Pontiac Engine 505ci

With Jeremy Cortner of MCR at the Controls and Brian Ebert of HiTech Motorsport in the driver seat, the Mustang MD-1750 SE dyno is being set up with the proper parameters for this GTO. Once done, the dyno will simulate real-world driving conditions and allow the tuner to see what this combination will do out on the street or at the track. Especially when using the FAST data logger, one can keep track of up to 14 different sensors and also watch the dashboard gauges while "driving" the car any way that's needed. Trying to do this out on the street would be difficult at best and in reality, quite likely dangerous.

If you read the Nov. '09 issue where we reported that Jeff Hutchens' twin-turbo 505 pegged the torque needle at 1,079 lb-ft and produced 1,073 hp during it's engine dyno tune session then perhaps you've been thinking about what this thing will be like on the street. It certainly would be easy to get a good bench racing session started with the numbers we saw.

But while dyno numbers are great for tuning and fun to debate, what really matters is how it all works in the car. That's why we are out at Muscle Car Restoration's facility in Chippewa Falls, Wisconsin, where Jeff's GTO will undergo a complete chassis dyno session.

While MCR utilizes a Mustang chassis dyno to "road test" all of it's projects to ensure that every part of the car is working perfectly before delivery, Hutchens' GTO also needs further engine and transmission tuning before it's ready to run free.

An engine breathes differently on the engine dyno than in the chassis due to added heat under the hood and the load on the engine from driving the car.

As a result, the tune from the engine dyno has to be slightly altered when the engine goes back into the car. Historically, the engine wants a richer air/fuel ratio and a bit less timing.

Since EFI can precisely control these functions, it's beneficial to tweak them with the engine in the car driving its actual torque converter (2,300 stall for this GTO), transmission (4L85E four-speed overdrive), and rearend (Moser 9-inch, 3.50:1 gears) during this part of the tuning.

So, Brian Ebert, president of HiTech Motorsport, Elk River, Minnesota, was called in to put this engine through every conceivable condition it might see on the streets, monitoring everything (such as air/fuel ratios, spark table, checking for detonation, and more) that is going on during low- and high-speed cruising and during transition periods such as gear changes, full throttle to closed, cruising to full throttle and so on. Here, the emphasis is not on raw power but rather on new-car-like driveability-how the Goat feels and responds. How does it come off idle? What's the throttle response like at different speeds? Does it return to idle cleanly after you lift off the throttle? Because Jeff's GTO will have already been "driven" there won't be any surprises once it's out on the street. Don't worry, we will perform full power pulls as well.

Also part of the chassis tuning process is setting up the transmission shift points. During initial chassis dyno testing, the transmission wanted to downshift to Second gear each time the pull was started. To gain all the control required to make clean pulls with no downshift and the converter locked up, a TCI transmission controller was employed. Through a set of 2D graphs (TPS vs. MPH), upshifts and downshifts can be very precisely set for any throttle position and speed. Other tables allow line pressure vs. TPS control (for shift firmness and holding power) and torque converter lock and unlock parameters. Brian noted that turbo motors don't like quick downshifts. Since engine load builds boost, it's often better to let the engine pull through a gear under a higher load than to drop a gear too quickly and lose the boost.

It's also necessary to check the effect that the air cleaners and the exhaust system will have on engine operation. Even the best full exhaust piping will increase the backpressure in the system and affect the efficiency of the turbos.

There is a small green curser that moves around the base tables (vertical axis is load, horizontal is engine rpm) as the engine is running. It shows you exactly what box or value the ECU is using at that point to supply fuel or timing to the engine. What Brian is doing is "driving" the car at various speeds and loads to move that curser over as much of the table as possible, so he can monitor and data log the engine under all possible operating conditions. He can then make whatever adjustments are necessary to the fuel, A/F, and spark tables to optimize engine performance under all conditions. Those boxes he can't "reach," he can interpolate using the surrounding data. When done, the ECU knows exactly how much fuel and spark the engine should have under virtually all operating conditions.

Because the wastegates empty back into the exhaust system as opposed to being open to the atmosphere (pretty much required for a street car for noise laws), a heavier internal wastegate spring is needed to return boost to open exhaust levels. In addition, boost pressure can be plumbed to the top of the wastegate diaphragm to extend its range of control.

Due to the way the engine breathes under different operating scenarios, the spark table is not linear. Electronic controls allow precise tuning of the ignition lead for optimum cylinder pressure at each rpm and load. We chose not to use a knock sensor due to the inherent mechanical noises of an HP engine, which are often misinterpreted as the sounds of detonation.