Cold weather and lower top speed & mpg?

[DAB]

A given amount of fuel has a fixed amount of energy. If the ambient temperature is lower, more of the fuel is used to generate heat giving less for mechanical work.

Doesn't quite work that way as what we're trying to achieve is a change in pressure (or pressure ratio). And a lower temperature also gives a more dense charge and the lower temp also makes for more efficient combustion. Quite a few factors influencing things, but generally cooler is better hence the reason intercoolers are used on many turbocharged engines to increase power and efficiency.

No, that is exactly how it is, Efficiency is the ratio of the useful work performed by a machine or in a process to the total energy expended or heat taken in. Nothing to do with power.

[TheMaverick]

A given amount of fuel has a fixed amount of energy. If the ambient temperature is lower, more of the fuel is used to generate heat giving less for mechanical work.

Doesn't quite work that way as what we're trying to achieve is a change in pressure (or pressure ratio). And a lower temperature also gives a more dense charge and the lower temp also makes for more efficient combustion. Quite a few factors influencing things, but generally cooler is better hence the reason intercoolers are used on many turbocharged engines to increase power and efficiency.

No, that is exactly how it is, Efficiency is the ratio of the useful work performed by a machine or in a process to the total energy expended or heat taken in. Nothing to do with power.

So if lower temperatures result in lower combustion efficiency as your suggesting, then why are intercoolers used to lower the temperature of the charge when it's temperature is elevated due to compression from a turbocharger?

[you you]

I remember years ago people installing water vapor-injection systems in their cars to increase mileage.
It seems that increasing the humidity of the intake air better incorporates the atomized fuel.
It may have just been another fad, too.

Yea, I remember dad running up the RPM and pouring a glass of water down the carburetor on a old chevy claiming it knocked the carbon off the pistons whist white smoke billowed out the tailpipe. That must have been a fad too because I never see anyone doing it these days... he crazy

My dad did the same thing. I asked him once about it and he showed me how well it worked.
He took a white shop cloth and held it over the exhaust pipe. It came off fairly clean.
He did it again as I dribbled the water down the carb and the cloth got quite black from the steamed off carbon.
Was it from the engine or the exhaust, I don't know for sure, but it did do something.
It's kind of hard to pour water through today's fuel injectors, LOL!!

Dave

Should you want to do it it wouldn't go through the injector. You would water spray through the throttle body. It's the air side, not the fuel side.

[homie]

It's kind of hard to pour water through today's fuel injectors, LOL!!
Dave

Thanks youyou Dave had me going there for a moment

[dgnyberg]

The fuel injector line was a joke, you know sarcasm, misplaced logic, whatever else you want to call it.

But Thanks to U2 for the directions for those who may want to try it.
Or, just add a quart of water to your fuel tank, that should do the same thing. . ./sarcasm off

Dave

[fish]

When I fill my Scion in the summer the dash shows my range to be 325 miles.
In the winter it will typically read 291miles after a fill-up.
Fish

[TheMaverick]

When I fill my Scion in the summer the dash shows my range to be 325 miles.
In the winter it will typically read 291miles after a fill-up.
Fish

I don't think there's any doubt that economy decreases for many - the interesting part is understanding why. One factor I read for cars is that rolling resistance increases by up to 20% and judging by the differences my FOBO system reports between starting (cool) tyre pressures and after-ride pressures (I've seen in excess of 5PSI on many occasions) I could well understand how less of an increase in temperature (and thus pressure) due to riding on very cold roads could very much made a significant difference to rolling resistance on a bike - and thus effect the economy.

Additionally, on my bike, the idle-stop function doesn't kick in until the engine is warm (which takes longer in winter) which also decreases fuel economy.