I called NGK this morning after noticing the difference in gapping between the TR55 and TR6 (for reference, this is for both the V-Power and Irridiums, and the TR55 is one heatrange colder than stock, TR6 is two heatranges colder).

Factory gapping for us is .060". The TR55 comes that way and is fine. NGK'* website shows the TR6 gapped at .039", and I'd never noticed that before (I was re-gapping mine to .060", and this is what I called to ask them). The tech told me the TR6 is actually gapped at .032", regardless of the website stating .039".

At this point, I asked him what I should be gapping to, based on my mods. He gave me a range of .040" to .045" for the TR6 in my car, and he agreed that because of my hotter MSD coils (and the same would hold true for the 97+ SSEi coils) I should tend to the bigger side, or .045".

The general rule of thumb is never change the gap larger or smaller than factory gapping by .008". In this case, the listed gap of .039" could be safely raised to .047 for my TR6'*, but the ACTUAL gap as I was told of .032" could only be safely gapped up to .040". With that in mind, he told me I'd be fine up to .045", just pushing the PAPER limits. The idea is to keep the faces of center electrode and ground electrode as parallel to each other as possible, and if you go too far, you induce an angle on the ground electrode, so the gap isn't even across the face of the center electrode.

Now to dispel some incertainty with Copper, Irridium, and Platinum in Forced Induction applications:

Platinum IS CONFIRMED bad news in supercharged, turbo, or nitrous (and even alcohol/methanol) injected applications. Irridium is as good as copper, as the core of the Irridium plug is still copper, and it'* just an Irridium plating (it'* actually a copper plug pressed into an Irridium jacket).

The interesting part is that people playing with heatrange changes often select the wrong Irridium plug. In alot of cases, you should go another heatrange colder when switching from copper to Irridium. In my case, since I'm just barely into the 2 heatranges colder need, I'll stick with TR6 if I switch to Irridiums, but someone else more heavily modded would want to run up to the TR7.

NGK plugs are reverse of domestic plug manufacturers in their heatrange specs. The lower the number, the hotter the plug. Higher numbers are colder. So the TR7 is 3 heatranges colder than stock, the TR6 is two colder, and the TR55 is one colder.

I probably won't make the switch to Irridiums simply because of the frequency I change my plugs. I do it once a year. If I went to full lifetime of the plugs, I'd probably do it, but the difference between $2 a plug and nearly $8 per plug seems ridiculous for my frequent plug changes.

Here'* a good plug FAQ I suggest for anyone wondering about plugs:
http://www.ngk.com/faqmain.asp
This is an authorized distributor of NGK, but not NGK themselves. I got alot more information on the specifics of my application from NGK directly.

I'm buying my plugs from http://www.ngk.com/ (authorized DISTRIBUTOR, not NGK the manufacturer). I typically have to order my plugs from NAPA, as most stores don't stock the TR6 on the shelf. NAPA ships quickly, but this time I'm getting shipping to my door, rather than having to go to the store to pick them up.

I also briefly discussed O2 sensors with the Tech (who was VERY knowledgeable), and he'* checking on whether or not NGK makes the AC Delco O2 sensors. If they do, try this for comparison:

www.ngk.com lists my O2 at $16.85 (p/n 21002)
www.gmpartsdirect.com lists my O2 at $26.40 (GM# 25162693 or AC Delco #AFS-20)
$10 savings.

I'll be talking with him next week to confirm that the NGK is the AC Delco sensor in sheeps clothing

I'm in the process of getting my plugs and wires here for a swap before WCBF. Might have to do it DURING WCBF if they don't get here soon. I have a high resistance on 2 of my plug wires right now, and my plugs may be fouled by my recent troubles with my alternator. Last time my alternator failed, my spark voltages were low enough to foul out a set of plugs rather quickly.

Let'* use this thread to accumulate what we can for a Techinfo article.

Sound like that was an interesting coversation. question for you
Why?

I'm running Autolite 104'* double platnium right now with no problems, 2 range colder and they are gapped @ .050

The electrodes erode quicker under high boost (high heat) conditions. Platinum has a lower melting point than Copper or Irridium.

So us SE'* that haven't turbo'd yet are safe with whatever we want to put in there?

How about this, What'* the point of all of these different metals? I've always used copper because it'* what was in there at the factory. Then they start coming out with new types and stuff. What'* all of it mean and what do we need?

So all the NGK plugs (TR6 for example) you buy from ngk.com are pre-gapped at .035? .045 was the max suggested gap?...interesting.

Gapping that small is going to cut a lot of power.... The bigger the gap, the better the spark and therefore more power potential..

IF you have the ignition to back it up.... it also depends on what type of ignition control you use... some spark off more then once to insure a complete burn and full power... some vary their output voltage per engineload and throttle position, and even angle of the vehicle

spark plugs are one of those weird sciences with cars ... with every mod you do for MAX potenial and power from the plugs you have to change something.

there was a GREAT write up on spark plugs and the things you can do to optomize them in an issue of Popular Hot Rodding ... may2004 Volume 44 #5

I tried to find it at the mags site but it wasn't posted.

Yeah, but willwren has MSD coils

I don't believe the MSD coils are any hotter than stock 97+ SSEi coils. Hotter than 87-96 coils, yes, and hotter than 97+ SE/SLE/SSE coils, but not SUPER hot. Maybe if I had a DIS4 system, I could open it up.

The point is that the plug needs to work efficiently, and it'* gapped smaller for a reason. It'll last longer if it'* gapped properly. The set that'* on the way right now will be gapped at .045 when they get here from NGK I'll let you know in 6 months.

Here'* a write up done by Will Rishworth (Overkill) of the Ontario Quebec Club Grand Prix. He brings up some interesting points. Last time Will dynoed his car he was at 313 whp.

Which Spark Plugs Should I Run?

Give me a spark plug 101

A spark plug has two main tasks: to ignite the air/fuel mixture properly, and to remove heat from the combustion chamber to maintain an optimal temperature.

Platinum, some hear that word and think BAM these are premium plugs. What makes platinum different? Well the answer is in the design of a platinum plug. So lets start there.

A spark plug'* firing task is to transfer electrical current or "spark" between a power and a ground electrode to ignite the air and fuel mixture. We want this spark to be powerful, to promote a nice clean burn of the mixture, as this will promote the best efficiency and therefore the most power. Now imagine two spheres electrically charged, hold them closely together and you'll see spark jump across it. Now try and separate them and you'll see the spark disappear. NOW try this with two sharp pointed electrical rods and you'll see you can hold them further apart and the spark will still jump between them. What does this mean? Sharp points will transfer the spark the most effectively. Ever notice the tip of the spark plug and how most platinum plugs are sharp tipped center electrodes?

Sharp tips are all well and fine, but thats a hot environment down there. Infact the biggest problem is withstanding the heat. A sharp center electrode will get very hot, this promotes easy ignition (less charge to spark the plug) and a clean running plug free of deposits, but try this with a standard copper plug and it'll melt! Platinum has a much higher melting point than copper which is used on the classic style spark plug, thus the tip can be sharpened like it is. Iridium is the new guy on the block; same thing, it has an even higher melting point, thus the tip can be sharp. Now a copper plug needs to have a wide body to disperse the heat over a larger area so its tip can run cooler. Now did that set off any light bulb on where that would be beneficial? If you said forced induction or nitrous applications, pat on the back! In applications where you want to minimize existing heat in the combustion chamber, platinum may not be a good thing.

Here is another stick in the spokes of the platinum bandwagon wheel: Platinum does not conduct electricity very well. Platinum was chosen due to its resistance to heat and erosion, however it conducts electricity about a third as well as copper. The new iridiums are an attempt to find a metal with similar heat and erosion resistance as platinum but better conductivity of electricity; however, iridium is still only about half as good a conductor as copper, iridium plugs are one of the best marketing tools for spark plugs today and nothing more in the authors opinion. Now this disadvantage of platinum is offset to an extent by the ease of firing that platinum plug design offers, with its sharp pointed tip. Whether a copper plug can produce as much spark energy with a smaller gap however, than a platinum counterpart with a wider gap, is a good point of debate. The author’* viewpoint is yes.


Before I read further, what plug do you recommend for my application?

My recommendation for GTPs is to use a copper Autolite plug whenever possible. Copper runs cool, will perform better than exotic metals in my experience, should last its user about 2 years, and best of all are inexpensive.

For a stock pullied car, if you are unmodified and looking for a maintenance recommendation for plugs rather than a performance one, look for Autolite platinums which are part number coded AP for platinum and APP for double platinum at the very beginning of the part number.

Non-intercooled:
3.8” factory: Autolite 605 @ .055-.057” gap (or AP605/APP605 platinums @.060”)
3.4-3.25” pulley: Autolite 104 @ .052-.054” gap
3.1-3.0” pulley: Autolite 103 @ .047-.050” gap
2.9-2.7” pulley: Autolite AR94 (4 range colder race plug) @ .044-.046”

Intercooled
3.25-3.0” pulley: Autolite 104 @ .050-.052”
2.9-2.7” pulley: Autolite 103 @ .046-.048”
2.6-smaller: Autolite AR94 @ .044-.046”

My recommendation for GTs is to again use a copper plug for performance since I have found them to perform as well or better than most exotic metal plugs, however platinum/iridiums can be used for longevity without the risks associated with GTPs.

Maintenance/Mileage:
Stock heat range platinum/Iridium @.060” gap

Performance:
NGK TR55 V-Power copper @.055” gap


Why does the author not recommend platinums in a GTP, aren’t they better?

Better? No, not in my book. And there is a good reason I recommend not using platinums in a supercharged application, and that’* because they run HOT. The small platinum tipped plugs are designed to run very hot to promote easy firing for mileage and emissions at idle and low vehicle speeds, along with erosion resistance so the owner of the car can neglect its maintenance for 100,000miles (yes, neglect is IMHO the appropriate word here!). These reasons are why they are considered better, but now that you know the whys, you know enough to make a judgement call for your own application.


Why do we step down heat ranges?

With a supercharged motor, the process of adding boost also adds heat to the incoming air. This is a normal byproduct of compressing the air. By running 10psi of boost from an M90 on a 3800, with pulley sizes anywhere from 3.8” to 2.7”, we are also adding 170-320F temperatures to the inlet air.

One of the spark plug’* functions is to remove heat from the combustion chamber, contrary to whatever you may have heard about spark plugs adding heat. We can use this function to remove or counter balance the heat which we are adding to the combustion chamber from the supercharger. By fine tuning the heat range of the spark plug we use, we can ensure an optimal temperature in the cylinders for proper combustion without pre-igniting the mixture from excessive heat.

Techie Note: The heat range of a spark plug is varied by the amount of the center body exposed in the plug; think of it as a mountain and the center electrode as its peak, the higher the mountain the hotter the plug. The shorter the mountain, the shorter the distance for heat to travel through the spark plug body and disperse into the cylinder head, the colder the plug.


How many heat ranges should I step down with my L67/L32 supercharged motor?

This will vary greatly on what pulley size you run. By going smaller and smaller to keep boost levels up, we are adding more and more heat by spinning the supercharger faster, even though we’re running the same amount of boost. As such, pulley size is a good basis for choosing a spark plug.

Stock pullied cars may find it beneficial to step down up to 1 heat range in plug, even without any mods. But many can also stick with stock heat range, since we assume if you’re running such a large pulley still that you are not entirely interested in any additional horsepower

3.4-3.25 pulleyed cars should step down 1-2 heat ranges, 3.1-3.0 2-3 heat ranges, and any 2.x” pulley sizes should really be running a race-engine-bread 4 range colder plug as offered by NGK and Autolite.

If you have an intercooler, you should step down one heat range less than normal. So if you were running a 3.0 before the intercooler on a 3 range colder plug, step up to a 2 after the IC. If you were running a 2 range colder plug on a 3.25 before and are moving to a 3.0 after the IC, you should be able to run the same plug. Reason being is that the intercooler drops the inlet air temperatures, thus less is needed to be removed from the combustion chamber with your plug selection.


Should I step down in heat ranges with my L36 non supercharged motor?

Under most circumstances, you should not be forced to step down heat ranges in your GT. As power is added onto a naturally aspirated motor, there are very few modifications that tend to add combustion heat (advancing timing through a PCM reprogram comes to mind though) and many which tend to help lower combustion temperatures (cold air intakes, free flowing exhaust systems). Once you have the right balance of modifications, your combustion temperatures should be relatively unaltered from factory. At most I would step down 1 heat range but only as needed.

Note: If you are having knock problems in your GT, especially after a DHP, you absolutely must ensure you are running a high octane fuel. Premium fuel is the FIRST step to combating cylinder heat, which is added from increased ignition timing. It should also be assured you are not running too lean, and that your engine is free of carbon deposits by running fuel injector cleaner regularly, using clean fuel from Sunoco or Pioneer, or best yet from a Motovac injector flush. Also, running colder spark plugs in an attempt to run lower octane gas with your DHP is a practice the author whole heartedly opposes, it is NOT a sound, safe or smart tuning practice and more trouble than its worth.


Why does the gap decrease as the plug heat range goes down, whats the link there?

The reason for the decrease in plug gap is in relation to the pulley size being run, not necessarily the plug itself.

First off, I think its unwise to run a copper plug at anything over .055” without a very powerful aftermarket ignition control box, so all copper plugs I recommend that gap as a maximum.

As you step down in pulley sizes, more air is being moved into the cylinders as more power is being made. This results in an increase in pressure in the cylinders on the compression stroke. It’* the author’* belief that more power is lost from incomplete combustion from a wider gapped plug than most realize. Due to the rise in pressure, it makes sense to decrease the plug gap slightly to correspond, to ensure good combustion for more power, and even less knock retard in some instances in my experience. Wider is not always better.

Keep in mind that if you want to run a wider gap, upgraded ignition wires can ensure that you can run as close to .055” as possible. With an MSD Digital+4 ignition box, gaps as wide as .070” have been run successfully on a GTP.


Is there any way to increase performance, using spark plugs?

Unlike the kid who rushes out to buy “race” plugs cause he assumes there will be a power increase, there are ways to increase your performance with spark plugs BTW race plugs are usually just a very cold heat range, nothing more.

First is to “index” your spark plugs. What this means is you want to install the spark plug so that the direction of the open gap faces towards the center of the combustion chamber or towards the exhaust valve. Due to quality control with the threads tapped into the cylinder heads and the threads on a spark plug, it is not always a guarantee that the plug will be properly oriented to achieve this when installed. We can achieve this by using indexing washers from companies like Moroso; you want tapered seat washers, they will come in a pack of 30 (10 each of 3 different thicknesses), approx cost of $30CDN whether you buy locally or from the states.
Tape or mark the spark plug socket where the ground electrode sits and screw it into the head, note the position of the mark. If it is between 5 and 7 oclock, torque it down to 11-18ft-lbs. If it is not, try another plug to be sure it is the head casting and not the plug causing it, and if the results are the same, follow the instructions on the package to install the appropriate washer to rotate the plug’* orientation counter clockwise (will usually be 90-180-270degrees). Once achieved, torque the plug down. Repeat on the rest of the cylinders. Note that it is usually the cylinder head casting that causes plug misalignment, thus that cylinder will require the same indexing washer each time you install a new one. If only 2-3 washers are required of the 6, keep the others handy as they can be used for multiple plug changes in the future.

Another trick is to “backcut” the ground electrode. On a copper plug, you want to position the tip of the ground electrode so that it is over the first 1/3 of the center electrode body and no more, and it can be as far out as the edge of the center body if longevity is unimportant (Plug should still last 10,000kms or more). This will normally require shortening the ground stap by filing or cutting it; be decreasing its length you are also decreasing the amount of time it takes for heat to transfer from it to the head and reduce its temperature as that ground electrode can get red hot and be a source of pre-ignition. If you buy Autolite race plugs or NGk V-Power TR5 (not TR55s) or TR6s, you will notice its already got shorter ground staps, and in the case of the Autolites a wider ground electrode for better transfer of heat.

A final trick is to file smooth the sharp ends of the ground electrode to make a smooth U shape, and also the sharp edges ontop of it. These sharp edges are the greatest sources of heat; by smoothing them you create a more uniform dispersal of the heat in the stap, making for a cooler operating temperature. This is again important, since they get so hot and can be a source of pre-ignition. Do not smooth the underside however, you want to retain the sharp points there since they are what the spark energy wants to jump towards.

Keep the rest of your ignition system healthy. Good quality ignition wires will ensure the energy from the coils reaches the plugs. And the coil terminals should be kept in good shape, aluminum will oxidize and brass will tarnish with time so inspect them regularly to ensure they retainer their shiney finish. A brilo pad will clean them up if tarnished, but ask the wife first or better yet spend the $2 and get one for yourself!

Finally, change your plugs often. You would be amazed at the performance gained by changing copper plugs once a year, it’* a harsh environment in there and dull edges and deposits can greatly diminish spark energy over time.


Disclaimer: This information is to be used as reference only. Its author is not responsible for any negative effects that may occur as a result of using the methods provided in this guide. He is however hopeful that it has been helpful in selecting the right spark plug for your 3800.

Cheers,