raised bonnets

[SR]

what is your opinion on this
i am reffering to the raising of the bonnet where it is hinged to allow a better flow of air out of the engine compartment

advantages
disadvantages
rice?
lets discuss

[seanf3000]

Ent they had a discussion on this in another thread??

[killersuzuki]

Not rice, allows the hot air to be pulled out of the engine bay. Used this on my elantra.

Disadvantage: Engine gets dirtier more quickly

[Dave]

i do this on race day only, really helps get the hot air out when the fans come on
intake is not as hot as it usually is with bonnet fully closed

[SR]

ok but waht about for non turbo applications
does make a big enough difference with temp drop on the intake manifold and throttle body to generate more horsepower if so what may be the possible gains in hp

[VexXx Dogg]

read a couple articles on this a while aback when i had my bonnet raised.
tests were performed by a guy with a crx(?) with a b16a
and engine bay temperatures actually increased instead of decreasing.
another drawback was that the hot air passing over the intake manifold also increased the temp..
cant remember where the article was but if i find it i will post up the link.

[flatline]

Ent they had a discussion on this in another thread??

http://forums.trinituner.com/forums/vie ... hp?t=72262

[wagonrunner]

http://www.teirney.net/civic/BonnetSpacers.htm

[seanf3000]

Ent they had a discussion on this in another thread??

http://forums.trinituner.com/forums/vie ... hp?t=72262

Ohhhh there it is.... Thnx flats!!

Think there was some difference in opinion as to whether opening up that space actually results in air flowing
1) thru bumper...over engine...and then out bonnet spacing
2)thru bonnet spacing and circulate around engine.
3)thru bumper around engine and under floorpan. (i.e. no change)

Then there was discussion as to whether this was hindering airflow and creating heatsoak on a whole.

In addition the topic was broached on what happens at standstill.

I know ryan did it and he says that he gets cooler temps out of his car in dex. I myself still trying to figure out the dynamics on this one.

[Dave]

now the early model civic(eg) didn't have a grill, would this play a factor in how the air enters the engine when being driven and the eventual channel it would take to be expelled?

[BlueIce]

helps me alot temperature wise, not to mention the extra rice effects it adds

[belalegosi]

http://forums.trinituner.com/forums/vie ... =bernoulli

its been discussed there tooo

[Raziel]

Simple answer

Whether it lowers engine bay temp is dependant on how the airflow coming into the bay works.

As for NA, I can tell you my Toyota 4A-GE 20V engine gets about as hot as most turbos, and cooler is always better.

BTW, for me, vent the bonnet and adjust the bumper intake points, I find the raised look just ugly ....

[RichieRich]

let madcrix tell you all bout the disadvantage

[Aaron 2NR]

Ent they had a discussion on this in another thread??

http://forums.trinituner.com/forums/vie ... hp?t=72262

i dont not agree wit that test...

if dey puttin a sensor to measure the temp of the air at back of the bonnet where it is raised it wud be higher dan if the bonnet is in its orginal position simply beause the hot air is escapin at that pt where as wen it is normal the air is not concentrated at that position so thats why it wud be lower...

i tink if dey wanted to test the temp of the air dey shud use a sensor at the centre of the engine bay an not at the back of the bonnet...

[SR]

i was thinking why wasnt the sensor measuring the temp of the intake manifold as this is where the difference would show

[Hook]

like sum1 correctly stated, the pressure differential between the slow moving air in the engine bay (high pressure) and the fast moving air flowing over the hood (low pressure) would cause a scavenging effect BUT that's in an aerofoil

because the rear of ur hood does not have an aerofoil shape there is some scavenging of hot air, BUT we run into (drum roll please).....DRAG (taadaaaaa)

drag in this scenario doesn't slow down the vehicle but it creates a barrier of irregularly swirling air that prevents the hot air from effiently leaving the engine bay...the result is a wall of eddies that let very little (if any) hot air out

some racecar drivers raise the bonnets not for heat scavenging actually, but for cooler intake charges (yup, believe it...it's an entry point, NOT an exit point) as the engine bay already employs more efficient heat scavenging methods like fender vents and reverse scoops above the exhaust headers

the air rushing over the hood is faster, lower pressure and lower temperature than at the point where the intake filter is and by raising the hood and running piping to place the air filter there u have this low pressure vortex of cool air just waiting to be sucked into ur intake


food for thought

[belalegosi]

some racecar drivers raise the bonnets not for heat scavenging actually, but for cooler intake charges (yup, believe it...it's an entry point, NOT an exit point) as the engine bay already employs more efficient heat scavenging methods like fender vents and reverse scoops above the exhaust headers

the air rushing over the hood is faster, lower pressure and lower temperature than at the point where the intake filter is and by raising the hood and running piping to place the air filter there u have this low pressure vortex of cool air just waiting to be sucked into ur intake


food for thought

so from the bold txt i'm assumin ure refferin to boosted cars like evos n sti ?

wat bout n/a cars?
and by runnin piping to place the air filter by the raised hood wouldnt that just complicate things and add restriction to the intake?

[Hook]

so from the bold txt i'm assumin ure refferin to boosted cars like evos n sti ?

I said some RACECARS drivers....Evos and Sti's are racecars BUT not all racecars are Evos and Sti's..lol..refrain from assuming..and it still have n/a racecars out there

and by runnin piping to place the air filter by the raised hood wouldnt that just complicate things and add restriction to the intake?

depends on how u wanna run it meng...I would think that running it to the rear of the raised hood would actually use less piping than trying to run a conventional low-mounted CAI down in front

but like I said, that's all dependent on ur making it easier for the hot air to flow out elsewhere

[MadCrix]

well SR i can say de disadvantage of rasing yuh bonnet is dat your batery pole is now exposed to would be criminal elements

it would be very easy to pry your pole off.. now the alram if it is a good one will have a backup battery most of them don't so you alarm will now be disabled.. mine did have a backup battery buh it was spolit ie not holding charge so when the theives broke in, the siren di dnot sound when they pryed off thepole

advantage : well it seemed that the engine ran cooler, buh without actually measuring the temp in teh enigne bay before and after, an actual difference is impossible to detect....

again to me IT SEEMED differetn. buh you know de seat of yuh pants is no sceintific measurement

[seanf3000]

like sum1 correctly stated, the pressure differential between the slow moving air in the engine bay (high pressure) and the fast moving air flowing over the hood (low pressure) would cause a scavenging effect BUT that's in an aerofoil

because the rear of ur hood does not have an aerofoil shape there is some scavenging of hot air, BUT we run into (drum roll please).....DRAG (taadaaaaa)

drag in this scenario doesn't slow down the vehicle but it creates a barrier of irregularly swirling air that prevents the hot air from effiently leaving the engine bay...the result is a wall of eddies that let very little (if any) hot air out

some racecar drivers raise the bonnets not for heat scavenging actually, but for cooler intake charges (yup, believe it...it's an entry point, NOT an exit point) as the engine bay already employs more efficient heat scavenging methods like fender vents and reverse scoops above the exhaust headers

the air rushing over the hood is faster, lower pressure and lower temperature than at the point where the intake filter is and by raising the hood and running piping to place the air filter there u have this low pressure vortex of cool air just waiting to be sucked into ur intake


food for thought

Aerodynamically....................this is what I thought the effect of the raised bonnet would be (thus the bernoulli reference).

Speaking of that.....I wonder if a raised bonnet would also create lift to some extent. Same concept eh.

[Hook]

to some small extent it does create lift which in this case is actually the hot air leaving the engine bay but, like I said, because the hood doesn't have an aerofoil shape the excessive drag created prevents this from occuring

[horsepwrjunki]

so idealy to get teh best of this theory is to vent the exaust an rad heat mid bonet... ie evo 5-6 hood vents.. and rout the intake through a sealed rear facing scoupe with a spoiler to create drag to suck the air in.. ie cowl induction.. or have a sealed forward facing intake socupe to force induction ie ram air...


see muscle cars again..

[seanf3000]

Well i guess with the evos...that mid bonnet vent was put their with the underbonnet airflow design in place. So the venting system going to depend on your airflow under the bonnet. How you going to figure that out i dunno.

I agree with the intake vent designs tho. And yes muscle cars again!!

[crazybalhead]

http://features.evolutionm.net/article/ ... tures/20/2

[Evolved Automotive Ltd]

not to sound too low tech guys

but the heat venting at stand still after a good run cause excessive condensation on windscreen depending on humidity of course( late evening) which cause rapid contraction and expansion on diferent areas of windscreen and hence potential to crack windscreen. or in my case where i had single ply, shatter it complete , combined with windblast at 160km, cause windscreen to shatter inwards blinding driver and almost causing crash and or permanent blindness LOL

so go brave i learned MY LESSON......

[seanf3000]

^^^ well thats an experience i would want to dodge definitely. I think thats a number one reason not to do this on a daily driver yes.

[SR]

not to sound too low tech guys

but the heat venting at stand still after a good run cause excessive condensation on windscreen depending on humidity of course( late evening) which cause rapid contraction and expansion on diferent areas of windscreen and hence potential to crack windscreen. or in my case where i had single ply, shatter it complete , combined with windblast at 160km, cause windscreen to shatter inwards blinding driver and almost causing crash and or permanent blindness LOL

so go brave i learned MY LESSON......

are you 100% sure this is waht caused the windscreent o crack/shatter
i have had a single ply windscreen shatter on me already while driving on the highway and it was hit from a very small stone then shattered

[VW_Exec]

I find a raised bonnet painted black does look COOL!

[Aaron 2NR]

not to sound too low tech guys

but the heat venting at stand still after a good run cause excessive condensation on windscreen depending on humidity of course( late evening) which cause rapid contraction and expansion on diferent areas of windscreen and hence potential to crack windscreen. or in my case where i had single ply, shatter it complete , combined with windblast at 160km, cause windscreen to shatter inwards blinding driver and almost causing crash and or permanent blindness LOL

so go brave i learned MY LESSON......

glass is made to witstand very high temperatures i.e more dan wat an engine wud produce so the heat comin out the back of a bonnet has a very small probability to cause it to shatter...