Paul,
The reason I mentioned both exhaust temp and coolant temps is that the
effect of timing on both of them is different.
Retarding the timing means the peak pressure and temp inside the combustion
chamber is lower. Less cylinder pressure means lower combustion temps and
therefore lower exhaust temps. However since the engine will produce less
power, more heat will be transferred into the coolant.
Advancing the spark, will produce the the opposite effect. Exhaust gas
temps and peak cylinder pressure will go up, and as more power is being
produced, less heat will be transferred into the coolant.
I suppose it might be possible to advance a running engine to the point that
the coolant temps started to go back up, but I seriously doubt you could
start it that far advanced.
While these differences don't amount to much on an LBC, when you start
looking at modern cars, these differences are critical. To combat NOX
timing is sometimes retarded to lower exhaust gas temps. (along with low
compression pistons) To warm up the engine and get the emissions contol
systems on line, timing is often retarded at cold start. If the car starts
to overheat, the computer will advance the timing to lower the heat load on
the cooling system.
On Mon, Aug 4, 2008 at 8:58 AM, Paul Hunt <paul.hunt1@blueyonder.co.uk>wrote:
> No, I'm correct. Whilst if the timing is retarded you will get higher
> running temps as more of the energy in the fuel is converted to waste heat
> rather than forward motion as the piston is too far down and the gasses have
> already expanded too much. The same thing happens if you advance the timing
> *too much* (as I said before). In this case more of the energy is expended
> while the piston is still moving upwards, and again becomes waste heat, as
> it cannot be used to push the piston down until it has passed TDC. This is
> only likely to happen in low compression engines over any period of time, in
> high compression you will get violent pinking if not detonation to
> (hopefully) alert the driver to the situation. With ideal timing you get
> maximum conversion of energy to forward motion, and the least amount to
> wasted heat.
>
> I don't see why you differentiate between coolant temp and exhaust
> temp, since it has to come out of the combustion chamber which is surrounded
> by coolant an increase in exhaust temp will also cause an increase in
> coolant temp.
>
> PaulH.
>
> ----- Original Message -----
> *From:* Richard Ewald <richard.ewald@gmail.com>
> *To:* Paul Hunt <paul.hunt1@blueyonder.co.uk>
> *Cc:* Daybell7@aol.com ; mgs@autox.team.net
> *Sent:* Monday, August 04, 2008 3:23 PM
> *Subject:* Re: [Mgs] 1972 MGB Timing
>
> If you are referring to coolant temps, then this is incorrect. Advancing
> the timing decreases coolant temp. If you were referring to exhaust gas
> temp then you would be correct.
> Rick
>
>
> >> if you start advancing the timing too much to try and get more power
> *that* will cause high running temps,
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