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In our last issue, we began our look at high performance exhaust systems, zooming in on three mufflers from the folks at Hooker Headers. We looked at two different configurations: One style is a modern take on glass packs while the other is a chambered design. One of the mufflers (the VR series) is 100% stainless steel, while the other two (the Aero Chamber and the Maximum Flow) are based upon aluminized steel cases. In that opening segment, we learned well-engineered mufflers can actually flow rather well, and today’s technology certainly helps.
There’s more, though: What about cross over or "balance" pipes? Do they work? In the high performance world, it has repeatedly been pointed out that balance pipes have two possible attributes: increased power and reduced noise. Many manufacturers advocate their use, if only to reduce the sound level. We’ve had personal experience with some of the x-style crossovers such as those manufactured by Hooker Headers, and they definitely improve performance and reduce noise.
Here’s why:
A typical North American V8 engine is built around a 90-degree crankshaft. If you examine a typical V8 crank you’ll see four sets of connecting rod journals, and all of them are positioned 90 degrees from each other. This is like having two big V4 engines hooked to one another by way of the same crankshaft. On each cylinder bank, two cylinders fire within 90 degrees of one another. As a result there are two exhaust pulses timed very closely together as they travel through the exhaust pipe. That’s why, on some big power V8’s (with 90-degree cranks), you’ll hear a distinct “pop” coming from the exhaust. Those “pops” are the exhaust pulses. That's the sound of two pulses arriving at the end of the pipe at almost the same time. According to the folks in the know, the pair of pulses can get tangled up and the result of this is lost power.
When you add an H-pipe to connect the exhaust pipes between two banks, it will smooth the exhaust flow and simultaneously lower sound levels. The x-cross is an improvement beyond the H pipe since it tends to re-synchronize exhaust pulsing and pressure spikes. Here, the pressures on both banks are equal and pulse free after the x-crossover, regardless of RPM. Additionally, secondary scavenging of the entire collector systems occurs in both banks. How this works (with a four-into-one header) is there is a slightly lower pressure in the exhaust system behind the x-crossover. That lower pressure creates the additional scavenging. Volumetric efficiency is improved at all engine speeds and you can sometimes see a power gain. Engines with high overlap cams will see an improvement in idle quality also. Finally, the pop you might have heard in the exhaust disappears. The reason is, the exhaust pulses have been smoothed out. But what you’ll get (especially if the system is open with no mufflers) is a higher frequency scream from the exhaust.
We have some personal insight into crossovers: When this writer toiled for a print based drag race magazine, we once tested a brand spanking new x-crossover (sans mufflers) on an NHRA-legal Buick Stock Eliminator car (x-crossover pipes were a top secret NASCAR design at the time and I managed to get ahold of one for test purposes). The tests were performed in the typical A-B-A format (in this case, with the crossover installed, without the crossover and then with the crossover installed again). We had a quality weather station on hand and we watched the environmental conditions closely. It didn’t gain much on the very well sorted out car, but it did add some weight to the Buick; the weight increase could have marginalized a small performance gain. But the really big news was the roar it caused in the pits. Many competitors figured the Stage 1 car was now fitted with (an illegal) 180-degree crankshaft! The car positively shrieked, and we all know that doesn't really happen with a relatively low RPM Buick stocker. There were plenty of grizzled “rail birds” watching every pass that Stage 1 made, and more than a few “casual” visitors showed up in the pit space. We never did show them the parts.
OK. There's evidence that carefully designed mufflers and free-flowing exhaust system parts can actually improve performance. What about decreasing noise? Describing sound is difficult, if not impossible. That's why decibel meters are used to measure sound. Unfortunately, the difficulties that arise when measuring sound are complex. For example, most modern car body panels can cover all of the exhaust system, but even minor changes in the way the exhaust exits the car can have an effect upon “noise.” If a car is equipped with turnouts on the exhaust, it can have a decidedly different decibel reading when the turnouts are moved to an alternate direction or where the exhaust exits straight back. Some cars with exhaust cross over systems are quieter than those without. In some cases, a muffler with a longer tailpipe will be quieter than one without. Because of these factors, it's in your own best interests to contact the exhaust manufacturer to determine how the system you have selected will perform from a noise perspective on your car and, equally important, your particular engine combination.
That’s a wrap for this issue, but we’re not quite done yet. In the next segment of our series, we’ll take a closer look at exhaust system construction along with materials choices. You might be surprised to find that not all stainless steel exhaust systems are created equal. Watch for it.
The most common North American V8 engine layout is based upon a 90-degree crankshaft. If you examine a typical V8 crank you’ll see four sets of connecting rod journals, and all of them are positioned 90 degrees from each other.
With a 90-degree crank, on each cylinder bank two cylinders fire within 90 degrees of one another.
“X” styles of cross overs are typically much more efficient than “H” pipes. The x-layout re-synchronizes exhaust pulsing along with exhaust pressure spikes.
While you can’t easily see inside, the actual shape of the x-crossover has an influence upon the effectiveness of the system as well as the power output.
There are two different versions of this exhaust system – one has 2.5-inch diameter pipes and mufflers. The other has 3.0-inch diameter pipes and mufflers.
