Can Performance Come and Go?

[tlong]

This sounds dumb but can my car run better sometimes? Friday I just blew away a car passing it. It seemed to scream a little louder, jump a little faster. Does climate and temp make that big a difference? Does the computer just occasionally have a 'good' day?

 

[fast.asleep]

Does climate and temp make that big a difference?

I notice a huge difference. On cool autumn nights the car has more "get up and go" than on hot summer days.

The thing that had the largest effect on the car was altitude. I knew there would be some but I was surprised at how much. When I first got to Calgary I thought there was something very wrong with the car! Nothing I could put my finger on, it had become a real dog. It could barely chirp the tires from a stop.

When I brought the car up here it was totally stock. I've done all the free mods, added headers, dual exhaust, porting, etc and it doesn't have the "get up and go" it had before.

I went from around 250 feet above sea level to 3440 feet above sea level. It feels like the move cost at least 50 hp :cry

 

[tlong]

Cold, dry, dense air. Wouldn't the ECM change with that to keep it constant? I guess for the most part it does. About a month ago it was 25* and low humidity. It seemed sluggish on a little 2 hour trip. Friday like 55* and overcast and it was about to jump out of its bridle. That seems wrong. Must be planetary alignment. This is really kind of an incoherent thread, isn't it?

 

[DRTH VTR]

In general, engine power is limited by how much air is moved in and out of it. You can squirt all the fuel that you want into a cylinder, but it needs the oxygen for combustion. Increased elevation, higher temperatures, and higher humidity all decrease the amount of oxygen available for combustion, so that becomes the limiting factor in power output.

 

[fast.asleep]

In general, engine power is limited by how much air is moved in and out of it. You can squirt all the fuel that you want into a cylinder, but it needs the oxygen for combustion. Increased elevation, higher temperatures, and higher humidity all decrease the amount of oxygen available for combustion, so that becomes the limiting factor in power output.

that's exactly what I was told. I'm sure the ECM accounts for the lack of oxygen to ensure a smooth running vehicle but with a smaller ratio of oxygen to fuel, it probably cuts back the fuel.

 

[G Winter]

Altitude makes a BIG diff. Going up in altitude is like removing a turbo charger or suppercharger. The air pressure is less. If you live in an area where the barometric pressure changes quite a bit you can even tell that .
Cool moist air also helps. Cool are is denser so you actually get more of it in a given volume. I grew up on the farm and when the sun went down you could almost pick up a gear on the tractor when doing farm work. The engine would even sound diff.


Glenn

 

[Edmond]

You could compare the engine to your body. There are optimal temperatures when you can work out and have a productive workout. And then try working out in hot temperatures where everything seems to be labored.

 

[vader86]

Altitude, temperature and humidity can make a huge difference in quarter mile times, so despite the ECM's adjustments, the engine will perform better when its cold, low elevation, and low humidity outside.

ECM is not a wonder-box, it only keeps the engine running smooth.