Church Automotive Acura RDX
Wilmington, CA, May 2007
Acura introduced their RDX small crossover to mostly positive reviews right around a year ago. This turbocharged jitterbug features Acura's (and parent company Honda's) first turbocharged automotive motor to ever be offered in North America. This pressurized motivation is channeled through Acura's Super Handling All-Wheel-Drive (SH-AWD) system - a combination of technology that should result in a seriously fun ride - but in our first test of the RDX last year we came away with mixed feelings. Despite claims of "lag free" operation, in stock form the 2.3L DOHC 16-valve 4-cylinder K23T actually suffers from more than a fair amount of boost onset delay, particularly as ambient temperatures increase. Secondly, while the SH-AWD system is capable of orchestrating heroic feats from time to time, the stock RDX's inherent chassis tuning suffers from a degree of understeer that can cause mild irritation. And with no manual transmission offered, the RDX's 5AT can also be a source of frustration during spirited driving.
Shawn Church was one of the TOV editors involved in our road test of the RDX last summer, and while I was scribbling complaints in my notebook about the RDX's too-safe understeer, insubordinate transmission, spongy throttle response, and boost onset delay, Shawn's devilish grin and "let's make lemonade" attitude hinted at the potential he saw in this vehicle. In his mind, Project RDX had already started.
Within weeks, Shawn made arrangements to get a brand-new (privately purchased) RDX into his Wilmington, California shop, Church Automotive. Over the next several months, Shawn would test and tune various tweaks on the vehicle, with the ultimate goal of making the RDX more palatable to the enthusiast. By late spring, the Project RDX had completed its first phase of development, and knowing my sentiments on the RDX, Shawn was eager for me to evaluate his work.
Shawn's still working out the details of pricing and packaging, but he feels that the modifications he's developed (along with Hondata) to this point might be offered as a "Phase I" package. The basic ingredients of the package include alignment tweaks, a +1 wheel and tire package, exhaust system modifications, and a special ECM reflash program developed and tuned in cooperation with Hondata.
The Chassis Doesn't Need Much
First of all, to address the understeer situation, Church specifies a camber kit for the front wheels. This keeps more of the tire's contact patch connected to the road during hard cornering, which provides more grip. Church decided that a good starting point for the street is about 1.5 degree of negative static camber up front, and zero toe all around. If you wish to get a little more aggressive and dial in more negative camber (at the risk of accelerated tirewear), a second camber kit (and a highly skilled alignment specialist) will be required. The next chassis upgrade is equally simple, yet puts a much larger dent in the budget. On this development car, Church fitted 19x9.5" SSR GT7 wheels (from the TireRack) and wrapped them in 245/45ZR19 Kumho Ecsta SPT tires. These tires are on the low end of the price spectrum but in our testing, this wheel/tire package resulted in a vastly improved overall feel with only a small (but easily digestible) penalty in ride quality. SSR wheels have a reputation for providing a great combination of high strength and low weight. This wheel/tire combo weighs around 5lbs less than the stock wheel/tire combo per corner, which means the suspension has to deal with that much less unsprung weight and the reduction in rotating mass aids drivetrain performance as well. Besides the impressive weight savings, these wheels look great on the RDX.
Though the modifications to the chassis are limited, the improvements are dramatic. The combination of more aggressive alignment up front with the grippier (and lower mass) tires results in a significant improvement in handling feel as well as overall performance. Initial turn-in response is much better than stock (so good, you have to remind yourself you're driving a compact sport ute) and the overall balance feels far more neutral. While oversteer is a concept that's completely foreign to the driving experience of a stock RDX, the Project RDX can actually be steered a with the throttle, and this generates huge grins. Peak cornering forces are increased dramatically, making for a seriously fun ride.
Give me a Brake
Perhaps one of the RDX's biggest chassis shortcomings is its stock braking system, which can be overwhelmed (with relative ease) by the RDX's kinetic potential. To that end, rather than bolting on an expensive big brake upgrade kit (and sending the "Phase 1" package pricing through the roof), Church ordered a set of custom brake pads from Porterfield. We installed the pads on the Project RDX immediately prior to our testing, and it's possible that we didn't fully bed them in properly, but during some spirited canyon runs I found that the aftermarket pads were still prone to more fading than we feel is appropriate for something with this performance potential. Additionally, I (and Church agrees) would also like a bit more initial bite from these pads, so another pad formulation will likely be tested.
SH-AWD needs a rheostat
A curious byproduct of the Project RDX's improved grip and turn-in response became apparent in our testing. While the SH-AWD tuning on the stock RDX is already pretty subtle, it seemed like I had to work a bit harder to get SH-AWD's torque vectoring to come into play on the Project RDX. At first I wondered why this was the case, but then I realized that the additional grip and improved turn-in response meant that less steering input is required to negotiate the twisties. SH-AWD's torque vectoring algorithms are based upon a number of factors, and steering angle is one of them, so with less steering angle input, the SH-AWD system responds with a lesser degree of torque vectoring. I found that I could largely overcome this situation by quickly jabbing some extra steering lock to increase the yaw rate, and then I could modulate the steering as necessary. It would be nice if there were a way to spoof the steering angle signals so that the SH-AWD system would apportion torque in greater proportion to steering input, but at the moment there's no such mechanism. Ideally, some sort of driver selectable control of this function would make a great feature on stock RDX's as well (perhaps offering "Sport", "Touring", and a third mode of some sort).
Under the hood, Church employed several proven methods for amping up the performance of the motor. First of all, a new custom downpipe has been fitted, reducing restriction on the outlet side of the turbocharger. Downstream from that, the RDX's restrictive exhaust has been replaced with a custom designed 3" stainless steel catback system, utilizing two mufflers and a resonator to keep the exhaust note in check. For now, the secondary catalytic converter has been deleted. To extract the greatest benefit from these modifications, Church and the wizards at Hondata have spent hours on the dyno meticulously crafting a tuned engine computer reflash to take advantage of this increased flow. Ignition timing, boost, fuel curves, and cam timing parameters have all been optimized for the improved exhaust flow. On the dyno, the results are tantalizing - horsepower and torque jump from 210whp@5000rpm/243lb-ft@3400rpm to 249whp@5500rpms and more than 290lb-ft@3400 rpm. (click here for dyno plot)
While those gains are impressive, on the street the most noticeable benefit is the spool time of the turbocharger. From a dead standstill this RDX shaves a full second off the RDX's 0-60 time, and you can really feel the improvement. If you don't believe me, take a look at the two plots to the right, which depict the two RDXs' 0-60 runs. The first one shows the time to distance, while the second plot shows the time to speed, with the Project RDX holding a clear and immediate advantage in both cases. With no brake torquing, we recorded a 0-60 time of 7.8 seconds in a dead stock 2007 RDX and the Project RDX did the same deed in 6.8 seconds. With brake-torquing, the Project RDX is capable of ripping off 0-60s in the 6.0s range, though repeated brake-torquing quickly takes its toll on performance, thanks to a significant amount of heatsoak. We didn't try brake torquing the stock RDX we had with us for this test, but another stock RDX we tested last year posted a best time of 6.9 seconds with brake torquing, so it's good to see that the Project RDX is capable of matching or surpassing this time without resorting to abusive techniques.
Time to Distance Comparison
Time to Speed Comparison
From the seat of the pants (and verified by the plots extracted from our GPS-based Racelogic gear), Project RDX's peak acceleration in first and most of second gear is noticeably stronger than stock, with the turbo spooling much sooner and much harder than a stock RDX. Note that I've only mentioned 1st and 2nd gear; in the upper gears, while performance is improved, the difference in pace between the Project RDX and a stock version diminishes considerably. This is primarily due to the smallish turbo that Honda engineers specified for the K23T. Bottom line, if you're looking to improve the responsiveness of your RDX in the cut and thrust environment of in-town driving, this package of engine mods delivers the goods and improves the fun-to-drive factor exponentially.
Church Automotive's first crack at the RDX is a good one. Not only is there a meaningful improvement in objective performance numbers, but there's also a significant improvement in subjective performance, making it far more of a driver's vehicle. It's so good, I would almost consider picking up my own RDX in order to apply this treatment, but the lack of an available 6-speed manual transmission remains a huge barrier to that event. While production of this kit hasn't yet been confirmed, Church estimates that if this package were to be offered, a full Phase I package would run around $3000-3500 (plus installation), with around half of that cost attributed directly to the wheel and tire package. On a tighter budget, one could skip the wheels and tires for a big savings, and go for the rest of the upgrades and still see a huge return on your upgrade investment.