Piping Power

Qualifying was underway for the 1995 Daytona 500, and the buzz around the track wasn’t just the roar of stock cars turning laps. The sound drawing attention around Daytona International Speedway was, in fact, closer to a high-pitched whine, something associated more with Indy cars than stock cars.

As Sterling Marlin drove the yellow No. 4 Chevrolet of Morgan-McClure Motorsports around the track, the car’s sound had the attention of television crews, print journalists, and spectators.

Runt Pittman, the team’s master engine builder, had found a new trick for restrictor plate engines, many reasoned. The distinctive sound made by the car was all the evidence needed. Further proof came when Marlin won one of the Twin 125 qualifying races. Then Marlin won the Daytona 500 for the second straight year, further validating Pittman as a top-flight engine builder.

Pittman had, no doubt, built a strong engine, putting him and the Morgan-McClure team at the pinnacle of the sport. But what about that distinctive sound?

Today that high-pitched whine is common at restrictor-plate tracks, and there’s a story behind how that came to be.

Sound And Fury

The folks at Morgan-McClure, in late ’94, were experimenting with their exhaust systems, trying to gain an edge, and trying to give Marlin the chance to do what only Cale Yarborough and Richard Petty had ever done—repeat as Daytona 500 champion.

Mark Giles, exhaust fabricator for the No. 4 Chevrolet, had contacted Boyd Butler just weeks before qualifying for the Daytona 500, asking if Butler had ovalized pipe that would work in Winston Cup. Butler, who owns Dr. Gas Exhaust Components, sent the team a set of pipes. Giles found a combination he liked, and Butler was soon boarding a plane.

“Larry McClure calls me on the phone and says, ‘Boyd, put every piece of tubing you can carry in your luggage and get back here right now.’ So I did just that,” recalls Butler.

After two days working with Giles to develop an exhaust system for the team, Butler headed back home to Utah. Before he left, dyno readings showed a gain of 4½ hp using Butler’s custom-made exhaust system.

“I don’t want to take anything away from Runt Pittman, because he was building great motors,” says Butler. “He might have won the Daytona 500 anyway, but they went down there with a great motor that had 4½ hp more than it had the week before. To just stick this on the back of the headers and gain 4½ hp is unthinkable.”

Under Pressure

Butler’s Dr. Gas exhaust system has been fine-tuned without undergoing drastic change in the time since Marlin’s odd-sounding Daytona 500 winner hit the track over seven years ago. Butler has worked to improve the bends and shapes of his pipes, although the hole sizes and basic layouts of his system are the same.

There are several basic tenets of Butler’s system, all built on ideas and methods perfected over the years in his quest to build better exhaust systems. One of the foremost beliefs he has developed is that backpressure in an exhaust system is never good.

“If you have a case where backpressure in the exhaust system causes the motor to make more power, it’s because there are other problems in the motor that have to do with tuning, such as primary valve timing, which is dictated by the camshaft and rocker ratio,” Butler says.

“What happens is, if you have a very efficient exhaust system and you lose horsepower with it, frankly, what it’s doing is it’s stealing some of the intake charge off of the exhaust during the overlap period (created when cylinders fire on opposite banks inside a V-8 engine).”

Primarily through the use of crossovers that tie pipes from each bank together, Butler’s system focuses on reducing backpressure and efficiently moving exhaust from an engine.

“It’s very simple physics,” says Butler. “The trick is there is a tremendous amount of energy that we waste, that we throw away. We vent it to the atmosphere through the exhaust system. We’ve simply found some tricks where we try to capture and reuse some of that energy before it’s wasted and gone, to reduce the pressure, or self-pump, the exhaust system down. The other name for that that’s commonly used is to ‘scavenge.’”

Rules To Race By

Here are a few tips from Butler and other exhaust professionals that can be applied to all levels of stock car racing.

Chris Kaufmann, motorsports director for Borla Performance Industries, says one common mistake is that racers sometimes make abrupt turns in their exhaust systems, coming straight back from the headers and building maximum velocity, for example, then abruptly pitching the exhaust out one side.

“They have probably cost themselves 10 to 15 percent of flow just in making that hard turn,” says Kaufmann. “Or they’ll find themselves constrained because of different chassis modifications or the way their car is built, so they end up putting sharp bends into their exhaust system, and those are killers. Anything they can do to make the turns in the exhaust system as smooth and as gentle as possible, the better.”

A common mistake many racers make is that exhaust systems are developed as an afterthought, according to Dale Dotson, Flowmaster’s motorsports manager. “For optimum performance, the exhaust system, either with or without mufflers, needs to be figured into the package at the beginning of the R&D stages,” says Dotson.

He recommends caution when installing mufflers, taking heed not to place the exhaust tubing too far into the muffler and cutting off flow. Plus, when building an H crossover, the H pipe should be butted against the exhaust pipe, not into it, to avoid creating a blockage.

Crossovers, according to Butler, are crucial to the performance of a finely-tuned exhaust system, and they’re a key to the success of Butler’s Dr. Gas system.

“If a racer goes with two pipes that never see each other, he should at the very least put an H pipe in there,” says Butler. “An H pipe is not very efficient, but it’s better than nothing. But then the best things are the X pipes and the Y pipes, the Y pipe just being a simple 2 into 1. The H pipes help to reduce the popping (associated with 90-degree crankshaft engines). Each pipe will actually take some noise out, but they’re not as efficient as an X pipe or a Y pipe.”

Kaufmann points out that exhaust systems built by Borla are tuned specifically for a particular engine, including what the engine builder is designing the engine to do, what the rpm range will be, where the torque level is maximized, etc. Nonetheless, certain techniques can be used to pull performance from any exhaust system.

“For the weekend warrior, he actually can do a lot of little things to find out, let’s say, where he would want to put his crossover,” says Kaufmann. “He would want to put his crossover in a place where the system started to cool down. In other words, depending on how rich he ran the engine, how it tested on the dyno, there’s going to be a point where it’s going to cool down.

“He could find it the old simple backyard way, which is to get in there with a can of spray paint and start spraying back on his exhaust system under load and find out where the paint quits blistering off, where the paint actually starts to look like paint. At that point is where he really would want to put his crossover. While the fuel is still burning in the exhaust pipe, you don’t want to interfere with flow. Simple things like that can give the backyard guy a performance advantage, sometimes as much as 5 percent, by merely getting that crossover tube in the right spot.”

Kaufmann stresses that durability problems with exhaust systems might be solved by using oxygen acetylene welding. “It disperses the heat over a wider area, so when you go through heat cycling, you’re not going to have as many points in the exhaust system that electronic welding a lot of time creates; places that don’t take the cycling well and cause fractures,” says Kaufmann.

“Most of the fractures you see in exhaust systems on race cars are right at weld points. The reason for that is the particular part where the weld is located got so hot and was dispersed over such a small area with an electronic weld that it becomes almost like a stress riser, only it’s basically a thermokenetic hot spot. It’s not necessarily bad engineering for them to consider using oxygen acetylene for welding their exhaust system because of the tremendous heat cycles that race cars go through.”

Often overlooked, according to Kaufmann, is an exhaust’s support system. “You really can’t over-support it,” he says. A system lacking adequate support will often develop fractures, leading to leaks that might reach the driver’s compartment and potentially to loss of power.

Since an exhaust system is closer to the ground than any part of a stock car, other than the tires, clearance issues sometimes arise. But Kaufmann says flat tubing may help alleviate potential problems. “Just make sure you do the mathematics to see that the square tubing ends up being the same amount of area as the round tubing,” he says.

Perhaps the key underlying concept to maximizing the performance of your exhaust system is simply to give it proper respect.

“The lesson I can tell people is you can’t overanalyze any single part, and you can’t do too much as far as maintenance,” says Kaufmann. “An exhaust system should be right in the nuts and bolts check from race to race.”