Bonnet modification

[Stephen W]

How many of you have opened the vents up in the 3 indentations on the bonnet? Did you see any benefit?

*not my image. 

[BenD]

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

[Stephen W]

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. 

 

 

[Dave Eastwood (Gadgetman) - Club Chairman]

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.

[Rory's Dad]

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.

[Dave Eastwood (Gadgetman) - Club Chairman]

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.

[toys4x4boys]

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.

[Tim Reid]

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.

[Thrustyjust]

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  !!

[DE04*]

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.