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The AEM water/methanol system eliminated all of the knock count that we estimated was caused by rough combustion (the way our EVO is tuned, we never have audible detonation). EVOs sometime develop knock count due to drivetrain lash and other mechanical noise but it is easy to detect spurious knock count by looking at the engine’s operation parameters in the logs. Knock count on lift throttle for instance is caused by drivetrain lash.
We also had other positive side effects. We had been tinkering with our boost tables trying to get a very aggressive boost pressure rise. With our highly efficient Full Race exhaust manifold, our turbo can spool so fast we were running into issues with compressor surge, especially when modulating the throttle in higher gears or doing 3-5th gear roll ons. This is pretty harmful to the turbo in long term use. However with the water injection, surge has been eliminated. We theorize that the water absorbs some of the combustion temp and drops the EGT’s enough to where the turbo spools a little slower in the 10-20 psi range and stays out of surge.
We also had a wonky O2 sensor that was contaminated while running race gas during a tuning session. The sensor had a slow response time and sometimes would not go into closed loop tripping a check engine light. A few minutes of operation under water injection operation literally scrubbed the sensor clean and it returned to normal operation which really boosted our fuel economy.
By our own experience, running a turbo car at moderate boost levels on the track with pump gas is always an iffy proposition, especially in Sothern California as most of our tracks are in really hot areas. So when doing track events, we always run 100 octane unleaded or VP 104 even if we are going to be running stock boost as a precaution. Turbo cars also tend to run hot under these conditions. In our experience, water injection really helps hold coolant temperatures down, sometimes even more than a large radiator. It also has a greater detonation suppressing ability than 100 octane fuel. We look forward to our AEM system giving us an extra margin of safety at the track with cheap pump gas without the expense of buying several $80 dollar tankfuls of racing fuel a weekend.
Stay tuned, next we will do a little experimenting with our tuning to see if we can get a significant power boost with the water system.
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