Hotter plugs,and colder t-stat,or vise versa ?

10secgoal · Dec 22, 2004

I have read many times that combustion is at it's best when the motor is around 200 deg. But the colder the intake charge the better, hence the lower t-stat. So what is the difference ? can you run a 190 t-stat, maybe one step colder on a plug ? Or do you run a 160 t-stat (if your system can handle it) and maybe a hotter plug ? I was just thinking out loud here. Seems to get low temp intake charge , run a 160 and use the hotter plug to help retain some of the cylinder heat for full combustion.

Route666 · Dec 22, 2004

I'd like to hear about this too. I'd imagine the WHOLE engine (combustion chamber pieces anyway) wants to be at that temp, so a hotter plug will just leave the plug hotter. I think with a hotter motor the mixture would get more heat in it and burn faster and therefore more thoroughly. Too much heat though and you start pinging, you want it near the edge to get the most out of the fuel.

darkhorse70 · Dec 23, 2004

The heat rating on spark plugs just affects the operating temperature of the plug's electrodes and doesn't directly affect engine temperature. A "hotter" plug just doesn't transfer heat away from the electrodes to the plug's body (and hence to the heads) as quickly as a "colder" plug, so the electrodes build up more heat. Plug temperature should be hot enough to keep the electrodes from building up soot but cold enough to avoid pre-ignition.

The temperature rating of the thermostat affects the temperature at which the thermostat valve opens, allowing more coolant to circulate through the engine and radiator. Once the engine reaches the thermostat's operating temperature, the thermostat stays full open. Therefore it only affects the engine's operation during the warm-up period and won't make any difference once the engine has warmed up.

ForceFed70 · Dec 23, 2004

darkhourse explained it best.

I'll just add that the cooler intake charge is wanted because it allows you to cram more air/fuel into the cylinder than a hotter charge. You don't want it too hot tho or else you can run into troubles with preignition.

10secgoal · Dec 23, 2004

darkhorse70 said:
The heat rating on spark plugs just affects the operating temperature of the plug's electrodes and doesn't directly affect engine temperature. A "hotter" plug just doesn't transfer heat away from the electrodes to the plug's body (and hence to the heads) as quickly as a "colder" plug, so the electrodes build up more heat. Plug temperature should be hot enough to keep the electrodes from building up soot but cold enough to avoid pre-ignition.

The temperature rating of the thermostat affects the temperature at which the thermostat valve opens, allowing more coolant to circulate through the engine and radiator. Once the engine reaches the thermostat's operating temperature, the thermostat stays full open. Therefore it only affects the engine's operation during the warm-up period and won't make any difference once the engine has warmed up.

The t-stat doesn't stay full open during operating temps. It has to close a little at some point or all the water would come rushing thru and the temp would drop past the rated temp. And the water temp has to play a factor in the engines operation. Hotter water equals hotter cyclinder heat temp, and that transfers to the intake. And a hotter intake charge. All this I know.
I don't think I explained it right. In "theory", Do you think that the porcelian of a hotter plug can retain enough heat in the cylinder to combust a cold air intake charge, the same as motor with colder plugs running at 200'?

mfp4073 · Dec 23, 2004

I always understood that heat ranges in plugs were designed to keep the plug hotter or cooler....not having to do with engine operation temp. For example you can run a cooler plug at the track because you are doing wide open runs that keep the plugs from fouling. But runnig around day to day traffic you need something hotter to keep the plugs clean in stop and go traffic. A plug that is too hot for your needs will burn itself up...a plug too cold for your needs will foul out.

Is that it?

10secgoal · Dec 23, 2004

mfp4073 said:
I always understood that heat ranges in plugs were designed to keep the plug hotter or cooler....not having to do with engine operation temp. For example you can run a cooler plug at the track because you are doing wide open runs that keep the plugs from fouling. But runnig around day to day traffic you need something hotter to keep the plugs clean in stop and go traffic. A plug that is too hot for your needs will burn itself up...a plug too cold for your needs will foul out.

Is that it?

Yeah. That's it. The porcelian is what retains the heat and keeps the plugs hot. The more porcelian showing, the hotter the plug. I don't think it will effect the engine temp as much. But I am just wonerding, if I can run a hotter plug, will the plug reatin the heat in the cylinder that I am removing by running a colder plug.

D.Hearne · Dec 24, 2004

darkhorse nailed it. the plug has nothing to do with the engine's operating temperature.

brianj5600 · Dec 24, 2004

The efficiency of a motor goes up the closer you can get the teperature of the cylinder to the actual temperature of the ignited fuel. F1 cars were getting out of hand with high pressure cooling systems, trying to run engines hotter w/o boiling the require H2O coolant until FIA set a max pressure. HP lost through warmer water temp was not an issue for them. Any heat removed by the radiater is wasted energy.

Now back to the real world, I have never seen a power adder company that did not recomend colder plugs. My guess is to control detonation. Most people I've talked to don't even want extended tips. I think HRM had some pics of Nascar plugs and they use more of a block on the side of the electrode as a ground strap. They said it was for erosion control, but I bet less detonation was a side affect.

My answer to the question is. If detonation is not a problem, a hotter plug will run cleaner and have a better spark. If detonation is not a problem, warmer t-stat will be more efficient. The cylinder wear also goes up fast at temps cooler than 180* according to a GM study. Plug temp will have more effect on detonation than t-stat.

zookeeper · Dec 24, 2004

That's what I've found out, too. I've used hotter plugs to "cure" blubbery carburation with good results. I had troubles with low speed response and after a couple days of trying, I threw in a set of one range hotter plugs and bingo! Problem solved! I'd be careful about going too far with that one though or detonation will be the result.

Hotter plugs,and colder t-stat,or vise versa ?

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That's why they call it "dope"

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Hotter plugs,and colder t-stat,or vise versa ?

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That's why they call it "dope"

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