<VV> Kamm Back and Exhaust Fumes - Quick test

Sat Mar 15 15:30:57 EDT 2008

This wouldn't happen with the original engine in place, sealing off the 
bottom of the engine compartment....

----- Original Message ----- 
From: "Charles Lee" <chaz at ProperProPer.com>
To: "james rice" <ricebugg at mtco.com>; <virtualvairs at corvair.org>
Sent: Saturday, March 15, 2008 12:15 PM
Subject: Re: <VV> Kamm Back and Exhaust Fumes - Quick test

>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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