Something about lifted hood.

[freeman1314]

Me and my friend were chatting recently and he suddenly brought up the topic lift hood.
I remember some guys who lifted their hood slightly higher at the part near the front wind shield told me that it is a method to let the hot air in the engine bay escape.

But according to my friend, by lifting the hood up, when you are traveling at higher speed, the air traveling above the bonnet is faster than the air traveling inside the engine bay therefore it generates lift which reduces the downforce of you car and also creates a vacuum in the engine bay resulting even hotter engine bay and reduced front down force.

Anyone got any idea about this?
His theory is, air got no restriction while traveling above the hood coz got nothing to block it, air that goes in from the from radiator vent will have alot of restriction due to the parts in the engine bay.

Is his theory correct or wrong? I would think it is correct but how bout other sifus?

 

[arturo]

i agree on the faster air on the outside n lower circulating air in the engine bay....this might cause some lift...but about the vacuum...if u have higher pressure air in the engine bay, that would mean u cant have a vacuum there since vacuum would mean lower pressure air

u will also need to factor in the front grille...air will also be pushed in thru the grille and the air will need to escape somewhere...the only way is to get a lifted hood n tape some plastic strips along the bottom and top edge of the lifted hood(near the rear opening) and see how those strips flow when travelling at speed.

there was an experiment done b4 where they tested whether a bullet hole would cause explosive decompression of an airplane but fast flowing air on the outside skin of the plane will not create a sufficient suction to pull air out of the inside...there is some movement but nothing huge. this being said, the air in the airplane was static with no outside air being forced thru it like lets say in an engine bay with the front gille being shoved with air as the car moves forward...i say try it out with the plastic strips n then can see how it goes...

 

[freeman1314]

I see.. because usually people will thing air comes in from the front grille and travels out through the vent created b lifting up the hood. But if the air is static in the engine bay, then still the hot air doesn't travels out better right ?

 

[arturo]

freeman...i think u got me wrong. i think that that lifting the hood up does help. u have air coming in thru the front....then cos u have an opening at the end of the engine bay....there should be air being pushed out from all the air being rammed in from the front. thats my logic after a few sifu's explained the reason ppl lift their hoods la. imagine blowing air thru a straw....small hole but since u keep pushing air in thru the front....the air will come out from the rear...

 

[freeman1314]

I see..so your theory is that it isn't the higher velocity air at the top of the hood that sucks the air in the engine bay out but rather the air that travels into the engine bay from the front grille that is pushing the air out right?

 

[K_Takuya]

Higher velocity at the hood top will help to suck the dense air from the bay.. the air from the bay will be replaced by new air from front grill...bay temp will be cooler...

unless running a high performance engine.. using lifted hood have less meanings..

 

[arturo]

yep. right out of my mouth!

 

[freeman1314]

Hmm...i get it. But now my question becomes, will the amount of air being sucked out get replaced fast enough?
Will the amount of air that exits the engine bay be more than the air that enters due to more restriction(e.g. small front grille vent size,radiators, intercooler etc) at the front grille causing lower pressure at the engine bay?
Or will the air the exits equals the air that enters so the pressure at the engine bay remains the same.

Thanks in advance.

 

[foofis]

the "cleavelage" the popping hood provides cooler engine bay tempt when your travelling below 60kph, where the air is not travelling fast enough. when you are drifting n high revving the engine, this popping hood helps to reduce by 1-3degree celcius, the result is noticable

 

[DanzEterna]

so arturo, conclusion is it better to lift the hood?

 

[arturo]

aiya Danz...i oni understand the logic oni...cant comment better or not to lift the hood wooor

forgot to ask u last time but when u lifted yr hood that time, got difference in temperature?

remember that time somebody said if lift hood n the hot air from engine bay flow across the windscreen n then in long run might cause the windscreen to crack cos of heat difference? is something that may or may not happen...depends on whether willing to take the risk or not...then the accident thing...if got frontal collision...wont the hood become like a knife thru the windscreen?

 

[DanzEterna]

err.....i understand the logic that heat escapes during standstill, like in traffic jams...but during highway drivin does it work?

yeah to me it does help during at a standstill...

to me my windscreen cracked cos was caused by the edges of the bonnet, not caused by heat. but heat does not makes the wscreen crack, maybe for single layer wscreen la...like kancil...

 

[arturo]

nono...not mentioning yr cracked windscreen case....i remember got 1 guy after i comment on the heat difference got say maybe in long run might weaken the windscreen....but then i just had a thought....our weather aredy so hot...sometimes 34-37deg during mid day...should be hotter than the hot air out of engine n + summore with the radiant heat from the sun...double layer shouldnt have a problem...single layer oso shouldnt be a problem kua?

only way to test if it works is to put the string or plastic strips on the under side on the hood edge n see when driving if the string/plastic strips will flow out n from there can tell if the air really flowing out fast or slow or no movement at all...

 

[DanzEterna]

Ooo ya remember got 1 guy asked that question, but i tot the wscreen is tampered glass? it was heated to few hundred degrees or heat..something like that....unless under the hot sun, if a small pebble hits the wscreen it will crack or worse shattered....

 

[arturo]

maybe la...normally hear stories of windscreen meletup is on older cars rite? maybe cos too long kena hot cold hot cold thats y shatter...my fren old 130y kena b4 on hiway...suddenly shattered...happened at nite summore n when he check, cant find the point of impact...

already lari topic leh hahahahah