Lifting rear of bonnet on its mounts

[chpd80]

Just wondering why a lot of the comp guys are lifting the rear of their bonnets up about an inch or so?
Is it just to help the heat get out?
If so does it have any drawbacks and what is the best way to do it.
Cheers

[bundyrulz]

I have had this in the past on a 75 Cruiser. It kept killing batteries. Got advice to lift the back of the bonnet. Did that and no more battery problems. I did it simply with large penny washers. There may be a better way.
The Comp trucks are big engines, going slow, so any help with cooling would be good.

Bundyrulz

[Greg_M]

I'd assume its for cooling. Because hot air rises, having twin thermo's pushing air into the engine bay and then allowing it to escape out the top would force a lot more of the hot air out of the engine bay, this would keep the engine and associated components cooler.

[tna racing]

helps push heat out of engine bay, keep in mind if you have aircon and aircon vents on the panel between your window and bonnet, dont lift your bonnet too much, as it will not get enough air for the air con and it wont get very cold

[dogbreath_48]

Drawback - possibility of extra stress on the bolts caused by the spacers (if not done 'properly') could result in the bonnet detaching in the event of a collision (then coming through the windscreen and chopping your head off ).

I've HEARD the maximum engineers will allow is 6mm spacing.

[chpd80]

Does it affect to latch at the front or do you need bonnet pins?

[BushTuckerNed]

Does it affect to latch at the front or do you need bonnet pins?

nope, but you might need to adjust your rubber stoppers a bit so it dosnt move around

[80's_delirious]

its done to improve air flow through the engine bay. commonly done on muscle cars with big V8 engines adn drag cars.
Ive done it in the past with nuts and washers as spacers and longer bolts if needed.
I was always told its not legal because of potential for oil to end up on the windscreen if you get a sudden leak

[love ke70]

its not legal for the fact that in a front on collision, theres points designed to stop the bonnet coming backwards towards you, instead, it crumples, with it lifted, it misses these catch points and you end up with a bonnet between your shoulders and your chin.

or so the theory goes...

cheers, andrew

[nzdarin]

At low speed the hot air comes out and at high speed cool air will flow in. It is down to the fact that the air pressure in front of the windscreen is high at speed where as inside the engine bay and under the truck is relatively low at the same speed. So it achieves what people want but doesn't do it the way that they think.
To prove this, if your bonnet was lifted at the rear test the temp of the air coming in the vents (into the truck) at low speed it will be warm but at higher speed it will be cool. (relatively speaking)

If you want air to always exit the engine bay then the vent needs to be in the front 1/3 of the bonnet. The other advantage of that is that it will then take out the hot air that has just come through your radiator.