2002 Hayabusa GSX1300R
"If you ride like there's no tomorrow, there won't be."
|Current Wet Weight: 499 Pounds ~ Stock Wet Weight: 550|
"A Day With A Master Tuner" (Link: Brock Davidson )
As a a personal user of a BDE Street Smart exhaust, I was curious about the specific power output and air/fuel ratio curves of my `02 Hayabusa. Being rather persnickety about my bike, I wanted an equally persnickety tuner to check it and I figured who better than the designer himself. So, I called Brock Davidson (BDE) at his Ohio headquarters and he agreed to take some time from his busy schedule to verify my engine performance using the maps that he developed for Power Commanders--the same maps that are provided to all Street Smart owners. When the dyno dust had settled, as Brock already knew, the session proved that his mapping was right on target. I had the opportunity to peek at some of the many dyno files on his computer and it was obvious that his maps are developed through countless hours of dyno work. I enjoyed spending the day with him as he focused upon my bike. It was interesting and enlightening. The man knows his stuff...!
During recent months, my Busa has been primarily ridden in the low and middle range of the power band, cruising local Interstate highways and running the twisties and sweepers around Deal's Gap, North Carolina. The Busa was overdue for a good, full-boogie, blowout to remove power-robbing varnishes from the injectors and intake valves, and carbon deposits from the combustion chambers and exhaust valves. Toward that purpose, Brock loaded a standard Busa "fuel" map into my PCIIIR and ran some oxygenated VP MR-9 (Ultimate 9) fuel through the Busa to clean it out. Adhering to his tried-and-proven testing methodology, Brock made some load runs to check air/fuel settings and then, the Hayabusa ripped a credible 174.6 horsepower run with 104.5 pounds of torque! The lightweight, thin-wall, Stainless header tubes were glowing red (click pictures below to enlarge).
Keep in mind that this is an internally-stock engine with a Street Smart exhaust, A PCIIIR, a BDE PAIR kit , and Brock's air box mod and lid without an air filter. 174 HP is about a 20 HP gain over the typical factory Busa horsepower! Not too shabby, eh? Brock commented that he had seen similarly equipped Busas' make slightly more power and others make slightly less power. In essence, mine was right where it should be and I was a happy camper.
Next, we moved on to the realm of gasoline. Brock pumped the VP fuel out the gas tank, replaced it with a few gallons of fresh Shell 87 Octane pump gas, and loaded his "027B" map into my PCIIIR. This is the exact map that is given to all `02-and-newer Hayabusa Street Smart exhaust customers. After a few runs to check the air/fuel ratios under various dyno loads (with a loose drive chain), the Busa produced 168.2 HP and 101 pounds of torque on the Model 250 Dynojet Dynamometer.
The peak power numbers are only part of the story. I explained to Brock that my drag racing years are over and that my riding is now done in mountain twisties and on casual sport touring trips (with the emphasis on "sport"). I asked him if he could tweak any more low and mid-range throttle response out of the Busa with the air filter installed--just as I ride it. As a professional drag racer who tunes for maximum performance, he may have thought my request was odd but, being an affable guy, he gave me an understanding grin and went back to work. I loved it.
The stock air filter was reinstalled in the air box and Brock put the Busa under load on the dyno in the lower gears while, again, carefully watching the air/fuel readings on the various map tables. After making surprisingly few map adjustments, he soon arrived at a point where he was essentially "splitting hairs" with map settings. Viola! The job was done and the minor map tweaks that he made for low/mid-range optimization confirmed just how good his standard maps are. The air filter cost almost 2 HP at the top end but the engine "barks" instantly from idle and the mid-range torque is, well...v-e-r-y rewarding for a power junkie like me. The power band is bountiful everywhere with an air/fuel curve that undulates gently just below a 13.0:1 ratio.
Since weight is the biggest enemy of performance, my Busa has been through extensive dieting and its current wet weight of 498 pounds (with a very small amount of gas in the tank), is a good 50 pounds less than a factory stock Busa. With 166.55 HP on tap in full street trim, the power-to-weight ratio works out to 2.99 pounds per horsepower compared with about 3.57 pounds per horsepower for a stock Busa. That translates into potent street performance that is entirely adequate for my riding style. What a bike! Happy camper? Indeed...!
Just to keep things in perspective, I am compelled to point out that, although dynamometers are excellent relative tuning tools ("relative" being the key word), the results of one dyno cannot be quantitatively compared with another dyno due to the many variables associated with their operation. Those variables are beyond the scope of this article so suffice it to say that your results will vary somewhat with either higher or lower numbers. Dyno numbers are absolute for that dyno, at that time, with that bike, and making comparisons with a different dyno is tantamount to comparing apples with oranges. Also, maximum possible peak power is certainly a desirable goal but, for many Busa street riders, it is unwise to obsess over peak numbers because the nature of the power band is equally important. Why? Simple, most time spent riding and accelerating is done in the mid-range area. Comparing two bikes and riders that are otherwise equal in all respects, the bike with the highest average power across the distance will typically win a contest of acceleration.
Note: It is strongly recommended that you check the setting of your Throttle Position Sensor (TPS). Mine was improperly set at the factory and the penalty is lost power. Brock adjusted it correctly and said he had seen several other Busas' that were out of adjustment. Also, we changed oil on the dyno from Motul 5W40 synthetic to Pro Drive 21 <0 (less than Zero weight) and immediately saw about a 2 HP gain...!
Happy trails. ~ Ride safely!
There are always many
questions about exhaust issues in the motorcycle world. This article will
attempt to dispel certain exhaust "legends" to clarify the exhaust
process as it relates to inline-four motorcycle engines. Much of this info was
extracted from a copyrighted article I authored several years ago titled Exhaust
Theory. If you think that designing and building an effective high
performance exhaust system is a mundane endeavor, please read on.
Let's establish a few facts first, straight from the discipline of contemporary Physics.
No header/exhaust system is ideal for all applications. Depending on their design and purpose, all exhaust/header systems compromise something to achieve something else. Before performing header or other exhaust modifications to increase performance, it is critical to determine what kind of performance you want. Do you want max low RPM power, max mid-range power, or max peak-RPM power? Maybe you just want an exhaust that looks cool. Or do you want the best of all worlds? In the latter case, a well-designed aftermarket exhaust system is where you'll find it.
If you are wowed only by peak HP numbers on a dyno chart, consider the following: For a vehicle to cover "X" distance as quickly as possible, it is not the highest peak power generated by the engine that is most critical. It is the highest average power generated across the distance that typically produces the quickest time. When comparing two power curves on a dynamometer chart (assuming other factors remain constant), the curve containing the greatest average power is the one that will typically cover the distance in the least time. This fact is what makes the nature of the powerband important. You don't want to give up powerful mid-range performance just to have the highest peak power numbers--that's only good for bragging rights and will hurt your acceleration because acceleration also occurs through the mid-range, not just at the highest RPM. Actually, we want both (maximum mid-range power and maximum peak power) don't we? I'll answer for you--YES!
In the strictest
technical sense, an exhaust system cannot produce more power on its own.
The potential power of an engine is determined by the amount of fuel
available for combustion. More fuel must be introduced to increase
potential power. However, the efficiency of combustion and engine pumping
processes is profoundly influenced by the exhaust system. A properly designed
exhaust system can reduce engine pumping losses. Therefore, the
primary design objective for a high performance exhaust is (or should be) to
reduce engine-pumping losses, and by so doing, increase volumetric
efficiency. The net result of reduced pumping losses is more power
available to move the vehicle. As volumetric efficiency increases,
potential fuel mileage also increases because less throttle opening is required
to move the vehicle at the same velocity. This is where the old bugaboo of
back-pressure rears it's ugly, mythical head. Much controversy and confusion
surround the issue of exhaust back-pressure which, in other terms, is a pumping
loss. Many performance-minded people (including some "professionals")
who are otherwise well-enlightened still cling tenaciously to the old cliché
"You need some back-pressure for best performance." WRONG--period
> if your definition of "best" performance is "maximum power
throughout the powerband".
For virtually all high performance purposes with a modern, in-line four engine...back-pressure in an exhaust system increases engine-pumping losses and decreases potential maximum engine power. It is very tempting to repeat this statement in huge letters for emphasis but maybe red letters will suffice. Are we clear about this?
Here is something to chew on: Theoretically, in a normally aspirated state of tune without special fuel or oxygen-rich additives, an engine’s maximum power potential is directly proportional with the volume of air it flows. This means that an engine of 750 cc has the same maximum power potential as an engine of 1000 cc... if they both flow the same volume of air. In this example, the powerband characteristics of the two engines will be quite different but the peak attainable power is essentially the same. In view of this reality, I have amended the old hot rod proverb "There's no substitute for cubic inches" to include..... "except more efficiency!"
Many "performance" people resist some of these notions but their resistance does not change reality nor the laws of physics.
Are you still awake? Okay, let's establish a few Rules of Thumb.
1- Longer header tubes tend to increase power below the engine’s torque peak and shorter header tubes tend to increase power above the torque peak.
2- Large diameter headers and collectors tend to limit low-range power and increase high range power. Conversely, small diameter headers and collectors tend to increase low-range power and limit high-range power.
3- "Balance" or "equalizer" tubes between the header tubes tend to flatten the torque peak(s) or widen the powerband.
4- Stainless headers do not transfer heat to the ambient air as fast as mild steel headers. Keeping more of that heat "inside" the header pipes aids exhaust flow because the exhaust gas is more energetic and it reduces the amount of heat flowing across the engine (and across you).
The objective of most engine modifications is to maximize air and fuel flow into, and exhaust flow out of the engine. The inflow of an air/fuel mixture is a separate issue, but it is directly influenced by exhaust flow, particularly during valve overlap (when both valves are open for "X" degrees of crankshaft rotation). Gasoline requires oxygen to burn. By volume, dry, ambient air at sea level contains about 21% oxygen, 78% Nitrogen and trace amounts of other gases. Since oxygen is only about 1/5 of air’s volume, an engine must intake 5 times more air than oxygen to get the oxygen it needs to support the combustion of fuel. If we introduce an oxygen-bearing additive such as nitrous oxide, or use an oxygen-bearing fuel such as nitromethane, we can make much more power from the same displacement because both additives bring more oxygen to the combustion chamber to support the combustion of more fuel. If we add a supercharger or turbocharger, we get more power for the same reason…. more oxygen is forced into the combustion chamber.
Perhaps the most important aspect of exhaust flow is the issue of flow volume verses flow velocity. This also happens to apply equally to intake events.
An engine needs the highest flow velocity possible for quick throttle response and torque throughout the low-to-mid range portion of the power band. The same engine also needs the highest flow volume possible throughout the mid-to-high range portion of the powerband for maximum performance. This is where a fundamental conflict arises. For "X" amount of exhaust pressure at an exhaust valve, a smaller diameter header tube will provide higher flow velocity than a larger diameter tube. Unfortunately, the laws of physics will not allow that same small diameter tube to flow sufficient volume to realize maximum potential power at higher RPM. If we install a larger diameter tube, we will have enough flow volume for maximum power at mid-to-high RPM, but the flow velocity will decrease and low-to-mid range throttle response and torque will suffer (the "back-pressure" myth probably arises from a misunderstanding of these factors). This is the primary paradox of exhaust flow dynamics and the solution is usually a design compromise that produces an acceptable amount of throttle response, torque and horsepower across the entire powerband.
Now, on to Hayabusa-specific exhaust matters.
In the picture above, a BDE/Hindle exhaust is used for
comparison with the factory system but it could be any of the top 3 or 4 Busa
Item # 1 - Note the "stepped header" tubes, a trick developed by drag racers. The first few inches of header tubes are welded to slightly larger diameter tubes for the journey to the merge collectors. This maintains high gas velocity at the head's exhaust port and allows for higher gas volume as the gases flow through the headpipes. Also, notice the smooth mandrel bends in the BDE tubes which allow the inertial gas colume to change directions with less resistance than sharper bends for reduced pumping losses.
Item # 2 - The differences between the BDE and factory tube diameters clearly show the higher flow capacity of the BDE tubes. Again, with gentle mandrel bends.
Item # 3 - This is the primary design bottleneck of the factory design. Suzuki uses an "X" collector/crossover which generates substantial turbulence (resistance) as opposed to the BDE merge collector which maintains a more laminar gas flow for reduced pumping losses.
Item # 4 - The factory and BDE tailpipe diameters are determined here. The BDE diameter is larger, but wait...! There are two tailpipes on the factory exhaust so it can flow more, right? Right, but the gas flow velocity drops dramatically in the factory exhaust because of it.
Item # 5 - The factory PAIR pump is shown with assorted hoses.
Guess what? There's more. It's called scavenging!
Inertial scavenging and wave scavenging are different phenomenon but both impact exhaust system efficiency and affect one another. Scavenging is simply gas extraction. These two scavenging effects are directly influenced by tube diameter, length, shape and the thermal properties of the tube material (stainless, mild steel, titanium, etc.). When the exhaust valve opens, two things immediately happen. An energy wave, or pulse, is created from the rapidly expanding combustion gases. The wave enters the header tube (or manifold) traveling outward at a nominal speed of 1,300 - 1,700 feet per second (this speed varies depending on engine design, modifications, etc., and is therefore stated as a "nominal" velocity). This wave is pure energy, similar to a shock wave from an explosion. Simultaneous with the energy wave, the spent combustion gases also enter the header tube and travel outward more slowly at 150 - 300 feet per second nominal (maximum power is usually made with gas velocities between 240 and 300 feet per second). Since the energy wave is moving about 5 times faster than the exhaust gases, it will get where it is going faster than the gases. When the outbound energy wave encounters a lower pressure area such as a larger collector pipe, muffler or the ambient atmosphere, a reversion wave (a reversed or mirrored wave) is reflected back toward the exhaust valve with little loss of velocity.
The reversion wave moves back toward the exhaust valve on a collision course with the exiting gases whereupon they pass through one another, with some energy loss and turbulence, and continue in their respective directions. What happens when that reversion wave arrives back at the exhaust valve depends on whether the exhaust valve is still open or closed. This is a critical moment in the exhaust cycle because the reversion wave can be beneficial or detrimental to exhaust flow, depending upon its arrival time at the exhaust valve. If the exhaust valve is closed when the reversion wave arrives, the wave is again reflected toward the exhaust outlet and eventually dissipates its energy in this back and forth motion. If the exhaust valve is open when the wave arrives, its effect upon exhaust gas flow depends on which part of the wave is hitting the open exhaust valve.
A wave is comprised of two alternating and opposing pressures. In one part of the wave cycle, the gas molecules are compressed. In the other part of the wave, the gas molecules are rarefied. Therefore, each wave contains a compression area (node) of higher pressure and a rarefaction area (anti-node) of lower pressure. An exhaust tube of the proper length (for a specific RPM) will place the wave’s anti-node at the exhaust valve at the proper time for it’s lower pressure to help fill the combustion chamber with fresh incoming charge and to further extract spent gases from the chamber via vacuum effect. This is wave scavenging or "wave tuning".
From these cyclical engine events, one can deduce that the beneficial part of a rapidly traveling reversion wave can only be present at an exhaust port during portions of the powerband since it's relative arrival time changes with RPM. This makes it difficult to tune an exhaust system to take advantage of reversion waves which is one reason why there are various anti-reversion schemes designed into some header systems and exhaust ports. These anti-reversion devices are designed to weaken and disrupt any detrimental reversion waves (when the wave's higher-pressure node impedes scavenging and intake draw-through). Such anti-reversion schemes include merge collectors, truncated cones/rings built into the primary tube entrance and exhaust port ledges.
Unlike reversion waves that have no mass, exhaust gases do have mass. And since they are in motion, they also have inertia (or "momentum") as they travel outward at their comparatively slow velocity of 150 - 300 fps. When the gases move outward as a gas column through the header tube, a decreasing pressure area is created in the pipe behind them. It may help to think of this lower pressure area as a partial vacuum and one can visualize the vacuous lower pressure "pulling" residual exhaust gases from the combustion chamber and exhaust port. It can also help pull fresh air/fuel charge into the combustion chamber. This is inertial scavenging and it has a major effect upon engine power at low-to-mid range RPM.
If properly timed with RPM and firing order, the low pressure that results from gas inertia can "spill-over" into other primary tubes, via the collector(s), and aid the scavenging of other cylinders in that bank.
There are other factors that complicate the behavior of exhaust gases. Wave harmonics, wave amplification and wave cancellation effects also play into the scheme of exhaust events. The interaction of all these variables is so abstractly complex that it is difficult to fully grasp. I am not aware of any absolute formulas or algorithms that will produce a perfect exhaust design. Even factory super-computer exhaust designs must undergo dynamometer and track testing to determine the necessary tube adjustments for the desired results.
We riders are the benefactors of this technology and the cost of 10 - 16 additional rear-wheel horsepower is a performance bargain.