In Part 1 of our Blitz Power Meter series, we provided a brief description of how the Blitz Power Meter can assist with the fine-tuning process. You may recall that the Power Meter is a companion component to the Blitz SBC i-D boost controller we tested in the April 2001 Dyno Cell. In Part 2 of the Power Meter series, we will delve into how the two units work together and illustrate their datalogging capabilities and ability to communicate via infrared signaling, which means no wiring is needed to join the two units. Our focus will be on horsepower datalogging (on-board dyno) and how to use this info to improve traction (boost programming).
The Power Meter's main job is to operate the SBC i-D's "Speed Map" option. The Speed Map function is a powerful tool when it comes to tuning the boost curve in vehicles that experience excessive wheelspin. We all know boosted front-wheel drives are the leading culprits, but super-tuned rear drives can granulate the Goodyears as well. The Speed Map allows the user to tune boost by vehicle speed. This comes in handy when setting up the car for gear changes. An example would be a car that needs to launch at low boost for traction reasons, then switch to high boost when traction isn't a problem.
Since the Speed Map requires the factory speed sensor and the Power Meter utilizes it to calculate horsepower, all the vehicle speed info is transferred to the SBC via infrared.
Even if wheelspin is present, the datalogging system built into the units can help provide information to better calculate shift points. Let's say in first and second gear we want to run 13 psi, 15 psi in third and 18 psi in fourth and fifth. Our goal would be to figure out each gear's ending mph at each of the required boost levels. Since we want to run first and second at 13 psi, the user has the ability to datalog the peak mph in both gears. Once the info is logged, the information can be used to predict when the user wants to kick in higher boost for the next gear. Say the engine is revved out of second gear at 50 mph, we can set Channel 1 boost setting to 13 psi and have the Speed Map kick in this level of boost from 0 to 50 mph. After 50 mph, we can then have the unit switch to Channel 2 for third gear. The datalogged information can be used to figure out each gear's shift point.
In Speed Map mode, vehicle speed is represented in a 16-bar graph with each bar accounting for 12.5 mph. The user has the ability to select four of the 16 bars and designate each for one channel of boost. In our example, the fourth bar (50 mph) would be tuned to Channel 1, which is programmed at 13 psi, Channel 2 (15 psi) would be programmed at the bar that corresponds with the datalogging for third gear, ditto for the remaining channels.
Our test car is a 1993 Toyota Supra equipped with a GReddy front-mount chiller, HKS VPC, HKS exhaust, GReddy Airinx air filter and SP Engineering downpipe. Since the JZA is equipped with a fuel-tuning computer, we decided to set the max boost pressure to 19 psi, keeping it on the safe side. Our first test was to analyze the accuracy of the Power Meter's chassis dyno function against a Dynojet. Our second series of tests would use the data gleaned from the dyno mode to determine the optimum boost and our shifting points by using the Speed Map option on the SBC i-D.
Power Meter Dyno Mode
When we first heard about the Blitz Power Meter, we figured it must have been a gimmick, but once we reviewed what the meter is based on, we realized that it functions in the same manner as a chassis dyno. Analyzing the function of our favorite test tool, the Dynojet dynamometer, horsepower is measured by the rate of time a vehicle takes to spin a roller, based on the roller's weight and speed. A Dynojet is equipped with a magnetic pick-up that mounts to the roller's shaft, which used to generate the necessary data. Using this same concept, Blitz allows the user to plug in a vehicle's weight with driver to represent a dyno's roller weight. The Power Meter also replaces the Dynojet's roller magnetic pick up with the car's vehicle speed sensor. The result is an on-board dyno that can calculate horsepower and (if the unit is run through the proper set-up procedure), can be calculated at the drive wheels rather than at the flywheel. Just like a Dynojet, the Blitz unit cannot calculate for wheelspin, so all test runs should be done in a gear that doesn't encounter wheelspin. To ensure the most accurate reading, one should calculate the weight of the gas and any other items in/on the car. Gasoline is a changing variable, so we calculated that a full tank of gas weighs in at 111 lbs (18 gallons in the Supra), which comes out to about 14 lbs per eighth tank. Fuel weighs 6.2 lbs per gallon, so calculate your own eighth of a tank appropriately. The numbers were programmed into the Power Meter and it was time to test. It should be noted that the weight can be updated on the meter by going into weight/power loss mode.
Power Meter Speed Map
Since the Power Meter data records horsepower and mph, this information can also be used to help set up the initial Speed Map portion in the SBC i-D.
The Speed Map can be calibrated to compensate for excessive wheelspin. With the Supra, we decided to set up the vehicle to run 13 psi in first and second, then jump up to 15 psi in third and onto 19 psi in fourth and fifth. With the first two gears at the same boost level, we logged the mph using the line graph mode and replaying the recorded information. The vehicle speed information was then logged into the Speed Map. Logging third and fourth in the desired boost levels followed the same procedure.
To illustrate the quality of the Speed Map, we decided to run the car in fourth gear, but modify the graph to kick in different levels of boost at designated vehicle speeds.
We set the boost level at 13 psi from 0 to 70 mph, after 70, the boost pressure was set to 15 psi up until 90 mph, where it switched to 18 psi. When we compared the graph vs. a normal 16 psi run (Dyno 2), a noticeable fluctuation in the two graphs gives a good demonstration on the accuracy of the Speed Meter. By making two mph changes and three different boost settings in the same gear, you can tell that the Blitz set-up can be accurately tuned for gear changes as power fluctuations are clearly evident.
Getting the hang of the units by themselves is a challenging experience. Once we had the two units interacting together, the task of understanding how they worked together was even more time-consuming. After a day of playing with the two, we became much more familiar with their functions and how to use these tuning weapons to maximize performance.
With the ability to datalog boost response, mph and horsepower, the Power Meter is a powerful tuning tool.