Bonnet design

[jddevel]

What bonnet design incorporated vents on the top as well as the sides. Was there a standard or was it a modification please?

[Steve Simmons]

It was an aftermarket modification. All bonnets were smooth except for the usual side louvers.

[jddevel]

Thanks Steve. What would be the purpose? Would it have been inconjuction with engine upgrades/performance?

[Steve Simmons]

Some people feel it helps to cool the engine bay better. Others claim it doesn't make a noticeable difference. I know it does let engine bay heat out because a friend said he could feel the extra heat on his face when using Brooklands screens. But whether or not that was helping to cool the engine, I don't know. I do wonder if it would negatively affect the crankcase drought tube since it seems to rely on air rushing past the pipe to create a vacuum effect.

[Herman 5560]

On my 7 style cars it made a huge difference.

This is a standard Birkin bonnet, never has any cooling problems.

This is a bonnet I made myself and this car was always marginal on cooling.In defense this was a fairly modified engine as it was my race car. Best on a dyno 103 Kw out of a normally aspirated 1600 engine.