[Diy_efi] RE: Timing and dyno pulls

M. Claywell clay0052 at umn.edu
Wed Dec 25 04:54:48 GMT 2002


On 23 Dec 2002, Adam Wade wrote:
> --- Grant Beaty <gbeaty at ufl.edu> wrote:
> 
> > Ah, so its all from the better transfer from engine
> > -> coolant.
> 
> Yeah, as you raise the coolant temp, the pressure
> rises (of course), but as you have more heat going
> INTO the coolant, you won't be able to get it out as
> easily as you get it in (because air is a lot harder
> to heat than metal or coolant).  Theoretically, you
> want the coolant as hot as possible, since it'll shed
> heat more quickly if it is hotter, but then you run
> into design issues with the cooling system's pressure,
> what to make the hoses from, etc.
> 
> > I already knew that heat transfer is proportional to
> > delta T ;) I was talking about pressure alone.
> 
> I'm not sure what you mean by that...  Again, the
> hotter the coolant temp, the more heat will be shed to
> air of a given temp, but to get coolant temps higher
> without reducing radiator area, you're going to
> itroduce heat more quickly than you can shed it (from
> additional coolant temp), meaning there's actually a
> disadvantge in the real world in most cases.
> 
> Particular engines seem to have a coolant temperature
> that they "like" best for best power.  I know a little
> of the science behind it, but not enough to really
> talk about it seriously.  I'd definitely be interested
> in knowing more about that.

Gotta agree with you there. I have done some coolant temp sweeps to try to
find a max power spot, while holding lamba constant, and somewhat adjusting
advance at each point. Volumetric efficiency goes down with increasing
coolant temp (due to heating of the air), but cylinder friction can go down
with increasing coolant temp (lower viscosity of oil), and thermal
efficiency and combustion efficiency can sometimes go up.

I think coolant temp has to be a comprimise between what the cooling system
can support in heat transfer, aero drag, and max power.

Mark 


> 
> 
> =====
> | 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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