Performance Results

Brucato Pro Control Unit shown with serial connection to notebook computer.

For wide-open engine operation, we tested our rig in a variety of situations. With two people aboard, we began our tuning by making adjustments using the Steamwheel while monitoring exhaust gas temperature. Remember, it is always better to make adjustments to the PCU with the engine under loaded conditions.  This situation will highlight RPM areas that need further fine tuning. 

Stage One - Two occupants, full load

Initially, we achieved 117 mph with an EGT reading of 1000 degrees. A careful adjustment of the Steamwheel allowed us to easily lean the mixture, providing a hot, yet relatively safe fuel mixture with an EGT reading of 1150 degrees. This yielded several 122 mph passes instantly, compared to a best of 118.2 mph that our Mercury ECU was able to attain under the same conditions.  It must be stressed that the purposes for this test are for experimentation, and extreme caution should always be exercised when leaning down the fuel mixture.  At the end of testing, we recorded a gain of 4.2 mph and 450 RPM. 

At this point we were stunned at the gains afforded to us by Brucato’s adjustable ECU. Remember that this was a finely tuned boat and engine to start with, so the gains we had seen so far were very significant. For the next phase of this test, we ran our STV with a light load of fuel and just the driver.

Stage 1 Test Results - Top Speed Mercury Sportmaster lower unit equipped with 1.87:1 gear ratio, Mercury 14.5 x 32P Lab Cleaver Mercury Digital ECU 118.2 MPH @ 8550 RPM Brucato PCU 122.4 MPH @ 9000 RPM

Stage Two - Single occupant, light load

The morning air was crisp, and we were going for all-out top speed. It is important to note that this part of the test was designed to get as much out of our setup and the PCU as possible. Our Mercury engine has been extensively modified, and the 1.75:1 gear ratio of the unmodified Mercury Sportmaster lower unit will better suit the the STV, now that 250 pounds of weight has been removed.

Although generally not recommended for engine reliability reasons, we removed the front cover plate from the engine cowl. This is risky, since the extra air entering the engine will indeed alter the fuel mixture, but our Mercury ECU has been set at 1.05 volts to compensate for the extra air. We have seen a 2 mph gain by performing this modification alone, although this was for experimentation purposes and not general use. We theorized that the PCU’s added adjustability would really shine here, and the Steamwheel’s instant access to fuel adjustment would allow us to compensate almost instantly for the extra air entering the engine.  Again,  starting our adjustments from a known rich mixture and  careful monitoring of exhaust gas temperatures is crucial.

It should also be mentioned that all setup procedures performed on our test boat are the result of many hours of research and testing.

For this stage of testing, we managed a top speed of 124.2 mph @ 8200 RPM with the Mercury Digital ECU.  Note the lower RPM reading, which is a result of switching to the 1.75:1 gear ratio.  Switching to the well-adjusted Pro Control Unit provided a top speed of 128.9 mph - a gain of 4.7 mph and 350 RPM over the Mercury Digital ECU.

Stage 2 Test Results - Top Speed Mercury Sportmaster lower unit equipped with 1.75:1 gear ratio, Mercury 14.5 x 32P Lab Cleaver Mercury Digital ECU 124.2 MPH @ 8200 RPM Brucato PCU 128.9 MPH @ 8550 RPM

For both tests, we saw significant improvements in top speed and acceleration.  Since the Brucato PCU effectively broadens the horsepower and torque curve on engines so equipped, our test results seem only logical.  But what about top speed?  In theory, the Mercury ECU can be set to provide the same fuel mixture as the Brucato PCU, so top speed should be identical between units, right?  Not necessarily.

Since the PCU allows us to tune the engine all the way up the RPM range, we are given more power to achieve new plateaus for top speed tuning.  Put simply, it takes horsepower to arrive at your top speed, not just produce it.  Further, with the Brucato PCU, we can adjust the fuel curve specifically at our top-speed RPM range affecting fuel mixtures at lower RPM settings.  For example, we set our top-speed mixture for an EGT reading of 1150 degrees, but we wouldn't necessarily want to run that lean of a mixture at midrange speeds.

Again, the key to these performance gains is careful adjustment of the PCU itself.

Page Five: Conclusion and Impressions