To meter more air and make more power, we needed to modify the signal from the MAF meter. This is only a good idea if you can also completely retune the ECU so it knows how much fuel to inject per the modified signal. DiabloSport, a Florida-based tuning company specializing in domestic tuning and ECU hardware, supplied us with its MAFia interface.
The MAFia is basically a variable potentiometer that plugs in between the stock MAF and the wiring harness leading to the ECU. By intercepting the MAF signal, the MAFia scales down the output voltage read by the ECU. This keeps the ECU happy as the output remains within its zero to five-volt constraints while maintaining the original MAF transfer function profile. The MAFia has eight selectable scaling factors for horsepower ranges up to 800hp.
For our purposes, modifying the airflow signal for up to 300hp of flow is acceptable, but only to an extent. Since the ECU will only read between zero and five volts before getting pissed off, scaling the signal to accommodate more airflow will decrease the resolution. For example, let's say the stock ECU was designed with 10 tunable points between idle and 150 stock horsepower's worth of air. That gives an accurate map to correct the fuel curve every 15 horsepower.
Moving 300hp's worth of air with the stock 10 calibration points can only control fueling between every 30hp's worth of airflow, which makes for a less accurate fuel tune map. Imagine what happens when correcting the MAF signal for 800hp. While the ECU can be modified to manage that kind of power, the large spread between tuning points would mean a rough engine that would offer questionable part-throttle driveability.
With the ability to measure more air, we also needed more fuel. The 42lb/hr (or 440cc/min) upgraded injectors added to our PTE kit operated happily at the 10psi peak boost off the wastegate, but if we were to add more boost, then we'd start to worry about needing larger injectors and, more importantly, replacing the stock fuel pump, which we think will only support up to 350bhp. The best way to find out was to start tuning and see how much more boost and fuel was needed.
There was yet one more limitation. The stock SVT manifold is a laughable plastic affair that uses crimp clamps to secure flexible hoses between the head and the manifold runners, unlike other solid metal or plastic manifolds. There was a good chance that these clamps (never meant for positive pressure) would pop right off if boost pressure went much further past the point we were already at.
After a whole day of 30-minute breaks while waiting for the ECU to reflash with a new program, we finally arrived at a decent compromise of 256 wheel-hp and 236lb-ft of torque at 12psi of peak boost. Just a 10 wheel-hp gain over the 246 wheel-hp the stock bottom end made before it grenaded. The low-rev difference in power is attributed to the change in compression.
While there's plenty more power to be made, 12psi of boost has pretty much maxed out the 42 lb/hr fuel injectors. We could have spent another $200 for a set of 60lb/hr injectors and continued to raise the boost, but based on FocusSport's experience, the manifold was only good for up to a reliable 14psi of boost. Two hundred bucks for two psi didn't seem worth it, so we called it a day.
At 256 wheel-hp, we're now on a level playing field with the stock Cobra, with hopefully less weight. If it sounds like we've shorted ourselves on the serious power that we'd need to beat the Cobra, we did. But 256hp to the wheels is seriously fast, especially when coming from a laggy GT2871R turbo. Much more and we'd waste effort fighting the car than trying to go fast. So, with the power issue resolved and potentially more power to come with an aftermarket exhaust, we're left to tune the chassis so it can stand a fighting chance against the Cobra.
Next time: brakes, cheater tires, suspension and maybe--just maybe--we'll be ready for the face-off. n
The simplest and quickest way to make boost is to plumb in a manual boost controller and pressure gauge. We used a TurboSmart Boost Tee and slowly dialed up the pressure with each successive dyno pass. We ended up at roughly 12psi of boost, compared to the 9 or 10psi we got off the stock wastegate. The Boost Tee also has a nice set-screw feature to prevent unintended changes. | 
All the boost in the world won't help if you can't meter it. DiabloSport's MAFia is used to intercept the stock MAF sensor output and rescale it down for the 300hp that we're looking at. The MAFia has eight settings, from stock up to 800hp. The trade-off is sensor resolution as the MAF sensor's metering range is increased. | 
This is what ultimately kept Project SVT from making power. These stupid little OEM crimp bands hold the intake manifold runners to the head. They were never meant to see boost. According to FocusSport, these bands are good for up to 14psi before something will blow off; 16 if you're lucky. Seeing our luck with Project SVT thus far, we played it conservative and kept the boost at 12psi and saved some money on having to get a new fuel pump and larger injectors. |