Warm weather performance

[Jay 02 TA ws6]

Does anybody else notice a HUGE difference between your car's performance on the way to work (when it is 65 degrees) and its performance on the way home from work (when it is 90 degrees)?

My car behaves SO differently... it is almost like I am taking off in second gear. I see a huge difference in performance. Is it just me? Because if it is, I think I might have something wrong here...

[FRMLAV8]

Thats usually pretty normal. The car will always perform better when it is cooler and less humid <- normally early morning!

The cooler air is more dense, and allows you to get more Oxygen into the motor which creates more power. That's why people install Cold Air Induction kits on their cars.
Cold air Good, Warm air Bad!

You probably already knew this, but I figured I would throw it in anyway.

[Jay 02 TA ws6]

Yeah, I did know that... so a little difference I wouldn't think so much of. But I can really tell, it's like night and day... I'm just a little worried it might be too much of a difference, that's all.

[FRMLAV8]

I don't know, 30 degrees and humidity will make a big difference!

There is probably some kind of formula to calculate the difference in HP based on temp and barometric pressure.

I know a couple of guys I have talked to about it run 3-5 tenths slower in hot, humid weather.

[99FirebirdGirl]

There is a huge difference in performance when it's hot out. Humid is also bad. That's why not as many people run at the track during the day or in the summer. I know here (In IN) my friends cars run a whole second or more slower when its hot and humid out.

[Jay 02 TA ws6]

Thanks guys... a little piece of mind is always nice

[Injuneer]

Temperature makes a huge difference, and it is easy to calculate on a modern EFI engine. Power produced is directly proportional to the "mass" (~pounds) of air you can cram into the cylinder, and the mass of air is a function of the density of the air, which is inversely proportional to the ABSOLUTE temperature. The thing to remember is that absolute temperature = degees F + 460 (or degrees Kelvin).

So....

65 + 460 = 525
90 + 460 = 550

525/550 = 0.955

Say you had 300HP....

300 x 0.955 = 286HP


sooooooo... running in 90degF air just cost you 14HP compared to 65degF air.

The ABSOLUTE humidity also has an effect, but it is much smaller. The molecules of water displace molecules of "air" (oxygen and nitrogen) so you have less air in the cylinder.

I bought my Formula new in southern California, so it NEVER saw cold weather. When I moved to NJ, the first time I got on it in 10degF weather I just totally blew the tires away with the extra power.... and going from 80degF to 10degF is worth 44HP extra on a 300HP engine.

[magnethead794]

laymens terms:

hot tires: high traction
cold tires: low traction
hot road: slippery at times, aka loose, more traction?
cold road: less slippery, tight
hot air engine: low performance
cold air engine: high performance

[Jay 02 TA ws6]

I am fairly certain warmer roads give you more traction than say - cold winter roads.

[88Cam]

.

Originally posted by Injuneer
Temperature makes a huge difference, and it is easy to calculate on a modern EFI engine. Power produced is directly proportional to the "mass" (~pounds) of air you can cram into the cylinder, and the mass of air is a function of the density of the air, which is inversely proportional to the ABSOLUTE temperature. The thing to remember is that absolute temperature = degees F + 460 (or degrees Kelvin).

So....

65 + 460 = 525
90 + 460 = 550

525/550 = 0.955

Say you had 300HP....

300 x 0.955 = 286HP


sooooooo... running in 90degF air just cost you 14HP compared to 65degF air.

FRED THE SCIENTIST!!!
thats a pretty cool equation you got there.
I live in Texas and houston the less so its always hot and humid

----------------nsity of the air, which is inversely proportional to the ABSOLUTE temperature. The thing to remember is that absolute temperature = degees F + 460 (or degrees Kelvin).

So....

65 + 460 = 525
90 + 460 = 550

525/550 = 0.955

Say you had 300HP....

300 x 0.955 = 286HP


sooooooo... running in 90degF air just cost you 14HP compared to 65degF air.[/B][/QUOTE]

FRED THE SCIENTIST!!!
thats a pretty cool equation you got there.
I live in Texas and houston the less so its always hot and humid

[88Cam]

and...

A simply post turns into a post of confusion...

[Joe 1320]

I always thought the rule of thumb is 3% change in power for every 10ºF.

[Joe K. 99 Zeee!!]

When I was flying helo's we had an equation for performance difference with variables for humidity, altitude, and temp. Can't remember it offhand now though.

TB Bypass also helps in the hot weather. It might surprise you how much that coolent running throught your Throttle Body heats up the incoming air.....I've seen dyno graphs showing a 5-6 RWHP difference!

[RangerBob]

What Joe said

The throttle body coolant bypass really works. I could tell the difference immediately.

[SteveH'95Formula]

Also...

The TB bypass makes a differance but if you have an LT1 a 160 degree thermostat would will make a differance too! I noticed when I did those mods. It makes performance more consistant in hot weather.