tuning myths...

Stamford I completely agree with you, if you follow through and make the upgrade a package then there will be an improvement gained . JMHO I worked in a Ford dealership , I was the night time shop foreman and over the years saw so many people fall for the ads put out by the aftermarket promising huge HP gains or ridiculous fuel mileage increases by simply bolting on their part. When I talked to customers who had problems with their cars created by those parts I had to explain to them that if there was HP or gas mileage to be gained by simply bolting on an air filter that the manufacturers would have installed them at the factory . Today's cars are amazing compared with cars years ago, they last 2 to 3 times longer mileage wise and get incredibly better performance along with increased mileage . Car manufacturers fight for every HP and MPG they get along with durability so if something is simple to do to increase any of those things I believe they were looked at very closely .
 
it should be mentioned that there are different "rules" for turbo and na engines and particually tuned turbo engines
for a start turbos produce an awful lot of heat so this raises the under bonnett temperatures considerably . And because the air filters are usually close to the turbos a properly insulated cold box can , and will , lower the temperature of the air going into a turbo engine. And a tuned turbo motor has bigger turbo(s) so benefits to a greater extent.
It also follows that if the temperatures are warmer under the bonnet then using colder air ducted into the cold box will imrove things as well.
So on a tuned turbo car a system of ducting cold air into a box with the filters in is the optimum set up.
It is temperature not the amount of air that is important

Because the car moves forward air is forced into the box and naturally is therefore naturally pressurised. It is therefore assumed by some that this is desireable when in fact it is just a consequence of using the air otside the car
It isnt about getting more air into the box it is just about getting colder air into the box.
 
IMO under bonnet temps are governed by the volume of airflow thru the radiator along the ability being able to exit the engine bay

Logic tells me that if it can't escape easily them the incoming cooling airflow will be reduced.

In many/most turbo cars incoming air has to pass thru an oil cooler and front mount intercooler as well as the radiator so the volume of incoming airflow is somewhat slowed down/restricted/reduced.

Some drivers/people think that raising the rear of the bonnet will allow the hot air to escape and help in getting more cooling air thru the radiator BUT this is actually a high pressure area and doing so is counter productive.

IF you are having overheating problems then the fix is to install some louvered vent in the front 1/2 of the bonnet [ Evo's or Sierra turbos are a good example] so that the under bonnet hot air can escape which allows in more incoming cool air to pass thru the IC and radiator.

PS the above advise/opinion assumes that you have a fully functioning CLEAN radiator as well as the correct thermostat in place.
 
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