OzE55

I’ve read, with interest, various members quite elegant methods for insulating the air intake tubes. I admire their handiwork.
My high school science suggested to me that air is a poor conductor of heat (unlike the plastic tube walls) and that in a fast moving column of air, the heat of the tube will have little affect on the temperature of the intake air.
So, I have placed a digital thermometer in various parts of the air intake system and have driven the car for several weeks to record the temperatures. I ran the lead from the sensor into the car and placed the read out on the dash.(picture 1)
I have used the cars (digitally displayed in the speedo) outside temperature sensor as the reference for ambient air temperature.
It’s important to remember that the sensor will suffer heat soak, like any solid object, and therefore doesn’t record instantaneous air temperature. The trends and observations should be a good guide, though. I have converted the Celsius measurements to Fahrenheit as approximations.
My car is a 2003. It’s unmodified except that I have unshrouded the front of the air intake tubes (picture 2).

Position 1 – In front of the intake tube mouth.
I suspended (so it wasn’t in contact with a hot surface) the sensor in front of one of the mouths of the intake tubes. In normal constant driving at any speed above 20mph the air temperature in front of the radiator and at the mouth of the intake is equal to ambient. It doesn’t vary no matter how long you drive. So the air movement here is sufficient to stop the radiator affecting the intake air temp. The temp. rises if the car is stationary (say 20 Celsius to 40C = 75F to 105F), but not higher.

Position 2 – In the engine bay.
I suspended the sensor in the engine bay beside the air tube. Temp. rapidly rises from 20C to 50-70C (75F to 125F- 160F) as the engine reaches full operating temperature. The temperature changes very little with driving. So, a cone filter in the engine bay would be sucking very hot air – bad idea.

Position 3 – inside the air tube.
(picture 3,4). I suspended the sensor in the middle of the air flow. With constant driving at >20mph the temp. stays around ambient indefinitely! Despite the tube being very hot to touch the air column is only 5-10C hotter (7-15F) at most. If the car is parked temp. rises to 70C (160F) due to heat soak. If the car is restarted while still hot and left to idle, the temp drops progressively. It cools to 5-10C above ambient with constant driving after 5-10 mins. So, as the car speed/engine speed slows the air column slows and suffers from heat soak radiated from the engine bay via the heat tube plastic. Once moving I suspect the air column cools very quickly – but I cannot measure instantaneous temp with this set-up.

Position 4 – inside the air filter box (engine side).
I chose the engine side (on top) of the filter as the airflow should be slowed by the filter. Unfortunately, I couldn’t really suspend the sensor as there is little room and I think the sensor will have been affected by direct heat conduction. At constant driving 30+mph the temperature is 10-20C above ambient ( 15-25F). In stop start driving the temp approaches 50C (125F).

Conclusions –
1. The air in the intake tubes is close to ambient during driving and probably suffers little from heat soak. Performance probably isn’t improved by heat wrapping the air tubes. I suspect that for the drag racers its important to lift the hood between runs and keep the engine reving before launch to keep the air column moving and cool. Obviously, this ignores the heat soak effects on the engine.

2. If you want to insulate something it should be the filter box. I suspect that this will only, temporarily, delay the filter heating up. (Isolating the air box from direct conductive heating from the engine block would seem difficult). In any event the greatest heating of the intake air is likely to be within the supercharger and intake manifold.

I don’t know if this helps anyone or is even of interest, but there it is.

Thanks.

OzE55

Here are the pictures.

Rafal

This is a great study, which proves that MB would have considered these factors before installing the flimsy plastic intake tubes. Thanks for sharing!

As enthusiasts, we think that we can improve, for a few bucks, on millions of dollars worth of R&D! But it's fun and keeps us interested in our cars.

I still believe that my car goes better after the mods, just as it goes better with Green Filters...or after I've washed it, for that matter! It's all in the mind.

vrus

Very good scientific data gathering!! Thanks for taking the time and initiative to do this.

To complete this experiment, the proper thing to do would be to wrap the intake tubes and rerun your tests. Compare the temperature readings and see what the delta is (wrapped vs unwrapped).

As far as the intake tubes are concerned, I've always stated that wrapping them alone is not sufficient. You have to wrap the air boxes, intake tubes, and Y-pipe if you want to see any real benefit.

stevebez

Does anyone know how good carbon fibre is as an insulator ? I was thinking of wrapping the air box with carbon fibre (for improve looks), while laminating a sheet of asbestos in between the airbox housing and the fibre sheet. This is the next best thing to having an air box housing that is double skinned and filled with some inert gas / vacuum as per a thermos flask - that would be a great task for a pro welder!!! This is complete overkill but hey while we throwing ideas around ...

You could also line the inside of the air box with some carbon fibre / asbestos / polystyrene. I am not sure if decreasing the air volume in the air box would matter much though if the polystyrene was thick...

Also I think the intake manifold is where most of the heat soak is ... it starts in the air box and the manifold just compounds it and then the S/C multiplies it ...

Has anyone thought placing heat sinks on the intake manifold housing ? Would this help reduce internal manifold temps or would this ADD to the heat soak ?

Intake manifold and S/C is where the main issue lies in my opinion...

BUT the temps increase and soak at different driving conitions - the air box and maniifold at high speeds will be pretty much at ambient ... the S/C will add IAT's through compressing the air - not too much you can do about that without a larger or more efficient I/C setup.

The only time the manifold / air box will get soaked is in start stop traffic or in very high ambients. The above insulation remedies may delay the progress of this .... but ultimately think you will reach the same soak level - or will you maybe reach a lower equilibrium level ?

Off the wall idea but how about redirecting - for short bursts - ice cold air conditioned air directly into the air box? This won't be pleasant for the passengers - but I would be pretty interested to see what effect it has on power output.... and for how long

Rgds Steve.

OzE55

Agreed.
After seeing that the temp. in the air tube stayed at ambient I couldn't see the point in insulating it and redoing the measurements.
I think the supercharger and inlet manifold are likely to be the biggest contributor to intake air temperature.
I was suprised at how hot the air in the engine compartment became. It must be very poorly ventilated. Perhaps there is an easy way to improve the ventilation - without putting vents in the hood.

ENDSMTG

Excellent work! You have earned an A here!

ima55r2

Wrapping the air box seems like it would be a little cumbersome. I'd suggest doing the inside of the box with ceramic paint. Google it for info.

Rafal

...or you can line it with heat shield fabric stuck with heat resistant silicone.