Hi all.
My '92n MY V12 has the original air intakes, the ones that end inside the hot engine bay. I have seen that on later cars the intakes go up to the top of the radiator and receive fresh cool air.


I'm guessing that this was done for a good reason...........pros..cons ?
Is this a good mod to contemplate as my cars in hot humid Florida

 

Cool air is denser than warm air. Thats usually one of the first modifications I make to increase performance.

 

I have bought some nice flexible hose to do this mod...... the next part would be getting another radiator top panel off a scrap car and then seeing if I could somehow make an opening in it between the top of the radiator and the hood. Based on the horrific heat under the hood with the engine running, I am completely convinced you would increase performance if you could get colder air in.

Your post has inspired me to get back into this...... may give it a try over the coming long weekend, assuming I can get the headliner replaced in my XJ40 without killing myself

 

Air density is like this.
kg/m3 means, it's the weight per 1m3 at the temperature.
So if the same volume is inhaled by an engine, the actual mass of the air will be different if the temp is different.
That is why there is a air temp sensor on the air filter box. It adjusts the fuel amount to suit appropriate air mass.


@0°C 　1.2756 kg/m3
5°C　 1.2527
10°C　1.2306
15°C　1.2092
20°C　1.1886
25°C　1.1686
30°C　1.1494
35°C　1.1307
40°C　1.1127
45°C　1.0952
50°C　1.0782
55°C　1.0618
60°C　1.0459
65°C　1.0304
70°C　1.0154
75°C　1.0008
80°C　0.9866


So, in a winter season and outside temp is 5°C and the engine room temp is 40°C, there will be a nearly 13% difference of air mass if you get the air from out of the engine room.

That means, while cold air produces more power, hot air will decrease the fuel and fuel economy will theoretically be better.

 

Somewhere I had a chart which read how much the BHP changed with the air temp. How much extra power 11% more oxygen gives I do not know. But it gives quite a bit, as once I drove home from Italy at an air temp of minus 14°C and the car was an absolute rocketship.

Greg

 

Here is something I just found on air temp vs BHP. From say 20°F to 80°F might give an 8% difference = 24BHP straight to/from the wheels:


Greg

 

not sure if this is relevant, but my V12 on a Dyno-jet roller dyno, i tried with hood closed and then open,with a large overhead fan 4 ft dia. blowing straight down into the engine compartment.

test closed hood to test open hood made about 5 whp more! and i know there would be some variables involved, but i question about 24 whp more!

and of course i'm familier with cold air inlet systems, i'd be more interested in cold air for detonation control, especially for endurance racing,or simply a long full throttle hy-way run ,like a west Texas I-10 ,(100s of miles without letting up).