Short Wave Sportfishing wrote in message . ..

It is my understanding that a "hot" plug is aimed more towards keeping
heat available to burn off deposits quicker

as in, burn the deposits off the plug itself so the plug stays clean.

and help with a cleaner,
quicker burn when the fuel/air mixture is ignited.

Once ignition has taken place, the spark is no longer a positive
influence to enhance the burn, the ball is rolling, the cat is out of
the bag, Elvis has left the building.

A dirty plug will not give a consistent spark on every compression
stroke, so poor running will result. A plug too hot will pre-ignite.
In between is a plug that stays hot enough to stay clean but cool
enough not to pre-ignite. The penalty for getting too hot a plug may
be the purchase of a new piston.

It is also my
understanding that engine manufacturers allow for a range of types of
hot to cold plugs to adjust for varying conditions like altitude,
emissions requirements and other issues.

I have adjusted plugs for hot/cold on high performance engines because
of the varying temperatures in different cylinders - all within a
range of course but all on the same engine.

That's an interesting idea. Assuming there isn't a problem of uneven
ring wear or uneven carburetion, or uneven crankcase condensate drain
(on a 2-stroke), then you may be left with a slight unevenness of head
temp from one cylinder to the next. In that context it makes perfect
sense to run a hotter plug on a cold cylinder, or vise versa, to
lessen fouling of the plug in the cold cylinder or lessen pre-ignition
in the hot cylinder. What you're doing is getting the plugs to be at
about the same temperature despite the uneven head temp.

%mod%

On 25 Feb 2004 07:39:44 -0800,
(modervador) wrote:

Short Wave Sportfishing wrote in message . ..

It is my understanding that a "hot" plug is aimed more towards keeping
heat available to burn off deposits quicker

as in, burn the deposits off the plug itself so the plug stays clean.

and help with a cleaner,
quicker burn when the fuel/air mixture is ignited.

Once ignition has taken place, the spark is no longer a positive
influence to enhance the burn, the ball is rolling, the cat is out of
the bag, Elvis has left the building.

A dirty plug will not give a consistent spark on every compression
stroke, so poor running will result. A plug too hot will pre-ignite.
In between is a plug that stays hot enough to stay clean but cool
enough not to pre-ignite. The penalty for getting too hot a plug may
be the purchase of a new piston.

It is also my
understanding that engine manufacturers allow for a range of types of
hot to cold plugs to adjust for varying conditions like altitude,
emissions requirements and other issues.

I have adjusted plugs for hot/cold on high performance engines because
of the varying temperatures in different cylinders - all within a
range of course but all on the same engine.

That's an interesting idea. Assuming there isn't a problem of uneven
ring wear or uneven carburetion, or uneven crankcase condensate drain
(on a 2-stroke), then you may be left with a slight unevenness of head
temp from one cylinder to the next. In that context it makes perfect
sense to run a hotter plug on a cold cylinder, or vise versa, to
lessen fouling of the plug in the cold cylinder or lessen pre-ignition
in the hot cylinder. What you're doing is getting the plugs to be at
about the same temperature despite the uneven head temp.

I came across this idea from talking with Chuck Etchells at a
basketball game (our kids know each other pretty well) who ran (or
maybe still does) NHRA funny cars for many years. I tried it on a 440
hemi and I gained about 10% more horse power on a dyno.

Again, it's anecdotal evidence, but it made sense to me at the time
and thinking back on it, still makes sense.

Later,

Tom
S. Woodstock, CT
----------

Basic Fishing Program:

10 - Fish
20 - Eat
30 - Sleep
40 - Goto 10

If this were true, there would be no need for a choke
on a carbed engine.

Short Wave Sportfishing wrote:

On Mon, 23 Feb 2004 20:10:04 GMT, "Geoff 93 RRC"
wrote:

It seems most new boats have a 160 thermostat these days. I have a '93
Mercruiser 4.3LX. Can I use the 160 thermostat? I boat exclusively in
fresh water. I want to get the cleaner combustion that the higher temps
give.

Ok, I've a different opinion.

I prefer to run a little cooler thermostat with a hotter plug. I've
done this on my antigue trucks and this technique works great.

If you are looking for power and clean combustion, a hotter plug is
always the best choice over fooling around with the thermostat. You
have to remember that the reason you have a thermostat is to maintain
a constant temperature on the block for expansion/contraction reasons
- not for combustion. Combustion is strictly the pervue of how hot
the spark is.

Curiosity question - raw water cooled or fresh.

Later,

Tom
S. Woodstock, CT
----------

Basic Fishing Program:

10 - Fish
20 - Eat
30 - Sleep
40 - Goto 10

On Tue, 24 Feb 2004 02:36:53 GMT, Jim Kelly wrote:

If this were true, there would be no need for a choke
on a carbed engine.

Huh?

What does choking an engine (limiting the air in the fuel mixture for
a quicker start) have to do with hot plugs?

Just curious.

Later,

Tom
S. Woodstock, CT
----------

Basic Fishing Program:

10 - Fish
20 - Eat
30 - Sleep
40 - Goto 10

I am questioning your assertion that "combustion is strictly the pervue
of how hot the spark is." I contend that that it is necessary to
increase the fuel to air ratio on a cold engine because the engine is not
imparting enough heat to the mix to create a combustible mix regardless
of the heat range of the plug. Therefore, engine temperature has a
direct effect on combustion.

I agree with your contention that mechanical clearances in the engine are
designed around a certain operating temperature. If the engine is
operating above or below the design temperature, thermal expansion rates
of the materials in the engine will result in clearances that are
different than the design criteria.

Short Wave Sportfishing wrote:

On Tue, 24 Feb 2004 02:36:53 GMT, Jim Kelly wrote:

If this were true, there would be no need for a choke
on a carbed engine.

Huh?

What does choking an engine (limiting the air in the fuel mixture for
a quicker start) have to do with hot plugs?

Just curious.

Later,

Tom
S. Woodstock, CT
----------

Basic Fishing Program:

10 - Fish
20 - Eat
30 - Sleep
40 - Goto 10

On Wed, 25 Feb 2004 02:01:22 GMT, Jim Kelly wrote:

I am questioning your assertion that "combustion is strictly the pervue
of how hot the spark is." I contend that that it is necessary to
increase the fuel to air ratio on a cold engine because the engine is not
imparting enough heat to the mix to create a combustible mix regardless
of the heat range of the plug. Therefore, engine temperature has a
direct effect on combustion.

I can agree with that. However, combustion has to be initiated by the
spark. The fact that a cylinder is operating at certain temperature
only assures that the fuel/air mix on entering the chamber is fairly
evenly dispursed. The source of ignition is still the spark. A
hotter spark means that more energy is imparted to the explosive
mixture resulting in a cleaner burn with more energy transfer. The
gas expansion rate is better because the burn is initiated quicker.

Additionally, a hotter plug in a cold normally aspirated engine means
that one can use less choke on starting. Faster start, faster warm
up.

Later,

Tom
S. Woodstock, CT
----------

Basic Fishing Program:

10 - Fish
20 - Eat
30 - Sleep
40 - Goto 10

"Jim Kelly" wrote in message
...
I am questioning your assertion that "combustion is strictly the pervue
of how hot the spark is." I contend that that it is necessary to
increase the fuel to air ratio on a cold engine because the engine is not
imparting enough heat to the mix to create a combustible mix regardless
of the heat range of the plug. Therefore, engine temperature has a
direct effect on combustion.

You have the right idea. The spark delivered to the combustion chamber is
the same regadless of the plugs heat range. The only way to get a hotter
spark is if you use a hotter coil. And using a hotter plug than the
manufacturer recommends is can damage the engine. You will always need a
richer mixture in a cold engine, the fuel doesn't atomize as well when cold.
I installed an aftermarket programable fuel injection in my truck. It takes
30-40% more fuel for cold starts.

Rich

Short Wave Sportfishing wrote in message . ..

On Tue, 24 Feb 2004 02:36:53 GMT, Jim Kelly wrote:

If this were true, there would be no need for a choke
on a carbed engine.

Huh?

What does choking an engine (limiting the air in the fuel mixture for
a quicker start) have to do with hot plugs?

I think he was responding to:

You
have to remember that the reason you have a thermostat is to maintain
a constant temperature on the block for expansion/contraction reasons
- not for combustion. Combustion is strictly the pervue of how hot
the spark is.

Gasoline will ignite only within a range of mixtures with air. While
the block is cold, fuel in the mixture condenses on the cold surfaces
so there is not enough fuel in vapor phase to be ignited by spark.
Thus, the choke is closed to introduce more fuel to get the mixture
right, till the engine "warms up."

So we see that one function of the thermostat is to keep the block
warm enough to eliminate fuel condensation, for purposes of
combustion. And we see that combustion is the pervue of not only how
hot the spark is, but also air/fuel mixture.

%mod%

The boat is fresh water cooled. What hotter range plug would you recommend
and how much hotter is it than the standard plug?

Thanks,
Geoff

"Short Wave Sportfishing" wrote in message
...
On Mon, 23 Feb 2004 20:10:04 GMT, "Geoff 93 RRC"
wrote:

It seems most new boats have a 160 thermostat these days. I have a '93
Mercruiser 4.3LX. Can I use the 160 thermostat? I boat exclusively in
fresh water. I want to get the cleaner combustion that the higher temps
give.

Ok, I've a different opinion.

I prefer to run a little cooler thermostat with a hotter plug. I've
done this on my antigue trucks and this technique works great.

If you are looking for power and clean combustion, a hotter plug is
always the best choice over fooling around with the thermostat. You
have to remember that the reason you have a thermostat is to maintain
a constant temperature on the block for expansion/contraction reasons
- not for combustion. Combustion is strictly the pervue of how hot
the spark is.

Curiosity question - raw water cooled or fresh.

Later,

Tom
S. Woodstock, CT
----------

Basic Fishing Program:

10 - Fish
20 - Eat
30 - Sleep
40 - Goto 10

Woops, I meant raw water cooled - no heat exchanger. I think I am sticking
with the cooler 143 degree thermostat. We boat on Lake Travis in Austin, TX
and although very clean, its "hard" water. I have the scale on my outdrive
to prove it. Seems the cooler running temps will limit mineral precipation
as it does for sea salt.

Thanks for all of the replies.

"Geoff 93 RRC" wrote in message
m...
The boat is fresh water cooled. What hotter range plug would you
recommend
and how much hotter is it than the standard plug?

Thanks,
Geoff

"Short Wave Sportfishing" wrote in
message
...
On Mon, 23 Feb 2004 20:10:04 GMT, "Geoff 93 RRC"
wrote:

It seems most new boats have a 160 thermostat these days. I have a '93
Mercruiser 4.3LX. Can I use the 160 thermostat? I boat exclusively in
fresh water. I want to get the cleaner combustion that the higher
temps
give.

Ok, I've a different opinion.

I prefer to run a little cooler thermostat with a hotter plug. I've
done this on my antigue trucks and this technique works great.

If you are looking for power and clean combustion, a hotter plug is
always the best choice over fooling around with the thermostat. You
have to remember that the reason you have a thermostat is to maintain
a constant temperature on the block for expansion/contraction reasons
- not for combustion. Combustion is strictly the pervue of how hot
the spark is.

Curiosity question - raw water cooled or fresh.

Later,

Tom
S. Woodstock, CT
----------

Basic Fishing Program:

10 - Fish
20 - Eat
30 - Sleep
40 - Goto 10