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Originally Posted by IsaacMTSU
I'm wondering the same thing... Higher compression on regular gas is fine for hypermiling because you are going to be driving easy anyway right? Would it help to put some HC pistons in?
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Would depend on the engine. A fully variable duration intake valve equipped engine would do fine on low octane gas, since the temperature at ignition will be considerably reduced. A throttle plate can be thought of as adding the pumping losses it induces to the intake charge in the form of heat, so the amount of extra detonation headroom you get when running at part load is smaller. I don't know how much you have to restrict your load due to running lower octane fuel, but if it forces you to remain at very low load levels where the engine isn't very efficient, then it might be better to buy higher octane fuel and just burn less of it. If you're just sitting at part throttle on the open highway, no pulse and glide, then regular gas would probably save you a bit.