[bobcat]

Originally Posted by ttacornwall

Just had a look at my owners manaul re specifications Engine:
Engine type B5202S 10 valve, B5252S 10 valve, B5204S 20 valve, B5254S 20 valve Volvo recomends 95 RON min 91 octane.
Engine type B5204T 20 valve, B5234T 20 valve, Volvo recomends 95 RON min 91 - 98 octane.

For the B5234T5 Volvo recommends 98 RON lead-free petrol for the best performance, but will run on any fuel with an octane rating of 91-98. This is with a standard ECU, when the ECU is modified with either a chip or remap bobcat states that the ECU will still recognise the octane rating and will adjust the timming, but I assume there is limitations, with 95 RON in a modified car it is safe to use as long as you don't floor it or take the rev's over 4k as this may produce knock?
However if you want to eliminate knock when you floor it or take the engine over 4k rpm then a higher octane rating is needed to prevent knocking?

As Volvo already recommend 98 RON in the B5234T5, it would therfore make sense to use nothing less than 98 RON in a modified car.

If a remaped or chipped ECU can still make adjustments to the timing etc and detect what octane rating the fuel being used, (as the same way a standard ECU would) then in theory anyway you could use 95 RON fuel. That is unless the ECU has been chipped or remapped wrongly then using a higher octane rating will cover up/help hide any issues with the ECU that has been chipped or remapped. Is this a fair assumption?

thankyou for that post ttacornwall.

so as you can even volvo recomend 98 ron on their turbo cars, but their ecu's can allow the car to pretty much run on anything.

and also look at what volvo recomend for non turbo cars!!!!!!!!!!!!!!!!!!!!!!!!!!

i would like to ask an open question of why that is?

and that is one of the reasons why i run 95 ron.