fbh-velocity

I'm wondering how much power I'm down for each 10 F the intake temperature is raising.? In the spring when the water was about 50F. And air was 60F i could turn 5300 RPM 26 B1 lab finished prop 1.5 ratio Bravo 1 drive 454, 500+ HP.
Now the water temperature is 77F. and air is 100F. I can barely make 5100 RPM and 3-4 MPH down in speed. After hot run the temperature under the hatch is raise to more than 140F. Is this a normal power loss and how does it affect jetting?

Payton

That seems awefuly hot. I had a friend that found out he had an air intake problem when he was able to make a high speed run with the hatch open about an inch or so. I am sure the water will have to be pretty smooth and not make a habit of doing this. But, it may help you find out if you have to add some vents.

That being said, you won't make as much power in 100*air as you will in 70*air. Someone else may know how much less.

SB

iTrader: (1)

General rule is air temp increase of 10°F equals 1% loss.
Therefore:
100°F increase equals 10% loss.
50°F increase equals 5% loss.


This is because of oxygen content and assumes tune for the weather is right on. If the tune is not changed then your actual results may be different ± .

CigDaze

SB is very close, and it is a good rule of thumb.

An engine with a rated horsepower in accordance with and certified by SAE J1349, it would make 100% of it's rated horsepower at 77 degrees F, at a pressure of 29.235 Inches Hg Barometer, at an altitude of 0 feet, and at 0% relative humidity.

For comparison's sake, let's say 77 degrees is where you make 100% of your rated power. The following is the power you'd make at different temperatures, assuming all other things are equal:

Deg F - % Power
30 - 105.6
40 - 104.4
50 - 103.1
60 - 102.0
65 - 101.4
70 - 100.8
75 - 100.3
77 - 100.0
80 - 99.7
85 - 99.2
90 - 98.6
95 - 98.1
100 - 97.6
105 - 97.1
110 - 96.6
115 - 96.1
120 - 95.6