really struggling to get to 40mpg combined

[guest001]

ok, great info. you brought up some really good points that's helping me understand this. esp. a lean mixture and the waste from ignition until TDC. This forum rocks, even though its about fuel economy other then making power, people seem to formulate better info, thats proven and scientific.

what I meant though on the total pressure. was, when the ignition ignites and starts to burn, after TDC the force at 1 degree, 2 degree, etc. till 180 degree added up together would be less if the peak pressure wasn't happening at that sweet spot.

y not fire the plug at the sweet spot, like direct injection? generate to much and wouldn't that be technically detonation. buy this logic. simply used parts that are way more resistant to heat and stronger, the motor would make more power not allowing the coolant to reduce thermal efficiency. but then are air cooled motors more thermal efficient??

[Wyldesoul]

The problem with firing ignition at the "sweet spot" is that the burn is not instantaneous. So, actually, a well tuned motor IS firing the ignition at the "sweet spot" when the peak burn pressure occurs at around 12-15 degrees after TDC "sweet spot". So there's a difference between the ignition sweet spot, and the burn pressure sweet spot.

And you're probably right that there's going to be more power (force x time) upon the piston through optimum ignition timing.

But if you get the timing down right, to where you make the most horsepower for a given setup, you are finding that sweet spot.

All this is a very, very compelling reason to get any modified car dyno tuned, even if conservatively.

Air cooled motors are far less efficient than water cooled. With an air cooled motor, it's ALWAYS losing heat to the outside, and there is no way to accurately control the temperature. A water cooled motor can actively control the temperature through use of a thermostat. There's always going to be waste heat, but a water cooled motor can keep the engine block hot enough for optimum burn efficiency.

[guest001]

I meant, like if there was a way to burn the mixture all at once, like with more then 1 plug, or a stronger ignition. there's this really interesting thread I was reading on how compression actually makes power. and the person mentioned this idea.

http://forum.miata.net/vb/printthread.php?t=307292

o, yeah the thermostat. derr, in a book I'm reading they say how in nascar there using higher temp thermostats. it's about turbochargers but they talk a lot about what actually makes power, heat, and efficiency of an internal combustion engine, recovering wasted exhaust to do work.

[Wyldesoul]

There is, and those can be taken advantage of. There are engines out there with multiple spark plugs, and there's always a quest for a better mixing combustion chamber design for faster, more efficient burns. But for most common use... You just need to time the ignition properly.