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Thread: Does 98 Octane petrol improve performance of 4.2 petrol GQ

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    Advanced LandRoverGhost's Avatar
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    Question Does 98 Octane petrol improve performance of 4.2 petrol GQ

    I , I come from a V8 Range Rover 4.6 L engine. Now own a beautiful Nissan patrol GQ with the 4.2 Petrol. In my Rangy running 98 Octane Petrol ( V-power , Ultimate, etc. etc. ) made a definite difference in performance. Has anyone similar experiences with the 4.2 L. ... or not ;-) ??

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    Expert billyj's Avatar
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    will make stuff all difference unless you advance the timing to get the most out of it.

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    Advanced LandRoverGhost's Avatar
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    That makes sense !!! So use to that Computer Controlled Rangie - I totally forgot about timing advance etc. - have to learn it all over again ;-)

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    Patrol Freak garett's Avatar
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    my old laser went from 300km a tank on e10 to 500 km a tank on 98 with a msd 6al, coil, and timing and carby tune. it also hauled a$$. traction became the biggest problem
    if its worth doin its worth over doin

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    Moderator MudRunnerTD's Avatar
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    Yeah my old XR6 ute loved the 98. After a tank or so it would return 50 to 100kms better per tank with better performance the whole time.
    Its a Nissan! =====> Its a Keeper!! ....... Got a TD42 in it BONUS!! ....... I'm a lucky bugger! I've got 2 of em!
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    Thanks - so 'just' using 98 is not enough - so much is clear - tuning it to 98 is the only way !

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    makes some things run hotter too. No idea about a big old Nissan 4.2 though.
    Between Patrols ATM. Had a beaut GU with 6.5 Chev TD. Next is a GU ute with a 4.5 litre Cummins conversion and a camper on the back.

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    Advanced Arfa Brayne's Avatar
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    This one is an old furfy.
    I also do a bit on a lawn contractors forum, and there is the anecdotal theory that 98 premium will make the mowers go harder too. (rubbish)
    The only reason to have a high octane fuel is to cope with higher compression ratios.
    If you have a compression ratio of 10:1 or higher, igniting the fuel the same BTDC as a 8:1 engine will burn the fuel faster and increase cylinder pressure enough to make the charge detonate (pinging). TO avoid pinging the timing has to be retarded in high compression engines that are trying to run standard unleaded fuel.
    If you have a compression ratio of 8.5:1 (tb42), running 98 premium means the fuel will burn slower - effectively retarding the timing and making the engine run hotter with less efficiency. Modern engines that set ignition timing based on knock sensors will run almost identical to running the engine on 91 unleaded. However the ignition timing will spark further before TDC which can rob an engine of power.

    If you really want to test the theory, run your engine on LPG - it has an octane equivalent of 110. = Runs hot with less power.
    Increase the compression to around 11:1 and run LPG = better fuel economy, more power and cooler running.
    Run 11:1 compression with wet injection LPG and you'll get better power and fuel consumption than the same engine fuelled with petrol.

    May as well try feed a bulldog rib eye fillet steak to make it run like a greyhound.
    "Can't" is a dirty 4 letter word.
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    Quote Originally Posted by Arfa Brayne View Post
    This one is an old furfy.
    I also do a bit on a lawn contractors forum, and there is the anecdotal theory that 98 premium will make the mowers go harder too. (rubbish)
    The only reason to have a high octane fuel is to cope with higher compression ratios.
    If you have a compression ratio of 10:1 or higher, igniting the fuel the same BTDC as a 8:1 engine will burn the fuel faster and increase cylinder pressure enough to make the charge detonate (pinging). TO avoid pinging the timing has to be retarded in high compression engines that are trying to run standard unleaded fuel.
    If you have a compression ratio of 8.5:1 (tb42), running 98 premium means the fuel will burn slower - effectively retarding the timing and making the engine run hotter with less efficiency. Modern engines that set ignition timing based on knock sensors will run almost identical to running the engine on 91 unleaded. However the ignition timing will spark further before TDC which can rob an engine of power.

    If you really want to test the theory, run your engine on LPG - it has an octane equivalent of 110. = Runs hot with less power.
    Increase the compression to around 11:1 and run LPG = better fuel economy, more power and cooler running.
    Run 11:1 compression with wet injection LPG and you'll get better power and fuel consumption than the same engine fuelled with petrol.

    May as well try feed a bulldog rib eye fillet steak to make it run like a greyhound.
    Tanks for the detailed and very sensible reply. I did actually increase the compression ratio on my old Range Rover P38 - hence better running on 98. But sort of suspected what you explain so well for my TB42 , it runs already extremely well on LPG though. Not sure if previous owner worked on compression.

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    Patrol Freak Bigcol's Avatar
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    if yours is a TB42 with Gas conversion @LandRoverGhost

    some of what Arfa has said is possible

    just remember, your petrol will normally be set at about 8*BTDC - and if your Gas has been set up correctly, you should be closer to 16*BTDC

    it will depend on who tuned it, and how they tuned it
    for Petrol / Gas economy (so you use both fuels)
    for Petrol (because they dont know how to tune a car with Gas - and they ARE out there)
    for Gas Economy
    for Gas Power
    for Gas Performance

    if it has been setup for Gas - using 98 petrol will be a waste of time & money


    sounds like the previous owner has it set for Gas Power
    Tidy Whitey - 99 GU TD42Ti - Diesel Gas, (GUIV Turbo & Intercooler 8Lb boost), 33" Micky T's Baja MTZ's, Dual Batt's, Cargo Barrier, rear draws, HID Super Oscars, winch, Grinch & witch attached and more goodies to come

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