Are clearances between moving parts greater on a marine engine vs a car engine?

[JustJason]

~~
The heat range is controlled by the ceramic insulator size. It will control pre ignition. Maybe that is what you are thinking. Pre ignition will cause things to heat up if the explosion is too soon. If that's what you meant then I agree with you.

No, that's not what I meant. What I meant is that it does help regulate the temperatures of the cylinder/combustion chamber/whatever you want to call it. Heat range does help control the heat of the plug itself, but also the combustion chamber. The hotter the combustion chamber the hotter the plugs going to be, tip and body. The cooler the combustion chamber the cooler the plug is going to be, tip and body.

Try and envision this. Take 2 identical engines, and have them run side by side on matching dynos, with the load on each engine being the same. And you run them for a period of them. Shut them off. Very quickly pull a spark plug, and then drop a thermocouple down the plug hole. The cylinder with a hotter plug will have a higher temperature than the one a cooler plug. I'm not talking about the temps of the plugs, I'm talking about the temps of the cylinders.

That's what I'm talking about. That's what NGK is talking about on that web page link I gave you. And that Is what is being taught in the tech schools as well. The plug helps radiate cylinder heat into the cooling system, or it helps to prevent that, and keeps the heat in the cylinder.

 

[soggy_feet]

No Title

A cold plug is going to transfer (by design) heat into the cylinder head better than a hot plug.

 

[bruceb58]

http://en.wikipedia.org/wiki/Spark_plug

Like I said before, the heat range is for the temperature of the tip of the spark plug.

The operating temperature of a spark plug is the actual physical temperature at the tip of the spark plug within the running engine.

The heat range of a spark plug has only a minute effect on combustion chamber and overall engine temperature.

 

[JustJason]

~~http://en.wikipedia.org/wiki/Spark_plug
Like I said before, the heat range is for the temperature of the tip of the spark plug.


The operating temperature of a spark plug is the actual physical temperature at the tip of the spark plug within the running engine.

The heat range of a spark plug has only a minute effect on combustion chamber and overall engine temperature.

Looks like we have a battle of competing information on different webpages. Wikipedia vs NGK!

 

[MBAKER]

sorry double post....

 

[MBAKER]

I would run the coldest plug you can without fouling. Under normal conditions this would keep the deposits burnt off and clean at idle and part throttle but keep tip temperatures down as much as possible to prevent the plug from acting like a glow plug and causing pre-ignition under load. If anything I would go slightly colder to be safe than slightly hotter. Worse that happens is you have to change a fouled plug, go hotter and you might burn something up. An engine that sees a lot of idle and part throttle low load conditions, may require a different plug than a WOT and/or heavy load condition.


I don't see a spark plug having any overall effect on engine temperature, as long as its not causing detonation and increasing temps that way.

I can see it having a very, very minor effect on chamber temp simply because the plug removes some small amount of heat that it gains during combustion and transfers it to the cooling system. While it is regulating the plug temp itself, the plug has to gain heat from the chamber first then transfer it to the cooling water.

 

[bruceb58]

Looks like we have a battle of competing information on different webpages. Wikipedia vs NGK!

It's not just one site. I read it everywhere.
http://matchlessclueless.com/mechani...g-temperature/

Engine temperature is governed by factors such as the timing and fuel-air mixture settings, running conditions, lubrication quality, compression and cooling system design to name a few, but certainly NOT by the spark plugs heat range. The spark plug gets its heat from the burning fuel in the combustion chamber, and not the other way round!

I can see that you get confused by that one NGK site though. Its a bit ambiquous.

 

[Walt T]

That so called Speed Shop guy was BS'n you because he doesn't know what he's talking about and is trying to impress people. Don't ask him any more questions.

 

[JustJason]

~~I can see that you get confused by that one NGK site though. Its a bit ambiquous.

I'm not confused. This is what is being taught in tech schools. The plug is the only connection between the combustion chamber and the water jacket in the cylinder head. If you increase the engines load, the horsepower, the timing ect. Combustion chamber temps will go up. The only way to keep them from going to high is by running a plug that effectively removes heat from the combustion chamber, and transferring it to the cooling system. The plug has to keep the combustion chamber hot enough to allow the plugs to be self cleaning, but not so hot you get pre ignition.

I know we are going to agree to disagree on this one.

But I think we can agree NGK is the largest OEM plug supplier in the world, it is claimed here.

http://en.wikipedia.org/wiki/NGK

NGK also goes as far as saying the torque on the spark plug can effect heat transfer between the plug, and the head.
Here is the source on that - http://www.ngksparkplugs.com/tech_su...x.asp?mode=nml

Quote "~~Torque is one of the most critical aspects of spark plug installation. Torque directly affects the spark plugs' ability to transfer heat out of the combustion chamber. A spark plug that is under-torqued will not be fully seated on the cylinder head, hence heat transfer will be slowed. This will tend to elevate combustion chamber temperatures to unsafe levels, and pre-ignition and detonation will usually follow. Serious engine damage is not far behind."

If you can't believe NGK I don't know who you can believe. But I can tell you this. If you take a GM V whatever, and stick 43's in 1 head, and 44's or higher in the other head. You don't even have to drop a thermocouple in the cylinders to see the difference. The exhaust manifold will run hotter on the side with the hotter plugs in it. It is taught in schools this way, and that is one of the demos they use in the classroom. And the way the prove the lesson is they swap the plugs from 1 head to the other and the heat will follow the plugs. The exhaust gases will be slightly hotter on the side that has the hotter plugs. And the hotter the plug the hotter the gases, and the hotter the manifold gets.

 

[bruceb58]

I know we are going to agree to disagree on this one.

Yep. All good though! I learned new stuff too.

When I worked for GM, I was doing some design for some cylinder pressure sensors that we were working on with Toyota racing. Was interesting stuff.

 

[Maclin]

Heat range of the plug used to be a spec for how well the sparkplug dissipates it's own heat from each combustion event. If it stays too hot then it could cause pre-detonation misfire. If it cools too quickly it can foul easier. I suppose the heat must go into the head, so that writeup from NGK may be "the REST of the story" perhaps.

 

[Tail_Gunner]

Something to ponder.....a marine engine block run colder than a automotive block that is a fact....the combustion chamber in a marine block is going to be colder that a automotive block. Now will the piston run cooler in a marine block????????????????? will the oil temp run cooler in a marine block?????

Now how about expansion rate's in marine vs auto that's a subject matter in one's pushing 800hp out of 500 cid motor..for the rest of us it's PTA meeting...To the OP yes a race machine shop is going to say such thing's it is there lively hood and way of life and for high HP under duress yes marine HP is a different game.