[Diy_efi] RE: Timing and dyno pulls

[Adam Wade]

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

> 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?

I guess your sample size isn't big enough.

Obviously, the ones you are working on are venting to
one dergee or another, if the ones with a lower cap
blowloff pressure are leaving higher reservoir levels.

> Seems a bit ludicrous to imply the system
> doesn't pressurize to the cap pressure,

On a goodly number of vehicles, it doesn't.  For
instance, vehicles without a reservoir don't leave
coolant all over the ground, ergo...

> 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.

Which designers told you this was their reasoning?

The location of the cap, in my experience, has far
more to do with where air ends up in the system than
anything else.

> Unless there is air in the system, the cap must be
> the limiting factor for system volume

ITYM system MASS, unless you are counting coolant
outside of the actual cooling circuit as part of the
"system".

> 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.

True.  How much do you think coolant expands when
heated?  Short of reaching its vapor pressure, of
course.

> 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.

How odd.  I wonder how people manage to do so without
blowing coolant hoses left and right.  Tractor
trailers do so on mountainsides all day long.  Racing
vehicles do so on courses like Daytona without any ill
effects.  Hm.

> 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.  

Unless the temperature is different, that's not
possible, as far as I can see.  Fourier's Law doesn't
factor in pressure.  Heat transfers based on
conductivity and temperature differences.  Pressure
increases raise your boiling point, but if your
coolant temp doesn't change, heat transfer isn't
affected.

> 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.

If you have proven Fourier's Law wrong, your name
should be in the physics journals!

Raising the boiling point of the coolant by
pressureizing the system raises the delta temp between
ambient and coolant, which will increase heat transfer
to a point.

> NASCAR claims they like it because they can reduce
> the size of the radiator and therefore improve
> aerodynamics.  Are you saying this is incorrect?

After thinking it through while answering, it sounds
like you are missing how those concepts of boiling
point and system pressure are linked.

> 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.

Seems to me that if your water pump exceeds cap
pressure, it'll pump coolant out of the system without
any coolant heating at all.  Have you observed this is
an air-tight system?

=====
| Adam Wade                       1990 Kwak Zephyr 550 (Daphne) |
|   http://y42.photos.yahoo.com/bc/espresso_doppio/lst?.dir=/   |
| "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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