2 replies to this topic

[R32Egor]

Thinking out loud -

 

If i use 98 Octane in an SPI would this lead to slightly over fueling due to the fuel maps in the ECU setup for 95 Octane??

[sonscar]

Octane will not affect fuelling nor will it necessarily give more power,it just costs more or less.Too low may cause engine damage.Steve..

[mini13]

yeah,

 

essentially if you build an engine to run optimally on 95 octane with as high a compression ratio as the fuel will allow, if you run it on 92 you run the risk of pre-ignition or even detonation,unless you retard the ignition, if you run it on 98 octane the octane additives are taking up "space" for calorific content so you may actually make less power.

 

its a  balanceing act with engine design, which has admitedly been made a lot easier with modern ecu's that will trim ignition values ( although that dosen't apply to minis)

 

another way to think of it is to swap the term compression ratio for Boost, a motor ( and ingition timing) designed for 10 PSI boost on 95 octane, may be able to go to 15psi boost on 98 octane, but on 92ron you might not be able to go any higher than say 7 psi, ( disclaimer arbitary numbers used here).