how much does hot weather affect performance?
Thread Starter
Pro
Joined: Jan 2003
Posts: 515
Likes: 3
From: newark DE
how much does hot weather affect performance?
heres my dilemma. last year i had a best time of 13.20 at 104.22mph with a 1.87 60ft. over the winter i added a 2500 stall converter, a larger Borla rear ypipe, and eliminated my mufflers. due to the intense rain we had at the beginning of the race season, the earliest i made it to the track was July. i ran a disappointing 13.23 at 103.21, however with a better 1.78 60ft.
i obviously saw in improvement from the converter (better 60fts), but i expected my E/T to drop as well. my mph went down too, even though i installed a higher flowing catback exhaust. could it just be the weather thats bringing me down? whats the usual amount of decreasing performance due to hot and humid temps?
i obviously saw in improvement from the converter (better 60fts), but i expected my E/T to drop as well. my mph went down too, even though i installed a higher flowing catback exhaust. could it just be the weather thats bringing me down? whats the usual amount of decreasing performance due to hot and humid temps?
Burning Brakes
Joined: Nov 2002
Posts: 807
Likes: 21
From: Los Altos CA
Re: how much does hot weather affect performance? (tpivette)
Weather conditions have a big effect. This is because ambient temperature affects the air density and the amount of oxygen available for combustion.According to Obert, Internal Combustion Engines, other things being equal, the power is inversly proportional to the absolute temperatue. Absolute temperature is the temperature in deg. F plus 460. A correction to power from 70F would be 530/(460 + T deg F). If the outside temperature were 100F, you would find the power reduced about 5%. Actually, it will probably be worse than that. A hotter charge produces a greater tendency to knock, so the knock sensor may retard the spark a bit. Furthermore, the above correction is for what is known as indicated power, the power the combustion gases do on the piston and not the brake power, which is less due to engine friction and accessory load. While the indicated power drops, the friction and accessory power doesn't change much so the brake power (the difference between the indicated power and the friction and accessory power) will decrease a greater percentage. Humidity also affects the power, but ususally not as much. Moisture in the inlet air reduces the amount of available oxygen.
Drifting
Joined: Oct 1999
Posts: 1,722
Likes: 0
From: Gloucester Va
Re: how much does hot weather affect performance? (TA)
Hot weather is the worse. I live here near the VA beach area, and I can feel a a night day difference in my cars power from the mid day heat and then at night right after it rains and cools off a great deal..
Le Mans Master
Joined: Aug 2000
Posts: 7,760
Likes: 0
From: Lost in the mountains of TN
Re: how much does hot weather affect performance? (88_vette)
A 30°F difference (95°F down to 65°F) on the dyno gave me a 17hp and 17ft-lbs difference on the dyno. This was at the wheels too. So it was ~ a 20hp gain in the cooler weather.
Le Mans Master
Joined: Mar 1999
Posts: 6,744
Likes: 1
From: delmont pa
Cruise-In I Veteran
Cruise-In II Veteran
Re: how much does hot weather affect performance? (tpivette)
you loose 1% in HP for every 10 degrees the inlet temp goes up, and hi humidy replaces the oxygen in the air with moisture and water does not burn. :chevy
Drifting
Joined: Aug 2000
Posts: 1,614
Likes: 0
From: Colleyville Texas
Re: how much does hot weather affect performance? (tpivette)
We raced last week at the Texas Muscle Car Challenge at an 1/8 mile track. Temp was 95+ and track temp was well over 100+. Alot of guys move out of the Pro Muscle Class, 7.64 and faster, at this race. At the November race on the same track we move back to the Pro Muscle Class. 4-5 tenths and 3 MPH difference is not unusual. Someone said 10 degrees is worth a .1 all things being equal?
