lifting the back of the bonnet to let hot air out

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harvey01

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hi all has anyone lifted the back of there bonnet to let hot air out as ive done it with a few of my past cars but not shore with the s3. But as the turbo is at the back of the bay it should work ok
 
Just take the rubber sealing strip off that will let plenty of hot air out if that's what your after ;)
 
Just be aware that removing the rubber and/or lifting the bonnet at the back allows water to enter the back of the engine bay... have seen corrosion etc as a result

<tuffty/>
 
This is only useful when you're stationary, the way the air travels over the bonnet when moving doesn't let any air out. This is not called the Venturi effect.
 
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Lemon S3 said:
This is only useful when you're stationary, the way the air travels over the bonnet when moving doesn't let any air out. This is called the Venturi effect.
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No it's not?! There is no fluid pressures involved for it to be classed as a venturi, the technical term is "**** airflow."
 
16Klappe said:
No it's not?! There is no fluid pressures involved for it to be classed as a venturi, the technical term is "**** airflow."
Click to expand...

Soz, you're right, confused myself with the proper meaning for the effect of pressure at the back of the bonnet. Still....lifting the bonnet doesn't make a difference when in motion.
 
The first reason for liftinG the bonnet was so u could shoe horn a bigger/taller engine in the bay without using differnt mounts

mainly civics with 2.2 engines
 
Or a toilet flap or poop scoop like top gear?
 
Back in the day mark 1 rs ts had no bonnet vents so we used to fit them to let the heat out then ford released the mk2 Rs which came with vents in the bonnet and back in the day we wouldn't dream of ruining the lines by raising the bonnet at the rear

i have been around a long time!
And it was jap scrap in the states that started it

It was a/is schoolboy mod
 
in summer i just take the seal out from the back of the bonnet just to let heat escape whilst moving slowly through traffic or whilst stationary. You can see the heat escaping. But it will only escape whilst stationary or not moving very fast.
 
superkarl said:
in summer i just take the seal out from the back of the bonnet just to let heat escape whilst moving slowly through traffic or whilst stationary. You can see the heat escaping. But it will only escape whilst stationary or not moving very fast.
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ItIsTrue.jpg


This seal ?
 
It must have some effect whilst moving, hot air under the bonnet will have a higher pressure than the air flowing over the bonnet, the high presure air will want to go to the low pressure air, the gap at the back should act as a heat extractor. If you fit bonnet vents they dont force cold air into the engine they draw hot air out, some cars have vents in the wings, like the escort rs cosworth or clio 197/200 which work in the same manor. Although some cars do have a scoop like scoobys and GT4s that force air into the engine or intercooler on these cars.
 
mk1chopper said:
It must have some effect whilst moving, hot air under the bonnet will have a higher pressure than the air flowing over the bonnet, the high presure air will want to go to the low pressure air, the gap at the back should act as a heat extractor. If you fit bonnet vents they dont force cold air into the engine they draw hot air out, some cars have vents in the wings, like the escort rs cosworth or clio 197/200 which work in the same manor. Although some cars do have a scoop like scoobys and GT4s that force air into the engine or intercooler on these cars.
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base of your windscreen/top of bonnet is going to be area of high pressure when moving. Compared to lower pressure under the bonnet. Therefore its not going escape. Its debatable that cold air might go in though

And hence might actually be venturi effect by bernoullis principle
 
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You couldn't be more wrong.

Base of windscreen is a high pressure area, not low, air will be drawn IN, not out by raising the back of the bonnet.

Don't do it. No gains.
 
thank god for superK, I tried to type that 45 mins ago but my net connection is so dire it failled repeatedly.

Thankfully, Karl has already set the record straight.
 
If only you could mount the filter right up under the scuttle for that high pressure. Bit like the Gruppe M intakes for EP3`s having the scoop on the scuttle.
 
Gruppe M have always been spastic high on price but its nice carbon and they are good tbh but still i wouldnt ever pay for one lol.
 
Prawn said:
You couldn't be more wrong.

Base of windscreen is a high pressure area, not low, air will be drawn IN, not out by raising the back of the bonnet.

Don't do it. No gains.
Click to expand...

In principal I was correct, higher pressure will want to go to low pressure, but I hadnt taken into account higher pressure at the base of the windscreen. One question though if air is being forced in due to the high pressue at the base of the wind, is the air being forced in cooler than the air under the bonnet and would this have any benefits? Would lifting/removing the seal be benficial in certain circumsatnces, the high pressure area at the base of the windscreen will be speed relative,so say for example your are tracking your car which has several slow speed corners during these slow speed corners would you see lower pressure at the base of the windscreen and the reverse happening (heat extraction). The gains might be tiny but im just woundering if this would aid cooling in this situation.
 
Without stupidly minute testing, you could never answer that.

Based on the theories you could say the air going in would cool things. But who reeeaaally gives a **** for a few degrees
 
It looks alright on a track car but not something I would want to do as there is no gain I guess.

I supposed you could fit some washers on the bolts to raise it up a bit but im good with how my bonnet is now
 
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