Bonnet design

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jddevel
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Bonnet design

Post by jddevel » Sat Mar 23, 2019 10:47 am

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

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Steve Simmons
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Re: Bonnet design

Post by Steve Simmons » Sat Mar 23, 2019 10:49 am

It was an aftermarket modification. All bonnets were smooth except for the usual side louvers.
1949 TC8975 / XPAG 9609
1948 TC6011 / XPEG1182 (XPAG6472)
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jddevel
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Re: Bonnet design

Post by jddevel » Sat Mar 23, 2019 11:01 am

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

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Steve Simmons
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Re: Bonnet design

Post by Steve Simmons » Sat Mar 23, 2019 11:18 am

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.
1949 TC8975 / XPAG 9609
1948 TC6011 / XPEG1182 (XPAG6472)
http://www.mgnuts.com

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Herman 5560
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Re: Bonnet design

Post by Herman 5560 » Sat Mar 23, 2019 8:28 pm

On my 7 style cars it made a huge difference.
Birkin small.jpg
This is a standard Birkin bonnet, never has any cooling problems.
442 small.jpg
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. :thumbs:

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