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Hey Guys / Andre.
So tuning my GTR to suit 98 Ron as thats what I run the car on... But im doing a road trip across Australia and am a little worried I might not have access to 98 everywhere and may get stuck with 91...
Once I got my ignition numbers optimized on the dyno to suit 98 would I be safe to say just remove 5 degree's of timing in the higher load/rpm areas? maybe more maybe less? The car does have knock detection but I dont know how good the stock knock sensors with Haltech PNP are yet..
The only way to really be able to know for certain is to actually test on 91 octane fuel and find out how bad it is and hence how much timing you're going to need to remove. My own experience with 91 in a handful of cars where the customer had mistakenly filled with the wrong fuel, has been that you'll find yourself severely knock limited. That being said, RB26's in lightly tuned forms on 98 octane fuel are not normally overly knock sensitive, and this may work in your favour.
If you're that worried, I'd grab a tank of 91 octane and find out exactly what the engine needs to be safe. Personally I tend to pull out timing and reduce boost in tunes that I do for a 'just in case' situation.