let's say, hypothetically speaking, i removed my entire exhaust system.  what
affect would this have on my car?

19 responses total.

Aside from the blue smoke filling it up?

Back in the early '80's I had a friend who owned an old Firebird that
had been set up as a "quarter mile car" in a previous life.  The car
was in good shape, but the bottom of the trunk was totaly rusted out!
He claimed that it was from the exhaust being terminated just shy of 
the rear axle in its previous life.  He had put in exhaust that went
about 6 in. beyond the rear bumper, but fumes were still sucked up
through the rear deck and seat due to the back-draft when the car was
moving.  I got one of the worse headaches of my life after going to 
Detroit and back in that car!
Did the exhaust really cause the trunk to rust out?  I don't know but
considering how fast the exhaust system in my car goes, I would  not 
be surprised.

   The loss of backpressure is not good for some cars, I know that.  What
it would do to your car can only be guessed untill/if you try it.

   What *will* happen is that anyone who lives near it will hate it, and
you'll find a cop on your tail before long.  I recently heard a Volvo
240 series after its exhuast was removed for an overhaul; gods, what a
noise.  I was informed that all cars act like this if you remove all
restraints...

The loss of backpressure due to a minimal exhaust system only in-
creases fuel consumption as far as I know.  I don't think you can
hurt the engine by reducing the back pressure.  Go to the auto parts
store and get one of those "turbo muflers" and fit it to the end of
whatever solid pipe remains.  It will be loud in the car, but not
too bad for others who have to listen to your heap go by.

Throw a punch under water, then throw the same punch in the air.
Pretend you're a valve.

I've fiddled with engines since the mid 60's.  #5 makes no sense.
The exhaust system has an effect on tuning.  If you change it, you
change the tuning of the system which effects back pressure, which may
well be a vacuum at some RPMs.  You will effect fuel economy because
valve timing may be adjusted for optimal economy.  Changing the exhaust
system may cause more or less exhaust to exit the cylinder during the
exhaust cycle because the pressure in the exhaust manifold may now be
different.  Does the engine no harm.

Wrong.

Answers without reasons = nonsense.

Proverbs are only of use to those who care.
 
Hmm, then again, thats a proverb too... hahahahahahah

On most older cars, say, before 1970, removing the exhaust system is
certainly not going to be a major inconvenience to anything except
people's hearing.  Except perhaps for race cars, there really wasn't
anyting that finely adjusted, nor much need; a slight tune-up might be
all that's needed, the engine itself would end up with significantly
more power without the back pressure, but probably slightly worse fuel
economy (in fact, one of the early economy measures was to deliberately
introduce some exhaust into the input air stream at low speeds -- saves
energy that way.  Many high performance aircraft engines feature
extremely short individual exhaust pipes leading to the outside world.
Fuel economy isn't nearly as important as power-to-weight ratios there.

Certainly, the theory of #5 makes no sense.  The most important forces,
by far, on the valve, include the pressure from the power stroke, the
impulse imparted by the valve train including that of the cam shaft &
the spring, & stress caused by heating & cooling including that of the
exhaust gas and the valve seat.  The exceedingly small amount of force
caused by air resistance is going to be exceedingly minute compared to
these other stresses.

An interesting factor for the exhaust system & back pressure might well
be the harmonics -- the length of the exhaust pipe is going to be as
significant as anything in determining how loud it's going to be, and
how much back pressure will exist.  Sometimes, on high performance
engines, you'll see that the exhaust manifold will have strange kinks in
it for various cylinders -- this is in an effort to equalize the whole
system and get the best performance (this is even more important for the
intake manifold, as you might well imagine.)

'Course, in modern cars, there's another factor -- the oxygen sensor.
You still need enough exhaust pipe to collect the exhaust together, and
it should probably have a configuration roughly similar to what it was
designed with, so that the engine's electronics will be able to
determine the optimal fuel/air mixture for the engine.  At the same
time, that means there's a fairly good chance you could just cut the
exhaust off past the sensor with no problems -- it'll adjust its timing
& fuel mixture automatically.  If you don't mind risking the wrath of
the neighbors, the noise, & all, shouldn't be a problem.

Corrosion does sound a very likely problem.  The problem is that any car
is going to emit a very acidic exhaust.  There are going to be major
amounts of water vapour -- so any cool metal surface it comes in contact
with is going to get nice warm water deposited on it.  Add to that the
large amounts of co2 & small amounts of so3,so4,nox, &etc., and you have
instant acid with no doubt trace quantities of various unstable reactive
chemicals and you indeed have a very nasty threat to your car's
underbody.  The only reasion your car's exhaust doesn't fall sooner is
that it gets hot enough in operation that the water doesn't condense
out.  That's why, if you only drive your car short distances, the
exhaust rusts out a lot faster.

The volvo 240 has an incredible exhaust system with not 1, but TWO
mufflers, and on the more recent cars, it's aluminum plated.  My volvo
is now 3 years old, and still rather quiet.  The exhaust is rusting out.
From the end in -- it's now reached back about 2 inches from the end of
the tale pipe.  It's a shame they don't plate the cut edges but I still
can't complain.  I've never had an exhaust system last this long before.

In most cars the oxygen sensor is in the exhaust manifold making it
difficult to cut off by removing too much pipe.  It is a good point
though.
My '80 AMC Spirit came with an aluminized exhaust system.  It lasted
for 5 years.  Subsequent systems never came close to this figure.
I notice that J.C. Whitney sells stainless straight pipe that can
be bent with standard exhaust bending equipment.  All one needs to
do is find someone willing to bend it for a reasonable price...

Muffler Man will bend pipe... in fact, they dont even stock anything
other than straight pipe...  low (no) inventory on special bent pipes.

Thanks craig.  I will check into it.  Our '86 Nova is getting louder
every day.  The pipe  near the muffler has rusted through after only
1.5 years.  I think an investment in stainless would be well worth it
on this car.

I never considered the possible corrosive effects of exhaust until reading this
.  Glad I had my car fixed now.  The aspirator tube to the front catalytic
convertor (yup, there are two for California emmissions Omni's) had broken
free (when the mech at the dealer was 'inspecting' the system) and there
was a 3/4" hole.  Dealer wanted to relpace the convertor since the mounting
which comes built into the convertor was useless.  Meineke's guy just
welded the tube back in place for a $10 tip.  Jodi's car has the same 
problem and will go in this week.

Sounds like a dealer to avoid.

I dont think that exhaust gasses are very corrosive.  They can get
very hot though and burn paint/undrercoating off, exposing bare metal
underneath to where road salt can get to it.  Elevated tempratures also
increase chemical activity, including the process of rusting.  Most of
my exhaust systems have rusted from the outside in.

That may depend on the mean length of your road trips.  In theory, short
trips ought to favour from the inside out, while long trips might well
favour from the outside in.  It's absolutely true the gasses aren't very
corrosive -- the issue is whether it gets a chance to condense and form
liquid acidic water droplets, which *are* corrosive.  But there's a lot
of other factors that complicate it all.  For instance -- stress
promotes corrosion - so if your exhaust system isn't well supported, or
if it has a lot of residual internal stress left over from the
fabrication process, it's going to rust out a *lot* faster in the places
that have the most stress.  Cracks and other structural flaws can also
leave gaps where corrosion can get an ugly grip.

Re 15- I've actually had wonderful service from the dealership side of Arbor
Dodge, it's the actual serviec department that has given me and several others
I've talked to problems.

Those aspirator tubes fall off constantly.  I had the one on my Horizon welded
almost 4 times before I sold the car.

I think that the acidity of exhaust gases is negligible to nonexistant unless
it comes in contact with parts of the car that aren't normally exposed to
the road salt.

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