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'[OT]: Building a Servo "Bottom Breathers''
2001\08\13@143800 by Jim

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Got any specific examples of these models?

Jim

----- Original Message -----
From: "Mike Mansheim" <spam_OUTMichael_J_MansheimTakeThisOuTspamGRACO.COM>
To: <.....PICLISTKILLspamspam@spam@MITVMA.MIT.EDU>
Sent: Monday, August 13, 2001 12:14 PM
Subject: Re: [OT]: Building a Servo


> Even though they may appear to be 'bottom
> breathers', the air-intake (for combustion air as
> opposed to cooling air/radiator air) is still usually
> taken from one of the upper most 'slits' via a scoop
> and appropriate tubing to the air cleaner/filter with
> the next stop being the airmass flow sensor/throttle
> plate assembly ...

I think we've come full circle.  The original point was that even though
many newer cars appear to have conventional air intakes, they are
actually 'bottom breathers', as evidenced by their ability to ingest
water, with deleterious effects on the engine.

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2001\08\13@150530 by Jeff DeMaagd

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I can think of either the Chrysler Cirrus and Dodge Stratus.  At least one
of them has a faux grille that is plastic with ridges to make it look like
it is a grille but is really sealed up from behind.

Jeff

{Original Message removed}

2001\08\14@171602 by Mike Mansheim

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> Got any specific examples of these models?

BMW 5-series is the one I was asked to help with.  Have to admit
that I haven't actually traced the airflow path.  I just discovered
the blown engine, the BMW mechanic said it was from ingesting
water.  Another mechanic friend said that "many newer cars are
bottom breathers" (I don't have any specific examples from that
statement).  Since the owner was driving in a rapidly flooding
parking lot in water nearly up to the door sills when the car
stalled, and the engine never ran again (actually, never turned
over again), I  accepted the bottom breathing, water ingestion
diagnosis.
Completely unrelated:  this was a bit of an eye opener for me - I
don't drive this type of car - I drive "extremely inexpensive" stuff,
to be polite.  The car's owner told me BMW wanted $15,000US for the
engine and $2,000 to put it in - figures I found truly staggering.

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2001\08\15@010525 by steve

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> > Got any specific examples of these models?

> Another mechanic friend said that "many newer cars are bottom
> breathers" (I don't have any specific examples from that statement).

The Ford Model A (circa 1920's) had an updraught carb. Does that
count as a bottom breather ? I guess it doesn't count as "newer"
though.

Steve.

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2001\08\15@041019 by Alan B. Pearce

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>Since the owner was driving in a rapidly flooding
>parking lot in water nearly up to the door sills when the car
>stalled, and the engine never ran again (actually, never turned
>over again), I  accepted the bottom breathing, water ingestion
>diagnosis.

This sort of problem also afflicts motor boats. In this case what can happen
is a misfire in the engine makes the crankshaft kick in the reverse
direction, typically when starting the engine. This in turn can suck water
up the exhaust pipe into the engine, which then tends to cause damaged
pistons, valves and crankshaft when another cylinder does actually manage to
fire.

The standard method of avoiding this problem is to have an expansion chamber
somewhere in the exhaust system which has a volume greater than the total
swept volume of the engine. The incoming exhaust pipe needs to be above the
water level in this chamber if the engine did manage to complete a full
revolution in reverse so it does not suck any water back into the cylinders.

Needless to say this chamber should be above the waterline when the boat is
at a mooring so it is not full of water before you even try and start the
motor!

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2001\08\17@215551 by Jim

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       "Since the owner was driving in a rapidly
        flooding parking lot in water nearly up
        to the door sills"

I would think this would also place the water over
the hood (given today's sleeker wedge shaped designs)
- and then there is 'wake' he would be pushing into as
well (and into an intake scoop that could inhale water
even if it were in the upper half of the grill!).

He may have made it given a 'snorkel' ...

Jim




{Original Message removed}

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