<VV> Kamm Back and Exhaust Fumes - Quick test

Sat Mar 15 23:00:23 EDT 2008

Good point, that air flow is reversed with V-8s ... I'll share this him 
someday ...

----- Original Message ----- 
From: "Shaun McGarvey" <shaun_mcgarvey at shaw.ca>
To: "Charles Lee" <chaz at ProperProPer.com>; "james rice" <ricebugg at mtco.com>; 
<virtualvairs at corvair.org>
Sent: Saturday, March 15, 2008 12:30 PM
Subject: Re: <VV> Kamm Back and Exhaust Fumes - Quick test

> 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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>>
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