[Diy_efi] RE: Timing and dyno pulls

[efi student]

Depends on whether it is venting?  If it isn't venting, then why do I =
see a
difference in the reservoir level between hot and cold on every single =
car
and bike I have worked on?  Seems a bit ludicrous to imply the system
doesn't pressurize to the cap pressure, or why system designers are so =
damn
picky about where you put the cap in the system so that it isn't
artificially affected by pressure from the water pump.  Or even more =
simply,
coolant is relatively incompressible.  Coolant expands when heated.  =
Unless
there is air in the system, the cap must be the limiting factor for =
system
volume because the coolant MUST expand when the engine starts =
transferring
heat, that means the level in the coolant reservoir goes up, but not =
until
the cap pressure is exceeded.

Let's press on with cooling system fundamentals.  I've seen the radiator =
for
an engine producing 1000 hp all day long.  It's a lot bigger than I am, =
and
I'm 6'2".  What vehicle is capable of supporting a radiator that size?  =
None
that I have seen, except one of those Terex dump trucks, but they're
electro-motive so it's apples and oranges there.  I have yet to see a
production vehicle, car or bike, that had a cooling system capable of
sustaining full throttle for more than a minute without being =
overwhelmed.
Sure, it's a design decision that all engineers have to make, how big =
can I
afford to make this radiator, but the point is they all insist that =
higher
system pressure gives better heat transfer both from engine to coolant =
and
coolant to heat exchanger.  You're saying they're not getting it, that
cooling system pressure only applies if you are exceeding design =
pressure?
Maybe I don't understand what you are saying, but all the evidence I =
have
both researched and experienced indicates that higher system pressures =
give
better heat transfer.  NASCAR claims they like it because they can =
reduce
the size of the radiator and therefore improve aerodynamics.  Are you =
saying
this is incorrect?

Oh, I do understand that an engine at idle is pretty unlikely to exceed
design pressure unless the water pump is turning so slowly that the =
coolant
is boiling in the heads.  Completely different world at WOT.

Lance

-----Original Message-----
From: diy_efi-admin at diy-efi.org [mailto:diy_efi-admin at diy-efi.org] On =
Behalf
Of Adam Wade
Sent: Tuesday, December 24, 2002 5:52 PM
To: diy_efi at diy-efi.org
Subject: RE: [Diy_efi] RE: Timing and dyno pulls


--- efi student <efi.student at sbcglobal.net> wrote:

> What about the effect of a higher system pressure on localized boiling =

> and surface wetting for thermal transfer?

That is a specialized example of the general rule in
the post you're responding to.  So IOW, I already
covered that.

> Isn't a higher cap pressure going to reduce the size
> of the steam bubbles around the exhaust ports and
> improve thermal transfer?

That depends on whether the system is venting=20
through the lower pressure cap or not.  As I
mentioned, if the cap is not venting, then getting one
with a higher venting pressure won't make a difference
in system pressure.


=3D=3D=3D=3D=3D
| Adam Wade                       1990 Kwak Zephyr 550 (Daphne) |
|   http://y42.photos.yahoo.com/bc/espresso_doppio/lst?.dir=3D/   |
| "It was like an emergency ward after a great catastrophe; it  |
|   didn't matter what race or class the victims belonged to.   |
|  They were all given the same miracle drug, which was coffee. |
|   The catastrophe in this case, of course, was that the sun   |
|     had come up again."                    -Kurt Vonnegut     |

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