Remember that radio and TV commercial about the piston engine going "Boing-Boing," when it out to go HUMM? Well, all V8 engines with 90 degree cranks, have an out of sync imbalance in their firing order between the right and left cylinder banks.
, they do go "Boing-Boing." The firing order imbalance is a necessary sacrifice for dynamic balance of the rotating and reciprocating crank, rods and pistons. Each time the firing order is completed (two full revolutional), two cylinders within each bank will fire and exhaust within 90 degrees of each other. These two cylinders will be exhausting into the header collector or exhaust manifold almost simultaneously. This overlapping condition creates a lot of back pressure and a pop sound. Meanwhile, the opposite exhaust manifold has no activity (or pressure) in it at all. This is where the characteristic, low harsh popping V8 sound comes from.
The most common way of reducing this out of sync imbalance is with rebalancing crossovers such as H pipes and over-and-under X style crossovers. These provide both noise reductions and efficiency (power) improvements. H pipes are effective only at low and mid range. The over-and-under X crossover works a little better but still does not completely rebalance the exhaust at high RPM.
Dr. Gas, Inc. has developed a new generation of crossovers that uses a tangentially siamese junction, in place of the H or over-and-under X. It evenly splits, smoothes, and synchronizes exhaust pressures at all engine speeds. The high and low pressure pulses in the two pipes are evenly imposed on each other, leveling out the pulse time history pressure differences between right and left cylinder banks. Re-synchronizing the exhaust pulses reduces back pressure, cancels sound, and provides additional scavenging. Tests have sound 6 dBa (75%) reduction in sound levels, and increases of 10 to 30 hp, and up to 40 ft-lbs. of torque! Economy, and throttle response are improved. Exhaust flow after the crossover is completely smoothed out. The job the headers started is finished.
One of the most appealing benefits of this system is the modified exhaust note. The deep growling and popping sound is replaced by a higher pitched smooth sound. The exhaust note is similar to a 180 degree header system without the nightmare of tubing.
Here's a clue. Bobby Labonte got upside-down at Daytona during his 125-mile qualifier and showed the world how his guys mate the exhaust from the right and left side of the engine. This system is similar to the one created by Dr. Gas. (Sam Cranston, Daytona Beach News-Journal)
The early-season upside-down adventure at Daytona of one Bobby Labonte provided onlookers with a worm's eye view of one of Winston Cup's best kept secrets - and solved the mystery of the unusual sound of two-time Daytona 500 winner Sterling Marlin's car. In 1995, most technically astute patrons at the NASCAR® season opener, including pit road reporter Mike Joy for CBS, perceived a different sound to Marlin's car, as if it were fitted with 180° headers. The next hypothesis - that the Morgan-McClure team was using a "flat" crank - was simple, logical… and dead wrong. Turns out it was the exhaust system past the headers that accounted for the change in engine note.
With Labonte's timely escapade, most observers figured they had a handle on the deal, The exhaust pipes were joined in an "X" pattern under the car. Close, but no cigar. That's when SCR decided to poke around. As luck (skill?) would have it, we discovered the real answer. And it wasn't even close to NASCAR®-land. The equipment responsible for the exhaust note originates from the sleepy confines of Sandy, Utah.
There, Boyd Butler, the owner of Pro Motorsports Engineering, has made an exact science out of exhaust system tuning. One of his products is the Dr. Gas crossover - the piece that has turned Winston Cup upside-down (figuratively.) Here's how it works.
All V-8 engines with 90-degree cranks have an imbalance in the firing order between the right and left cylinder banks. The firing order imbalance is a necessary sacrifice so that a dynamic balance of the rotating and reciprocating assembly (crank, rods and pistons) can be maintained. Each time the firing order is complete (two full revolutions of the crank), two cylinders within each bank fire and exhaust within 90 degrees of each other. Because of this, this pair of cylinders will be exhausting into the header collector (on one bank) almost simultaneously. This overlap creates a back pressure. Meanwhile, the header on the opposite bank has no activity (or pressure) in it at all. Conventional full-length four-tube headers help separate the exhaust in the cylinders until it reaches the collector. After the header primary tubes dump into the collectors, the two cylinders close to each other in the firing sequence again are fighting for space in both the collector and exhaust pipe. This results in reflected pressure waves traveling backwards though the exhaust system. What you get is more backpressure, diminished power and fuel economy, and the V-8's characteristic growl.
Wouldn't a traditional H-pipe crossover, or equalizer, allow some of this excess pressure to bleed over to the "quiet side" of the exhaust system? Jere Stahl ran 330 gallons of fuel through a pair of street engines in part throttle dyno testing to find out. One was a 350 small block, the other a 400 small block. Testing at 2550 RPM and 3050 RPM, primarily at part throttle, in HP ranges from 35 to 125, Stahl found that a balance tube actually hurt fuel distribution on every manifold/header combination he tested. It never helped at full-throttle power, either.
Some people have found small low and mid-range torque improvements using an H-pipe. But at high RPM, the gases cannot bleed across the H-pipe fast enough to help power very much. The double cross, X-crossover, is an improvement beyond the H-pipe, but does not resynchronize pulsing and pressure spikes completely.
That's where the Dr. Gas Crossover differs. It evenly splits the flow in the crossover junction. The pressures on both banks are equal and pulse-free after the crossover, regardless of RPM. In addition, secondary scavenging of the entire collector system occurs in both banks are equal and pulse-free after the crossover, regardless of RPM. In addition, secondary scavenging of the entire collector system occurs in both banks. Volumetric efficiency and power are improved at all engine speeds. Engines with high overlap cams (a typical race engine) will also see an improvement in idle quality.
As many observers at Daytona suggested, the engine exhaust not is changed with this system as well. The deep growl common to V-8s is replaced by a smoother, higher-pitched sound, almost like a high-RPM Japanese motorcycle engine or the shriek of an Indy car. Typical sound reductions of 4 to 6 DBA (a 75% decrease) are realized, with an overall increase in power.
Just now much power are we talking about? This is one of those "it depends" things. Every combination sees different gains, but in testing, the power increase range runs from 5-20 HP at wide-open throttle (with corresponding increases in torque output). Your typical Cup car can see something in the neighborhood of at least 5-10 HP in restrictor trim with this combination. Incremental gains are seen through the entire RPM range.
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Awesome article! 
i've scraped a couple times but as long as you go slow over rail road tracks your fine, plus im lowered an extra 2".
