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I've been wondering lately about the effect of MBT on economy and if economy can be increased (while still keeping "best torque") by giving more timing while the torque is in the "plateau" area on the graph (assuming of course the engine is not knock limited). Has anyone tested this idea out? If you have what did you find? Is MBT the optimum for both torque and economy or can we squeeze more economy out of an engine by giving more timing on the torque plateau?
Yes, when you look for MBT you will find the best fuel consumption.
MBT point have the lower BSFC because you increase torque until max torque for same air/fuel mass.
I understand what MBT is but torque itself plateaus at MBT and you can increase timing and still have the same torque, torque then decreases rapidly after the plateau event. I thought that economy may increase with more timing during the plateau event but it seems it doesn't.
There are definitly no advantages of over advancing ignition timing. As Leo already mentioned, if the fuel and air mass is fixed, you get best efficiency at the point you reach max torque.
You really should not advance the timing more than MBT in any case! It can harm the engine! Ignition timg past MBT will ignit the combustion to early and the pressure works against the piston before it reached TDC. That will hammer to the rods and bearings.
You can improve fuel economy by using a different target lambda(1.05 lets say).Fuel economy doesnt depend on ignition.If I am wrong correct me plz
Vasilis timing can have dramatic effects on economy. My interest is finding out where the limits of these effects are with regards to maximum torque.
As far as timing goes, MBT will yield the best fuel economy.
Think about what we are trying to achieve - We want the most amount of engine torque for a given mass of fuel and air. This is what we are achieving when we tune the ignition to MBT. Advancing the timing beyond MBT may have no detrimental effect (provided the torque remains on the plateau) but will also give not advantage.
Vasilis, fuel economy depends on ignition timing as we already explained but it also depends on richness. As you said usually you can find best BSFC close to 1 or not far in the lean side.
Thanks Andre that's what I was wondering.
Thanks everyone for your input.
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