Bonnet raisers..

[RattyMcClelland]

But what do I know, I put big wings on FWD cars

However im sure you know big wings on the rear has nothing to do with drivetrain layout. Purely aerodynamic if used right for stability on any drivetrain layout.

[vetrox]

Yeh....that must be why I do it

[bb1boy]

On occasion some engine transplants need the bonnet raised (evo lump into proton) to clear parts.

That makes complete sense, but on cars without bonnet clearance issues it's for looks and [possibly imaginary] cooling gains. I see. Thanks

[MaccaIRL]

Ah crap .. ive a set here i was gonna install lol

Seems to be the last mod you do in this country :p

[NafemanNathan]

The vacuum effect is caused by the fact the underside of the engine bay is open. The air travelling under the car causes a vacuum on the large opening to the underside of the engine bay and so draws the air out of the bay. This in turn causes air to be drawn from the top of the engine, whether it be from the front grill through the radiator or from above the scuttle panel if the bonnet is raised on risers.

Seal the underside of the engine bay off and you'll no longer have the vacuum, and so instead it will become a thoroughfare for air to travel through (As most people imagine will occur without any other mods). It'll then become a battle between which will become the intake and which will become the exit.

... Grill = intake, scuttle panel = exit.

The only other arguement would be to suggest that as standard the vacuum from the underside of the car on a car without bonnet raisers will aid the flow of cold air through the radiator (alongside the obvious "ram" effect). Seal off the underside of the engine bay and raise the bonnet and now you only have the "ram" effect through the radiator. In most cases, with a decent cooling system, this will be enough.

[vetrox]

Ah crap .. ive a set here i was gonna install lol

Seems to be the last mod you do in this country :p

I didn't realise U could by these as an actual thing!? I just use longer bolts spaced out with nuts with silicone tubing over the top. Costs nothing if U got a spare bits box

[NafemanNathan]

That's essentially all they are, turned spacers. You can get car specific spacers that are one long spacer with the two holes in though.

[MaccaIRL]

That's essentially all they are, turned spacers. You can get car specific spacers that are one long spacer with the two holes in though.

I got blue ones lol