Over the past couple of years, I've noticed more knock readings while datalogging on my 2015 Subaru WRX, mostly in highway cruising, but I'd semi-regularly get a knock reading at WOT as well. I'm no longer able to tune out the knock since the EPA nerfed my tuning software, so I decided to try some fuel system cleaner. The engine has around 55k miles, and still has the original spark plugs, which are due to be changed at 60k. It's tuned for 87 octane E10.
I used Gumout Regane High Mileage (Canadian blend, 26% PEA), at 70% of the recommended dose, which works out to 940 ppm PEA.
Here are the results for knock during highway cruising, in knock events per hour, before treatment, on the first tank, and on the subsequent two tanks with diluted PEA content. Average engine speed, load, temperature, and manifold air temperature were all similar between runs.
Knock Events Per Hour:
0 ppm PEA: 96
940 ppm PEA: 3
210 ppm PEA: 299
15 ppm PEA: 86
After the first treatment, the knock was virtually eliminated. After diluting the PEA to 210 ppm on the next tank, the knock events increased 100-fold. This is consistent with some studies that show that PEA has a "hump effect", where combustion chamber deposits are reduced at high doses, but they actually get worse at low doses (~130 ppm), which increases the likelihood of knock. With almost no PEA left in the tank, knock was similar to before the treatment.
Previously I'd get a knock reading on at least half of all WOT pulls. After PEA treatment, I haven't had a single knock event at WOT, but I've only logged 5 WOT pulls. I'll need to do more pulls to be sure, but the PEA seems to have helped.
My next project is to replace the spark plugs. I might just replace the two plugs on the more knock prone cylinder bank and use the other bank as a control to test the effect of new plugs on knock frequency.
I used Gumout Regane High Mileage (Canadian blend, 26% PEA), at 70% of the recommended dose, which works out to 940 ppm PEA.
Here are the results for knock during highway cruising, in knock events per hour, before treatment, on the first tank, and on the subsequent two tanks with diluted PEA content. Average engine speed, load, temperature, and manifold air temperature were all similar between runs.
Knock Events Per Hour:
0 ppm PEA: 96
940 ppm PEA: 3
210 ppm PEA: 299
15 ppm PEA: 86
After the first treatment, the knock was virtually eliminated. After diluting the PEA to 210 ppm on the next tank, the knock events increased 100-fold. This is consistent with some studies that show that PEA has a "hump effect", where combustion chamber deposits are reduced at high doses, but they actually get worse at low doses (~130 ppm), which increases the likelihood of knock. With almost no PEA left in the tank, knock was similar to before the treatment.
Previously I'd get a knock reading on at least half of all WOT pulls. After PEA treatment, I haven't had a single knock event at WOT, but I've only logged 5 WOT pulls. I'll need to do more pulls to be sure, but the PEA seems to have helped.
My next project is to replace the spark plugs. I might just replace the two plugs on the more knock prone cylinder bank and use the other bank as a control to test the effect of new plugs on knock frequency.