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Driver
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I think it varies with what the manufacturer recommends, since they tune it for whatever gas they want the consumer to use. I'd still get premium though, since it's just a better fuel.
 

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Garage Sultan
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Discussion Starter #4
stealthb14- sorry, i should have posted it there in the first place. wasnt thinking...

Im just curious, because if they can get turbos to run on 87 octane without knocking and pinging, then how can i do the same kinda thing on my vehicle if i was to turbo it??

-Nick
 

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i may be way off base here....

but im pretty sure it has to do with the compression. the lower the compression the factory uses on their ride the lower the gas can be..... but dont quote me on that.
 

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Any current production car that's out there made by Nissan has a knock sensor, regardless of turbo or not. The tune the ignition and fuel mapping around 91 octane fuel for best performance and fuel economy. They can run more ignition advance and slightly leaner.

Now when you put 87 octane into the car, the knock sensor is going to tell the ECU to retard timing. If the ECU still sees a lot of activity from the knock sensor, it will switch to a low octane map and retard the timing and richen the mixture. On a Z32 it also lowers the boost pressure. It will stay on the low octane map until you cycle the ignition switch.

Since Nissan doesn't sell and turbo cars in the US at the moment, I can't say what their recent thinking is. On Nissan's current engines it is more aggressive about switching back to the high octane map and will try to do it without cycling the key.
 

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you should use what the O/M recommends. If it says 87, then run 87 and you are fine. If it says 87 and you run 91, you won't get any benefit. If you run 91 and advance the ignition timing 3-5 degrees, then you will take advantage of the 91 octane and pickup some HP. If you run the 91 and change nothing, then you are wasting money if the O/M doesn't recommend it.
 
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I have to backup what Nismo Skyline said. I bought a WRX last year. O/M said to run 91 and up, anything less could damage the engine. Of course we all know the damage would be from detonation. Sometimes the O/M will specify, something like "for best performance use only 89-91 octane unleaded gasoline", or it might say use only 91+ octane. On some engines, mostly N/A, it won't make much difference in performance if you don't follow what the O/M says. But in other engines, it can be crucial. More so with any engine that happens to be turbo or super charged
 

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bitter old man
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Octane requirement is set by the engine design. Turbo engines can easily enter detonation conditions, so they are usually spec'ed for high octane. Turbo versions of an N/A engine generally use lowered compression and less aggressive cams to stay out of detonation. More sophisticated set-ups will use timing and fuel flow adjustments as well as intercoolers and some sort of anti-detonation fluid.
 
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