jjwalker

Anyone know generally, for every 5 or 10 degree drop in temperture how much hp do you gain?

al503

for every ~11 degree delta, you get +-1 psi. I don't know what that translates into bhp but the cooler the air, the more dense the intake charge, and the more power you get.

Cornellian

With those numbers you would gain about LESS than ~ 4% increase in HP.

Crazy Yoda

Many of the guys that I would race with at the drag track would build a "cool box" on their musclecars. They would put dry ice into the box to cool the air temp way down to get a boost in hp since it is so hot here all the time in Florida.

Gernby

iTrader: (1)

Dry ice?! That seems counter productive to me. Dry ice is just frozen CO2, right?

al503

I believe he's referring to having the air pass around the 'box' holding the dry ice to cool the intake charge. The resulting co2 from the dry ice melting itself does not go in the intake charge.

There are many variations to this such as cooling the intake manifold with ice packs put on top of it between runs, etc.

ChaddyC

That is something that is very hard to predict without alot of data. There are alot of variables in there that can effect the HP correction factor. Here is a link to an article that explaines it a little in detail

http://www.quarterjr.com/members/weathertech4.htm

I am an avid drag racing and owe a 2002 supercharger trans am making 517 rwhp . I have never really looked into HP corrections as much as density altitude corrections are alot easier to calculate. I am not racing prfessionally so I am more curious in what it would have run had the air been better. For example I ran 11.6@119mph one day and that would equate to 11.0@121 had the air been optimal. I live in Calgary Alberta which is 3500 ft above sea level. Our air here is so crazy, becuase with corrections to density altitude(which is calcuatated using temp, humidity, barometric pressure) it can be the equivalent to racing at 6000 ft. Which really takes away from HP and in essense 1/4 mile times.

Looking into the corrections graph a little I would suspect that you would loose around 2-3% per 10 degrees. Of course that graph does not state what the engine being, but I would assume that it would be a drag car. Since drag cars tend to have alot less coefficient of friction in the motor, pistons are very loose in the cylinders, I would expect the IS350 would be slightly higher than that particular graph. Forced induction is alot more sensitive to this as I know from past experience when you are running boost and it gets a little cold, might not want to get on it too hard. It was about 40 degrees F out when I blew up a piston, due to too much air and not enough fuel.

Hope that helps a little.

NovaIS350

ask lobuxracer. I've seen people put bags of ice on and around turbos, intakes, and piping coming from the intercooler. I thought nitrous fogging systems mounted on intercoolers did that as well. by "did that" i meant cool the intake charge, thus reducing power loss from heat soak. I didnt actuall think you gained HP with lower temperatures. I always assumed you lose less power to the wheels when its colder out.

Cornellian

I calculated those numbers using my background in Automotive Engineering. I included Temp, density, airflow, F/A ratio, Heat capacity, etc....

lobuxracer

iTrader: (2)

It all depends on how complicated you want to make the discussion. If you want to keep it really simple - basically how does temperature affect my production car, then the numbers we've seen are good rules of thumb.

If you want to talk about chilled airboxes, or heat exchangers running intake air on one side and refrigerant on the other, then things get strange fast.

There are so many heat changing events between the atmosphere and just the end of the intake stroke, it's hard to account for it all - for example - anytime you go from high pressure to low pressure the change is endothermic. The inverse case is from low pressure to high pressure, and it's exothermic. So the intake charge at low throttle openings is getting cooled right where the air passes through the throttlebody and where it exits the intake ports and goes into the cylinder. It tends to warm up in that big plenum you stuck on the intake side simply because the pressure increases (which is why you did it in the first place - create a high volume, high pressure region as close to the valves as possible.) Changes in tuning, changes in atmospheric conditions, changes even in fuels (keep in mind, that ethanol you got in your gasoline has a very large cooling effect compared to the base fuel) all make differences.

So the charts are great for taking a known combination and applying a correction factor that puts you in the ballpark. Change anything about that known combination, and you're back to sorting it all out again with testing. As always, YMMV.

We won't even get started about how poorly fuels vaporise in cold air, and how thermal efficiency (and power) is severely compromised by overcooling as much as it is by undercooling. That's a whole different subject.