93 or 95 Unleaded?

[Tsepz_GP]

My little 900cc Turbo says 95 or 98. Never put anything less than 95 in it.

 

[Sinbad]

Forced induction = highest octane available, end of story.

 

[SykomantiS]

https://www.news24.com/MyNews24/The-Octane-Rating-Conspiracy-20150122

Interesting read......

And....

Any engine with a compression ratio above 10.5:1 should run 95 octane fuel

if you run lower octane you stand the risk of detonation, which could leave a nice big hole in your piston. The reason for this is that the higher the octane the cooler the explosion is that is why the octane increases when you go to the coast, because the atmospheric pressure increases, thus your compression ratio increases.

To summarise, running a high octane on any engine will not cause any damage, but running a low octane on a high compression engine can cause damage.

The Ford Fiesta 1.4 Ambienta's compression ratio is 9.8:1, so no need to fill up with 93.

Controlled ignition is not an explosion. And your compression ratio doesn't change with altitude... Ambient pressure changes, sure, but the CR doesn't.

So let me explain. The higher the octane the more difficult it is for the fuel to ignite on its own.

So hot spots on the cylinders, warm days , hot intake temps etc etc etc , will cause the fuel to pre ignite. Detonate to early. This can cause engine damage. So your cars ecu is clever and it learns. so to prevent detonation it will reduce performance, pull timing and increase fuel injected to help cool cylinders.

So you use more fuel when using 93 and have worse performance.

95 resists pre ignition , so your car needs less fuel to cool the cylinders, it can run more timing and in general give you more performance.

So you have a cleaner burning engine, running safe and efficient.

This is all predicated on whether the vehicle in question will experience detonation on 93 octane. If it doesn't, than all of this goes right out the window.

 

[RedViking]

Whatever is the cheapest.