I have an idea..

[rsty]

I was just looking around this site and saw how many mods block airflow to the engine bay. The hotter the engine runs, the lower rpms, .. and the lower rpms, the less distance for the gas your consuming. So I was thinking of a system where you get your aerodynamics with no drag. I was thinking about testing it on my focus when i get my new front bumper.

Diagram 1



Diamgram 2



NOTE: You can still block up the grill if you want too, this project is done below the grill between your foglights.

This is what inspired me and gave me an idea for the duct.


Please dont flame :P

[avitet]

i cant tell for sure but are you stop all airflow to the rad? either way it dosnt look like it would be a very good idea id think youd be better off stoping the air from getting to the underside of the car in the first place but if im not mistaken your focus is a bottom breather which is the reason for the opening in your new bumper anyway

[Johnny Mullet]

The guy behind the wheel seems thrilled about it

[MetroMPG]

Hi, rsty - have you seen this thread?
aero-mods,installment#9(internal drag)

Lots in there about designing cooling airflow pathways to significantly reduce drag. It can be done with careful design.

[rocket]

Where are you getting "The hotter the engine runs, the lower rpms, .. and the lower rpms, the less distance for the gas your consuming" from? the only time engine temp affects engine speed is while idling. You need Xrpm to get Ympg in any given gear you are in (auto's are not an exact ratio, unless they lock-up).

On warm/hot days, you need some flow through the radiator to keep the engine from over-heating. Pulling air into the back of the engine compartment won't do that, plus an additional fan will only draw more current from the alternator, reducing MPG.

I'm not flaming you, i do applaud your creative process! Keep it up!

[elhigh]

Reducing airflow through the radiator doesn't do anything to the engine's rpms, it only permits the engine to reach operating temperature faster, and thus enter closed-loop operation which is more efficient than the open-loop operation. In Fuel Injected World, open-loop is the same as running with the choke on in Carbureted World - necessary but wasteful, so you want to get out of that state as quickly as possible.

The other point behind reducing airflow through the radiator is to get more of the air flowing around the car where the flow is smooth and less draggy. Allowing only enough air as is necessary for cooling will reduce how much air gets introduced to that craggy, not-streamlined lump of iron and then dumped to the similarly high-drag region under the car.

The engine's rpms are not affected by the engine's temperature at all. The driver controls that, influenced by his desired road speed and the gear he has chosen.

Keep thinking, though. A sealed engine compartment with a remote radiator has been done before to great effect. Now, if we can just make that happen on one of these Metros or some such...

[lunarhighway]

the problem with conventional radiator setups is they are set up to provide enough cooling under all circomstances. for exmample very slow moveing traffic on a hot day. under most driveing situations it's to big, and sometimes , when the engine is not warmed up for example or in cold weather no airflow is needed.

in perfect setup with curent technoligy what you want is to have an exit path for the air that enters trough the radiator, much linke it was done on WW2 figher planes, however as there where constantly moveing the setup for a roadgoing car might not be completely adaptable,

another solution is to create a variable grillblock, that opens and coloses to allow just enough air to pass trough the radiator to keep the enging at the ideal temperature, but not more.

if you get stuck in traffic the door is fully opened and allows max air to enter to keep your car form blowing up, but when you start the car in the winter it's closed all the time and makes all air pass around the smooth contours of the car.

i like your idea, but i don't think it will work in practive, also the problem in the real world is there isn't enough room in the engine bay of a modern car to make such a duct.

so to summarise my take in this is that, it's a good idea to provide a smooth path for the air that gets into the engine bay, but that it's better to try and keep as much air out of the bay as possible.

[thecorrupterx]

could you also take the vent gas from the radiator vent you suggested and make it exit at the top/back of the hood, vented to move smoothly up and over the windshield. would this remove anything from the drag coefficient or would it have negative impact. I guess it boils down to how it is executed.

[rocket]

Originally Posted by lunarhighway

the problem with conventional radiator setups is they are set up to provide enough cooling under all circomstances. for exmample very slow moveing traffic on a hot day. under most driveing situations it's to big, and sometimes , when the engine is not warmed up for example or in cold weather no airflow is needed.

The radiator has no influance in how fast the engine warms up; the thermostat is closed until the coolant reaches ~180 (i know each engine is different, but usually 160-190F). Coolant will not reach the radiator until the thermostat opens (when the engine is warm)

Originally Posted by thecorrupterx

could you also take the vent gas from the radiator vent you suggested and make it exit at the top/back of the hood, vented to move smoothly up and over the windshield. would this remove anything from the drag coefficient or would it have negative impact. I guess it boils down to how it is executed.

It would not vent there: at the base of the windshield is a higher pressure area (bubble, like the bed of a truck) (thats how cowl induction works). running a vent would just cause the air to flow from the cowl to the engine bay, changing the current air flow path (for worse )

[lunarhighway]

The radiator has no influance in how fast the engine warms up; the thermostat is closed until the coolant reaches ~180 (i know each engine is different, but usually 160-190F). Coolant will not reach the radiator until the thermostat opens (when the engine is warm)

that's true, but that means that all air that passes trought the radiator up untill the point where the thermostat opens is 100% useless drag, and even after the radiator is used for cooling for, perhaps a few minutes it might be able to cope without direct airflow.

the fact a lot of people employ full grillblocks proves that the average cooling system is able to cope with engine cooling a large portion of the time WITHOUT a lot of air supplied direcly to the radiator. however the rest of the time where cooling air is reqired (and most grillblockers manually intervene) the average joe would just blow up his engine, unless the car is smart enough to remove the blockage itself... since it can swith on a fan why not have it open the grill just prior to that.

if the cooling is responsible for 30% of all aero drag eliminating this even 10% of the time (but most likely much more) would mean a 3% improvement in average overall drag) that's going from a 0.29Cd to 0.28, but since the system would likely open most on stop go traffic where aero is of little improtance the benefit would be far greater!

as far as air venting trough the bonnet, it's a good idea but pressure differences are indeed imprtant, there's negative pressure at the front (lift) where the air moves faster to make it over the car, and positive pressure (downforce) at the back where the air hits the windshield, and where the cooling inlets are located as this pressure forces air in (also the reason why the radiator is in front of the car as there's also high pressure)

good airflow needs a pressure difference... so the bigger the difference between the intake and the oultet, the better air will flow

so, the less air you need to get the same cooling and so the smaller the intake can be = less drag