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Date:         Wed, 26 Aug 2009 14:59:59 -0400
Reply-To:     greg@POTTSFAMILY.CA
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Greg Potts <greg@POTTSFAMILY.CA>
Subject:      Drafting (was Re: Engine to auto-tranny match and the Indy 500
Comments: To: Marc Perdue <mcperdue@GMAIL.COM>
In-Reply-To:  <c2c43a7e0908261118t6cdeda96q60ef9500fb11f879@mail.gmail.com>
Content-Type: text/plain; charset=ISO-8859-1; DelSp="Yes"; format="flowed"

Hi Marc,

The benefit of "drafting" is the reduction in relative wind speed lessens the load on the engine.

I have a cylinder head temp gauage on my aircooled baywindow and have been driving a LOT of highway miles in the past few weeks. When I can get behind a semi at a range of 3-4 carlengths at 60MPH I see a drop of about 50F on my head temps within 20-30 seconds, every time.

The advantage of the wind break (reduced HP requirement from the motor) definitely compensates for the reduction of cooling capacity in the reduced wind speed. If there's enough wind to keep my aircooled engine happy then I can't see it being a problem for the waterboxers.

Another plus: Over two recent 4hr runs I documented a considerable fuel economy improvement, achieving 23MPG on a vehicle that would normally run in the 18-20 range.

It helps a lot that Ontario recently mandated the use of speed limiters on all trucks keeping them to a maximum of 110kph. It's a lot less stressful driving on the bigger highways now that there are no more big rigs bearing down on you at 140KPH (85MPH)... In the past I found it hard to stay with a truck going faster than 115 KPH.

The downside of drafting is the reduced reaction time available in case of something unexpected. It's not something to be done lightly.

Greg

Quoting Marc Perdue <mcperdue@GMAIL.COM>:

> Regarding running behind semis, it was my understanding that doing so > would affect the airflow across the cooling system and make it more > likely to overheat. Given the Vanagon's "natural" tendency to do so > on a good day (joking), this doesn't seem like a good idea. Having > said that, I suspect that this effect would be fairly minimal over a > short period of time, less desirable to do over a great distance. >


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