[Diy_efi] RE: Timing and dyno pulls

Tue Dec 24 11:52:05 GMT 2002

Hi Lance,

On a related issue, some 5 years ago I had a cracked aluminium
(aluminum in USA) cylinder head on the Nissan RB30ET engine,
and its quite common on my type of car due to the radiator top
being some 8cm below the highest galleries in the air gatherer
and cylinder head... The Nissan TI3.0 has the same motor but
rarely (if ever) suffers from this problem due to its higher
radiator position.

Now, GMH released a service note on the cooling system some 3
years after the car was introduced (most dealers didnt read it
or think it appropriate), anyway it stated that two bleed holes
(one on the inlet manifold and the other higher up on the top
of the 'air gatherer') needed to be cycled whilst simultaneously
raising the water inlet above the top of the radiator by 300mm
or so - whenever servicing the cooling system. Ostensibly to
ensure no trapped air bubbles during service.

Anyway to (now) cut a long story short, I added a small water pump and
a solenoid so I can purge the cooling system of bubbles whenever
I like without major drama and avoid another cracked cylinder
head de to loss of coolant - especially since I have a turbo.

I have some pictures on this link if anyone's interested,
http://members.iinet.net.au/~erazmus/Twin_tyre_vehicle/
 most pic descriptions are reasonably on target.

What I noticed in late spring and early summer is that
if I first raise the coolant pressure to the 15psi max as set
by the radiator relief valve then overall I notice the
average engine temperature a little cooler than allowing
the coolant pressure to rise purely by engine dumping its heat.

Also what I noticed is that after each 200 or so Kms there is
a fair amount of bubble buildup, looks like 50-100cc from
time to time and seems to be circumstantially related to those
occasions i really push it. I am guessing the head gasket is acting
like a one way valve and letting a little blowby gas through on those
occasions - I am not however losing coolant and had a pressure
test to 40psi without any coolant loss!

I've not been an adherent to the paradigm that when the engine
dumps its heat the coolant *will* rise to the set pressure allowed
for by the radiator end cap.

My theory is that vapour forms (in those head hot spots) 
which momentarily raises the
pressure but the vapour bubbles get moved around to cooler
regions and collapse thus the average pressure rarely reaches
the 15psi max allowed for.

What I think is happening is that by artificially raising the
pressure before I set off I am making it more difficult for
vapour areas to form which reduce cooling. I also dont think,
that in the convoluted galleries of the head, that exhaust
gasket blowby, or vapour bubbles are necessarily free from
sticking to the ally head. ie. There may be eddies and swirls
in the flow pattern which means some bubbles get caught and
stick etc. By running a separate pressure pump and purge
solenoid I am thinking this *ensures* there is minimal
likelihood this occurs at all rev ranges as they seem to
be forced from the galleries at higher revs due to the higher
flow rates from the main water pump. At moment the
system is manual, though when I get time, i'll put in a
micro, pressure switch etc etc, To do this periodically
during starting and when engine running, the pump is a A$10
pump and solenoid is a fuel/water for carbies, cheap and
effective - The bleed lines are fed together to the purge
solenoid.

rgds

mike

At 01:54 AM 24/12/2002 -0800, you wrote:
>What about the effect of a higher system pressure on localized boiling and
>surface wetting for thermal transfer?  Isn't a higher cap pressure going to
>reduce the size of the steam bubbles around the exhaust ports and improve
>thermal transfer?  That seems to be the concensus from a number of sites I
>have seen discussing cooling system performance and from empirical
>experience.
>
>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: Monday, December 23, 2002 11:25 PM
>To: diy_efi at diy-efi.org
>Subject: Re: [Diy_efi] RE: Timing and dyno pulls
>
>
>--- Grant Beaty <gbeaty at ufl.edu> wrote:
>
>> I was wondering if cooling system pressure effected
>> the heat exchanged with all other things being
>> equal,
>
>With a non-compressible (like coolant, for all
>practical purposes) you can do two things by
>increasing the pressure; you can increase the flow
>rate through the system, which may or may not make the
>system able to move more heat (depends on how fast the
>coolant can pick up and shed heat), and you can raise
>the boiling point of the coolant (which is probably
>the most important bit).
>
>> including radiator inlet temps. I noticed no
>> higher coolant temps (the probe is where the coolant
>> exits the block) with a 19-21 psi cap compared to
>> stock 16 psi.
>
>Well, if you're not blowing off the valve in a
>lower-pressure cap, putting on a higher-pressure cap
>won't change a thing.  It would only make a difference
>once coolant pressures got ABOVE the blow-off point
>for the lesser cap.
>
>> On my car, doing dyno runs with cold coolant didn't
>> change the HP output at all - although I didn't
>> exactly try and optimize timing and fuel maps for
>> the cold temps.
>
>I was meaning more something along these lines; GSX-R
>motors seem to make best power at right about 200 F
>coolant temp.  At 180 they are down a bit, and at 220
>they are down a LOT.  They seem to do best at 200 F,
>when tuned for best power at a given coolant temp. 
>That sort of thing.
>
>> On the street, I don't see any more knock with the
>> stock (180F) thermostat than a colder one.
>
>Would a slightly hotter one make better power?  LEss
>pinging?
>
>> Of course this is veeery far from scientific
>> testing :)
>
>Gotta start somewhere.  ;)
>
>=====
>| 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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