Date:         Thu, 3 Nov 1994 13:38:17 -0800
Sender:       Vanagon Mailing List <vanagon@vanagon.com>
From:         wabbott@townshend.Corp.Megatest.COM (William Abbott)
Subject:      RE: air dams (was mpg enhancements)


	Dave Carment wondeers about airdams effects on aircooled engines.
	Cooling air for Type II (upright) and Type 4 (pancake) engines 
MUST flow from above the engine to below. VW went to considerable trouble to 
fully enclose the engine compartment with sheetmetal and rubber seals to 
insure that hot air exhausted from the bottom of the engine did not get
back to the top where the cooling intake is.
	I don't know if the same sheetmetal is present in air-cooled Vanagons.
Waterboxers do not have this sheetmetal- you can see the top of the engine
and the ground underneath when you open the access hatch.

	Airdams lower drag by preventing air from going under the
front of the vehicle. Pushing it out of the way is less drag than
having it trapped between the moving vehicle and the stationary road
surface. Airdams therefore lower the pressure below the vehicle,
and that ought to help the cooling system, in theory, by drawing air
through. With the engine all the way in the back, its an open question
whether a front air dam will have any effect at all. However, its
worth noting that the later VW Porsche 914 had air deflectors mounted
on the underbody just ahead of the engine to reduce pressure directly
under the engine and allow it to run cooler.

	Regarding the 'aerospike' used in the Trident missle to increase
its streamlining by sticking a pole and a small deflector out front- I 
suspect that worked great above Mach 1 but not so well at the speeds
we usually drive our busses. But an experiment should be easy to put together...
Don't hit anybody with it though!

	Bill