S3 Engine bay heat exhausts, help needed
Discussion
Dear all,
I need some input on how to improve hot air exhaust from an S3C engine bay at low speed and stationary (stuck in a que…).
I have searched the forum and not really found any conclusive info on this topic.
The air inlet is plenty so that is not an issue.
On the air exhaust side the newer S4/SV8 has the rectangular ports longitudinal in the bonnet. The older does not. No doubt this is an improvement but difficult to copy in an S3 bonnet on a nice way.
When driving at speed the airflow exiting under the car would probably be sufficient but achieves limited cooling of the manifolds and intake components as a very limited airflow would exit upwards.
On the S1/S2/S3 some owners seem to have removed the rear bonnet seal to increase air existing at the rear of the bonnet. Others claim that this has little or no value as the area in front of the window is a high pressure area preventing air to exit. I would be nice to hear if someone have more input here.
If the pressure created under the bonnet indeed is higher than the high pressure created by the screen it is easy to drill additional holes under the bonnet towards the front window to allow more exit area than achieved by removing the seal. One could drill 5-8 20-30mm holes on the engine side of the bonnet on the “lip”. Has anybody attempted this? If it helps it could be a nice option as it would not be visible from the outside.
An alternative would be to cut one or two holes, round or rectangular, in the rear of the bonnets about 20cm in from the wind shield. Would that help? Or do they need to be further forward*?
Not really worried by originality or aesthetics at this point, all those issues comes later…
All input appreciated
Kind regards
//Rob
I need some input on how to improve hot air exhaust from an S3C engine bay at low speed and stationary (stuck in a que…).
I have searched the forum and not really found any conclusive info on this topic.
The air inlet is plenty so that is not an issue.
On the air exhaust side the newer S4/SV8 has the rectangular ports longitudinal in the bonnet. The older does not. No doubt this is an improvement but difficult to copy in an S3 bonnet on a nice way.
When driving at speed the airflow exiting under the car would probably be sufficient but achieves limited cooling of the manifolds and intake components as a very limited airflow would exit upwards.
On the S1/S2/S3 some owners seem to have removed the rear bonnet seal to increase air existing at the rear of the bonnet. Others claim that this has little or no value as the area in front of the window is a high pressure area preventing air to exit. I would be nice to hear if someone have more input here.
If the pressure created under the bonnet indeed is higher than the high pressure created by the screen it is easy to drill additional holes under the bonnet towards the front window to allow more exit area than achieved by removing the seal. One could drill 5-8 20-30mm holes on the engine side of the bonnet on the “lip”. Has anybody attempted this? If it helps it could be a nice option as it would not be visible from the outside.
An alternative would be to cut one or two holes, round or rectangular, in the rear of the bonnets about 20cm in from the wind shield. Would that help? Or do they need to be further forward*?
Not really worried by originality or aesthetics at this point, all those issues comes later…
All input appreciated
Kind regards
//Rob
I faced a similar problem on my V8S.
I removed the rear trim from the bonnet. This is in a high pressure zone in front of the windscreen, and lets cold air blow into the engine bay at high speed. (I took advantage of this by putting a cold air intake here.) At low speed and in traffic, it acts as a slight leak which lets hot air convect out of the engine bay. Although there isn't much air coming out, it has a bigger effect than you might expect. I think that without this leak the hot air above the exhaust headers just gets hotter and hotter, and once it's got really hot buoyancy tends to keep it there.
Thermal wrapping the exhaust headers reduces the heat into the engine bay quite substantially.
Ceramic coating has less of an effect but still seems to make a useful difference, and is far more durable. It also means you haven't lost any engine bay noise - you might view that as a pro or a con.
If you have a cooling problem, make sure you duct the radiator to prevent hot air from the engine bay from being pulled round the edges and back to the 'cold' side of the rad. 10% hot air recirculation here means 10% cooling capacity lost.
Before fitting the supercharger I went for a slightly more extreme solution: I added a line of 6"x3" vents down both sides of the bonnet, roughly over the headers. This convects nicely when it's stationary, and allows hot air from the main cooling fan to escape carrying the hottest air from the engine bay with it, and it also in a very low pressure area at high speed. It was strange to see wool tufts standing straight up on the bonnet at 100 mph.
I removed the rear trim from the bonnet. This is in a high pressure zone in front of the windscreen, and lets cold air blow into the engine bay at high speed. (I took advantage of this by putting a cold air intake here.) At low speed and in traffic, it acts as a slight leak which lets hot air convect out of the engine bay. Although there isn't much air coming out, it has a bigger effect than you might expect. I think that without this leak the hot air above the exhaust headers just gets hotter and hotter, and once it's got really hot buoyancy tends to keep it there.
Thermal wrapping the exhaust headers reduces the heat into the engine bay quite substantially.
Ceramic coating has less of an effect but still seems to make a useful difference, and is far more durable. It also means you haven't lost any engine bay noise - you might view that as a pro or a con.
If you have a cooling problem, make sure you duct the radiator to prevent hot air from the engine bay from being pulled round the edges and back to the 'cold' side of the rad. 10% hot air recirculation here means 10% cooling capacity lost.
Before fitting the supercharger I went for a slightly more extreme solution: I added a line of 6"x3" vents down both sides of the bonnet, roughly over the headers. This convects nicely when it's stationary, and allows hot air from the main cooling fan to escape carrying the hottest air from the engine bay with it, and it also in a very low pressure area at high speed. It was strange to see wool tufts standing straight up on the bonnet at 100 mph.
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