1engineer
Moderator
Many of us have experienced colder than normal temperatures in the past few days. Two days ago I was riding my bike in 70 degree F temperatures in SC. This morning it was 7 degrees F at my house, which is quite a bit of difference. As I was driving this morning, I noticed my TE throttle was more responsive. I knew immediately why but thought I would share it with you guys too.
The Rules:
For every 10- to 11-degree Fahrenheit rise in intake air temperature past 77 degrees, (SAE J1349 standard test correction temperature), you can expect engine horsepower to decrease by about one percent at the same barometric pressure. That works out to a 6.80-percent increase in horsepower for every 1-psi rise in barometric pressure, and a 6.8-percent drop in horsepower for every 1-psi under 14.7 (ambient sea level)
Credit: SAE
Dynojet's rule of thumb is that a 1% increase in power occurs for every 10 degrees F cooler. So,
Our 4Runners have 270 HP at sea level and 77 degrees F.
Alright, now that I have given you the background, here is what I calculated my horsepower was in my TE this morning:
270hp * 1.07 = 288.9 or approximately 290 HP! The 1.07 comes from the differential temperature of tested vs actual. Now, barometric pressure comes into play also and it just so happens that the pressures were within 2 millibars of each other at these different locations so they were a wash.
To conclude, I had around 270 HP on Sunday and 290 HP today. 20 more HP and I did not spend a dime lol. If you guys would like I could make a chart except barometric pressure factors into this equation too. I was lucky and had almost the same pressures even though the altitude is over 2000' different from where I rode Sunday to where I am today. Normally the altitude would have negated any gains caused by temperature. Anyway, just thought it was interesting and you would like to know how temperature affects horsepower either for the good or bad.
These Chart(s) are THEORETICAL! I added a chart on HP vs. Altitude also. It really all depends on air density and altitude or temperature effect density. Here you go:
The Rules:
For every 10- to 11-degree Fahrenheit rise in intake air temperature past 77 degrees, (SAE J1349 standard test correction temperature), you can expect engine horsepower to decrease by about one percent at the same barometric pressure. That works out to a 6.80-percent increase in horsepower for every 1-psi rise in barometric pressure, and a 6.8-percent drop in horsepower for every 1-psi under 14.7 (ambient sea level)
Credit: SAE
Dynojet's rule of thumb is that a 1% increase in power occurs for every 10 degrees F cooler. So,
Our 4Runners have 270 HP at sea level and 77 degrees F.
Alright, now that I have given you the background, here is what I calculated my horsepower was in my TE this morning:
270hp * 1.07 = 288.9 or approximately 290 HP! The 1.07 comes from the differential temperature of tested vs actual. Now, barometric pressure comes into play also and it just so happens that the pressures were within 2 millibars of each other at these different locations so they were a wash.
To conclude, I had around 270 HP on Sunday and 290 HP today. 20 more HP and I did not spend a dime lol. If you guys would like I could make a chart except barometric pressure factors into this equation too. I was lucky and had almost the same pressures even though the altitude is over 2000' different from where I rode Sunday to where I am today. Normally the altitude would have negated any gains caused by temperature. Anyway, just thought it was interesting and you would like to know how temperature affects horsepower either for the good or bad.
These Chart(s) are THEORETICAL! I added a chart on HP vs. Altitude also. It really all depends on air density and altitude or temperature effect density. Here you go:
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