spark plugs
10-31-2006, 09:48 AM
#1
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ok so this is kind of a dumb idea....
so the factory runs 7's and 9's for spark plugs, 9 is 2 steps colder and goes in the trailing hole.
when we mod the crap out of the car, we generally put 9's in the leading spot, this seems to work ok, but souldnt we really be running like 9's in the leading and 10.5 or 11's in the trailing? this is just keeping the factory heat range split....
so the factory runs 7's and 9's for spark plugs, 9 is 2 steps colder and goes in the trailing hole.
when we mod the crap out of the car, we generally put 9's in the leading spot, this seems to work ok, but souldnt we really be running like 9's in the leading and 10.5 or 11's in the trailing? this is just keeping the factory heat range split....
10-31-2006, 10:52 AM
#3
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Originally Posted by j9fd3s' post='843311' date='Oct 31 2006, 10:48 AM
ok so this is kind of a dumb idea....
so the factory runs 7's and 9's for spark plugs, 9 is 2 steps colder and goes in the trailing hole.
when we mod the crap out of the car, we generally put 9's in the leading spot, this seems to work ok, but souldnt we really be running like 9's in the leading and 10.5 or 11's in the trailing? this is just keeping the factory heat range split....
Ive been wondering this as well. I just ordered 2 NGK R672510-5's and will only use them when running high boost and race gas.
I was recently told that I should run the 10.5's in the leadings and the 9's in the trailings...which confused me a little based on the above mentioned theory.
Other than that, I'll run 9's all around on pump gas. I have no problems with that so far.
10-31-2006, 06:31 PM
#4
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The factory probably wants colder plugs in the trailing side because the trailing is so shrouded.
Have you ever seen a spark plug non-fouler? It is a very cheap temporary fix for a piston engine that is burning so much oil in one cylinder that it keeps fouling the spark plug out. The non-fouler is basically just a shroud that you thread into the plug hole, then you thread the plug in. It effectively makes the spark plug "hotter" and prevents fouling.
Let's look at that again.
Shrouding the spark plug effectively makes its heat range hotter.
Now that (we think) we know why Mazda wanted colder plugs in the trailing side, it certainly does make sense that we would want to keep the same heat range difference!
What would be the worst thing that could happen if the trailing plugs were too cold? Trailing misfires, slight drop in power.
What would happen if the trailings were too hot?
Have you ever seen a spark plug non-fouler? It is a very cheap temporary fix for a piston engine that is burning so much oil in one cylinder that it keeps fouling the spark plug out. The non-fouler is basically just a shroud that you thread into the plug hole, then you thread the plug in. It effectively makes the spark plug "hotter" and prevents fouling.
Let's look at that again.
Shrouding the spark plug effectively makes its heat range hotter.
Now that (we think) we know why Mazda wanted colder plugs in the trailing side, it certainly does make sense that we would want to keep the same heat range difference!
What would be the worst thing that could happen if the trailing plugs were too cold? Trailing misfires, slight drop in power.
What would happen if the trailings were too hot?
11-03-2006, 05:47 PM
#6
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Originally Posted by heretic' post='843405' date='Oct 31 2006, 05:31 PM
The factory probably wants colder plugs in the trailing side because the trailing is so shrouded.
Have you ever seen a spark plug non-fouler? It is a very cheap temporary fix for a piston engine that is burning so much oil in one cylinder that it keeps fouling the spark plug out. The non-fouler is basically just a shroud that you thread into the plug hole, then you thread the plug in. It effectively makes the spark plug "hotter" and prevents fouling.
Let's look at that again.
Shrouding the spark plug effectively makes its heat range hotter.
Now that (we think) we know why Mazda wanted colder plugs in the trailing side, it certainly does make sense that we would want to keep the same heat range difference!
What would be the worst thing that could happen if the trailing plugs were too cold? Trailing misfires, slight drop in power.
What would happen if the trailings were too hot?
I had a comlpete set of those non foulers on my old Chevy van. They work so good that it would loose some porclene from a tip now and then. But they were working on a slightly different mechanism than the same look in the rotary. The plug temps are somewhat controlled by the degree of exposure to the flame of the combustion chamber, and some by the heat must flow to get to the cooling jacket and be carried away.
The longer the path the hotter the plug runs. The nonfoulers had a broken path at the plug threads and another at the plug threads in the head, that was twice the thermal breaks of a stock plug. Nothing to do with the heat range of the plug. Most of the path is designed into the head or rotor housing. How thick is the aluminum where the threads are cut through the housing. How much coolant flows past this location and so on. The rest of the path is built into the plug, and determins the heat range.
This is very difficult to see on those plugs with the Mazda looking 360 degree ground electrode. Note here that Mazda plugs look just like aircraft plugs, and for the same reason. But on a more conventional plug you can see how long the center electrode insulator is before it joins the shell. In low performance equipment the path is long so as to mainain high enough nose temps to keep the plug clean and not foul up with carbon. Carbon is a conductor. It is what is used inside of resistors in electronic equipment. So a long heat path means a hotter tip. A short path, as in the porclene joins the shell right near the tip, means a colder plug and low nose temps.
Using too cold a plug for the performance situation, just means too low a nose temp and this may lead to a carbon fouled plug. This is a pain in the tailfeathers, but is cheap to cure. Using too hot a plug range means high nose temps, and when the engine is used hard, may lead to preignition from the white hot center electrode igniting the mixture before the plug fires (preignition). This can rapidly lead to detonation, and loss of the apex seals. So, if you plan on missing the heat range, miss it to the low side. Put in a colder plug than you think you need for the performance you plan to us.
In the olden times (where I came from), we used to warm up the engine with real high heat range street plugs. Once the coolant was up to temperature, we would shut down and switch to the ice cold racing plugs for the race. Everybody did this and it worked just fine. If there was a problem on the false grid that required a long shut down, there would be a good chance that one or two cars would foul plugs from having cooled off to far and not be able to restart. If one of the street plugs was not changed for the race, the engine would be destroyed. Both, very unhappy situations.
We need not do that anymore because we have the Mallory Hifire or MSD ignition systems where we can insert over one amp of electrical energy into the plugs per thousand RPM. The rise times are so short and voltages are so high, that even a carbon fouled plug fires before the lower voltage of the old Kettering system, can leak down across the carbon path. Note also that these systems provide enough energy per strike to kill you. The MSD also fires once when you turn it on and once when you turn it off. If you don't want a Spiedel shaped scar on your wrist, and a bad memory, do not screw with the plug wires with the battery connected.
We use the NGK R6725-115 plugs, gapped at .0010". They have a retracted gap and fine wire electrodes. The heat range is ice cold. I have never fouled one. We use a MSD for leading and trailing. Even driving slowly to the false grid on a cold morning, no problems.
There you go......more than you wanted to hear about spark plugs.
Lynn E. Hanover
11-03-2006, 09:31 PM
#7
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Originally Posted by Comitatus' post='843836' date='Nov 4 2006, 12:10 AM
Autolite and Champion both make plugs with a low enough heat range to race in a NA rotary.
I have no idea about turbos. We used Champion N57Gs for years. That is 3/4" reach medium tip gold palladium center electrode. Whatever they say is the replacement for that plug should work fine. A very cold plug.
I forgot the Autolite number but I saw a box while rooting in the trailer the other day. I will try to find them and publish that number. Auto Zone will order them under $7.00 a box of 4.
Always screw a new brand plug into a spare housing in both holes to be sure that there is no contact of the tip or threads running out in the hole. Usually it is the extended tips that cause the problems. Also there is a slim chance that the tip can extend into the chamber and destroy the apex seals. You wouldn't be the first to do it either. Look at everything.
OK I couldn't wait and went out to look. Frost on everything. the Autolite number is AR2592. A little off ice cold. I rebuilt a rotary that had 4 of these in it. No problems. And the price is right. I also noticed several boxes of Champion N86. So they may have replaced the N57Gs from years ago. Check with Champion on that.
Sombody is always asking for plugs at the track, so I gave away the Champions (we got for free) or the ACs we got for $7.00 and I kept the NGKs (we got for free for earning another invitation to the national championships).
Lynn E. Hanover
11-03-2006, 09:32 PM
#8
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Originally Posted by Lynn E. Hanover' post='843753' date='Nov 3 2006, 03:47 PM
We use the NGK R6725-115 plugs, gapped at .0010". They have a retracted gap and fine wire electrodes. The heat range is ice cold. I have never fouled one. We use a MSD for leading and trailing. Even driving slowly to the false grid on a cold morning, no problems.
There you go......more than you wanted to hear about spark plugs.
Lynn E. Hanover
yes!
11-04-2006, 01:10 AM
#10
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