<VV> Kamm Back and Exhaust Fumes

[james rice]

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