I have a SC system installed and would like to know what is the temperature of the air once it leave the SC head and before it enters the intercooler? I know there are a lot of things that come into play here but I'm just looking for approximate temperature.

 

I'm sure some other guys on here will give you a more scientific answer, but basically it depends on the outside temps and the superchargers head unit temps. So in 90 degree outside temps in stop in go traffic, the head unit will heat soak and the air being compressed once you begin to make boost will be hot. However if it's 50 degrees out and your cruise down the highway. The head unit will be cool and the intercooler will be cold. So head unit discharge will be nice and cold. Sorry I can't give you any exact numbers, all I can tell you is it's going to be a wide range of discharge temps depending on conditions.......


If I were to guess I would say temps could range anywhere between 40-200 degrees, just depends......

 

Yes outside temp would make a difference. Last night I came back from a drive and I could not keep my hand on the head unit it was so hot. This started me thinking about air temperature comming out of the head unit.

 

Exactly, there are a lot of things at play, so any "approximate" temperature you get is just a wild guess.
Instead, let me show you how to calculate the actual temperature:
First, you need to convert the ambient temperature into absolute temperature. Absolute temperature is the temperature in degrees F, plus 460, and has units of degrees Rankine.
Boost has to be converted into Pressure Ratio (PR). PR is how much more pressure you are running than atmosphere. It is calculated as follows:
(14.7PSI + BOOST)/14.7PSI , where "BOOST" is how much boost you are running above atmospheric pressure.
The theoretical formula for temperature gain is thus:
(PR^0.28-1)XTabs
Where 0.28 is determined by the universal gas constant.

So, for my car, running 10 PSI boost on a 90F day, the temperature gain of the intake charge is:
PR = 1.66
Tabs = 550Rankine
(1.66^0.28-1)*550
=84degrees absolute.

So, theoretically, my supercharger raises the intake air temperature by 84 degrees on a 90F day...
In PRACTICE, this would only happen if the supercharger was 100% efficient... In REALITY, my Vortech Si-Trim blower is 78% efficient (S-Trim is 73% and T-trim/Paxton Novi 1500 is 75%)
So the actual temperature gain is 84/0.78 = 107.7 degrees.
So, on a 90F day, my supercharger is, at BEST, putting out 197.7 degree air.
This of course assumes the blower is being operated at peak efficiency... What happens when you start seeking larger boost numbers is that the efficiency of the supercharger drops very quickly, so your "78% efficient" blower can actually be operating at 60% efficiency. I won't go into the details of that because it is not what you asked.
I will, however, point out that this temperature gain has a lot to do with why some forms of forced induction make a lot more power than others...
The typical efficiency of a Roots blower is 55%. The same 10PSI boost being made by a roots blower would have put outlet temperature at 243F, IF the blower wasn't heat soaked.
Intercooling efficiency is usually between 70% and 80%, so post intercooler temperatures will be the post supercharger temperature, divided by 1.7 or 1.8; 109 - 116F for the cetrifugal, and 143 for the roots, assuming for the roots that you can get an intercooler in the small space between the blower and the engine block that will do 70% efficiency (very difficult).
So, even with intercooling, there comes a point (for any FI method) where you simply can not prevent intake air charge temperatures from reaching the point where the fuel spontaneously ignites in the combustion chamber during compression.

Hope that wasn't too much information. For your ballpark answer I'd say: take whatever the ambient temperature is, and add 110degrees or so to it and that will give you an approximate outlet temp if you are running 9-10pounds of boost.

 

Thanks powerlabs!


I figured you'd have the scientific answer! Now if I can just remember some of those algebra lessons in college to figure out how to go faster...lol

 

Thanks PowerLabs very nice detailed description. This give me some idea of the temperatures we are talking about. The SC head sure feels a lot hotter then lets say your example of around 190. Anyway that intercooler is working hard.

 

190F is just the air discharge temperature; you have to remember that the head unit is bolted on to the engine head, which itself should be in the 220+F range, so it is not inconceivable that the SC could be running hotter than 190. Conversely, when running at part throttle the air discharge temperatureis near ambient, so the blower could also be much cooler than 190F. Bare metal at a temperature of 150F takes less than one second to burn skin, so the only way you can know for sure if by taking an IR thermometer to it... I recommend the Fluke 62; it costs about $99 shipped.



EDIT: I made a video of the underhood temps. You can see it here. The blower outlet was about 160F on a 70F day.

 

Thanks PowerLabs the Fluke is a great idea, I will check into it. Your help is greatly appreciated.