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Discussion Starter · #1 ·
I want to change the spark plugs out this weekend, but I wanted some recommendations. I've got a 90 5.2, .030 over with a hughes cam HER9204A and stock tbi. I know there are "cold" plugs and "hot" plugs and I suppose the "normal" plugs, too. I wanted some opinions as to what plugs would be best to run and some part numbers because I doubt the guy behind the counter at the part store will know the difference between the plug types. By the way, I'm looking for torque ;D

As an aside, when checking the cylinder preassure, what PSI should I be getting and should I check it with the engine cold or at normal operating temp?

My RAMona and I thank you in advance!

James
 

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Ive seen the question before and it seems its always a matter of opinion and what work with your own set up. I ve always been told that bosch are the best when running a perfomance ignition. Such as the orange box. But ive also been told that if your running close to stock to run champion plugs. Ive had nothing but bad luck and crappy performance with split fire and so did my brothers ford. So I wouldn't use them. Sorry if i didn't help much. Just my .02
 

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Discussion Starter · #3 ·
I've got champions now, and they run fine, i was just wondering if running a little hotter plug or colder plug would give any better results.
 

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Every engine is different in terms if it needs a hotter or colder plug. Generally either stock or one step hotter or colder is all you would need to experiment with. With Champion the bigger the number the hotter the plug. If your plugs are showing white but you dont' really think its too lean then go to a colder plug. If its building up deposits on the plug then go to a step hotter plug. For example I built up a 318 in my brothers Mirada and the recommended plug was RN14YC but the plugs were white around the ceramic but the car was obviously burning rich. I went to RN12YC and it then showed color on the plugs and that it was a tad rich.
 

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The heat range has to be done according to how your plugs look now, you have to read them you have to look at the insulator the ceramic white part that surrounds the electrode, look for a ring if the ring or deposit is low on the insulator then the heat range is ok, if it's high and close the end of the electrode it needs to be hotter to keep the plug clean, this is so very confusing there are so many things to look at discoloration on the ceramic, deposits or spots, but the ring on the ceramic depending it's position is how you know if it's in need of hotter or colder, however it could also be a carburator lean or rich or ignition to advanced, this gets involved.

However spark plugs that do there job and do it correctly and best suited for the job are:
AC Rapid fires these plugs are designed with how electricity works and in it's best fashion, electricity loves jumping from and to sharp points, this is the only plug designed for that.
Iridium spark plugs NGK and Denso make these and are very good, also have a good design for electricity and spark, small thin pointy electrode jumping to a grooved ground with several sharp edges. The only problem with these plugs is they don't last long, but i could care less as long as they do there job great.
Bosch + 4 A good theory, the only other plug i like but the electrode is alittle hidden and im not to thrilled with the theory of the grounds making a sun like spark with a factory ign, and kinda covering the plug making it hard to see.

When a spark plug loses it's sharp edeges, like a champion for example straight cut electrode round that sharp edge along it's circle when it rounds off, the plug is junk as is any plug when they lose there edge, the rounder things become the more energy to light it and the more chance for it to fire a second off and jump real weak, i would upgrade the ignition and gap at 60, you increased the motors ability to make power now light it off good
 

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Discussion Starter · #6 ·
Thanks for the responses, I'll read the plugs when I take them out.
Gap to 60! damn, that's a big gap! I actually have a mopar performance coil, but the instructions with it said to wire in this little resistor block that came with it. I don't know what it's puprpose is, but if it's suppose to go there.... With the performance coil and if i put some 8mm accel spiralcore wires, could i gap to say 40 or 45?
 

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Well i would use MSD SC wires yeah i think the factory ign will handle 45, but your next upgrade you do might be in the ignition, i meant to use 60 after you did some increases in the ign end
 

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I don't think I'd run .060 gaps unless your using one of the big dist caps with a lot of distance between the wire towers, stock chrysler cap wire towers are close together.You tend to get some spark jumping. Might try .045
 

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txs said:
I don't think I'd run .060 gaps unless your using one of the big dist caps with a lot of distance between the wire towers, stock chrysler cap wire towers are close together.You tend to get some spark jumping. Might try .045
Humm - I don't think arcing at the cap towers has anything to do with gap, but more how high the voltage is - it's a good point though, if your running more than about 45kv - 'course I'm often wrong :-\
 

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oldmanram said:
txs said:
I don't think I'd run .060 gaps unless your using one of the big dist caps with a lot of distance between the wire towers, stock chrysler cap wire towers are close together.You tend to get some spark jumping. Might try .045
Humm - I don't think arcing at the cap towers has anything to do with gap, but more how high the voltage is - it's a good point though, if your running more than about 45kv - 'course I'm often wrong :-\
Electricity flows along the path of least resistance. If you have too high of a resistance on a plug wire, then it may jump between the towers, but it would also take some messed up and cracked wires to do it.
If you want to run a .060 gap, make sure you have very low resistance wires in good condition, and you keep your plugs clean. You also need a high voltage ignition system. A stock distributor cap and rotor is not going to hold up either. Get an MSD cap and rotor, or another high end set.
 

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Actually D8564 is right it will take the path of least resistance, but i wouldn't tell you something i haven't done or tried, on a upgraded ign system going to 60 is no problem even 70, i have never went to the large caps on any of my motors and never had a mis fire under any rpm or any type of fuel use especially mis fires associated with the factory spaced terminals on the cap.
 

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I have not tried the irridium plugs, but I want to. Everything I own has Autolites. I took the plugs out of a brand new lawnmower and put in autolites before I added gas. Champions have a much shorter life span, and the autolites seem to work better even with the same heat range.
 

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I have run my .060 gap with my stock distributor (before I got my MSD) with absolutley no problems. Again, I have a complete Jacobs systems. Each one of the components in the system, (i.e. wires, coil, computer) allows me to open the gaps a certain amount with each item.
 

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Discussion Starter · #15 ·
thanks, that a lot of good info.
 
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I'm running an MSD 6A with Blaster SS coil, Taylor SpiroPro wires and Accel cap and rotor. I replaced the split fires today with Bosch +4's. Other than the electrodes being paper thin, the split fires were still in great shape. I have my doubts about the +4's but I'll see how they work after a few thousand miles.

A plugs heat range has to do with how well it dissipates heat. If it's made to dissipate heat more slowly, it's said to be a hotter plug. Like has been said, it depends greatly on the overall condition of your motor. Higher mile motors usually require a step or two hotter plugs due to ring and bore wear which allows a little more oil into the combustion chamber. Oil fouls a plug in a hurry. A hotter plug tends to burn the oil away. A bright white, or glazed ceramic after a thousand miles or so means the plug is too hot. A plug that fouls easily and looks black, sooty, or oily is normally too cold. That holds true only if the motor is in good running condition. A light tan color without any fouling, is just right

As far as plug gaps. I like to set mine at .050. I'm not a big fan of pulling the plugs every month or so to set the gaps. Setting them at .050 allows the plugs to wear a little and still stay within the gap range. The larger gaps will require more regular maintenance to keep them right.
 

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I was wondering the same thing that JAAMZG asked to start this topic. Now that I have read the other posts I have a few additional questions. What is the benefit of increasing your spark plug gap? I have a Mallory Hyfire ignition, MSD wires and a Mopar distributor. Should I increase my spark plug gap over the .035”? Does anyone have the part #’s of any major brands, for one step hotter or colder plugs? The part searches I have done only show what the stock spark plug is. The Napa was closed, so I asked the guy at AutoZone and he only knows what is in the computer. Thanks for all the info.
Streak-O-Lean
84 RC 318
 

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Increasing the gap allows the spark to fire off a larger area making the fuel burn efficient in the cyl, and also make for very quick starts
 

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Increasing the gap allows the spark to fire off a larger area making the fuel burn efficient in the cyl, and also make for very quick starts
 

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A bigger gap can give better, more complete combustion. The way it can do this is:
1) More flame kernal is exposed to the mixture, and...
2) A bigger gap requires more voltage to jump, and more voltage results in more "current", which is the heat that lights of the fuel (current lights the fuel, not the voltage).

Also, a biggger gap results in better flame propagation. As a spark is just igniting the fuel, the flame kernal "propagates" (increases in size) relatively slowly. When the flame kernal is about .100", it then propagates very rapidly. So, the closer you can get to the magical .100" the better.

I would definalty increase you gap. Most manufacturers would reccomend increasing the gap in .005" increments until performence drops off, then reduce gap by .005". If I were you, I'd start at .045, and if you have the patience, start expirementing.
 
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