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- Elgrand
- E51
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I'm interested in what you're doing and it's a good idea.
I think there'll be more power increase approaching 85% ethanol, better mpg with lower ethanol percentage... As one (power) goes up the other (mpg) goes down and vice 'versa. Power charts possibly using the £4per litre race fuel that is consistently blended for the full 85% ethanol and the remaining 15% petrol not the usual petrol you could buy from a forecourt. Power and torque will change with the percentage of ethanol in your car tank, there could be different power and torque after any fill up.
Ethanol is 'bio' if produced from crops but (and this is a reason it's not sold at UK forecourts) there wouldn't be enough land on earth to grow enough crop to produce enough ethanol for all the vehicles and even if there were that would mean no food crops could be grown. There's also an ironic factor in that growing crop for ethanol production means increased use of diesel and electricity for tractors and processing. 10% of all LPG sold in the UK is currently bio, this will be 100% in 2040.
With higher octane fuel you can get a bit more power and mpg by advancing ignition timing but a lot of people think maximum advance before causing detonation will make most power and that's not quite true. People are used to setting timing on petrol and comparing power when the engine is run flat out... it is mostly true for that condition but when we're talking ignition advance tuning we're talking about trying to get
the biggest difference in cylinder pressure on the power stroke versus the compression stroke taking into account the fuel takes times to burn and the piston is moving at a speed related to rpm and position in the stroke. Pressure at tdc doesn't do much because the piston is directly over the crank and regardless of how much we push or pull on the piston if it's directly above the crank it won't create a turning force on the crank, so it's not just peak pressures but also duration of pressure on the piston at both sides of tdc and position in the piston stroke at these pressures that matter. If we used a fuel that had super high anti detonation property (octane) we could end up advancing timing to the point pressure during the compression stroke builds to the point it detracts from that biggest difference in cylinder on the power stroke versus compression stroke and end up making less power even though it doesn't detonate. But in practice the ignition system won't allow that much advance even if the knock sensors don't detect knock, so using higher octane fuels we do gain a bit of power and mpg from advancing ignition timing when the system is trying to detect knock. It isn't trying to detect knock all the time, it does when you put your foot down, it might not at a part throttle light cruise. Timing is retarded during cranking to prevent the 'back spin' that could sometimes be experienced when trying to start an old points and distributor ignition system engine with a fairly flat battery that could crank the engine but at a lower cranking speed than normal, the 'backspin' was the result of the mixture being ignited during the compression stroke and building pressure in the cylinder quickly enough in respect to the upward speed of the piston that it pushed the piston back down before it reached tdc on the compression stroke so spun the engine backwards. In NDS2 on some Elgrands you can advance base ignition timing by a couple of degrees.