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Old 03-02-2012, 01:43 PM   #150
Scooby Specialist
Member#: 119958
Join Date: Jul 2006
Location: (IA) flyover cornfield country
1992 SVX LS-L


Originally Posted by madlife View Post
The turbo? Seriously? Did I miss that somewhere?
It is a 1.6 liter version of the GDI Turbo.

direct injection into the combustion chamber mitigates the need for high octane, since the fuel doesn't have to pass through the hot walls of the intake port in the head, where it can pre-detonate.

High octane just means it resists detonation more, not that there is more or less energy content in the fuel. It has to be used with carbureted or port fuel injected engines that run hotter, to prevent pre-detonation in the intake tract, or ignition too early in the compression stroke, which can cause damage to the engine. commonly referred to as "pinging" or "knocking." Knock sensors bolted directly to the engine listen to the acoustics of the engine to isolate that signature, and signal a dial back in ignition timing to prevent damage.

Lower octane gasoline actually requires less pressure or heat or spark strength to ignite. It burns more easily, which actually helps combust the full fuel charge, with less unburned hydrocarbons in the exhaust. Injecting that fuel directly into the end of the compression stroke prevents pre-detonation merely by the time aspect of when the fuel is introduced, so higher octane tends not to be required. It can also meter the fuel delivery to more approximate a stratified, leaner burn, rather than all the fuel, at a richer mixture, being delivered before ignition starts.
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