Finally, Project 9-2X gets a dose of boost and bolt-on power. So far, we've taken care of interior amenities such as the stereo and electronics and also set up the suspension, wheels and tires. It's taken us four installments on this project to get to the power department; doubtless you've become impatient. With only a cat-back exhaust, cold-air intake and a little tuning, we managed to squeeze out 25 whp, which is already a quarter of the way to our 300-whp goal. Seems like an easy target now, but I'm readying myself for the inevitability of diminishing returns.
Twenty-five horsepower and two simple bolt-on parts isn't a lot of material to take up an entire project installment. It's pretty straightforward if you are only interested in the power gains and not the why or how. The gains we made are pretty average for what you get out of an intake and exhaust on a small displacement turbo car in terms of numbers. The biggest improvement comes from the faster boost response.
Before we did any tuning, we had to pick the right exhaust. We tested two aftermarket cat-back exhaust systems and compared them to our current exhaust from Saab's accessories catalog. There are a lot of loud exhausts available for the 9-2X and finding a quiet one fitting for a refined sport wagon was a challenge. The Saab optional equipment exhaust features 2-inch piping constructed from thin, stamped steel sections typical of O.E. parts. It's pretty much a cosmetic piece with a polished taper cut tip. There is minimal increase in sound and almost no change in backpressure. I wanted a deeper sound that didn't accentuate the very noticeable exhaust pulses of the Boxer engine.
We tested A'PEXi's World Sport II and GReddy Performance Products' stainless-steel SP2 cat-back exhausts. The A'PEXi World Sport II uses 2.5-inch mandrel-bent, aluminized-steel piping with a stainless-steel muffler. The exterior welds seem rougher, but internally it has smooth rolled flange-to-pipe transitions and good gasket interfacing, not that flow properties will affect horsepower much at this stage. GReddy's SP2 is the more performance oriented system, with full stainless 3.15-inch construction and a smaller muffler unit. Internally the welds and transitions are rougher than the World Sport, but still vastly better than the O.E. piece.
To simply bolt on each exhaust and see which one made more power is moot. Without tuning the ECU specifically for each exhaust it's impossible to really know which system makes more power, especially when the difference might be a matter of splitting hairs. Moreover, power is not necessarily our ultimate goal, otherwise we would have used a straight-through design. It makes a lot more sense to measure exhaust gas backpressure and monitor boost pressure during a dyno pull. Measuring backpressure is a straightforward indication of how good an exhaust is, and by looking at the boost we also get an idea of the throttle response characteristics and the source of added power. With less exhaust restriction, the turbo's turbine side can turn more freely and thus generate more boost at the same shaft speed, and, more significantly, generate boost faster. This is why throttle response is dramatically better with aftermarket exhausts. We sampled exhaust backpressure at the exit of the factory catalytic converter just before the B-pipe exhaust flange. We also datalogged exhaust noise amplitude with a sound meter and compared the differences.
By appearance and sound alone, I would have picked the A'PEXi WS II exhaust. At idle the tone was just right, and as the revs climbed the Boxer and its overlapping exhaust pulses sounded fabulous. It makes that whooshing turbo sound too. Though it didn't make much power, the throttle response was a huge improvement. Even passengers could tell the difference in how the engine picked up and made its transition into boost. This exhaust would have definitely made power with a high-flow intake installed.
Considering our goal of 300 whp, we chose the GReddy SP2 exhaust with the 3.15-inch piping. Without tuning or an intake the exhaust made roughly 7 hp, which is pretty substantial. The larger piping was definitely louder at wide-open throttle, but still within reason. (Even though the data does not show a huge difference between the A'PEXi and GReddy pipes, the difference in sound was definitely audible; decibels, dB, are measured on a logarithmic scale.) The exhaust pulses are more noticeable with the SP2, but we'll hopefully deal with that later using equal-length headers. I'm still trying to come to terms with the exhaust's looks though.
With the exhaust picked out, I reverted the car to stock form and had Eric Hsu of XS Engineering custom tune the engine for more power. Using EcuTek North America software, tuning was a simple matter of re-flashing the ECU via the OBD-II port. The EcuTek software allows a tuner to directly communicate with the O.E. ECU and not only adjust spark, fuel and boost maps, but also correct for different hardware such as injectors, intake plumbing or turbos. This allows us to retain the versatility, closed-loop operation and adaptive capability of the factory ECU, while still allowing us to tune the car reliably to handle 300 whp and all the hardware required to make it.
Since factory tuning from the manufacturer is fairly conservative for the sake of emissions and warranties, there is room for improvement. As with most turbo cars, the main source of power is raising the target boost pressure and leaning out the air/fuel (A/F) mixture. Factory turbo tuning normally runs fairly rich to prevent detonation, so rich that power is often sacrificed. Hsu took about 1% fuel out of the stock fuel map, and raised the target boost to roughly 14 psi. Provisions were made to allow boost to drop to 12 psi after 6000 rpm for safety purposes. The factory calibration dropped to 7 psi. Hsu advanced ignition timing near redline to increase power and reduce exhaust gas temperature (EGT), as well as raising the rev and boost limit to 7300 rpm and 17 psi, respectively. The EcuTek software also allowed us to disable certain check engine light parameters to avoid throwing the engine management into a fault mode. The gain through custom dyno tuning is not so apparent at this stage, but later on as our hardware becomes more complex and unique, the advantage of custom tuning from a reputable tuner will far exceed what you get out of generic chips or flash programming.
With 215 whp and massively superior boost response, I'm temped to say Project 9-2X has become the car we would have wanted out of the box. It's definitely more fun as both handling and throttle response have vastly improved. With the ECU re-flashed, you can actually modulate the boost with the throttle, and the on-and-off feel the car originally came with is gone. The best part is that it's still fairly stock as far as appearance and sound. There are no strange sucking intake sounds or ricey sounding exhausts. The only fault we found with the more aggressive tuning is the car's sensitivity to sudden large throttle changes. That's just one of the drawbacks of a mechanical throttlebody.
For our intake we chose AEM's cold-air unit. We figured any open element intake will make a lot of noise, so we might as well go extreme and try to gain as much power as possible. AEM's years of experience in making intakes is pretty clear when you examine how well thought out the products are. We were pleasantly surprised to see that they even supplied a rubber grommet liner to fit around the sheet metal opening that the CAI pokes through. AEM's intakes are designed to make power out of the box without any tuning required.
Even so, we strapped the car back on the dyno at XS Engineering and tuned for both the intake and exhaust. The primary change comes from the reduced flow resistance on both sides of the turbo, which will increase the overall efficiency. This change does have an effect on the factory airflow meter. The extreme sensitivity of the meter means it will detect changes in flow from larger diameter piping or shorter flow lengths and deliver a signal that is no longer accurate for the changed airflow. This causes all of the fueling, boost and spark parameters to become slightly off. The EcuTek software allows the tuner to adjust the mass air flow meter curve and bring the A/F ratio and spark timing back to where they need to be. With the added flow at the very top end, Hsu further increased the timing and made the mixture slightly richer near redline. Watching XS Engineering's tuners at work sheds much light on their level of expertise for fine tuning. Data from each run was thoroughly analyzed to give the best combination of safety, power and drivability. This is one of the few tuners I've seen use stethoscopes to listen for knock. According to XS Engineering, the car will still pass smog when we're all done.
All this tuning and added drivability is whetting my appetite for more power. As we wait for parts to come in for our big power build installment, we'll spend some time getting the car ready to handle that power. Next time we'll test brakes, get a clutch and touch up on some odds and ends.
|TAIL OF THE TAILPIPE|
|Saab option part||B-pipe ||9.85 lb||Muffler Section ||19.6 lb||Total||29.45|
|A'PEXi WS II||B-pipe ||11.80 lb||Muffler Section ||21.05 lb||Total||32.85|
|GReddy SP2 ||B-pipe ||12.85 lb||Muffler Section||19.10 lb||Total||31.95|
At a Glance
Estimated time: 2 hours @ $50/hr = $100
A'PEXi World Sport II exhaust: $569.00
GReddy SP2 exhaust: $669.00
AEM cold air intake: $314.28
XS Engineering tuning: $1295.00
A'PEXi World Sport II exhaust
World Sport II exhaust tip
GReddy SP2 Exhaust System
GReddy SP2 Exhaust Tip
The A'PEXi WS II exhaust, left, features smooth internal transitions while the GReddy SP2 has ground down welds.
The A'PEXi WS II exhaust, left, features smooth internal transitions while the GReddy SP2
AEM cold-air intake
Backpressure, boost and sound intensity for the stock, A'PEXi and GReddy exhausts as logged by a Labjack datalogger. You'll note these boost traces do not match with the boost data from the ECU that is presented later. Regardless, seeing the trends still helps to evaluate the differences between each exhaust.
Backpressure, boost and sound intensity for the stock, A'PEXi and GReddy exhausts as logge
Dyno data for each exhaust without intake and untuned.
Exhaust backpressure bung placed directly after the last catalytic converter.