<VV> Kamm Back and Exhaust Fumes - Quick test

[Charles Lee]

A friend of mine had tested the air flow on his LM V8 (350/350) a while 
back, using simple strings attached to the vents behind the rear window.

The strings, to his surprise, were pointing up while driving.  Although I 
don't recall specifically if he tested this at different speeds, but I don't 
recall any difference being mentioned at different speeds.

His anecdotal result was that the air exited the engine compartment, rather 
than entering, from these rear vents (from undercarriage pressure ?)

Easy enough to test yourself though, with a little string and take a nice 
drive and watch what happens ?


----- Original Message ----- 
From: "james rice" <ricebugg at mtco.com>
To: <virtualvairs at corvair.org>
Sent: Saturday, March 15, 2008 10:10 AM
Subject: Re: <VV> Kamm Back and Exhaust Fumes


> ALL:
>
> Bob Hall said:  "Exhausts that exit straight back will be sucked back into
> the engine
> compartment and then the heater due to the Kamm effect at the squared off
> back  of
> the car.  That's why all stock Corvairs had exhausts that exit at the
> side."
>
> The Corvair does not have a "Kamm back".  I'm not about to get excessively
> historical and aerodynamically technical, because I don't want to take the
> time to consult my books or files on the subject.  So briefly, the Kamm 
> back
> affect was discovered by the German professor Wunibal Kamm in the late 
> '40's
> or very early '50's.  He was researching aero questions, and discovered if
> the slope of roof was maintained at about 15 degrees or less toward the 
> rear
> and then  "chopped off", the car would have the same drag coefficient as 
> if
> it had a really long tail normally associated with "stream-lines cars".
>
> There've been very few actual cars, race or street, with Kamm backs.  The
> first one specifically designed per his research maybe the Cunningham C4RK
> from LeMan's in '52.  Later there was the rebodied Ferrari GTO "Breadvan"
> and a couple of Maserati 151/3 with Kamm back's.  Station wagons and
> vans/Suv's etc are not actually Kamm backs because the bodywork does not
> slop.
>
> The Corvair ends where it does because that is all rear overhang needed to
> cover the rear engine/rear structure w/bumpers.
>
> I don't have any info why the Corvair exhaust comes out the side.  I 
> suspect
> it has more to do with clearance issues with curbs and slopping driveways.
>
> If you are getting exhaust fumes into the cabin, they are not coming from
> the exhaust gas coming up and over the rear bodywork and being sucked into
> the top of the engine.  If the car is moving, there is a high pressure 
> area
> at the base of the rear window onto the engine lid.  Dave Newell has 
> drawing
> from GM of where the pressure area is at speed on the EM.  The air flow on
> the LM enters the grill area at the base of the back window from the top 
> and
> the sides as air flows around the cabin.  At speed, the high pressure area
> on the LM moves to the center of the deck lid, and the fan actually has to
> suck air thru the grill area at the base of the back window.  This air 
> flow
> issue actually contributes to some head temperature numbers.  The Yenko
> Stinger has doors in exactly the right place for engine cooling airflow at
> speed.  Remember a well prepared Stinger is capable of over 130mph.  The
> Fitch top on LM's restricts air flow into the engine at any speed.
>
> Warren LeVeque did airflow/pressure studies on his Stinger about 25 yrs 
> ago.
> The inside of the  engine compartment was actually pressurized on his
> racecar.
>
> There is antidotal evidence the underside of the Corvair is very turbulent
> with little actual airflow and may actually be positive up around the
> transaxle.  If you have a leak at the manifold donuts and have holes in 
> the
> firewall you could be getting flow into the passenger compartment.  The
> passenger compartment being typically lower pressure than the underside,
> even with the windows open....! There is a reason the lower shrouds doors
> face the rear.  I suppose if the seal on the deck lid is bad, you might 
> get
> some flow back into the engine compartment at speed when the fan is 
> actually
> working hard trying to suck air.
>
> Empirical evidence.  Of course none of have them today, but do you 
> remember
> what the back of a oil leaker looked like when we were all young?  Oil and
> dirt all over the rear, but none of it ended up on the deck lid on either
> EM's or LM's.
>
> So find out where the CO is coming from in your exhaust system.  It is not
> coming up over the back of the car.
>
> Historically Yours,
> James Rice
>
>
>
>
>
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