Focus ST oil

[MVAR]

From what I remember:
- Detonation/knock is the fuel mixture unevenly combusting or only partly combusting. You get an uneven flame front or an exploding event/rapid uncontrolled ignition, but it's typically still initiated by the spark plug.

- Preignition is the mixture igniting before the spark plug fires, usually due to combustion chamber deposits. Engines that would "run on" were effectively running due to preignition.

I think they DO often get lumped together however and it could be argued there's some crossover.

With LSPI, you have the mixture igniting spontaneously before the plug fires, and due to what is generally high load (so lots of fuel + boost) and the position of the piston/rod in the stroke at the time (probably approaching or at TDC at the time of this violent eruption of the air/fuel) it will often completely destroy the piston.

Violent detonation can also crack/damage pistons, even if it's initiated by the spark plug.

Yes. That’s extremely similar to the definitions I’ve understood for years now.

I used to see what resembled ball peen hammer strikes to piston tops on engines that suffered preignition. We used to associate preignition with a “hot spot” in the combustion chamber igniting the mixture before the plug fires & detonation as too low of an octane being used. The results were the same so verbiage interchanged

The only difference I’ve heard about with TGDI engines is they’re more sensitive to oil additive chemistry than the MPI engines.

 

[OVERKILL]

Yes. That’s extremely similar to the definitions I’ve understood for years now.

I used to see what resembled ball peen hammer strikes to piston tops on engines that suffered preignition. We used to associate preignition with a “hot spot” in the combustion chamber igniting the mixture before the plug fires & detonation as too low of an octane being used. The results were the same so verbiage interchanged

The only difference I’ve heard about with TGDI engines is they’re more sensitive to oil additive chemistry than the MPI engines.

Yeah, ZDDP quenches LSPI, while calcium instigates it, so if you reduce ZDDP (which has been the case with API/ILSAC oils), you increase the propensity for LSPI. It also doesn't help that engines tuned for North America were intentionally running high boost and low RPM, which Euros, that had DI before these other marques, didn't do.

 

[TiGeo]

Preignition is detonation. I’ve read where people try to differentiate between the two but have yet to see anyone do so. When my Mazdaspeed6 detonated during a low rpm event, lspi was just starting to be talked about. Cole Mazda brought out an engineer to investigate my vehicle. When he said lspi I asked what it was. After he stated his explanation I just said “so preignition or detonation”. His response was only “yes”.

In that cars case it was a weak hp fuel pump & looking back, possibly oil chemistry from 2008 as well as a piss poor pcv system flooding the intake with an oily carbon mess that needed walnut shell blasting every 45k mi(or less).

Curious if the definition of lspi has evolved over the last decade and a half

Detonation and pre-ignition are different. Detonation is after the plug fires and results in less cylinder pressure than pre-ignition which is ignition before the plug fires. Detonation is when there are multiple wave fronts after the plug fires which is what results in the pinging/knock noise (crappy combustion). Both are irregular combustion events but are different. Typical spark knock/pinging isn't as destructive as pre-ignition.

 

[MrStamper]

I think folks are confusing standard det/knock with LSPI which are quite different.

More like people running a bad tune, motor blowing up running to the forums and blaming LSPI. I have a 2016 ST and I floor it in 6th all the time, 160K miles. And I pretty much ran high saps Mobil 1 0w-40 for most of its life, so I’m a worst offender. Just recently jumped on the VRP bandwagon like everyone but just for cleaning purposes. OP just run any 5w-30 synthetic, “it’s a just a focus” lmao