Stephen W Posted October 12, 2017 Share Posted October 12, 2017 How many of you have opened the vents up in the 3 indentations on the bonnet? Did you see any benefit? *not my image. Quote Link to comment Share on other sites More sharing options...
BenD Posted October 12, 2017 Share Posted October 12, 2017 im also interested in this but im sure ive read somewhere that it can have the opposite effect and draw air in rather than let it out but im not sure if this is just with a windscreen or not Quote Link to comment Share on other sites More sharing options...
Stephen W Posted October 12, 2017 Author Share Posted October 12, 2017 With the windscreen the base area of it is actually high pressure, so there would be a potential of stalling the air under the bonnet. I think where the Westie indents are they will be too far forward to suffer from this. Quote Link to comment Share on other sites More sharing options...
Dave Eastwood (Gadgetman) - Club Chairman Posted October 12, 2017 Share Posted October 12, 2017 If not done carefully the bonnet area can distort significantly with heat; grp is very flexible under strong sunlight or warmed from high underbonnet temps. If you have a windscreen, then the vent slots are largely in a very high pressure zone at any significant speed, (above 40mph, roughly, from personal experience). With a blade type aeroscreen, a high pressure zone will still be present, but massively reduced. With a double bubble style screen it should be reduced even more, possibly even completely... It would appear from all the things people have tried over the years that the single most effective way of removing air from under the bonnet, is to flare out the sides of the tub. Quote Link to comment Share on other sites More sharing options...
Rory's Dad Posted October 12, 2017 Share Posted October 12, 2017 Please note that the indents are present to stiffen the top of the bonnet at its widest span. Taking the indents out partly or completely will compromise its rigidity. 1 Quote Link to comment Share on other sites More sharing options...
Dave Eastwood (Gadgetman) - Club Chairman Posted October 12, 2017 Share Posted October 12, 2017 1 hour ago, Rory's Dad said: Please note that the indents are present to stiffen the top of the bonnet at its widest span. Taking the indents out partly or completely will compromise its rigidity. Exactly. I've removed one previously, being very careful to retain as much of the stiffening return edge as possible, and also bonding in stiff mesh grill in place of the removed material; it was almost as stiff as the original, but still moved a little over time. Quote Link to comment Share on other sites More sharing options...
toys4x4boys Posted October 12, 2017 Share Posted October 12, 2017 My car has vent holes in the side of the bonnet above the manifold. You feel some warmth escaping when stationary, I have no idea on the merit once moving. Quote Link to comment Share on other sites More sharing options...
Tim Reid Posted October 14, 2017 Share Posted October 14, 2017 On 12/10/2017 at 19:02, toys4x4boys said: My car has vent holes in the side of the bonnet above the manifold. You feel some warmth escaping when stationary, I have no idea on the merit once moving. Try attaching some ribbon and get a passenger to look if they blow in or out. Quote Link to comment Share on other sites More sharing options...
Thrustyjust Posted October 14, 2017 Share Posted October 14, 2017 A mate with a track based RX8 had issues with heat . He cut 2 large ish vents in his bonnet , with the view it would make it better. It didnt, it was worse. From the RX forums, he was told he had to make a proud lip at the front of the vent, which somehow would create a draw and pull the air out. He was sceptical about this, but put some alloy 10mm alloy angle at the front and it really worked. Looks pretty ugly, but it must be down to pressure difference being lower outside and it being able to pull the air out. Its an odd thing to think, but what you think will work, might not !! Quote Link to comment Share on other sites More sharing options...
DE04* Posted October 15, 2017 Share Posted October 15, 2017 I cut the insert in the bonnet out,the one nearest the windscreen and put a grill over it. After a few discussions at the Lodge at our monthly meets the talk was does it actually push air back into the bonnet. I tied a piece of ribbon to the grill,with the windscreen on at about 40 mph and above it does push the ribbon down into the engine bay. With the aero screen on (AA composite) the ribbon does wave about above the bonnet,so I guess air must be coming out. 1 Quote Link to comment Share on other sites More sharing options...
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