Myth buster lspi link

Faults and Technical chat for the Vauxhall Astra K
Post Reply
Redman
Posts: 1373
Joined: Sat Aug 20, 2016 7:16 pm
Astra Model: Astra elite nav 150
Astra Colour: red

Myth buster lspi link

Post by Redman » Mon May 03, 2021 7:02 pm

Thought this link would be helpful to people just discovering lspi exists. It states lspi is reduced by premium Higher octane fuel and gives other preventative measures. I have not put it on for the knowledgeable people.
https://pmmonline.co.uk/article/myth-bu ... -ignition/

msg
Posts: 6
Joined: Sat May 01, 2021 6:58 pm

Re: Myth buster lspi link

Post by msg » Thu May 06, 2021 2:25 am

Having read that article, shouldn't the low engine speed also mean that turbo boost isn't sufficient to cause preignition, and detonation?
My understanding was preignition occurs in turbo charged engines with very high compression ratio, so many such engines builders reduce compression ratios by using thicker head gaskets, and to achieve even higher turbo boost pressure, it is quite confusing really, because my understanding was that higher is the compression ratio, higher will be power yield, yet they lower the CR to boost more turbo charged air, which to me really counter acts any reduction in CR with a thicker gasket. In the old days one could adjust the timing by retarding it slightly to use lower octane fuels, but modern cars have detonation sensors and so ECU adjusts the timing as soon as it detects any detonation,

Redman
Posts: 1373
Joined: Sat Aug 20, 2016 7:16 pm
Astra Model: Astra elite nav 150
Astra Colour: red

Re: Myth buster lspi link

Post by Redman » Thu May 06, 2021 7:04 am

Lspi cannot be prevented by the knock sensor as the ignition source is mainly oil deposits coming from the piston ring crevices mixed with atomised fuel. The car makers try to prevent lspi incidents by adding excess fuel when the ecu detects the engine load and speed could promote lspi, this rapidly cools the cylinders. That is one of the reasons the injectors are no longer mounted at an angle, as this could put fuel on the cylinder walls. So they are mounted vertically to hit the piston crown. Higher octane fuels also tend to come with more cleaning agents and keeping the injector spray pattern at its best.
Oil now drastically reduces lspi by using different detergents in the oil.

Post Reply