What fuel octane are you running in your giulia – page 9 – alfa romeo giulia forum electricity in india first time


Amazing how much misinformation there is on this thread. Will 87 octane damage the car? No, not unless the knock sensor fails. I can guarantee if there were damaging detonation was was at Nearly every turbo charged car (and normally aspirated for that matter) that’s been made since the first Clinton admin. uses one. They sense knock and pull ignition immediately. Once, my dad put 87 in my Mitsubishi GSX Turbo and it accelerated to 60 in about 15 seconds. Did it damage the motor? No, it just ran terribly. A modern 2.0 liter with direct injection is FAR more resistant to the heat and combustion race that is detonation. Someone else chimed in that ambient air temperature doesn’t make a difference. Not true. Starting with 50-70 degree cooler air matters a lot.

1) Detonation can occur at any RPM, but we will use something low, like 1,500 rpm, to simulate detonation from lugging the engine. So, 1,500 rpm is 750 ignitions per minute per cylinder, or 50 ignitions per second. For the knock sensor to adjust timing, knocking must first occur and be sensed. Given that this will take several ignition cycles, it is clear that poor quality or octane gas will risk engine damage.

2) Modern knock sensors are much more effective in detecting knock and adjusting advance, but still suffer from the need to HAVE knock to sense it. It should be clear that even with immediate detection, the next 2 or 3 ignition events are already past the adjusting point due to fuel/air injection status and the net time to adjust. The reality is the sensors never work that quickly, as they are biased to reactly quickly only on heavy knock events. It really is crap when people discuss "milliseconds" for sensors to respond, because they are ignoring that the vibration/noise has to occur to be acted upon, so a fast reacting sensor is good, but not prophilactic.

3) An overly low octane product (i.e. 87 "regular") in a car tuned and programmed for 91+ octane will cause significant knocking and major intervention by the ECU at the behest of the knock sensor, resulting in reduced performace. This reduced performance can also result in plug fouling and carbon buildup. Also note that carbon buildup is a primary genesis of knocking outside of the engine load event knocking.

4) Knocking is not a "if this, then that" event…it is rather a signal of strain on the rotating components of the engine. This means that damage is always possible when knocking occurs, but auto manufacturers have become very adept at avoiding this problem. This is not to say you cannot hole a piston simply by using 87 octane, but that the ECU is programmed to make that very diffuclt.

As for ambiant air temperature impacting detonation, with a modern, MAF/O2/ECU controlled car, this parameter is adjusted for BEFORE the advance is dialed in and this is a non-starter. In the case of the Giulia, the MAF (Mass Airflow Sensor) effectively corrects for input temperature as the mass, rather than volume, of air passing through the sensor is detected and provides an effective intake temperature measurement. The measurement of the mass of air, rather than the volume of air, means that the fuel input is fine tuned more accurately, and that does have a significant knock-on impact on power production.

AlfaCrisis, you make some valid points. Running 87 or getting some mistakenly from a gas station (happens, more than you think. Just this weekend a California Chevron put diesel in the tanks. Yikes) isn’t going to grenade a motor, though. No detonation is good, no question, but it is runaway detonation that destroys motors. I’ve owned two vehicles that suffered detonation on hills, in heat, or lugging at low rpms and made it to 200,000 plus miles. I can promise the ring lands on those vehicles are nowhere near as strong as a modern piston’s.

Mass air sensors can and do make changes based on air density arising because of temperature change to help achieve a certain af ratio, but you can have a perfect af ratio with 0 degree air or 110 degree air and the air entering the engine is always different by 110 degrees. The MAS cannot change that. Ambient air temp. affects mixture temperature, and detonation is a race between heat build up from pressure (and consequently detonation) and completing combustion with an ignition source. Starting with a lower air temperature will always stave off detonation to some degree. Period. That’s the primary reason why turbo cars have intercoolers. Lowering intake air temp keeps detonation at bay. In fact, in WWII, engineers realized they could make as much power by adding water as air at some point, as it cooled the air and allowed the ignition to stay more advanced without detonating.