Synchronicity By Wayne Scraba
from Dr. Gas.com (this article is currently not available on line)
An upside-down car at Daytona helps solve a Winston Cup riddle.
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.
The heart of the Dr. Gas system is this crossover junction. At this point, the crossover is unwelded. As you can see, it's not a simple "X." instead, the separate halves of the exhaust system are effectively merged. (Wayne Scraba)
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.
In practice, the crossover tubing is kept the same size as the collector up to the crossover, the crossover should be located after the transmission and cross member have been cleared. This will usually be 12'-36' after the collector flanges. After the crossover, smaller tubing may be used since the flow is very smooth and pulsations are gone. Butler offers the system in many tubing sized, shapes and materials. Oval section tubing is available for low ground-clearance application (e.g., a Winston Cup car). The Dr. Gas crossover can also be built in carbon steel or 304 stainless Nickel plating and high-temp coatings are readily available too.
The crossover system approaches the same efficiency (and sound) as a true 180-degree header system without the nightmare of the tubes going everywhere. The riddle is solved.
"You boys better hold on 'cause I'm gonhafta stand on it" ~ Dad Seegle