The Lifted Bonnet thing....

[Dragger_Dan]

Ok, we seem to have two schools of thought on this idea:
One says that that this is pointless
The other says that this benefits your car's underbonnet temperature.

My questions on the situation -
1. WTF is heatsoak?, I've only ever heard that used on forums before
2. Can somebody explain why a few degrees less under the bonnet is a good thing. I can understand with open ITBs or a top mount why it could potentially make a difference, I just haven't seen a good justification to do it yet.

[flygt4]

heatsoak applies to everything that exists. if there is a difference in temperature the heat will transfer from hot areas to cold areas.

in a house for example, if you have cold tiles they will soak up a lot of heat. if you have heated tiles they won't and the available heat goes to other colder areas.

it applies to cars because everything thats metal and is at a lower temperature than hot areas around it will soak up heat and increase in temperature.engine bays are a good example. top mounted intercoolers are great at soaking up heat from the hot lump of engine below them, almost defying the point of intercooling to start with.

this affects the performance because cold air is more dense than hot air and therefore has more oxygen in it for the same volume. more oxygen = more power.

it has more effect in forced induction application but still applies to n/a engines.

[fivebob]

Put simply heatsoak is what happens when something cannot dissipate heat fast enough and therefore it's temperature increases.

As to whether a lifted bonnet has any positive effect on cooling, that's debateable, and unless someone has run tests and accurately logged temperatures (ambient, engine, intake and under bonnet) it's all just opinion and internet bench racing.

Aerodynamic theory would suggest it's not going to help and may actually reduce flow through the radiatior, it might increase the amount of cold air that enters the engine bay because the windscreen is a high pressure area. Though logic would suggest that this air will go straight under the car as that's a low pressure area.

The actual effect will vary from car to car. Anyone noting that their engine temperature gauge is running lower needs to check out their overall cooling system efficiency. A thermostatically controlled cooling system of sufficient capacity should not be affected by this mod

[Dragger_Dan]

Thanks flygt4, I figured it was something that simple that somebody have applied a buzzword to.

Anyone noting that their engine temperature gauge is running lower needs to check out their overall cooling system efficiency. A thermostatically controlled cooling system of sufficient capacity should not be affected by this mod

Seconded.

[evil_si]

the lifted bonnet became the craze after the first fast and furious

[sergei]

A lot of stupid shit became popular after that moronic movie

[stalker]

I liked the movie..but i wouldnt go out and do some of the ideas they did! Just like i liked Die Hard 4.0, but you dont see me going out there and driving a car into a helicopter

End of the day, if you want cooler air in your engine bay, buy a bonnet with vents and scoopes
(thats my 2c worth anyway)

[Lloyd]

Because vents and scoops weren't made popular by that movie or anything...

[Malcolm]

I actually think there's a bit more to this than "it's a high pressure area, so it wont work" (not that I'm suggesting fivebob's comment above is saying that, but most seem to be of that opinion).

I'd think that things such as - what the car is being used for & what the average speed it's travelling at would have a major effect on whether or not it's worthwhile. Obviously when stationary, having the highest point of the engine bay vented will allow heat to pour out, and this will occur until you reach a high enough speed that the pressure at the outlet (base of the windscreen) becomes higher than the pressure at the inlet (engine bay). Without doing some sort of testing it would be challenging to know when that is. I would think that for drag racing, where you spend a lot of time sitting in staging lanes, it would be a good way to keep temps down, but then so would opening your bonnet

Also I'd imagine that raising the back edge of the bonnet would slightly alter the aerodynamics around that area, as you'd expect some detachment/turbulence, so whether it remains a high pressure zone having had the bonnet lifted would also be difficult to say without doing some sort of testing/analysis

[Leon]

NB: not legal at MotorSport NZ events.

[RedMist]

It would certainly be interesting to measure the pressure differentiation between the firewall and windscreen.

I suspect that in the case of the ST205 the firewally is greater. Early WRC cars had problems at high speed with the back edge of the bonnet bowing upwards. Hence the idiotic addition of a wing spoiler to the trailing edge of the WRC bonnet. I suspect that all this spoiler does is act as an additional bonnet brace, but if you are having problems with high pressure differential underbonnet, why not just vent it? Cut the trailing edge back 1cm or so? Vent the pressure underbody? Or through the side guards? There must have been a million ways for TTE to have corrected this issue rather than the band aid that is the bonnet spoiler.

[Prymal]

heh - i have one of those idiotic wings ...

Still not sure if it aids much as she hasnt been faster than 200 KMH in my hands yet - but if its there for a reason , even if it IS a bandaid , its still better than no bandaid and a bleeding wound

Plus it is one of the things that makes mine a REAL group A rather than just an addition for the sake of looks .. So in my case , it stays..

[Mr Revhead]

It would certainly be interesting to measure the pressure differentiation between the firewall and windscreen.

I suspect that in the case of the ST205 the firewally is greater. Early WRC cars had problems at high speed with the back edge of the bonnet bowing upwards. Hence the idiotic addition of a wing spoiler to the trailing edge of the WRC bonnet. I suspect that all this spoiler does is act as an additional bonnet brace, but if you are having problems with high pressure differential underbonnet, why not just vent it? Cut the trailing edge back 1cm or so? Vent the pressure underbody? Or through the side guards? There must have been a million ways for TTE to have corrected this issue rather than the band aid that is the bonnet spoiler.

thats an interesting one
i wonder if the fron bonnet vent has anything to do with it.

[escortman]

i only had my bonnet popped when it was supercharged because the guy ran pipes over the engine to the front mount

[strx7]

I know that on my surf with the 2JZ in it, it makes a difference, Noticed mainly at speedway when doing a lot of high load, low speed/low airflow, ie continual starting of sprintcars.

As someone has already touched on, i think its probably more to do with the heat pouring out of the higest point of the engine bay effect.

[matt dunn]

We had a wee play with it and found that it did not help on the circuit car,
(AE101) To say that, it had overheating issues, and it did not help,

but, enlarging the hole in the centre of the bonnet, that would be behind the radiator, but in front of the engine did. ( same place as where evo's have them)
In fact putting a lip on the hole helped considerably.


Also to note. that if air did go in the raised bonnet edge at the back and out under the car, on a circuit car that equates to slower lap times and understeer, as air under the car = bad.

To the point where we tape up the brake ducts and 1/2 the radiator hole on the AE101 for qualifying and it equated to .05 sec/per lap at levels, with both drivers.
Onlt thing is you can do about 8 to 10 laps before things start to get hoy and you need to come in to cool it all down.


So as to if the whole idea works or not,

It gives differernt results for different cars depending one what you were hoping to achieve, and give different side effects too.

matt

[THA SHZ]

What about the celica group a rally cars which had backwards facing vent / bonnet scoop , how do you think this would help or hinder the performance of that car ?

[RomanV]

Stops gravel getting in?

[Jdawg]

the lifted bonnet became the craze after the first fast and furious

But has been around a lot longer. Used to do it on my old Valiants.
Biggest problem was dirty windscreen from engine bay fumes.

[THA SHZ]

Stops gravel getting in?

itssa niiiicccceeee