Everyone knows that guy who heard that mufflers rob horsepower, so he took a sawzall to his 1987 Camaro RS’s exhaust system and whacked them out, then proceeds to bounce it off the rev limiter as he leaves for work every day at 6:30 in the morning. Fortunately the polar opposite of “that guy” exists, and recently commissioned Tom Nelson and the team at Nelson Racing Engines to build him a ridiculously badass twin-turbo 447 cubic-inch LS engine, with one caveat: that it runs through mufflers, since it’ll be going into a 1955 Chevy Bel Air street car.
With the goal of making over 1,000 horsepower through mufflers on pump gas, NRE put together an engine that falls in between several of NRE’s different lines of engines, being an LS, pump gas, and twin-turbo street engine, and performs significantly better than expected.
To get 447 cubes, the team took the recipe for their “square” 441 cubic-inch LS combination of a 4.125-inch bore and 4.125-inch stroke, and then added an extra .020-inch to the bore diameter. A unique combination, for sure, but it’s only fitting, considering how unique this whole endeavor is.
The 72mm mirror-image turbochargers are Nelson Racing Engines-exclusive units, and they not only make for a symmetrical packaging option, but the billet compressor wheels, which rotate in different directions, develop more horsepower than their cast counterparts. “This engine is running the Gen 1 turbos, but the Gen 2 turbos will be out soon,” Tom Nelson says.
Plumbed into the outlets of the compressors are individual air-to-water intercoolers for each bank of the engine. They are located both for efficiency and packaging concerns, as when installed in the car, they will sit right behind the headlights of the ’55. The outlets of the coolers then feed into NRE’s billet “Alien” LS intake manifold with their “anteater” snout.
The exhaust consists of a beautiful set of turbo manifolds with the external wastegates plumbed back into the exhaust to control sound and meet packaging requirements in the ’55. Each bank of the exhaust is routed through a massive 3-inch inlet and outlet, 27-inch long oval muffler. Continuing with the interesting packaging, mounted directly to each side of the intake manifold are the dual fuel pressure regulators for the system.
Managing the fuel and spark for the combination is an Electromotive Tec 3 Engine Management System, which has been wired into the engine via some slick Deutsch connector quick disconnects, which not only allow quick removal from the dyno, but easy installation into the chassis.
On The Dyno
For the conservative first pulls, boost limits were set to only 5 psi.
“You’re never going to hurt this engine at only 5 pounds of boost,” Nelson says.
After a dyno pull where the dyno cell’s exhaust fan was louder than the engine for most of the pull, the screen showed some promising results. 752 horsepower at 6,100 rpm, and 706 pound-feet of torque at 5,000 rpm from a pull that sounded more like it was backing out of the driveway.
The next pull, the boost level was upped to 12.3 psi, which still isn’t taxing the Gen 1 mirror image turbos in the slightest. After a pull that was still ridiculously quiet for the kind of power being made, the numbers came up, with four digits to the right of the decimal: 1,053 horsepower at 6,200 rpm, and 993 pound-feet of torque at 4,700 rpm.
“The engine is super mellow at this power level,” says Nelson. “The cam is chill, and the engine is pretty happy.”
With all indicators solidly in the green, the NRE team added another pound of boost and ran it again. “It’s crazy; the intake air noises are louder than the exhaust,” Nelson laughs after the pull, which netted 1,084 horsepower at the same 6,200 rpm peak, this time with torque in the four-digit zone; 1,048 pound-feet again at 4,700 rpm.
Not happy until he hit the 1,100-horsepower mark, Nelson made a few tweaks to the map, added in another half-pound of boost and let it eat once again. The team was rewarded with the numbers they were looking for. With the same torque and horsepower peak RPM, the numbers were 1,046 pound-feet and 1,114 horsepower, through effective street mufflers. Also to note is the last 500 rpm of the horsepower curve was quite a plateau, only changing 16 horsepower between 5,700 rpm and 6,200 rpm.
How Much Are Mufflers Worth?
“I couldn’t leave well enough alone. I really wanted to find out if the mufflers were worth anything,” Nelson says. “They were extremely hot at the end of a pull, and I wanted to know if that was friction from the backpressure. Plus, I wanted to know what a 3-inch muffler is taking away from a turbo engine.”
With a scientist’s sense of curiosity, Nelson left the tuneup where it was, and opened the exhaust manifolds to the atmosphere, and made another pull. Besides being ridiculously louder, there were surprising results on the screen. First, the peak numbers were way up – 1,106 pound-feet of torque and 1,217 horsepower, for an increase of 60 lb-ft and 103 horsepower.
The really interesting part was the change in RPM peaks. The torque peak shifted up 500 rpm, and the horsepower peak only moved up 100 rpm, but maintained the same power plateau.
“There was more power throughout the entire RPM range, no sacrifices anywhere,” says Nelson. “I think we all knew that removing the mufflers would be worth power, but I had no idea that it would be 100 horsepower.”
“The engine is going to be in a street car, so we didn’t go crazy at all. We wanted super-reliable, quiet, and good power, and that’s what we got. 1,100, on pump gas, through mufflers,” Nelson says.
However, even Nelson was surprised by the results of the pull without mufflers.
“It’s pretty crazy. Of course you need mufflers on the street, but it made over 100 more horsepower without them. So, if you want it quiet, get a nice muffler and it will make it quiet, but with a penalty. Really, when you’re at 1,100 horsepower on the street, who cares?”