsepower numbers was created by loading the engine at 6500 rpm for 2.5 seconds. Even with the reduced nitrous flow, the Shoot-Out muffler test lost only 17 horsepower, which is 1.2 percent of the original power number. The collector muffler test decreased 34 horsepower from the baseline, which is a 2.5-percent loss. NOS's data revealed nitrous flow dropped four percent in the second test and eight percent in the third compared to the baseline.
The whole reason for running mufflers in the first place is to decrease noise. A dyno test is not an accurate place to measure noise, since it's not possible to duplicate the way the muffler is used in the car. Both Borlas did reduce the decibel level of the engine by approximately 4 dB, but the sound was also muffled by Duttweiler's built-in dyno mufflers located downstream of the dyno cell. In the normally aspirated test, noise levels dropped from 90 dB to 86 dB. According to Borla, typical race car applications diminish the noise level approximately 10 dB for 3.5-inch and larger mufflers. This is based on W.O.T.-drive-by measurements taken 50 feet from the vehicle.
While it's difficult, if not impossible, to predict how much four to eight percent nitrous flow is worth in terms of horsepower, it's a fair assumption that the mufflers probably were responsible for very little, if any, of the power difference. Unfortunately, that's as close as we were able to get to a precise evaluation of Borla's race mufflers. But when you consider you now have the ability to add mufflers to an engine capable of 1300 horsepower while losing little, if any, power, it's safe to say that we've come a long way from the days of lakes pipes and exhaust dumps. That muffled exhaust rumble you hear is the pleasant sound of power.
