How much gap?

[skittleoncrack]

I just got some new plugs for my car. I couldn't find the NGK's I wanted anywhere so I settled for Autolite Copper I just wondered how much gap would be recommended.

I'm going to use the plugs for track only and use iridium for daily driving. I have an LS3 with K&N CAI, Cat Delete, Mufflers replaced with glasspacks, and a Nitrous Express 150-shot. Nitrous tune is set for 11.7 WOT AFRs. I'm thinking .35ish from what I've researched.

[hypurone]

You might want to rethink the copper and stay with Iridium, see #4:

3. Try to find a 'non projected' plug. The design of a projected plug will usually aid ignition performance at low engine speeds by moving the spark position closer to the centre of the combustion chamber, the downside of this is that the centre electrode and central ceramic insulator become exposed to combustion gases and hence are at risk of damage under extreme conditions. By using a non projected or even a retracted spark position, the firing tip is more protected and plug failure is less likely. A non projected or retracted plug by design will have a shorter ground electrode which is beneficial for the reasons mentioned in 2. above.

4. Use a non resistor or Iridium type plug if available. Please note if your vehicle manufacturer recommends a resistorised plug as standard we would not recommend using a non resistor plug, interference with engine and safety management systems may result! Some plug designs are only available with integral resistors. By using a non resistorised type plug, the amount of voltage available at the plug's firing end is slightly increased and therefore the risk of misfire under load is reduced. If combustion conditions are particularly extreme then an increased 'spark jump' voltage is required. Effectively, when more fuel and oxygen are compressed in the combustion chamber (as occurs in nitrous/turbo/supercharger use) the result will be similar to that of increasing the plug gap - if the gap becomes too large for the available voltage then the spark simply won't be able to jump the gap. Iridium spark plugs can help as they have a greatly reduced firing voltage (despite an integral resistor) - lower overall than most copper non resistor plugs. High performance ignition leads (such as Magnecor KV85 leads) can also help supply maximum available voltage to the plug.

and this from Edelbrock under the spark plug section:

SPARK PLUGS
The last frequently misunderstood factor in adapting a nitrous system to your engine is the spark plug. Three important aspects of spark plugs must be looked at: their heat range, reach and gap. We advise lowering the heat range of your spark plugs 1 step for every 100 hp added with nitrous. The other aspects of a plug that must be looked at are the reach and gap. It is best to use a non-projected type plug. Projected plugs allow a greater portion of the electrode to be exposed to combustion gases and possibly cause pre-ignition. The spark plug gap also plays a large roll in nitrous engine performance, because increased cylinder pressure from the additional nitrous and fuel makes it harder for the spark to jump the gap. The same gap that worked for a non-nitrous set-up may be too much for nitrous, leading to excessive misfires and loss of power. Also, we recommend that you do not use platinum plugs. The platinum tips can get extremely hot and will cause detonation. Plus, there is a chance the tip may break off in even cases of mild detonation and can severely damage the engine.
Ideally a gap between .025" and .035" should be used on high horsepower applications where an inductive style ignition system is utilized. Engines equipped with capacitive discharge ignition systems may use gaps larger than .035". It's very important to learn how to read the plugs after a pass. A plug can tell you a lot of what is happening in the combustion chamber. CLICK HERE to view spark plug heat ratings.

Edelbrock suggest an NGK Spark Plug with a heat range of -9 to -11 depending on the nitrous power level being tuned. When in doubt, always go to the next colder heat range plug.

and from Nitrous Supply.com:

Spark Plugs and Nitrous Oxide:
What Works, What Doesn’t, and Why
Over the years there seems to have been a great amount of technical material written about the simple operation of a spark plug and what they can do in relation to the way an engine runs. There are a few basic characteristics about spark plugs that you need to know to make an intelligent choice about the correct spark plug for your application.
First, and most important; a spark plug must be of the correct design to operate within the environment of your engine not the other way around. This means that the spark plug has virtually no influence on how the engine burns fuel or runs in general. The correct spark plug will simply survive the conditions present in your engine. A spark plug must maintain a certain temperature to keep itself clean. The wrong heat range can cause an overheated plug or a fouled plug. The heat range refers to the temperature 0f the ceramic material surrounding the center electrode.
Lean air/fuel ratios are more difficult to light because there are less fuel molecules in the area of the plug gap when the plug is scheduled to fire; thus, protected nose plugs were designed for late-model lean-burn engines. Modern high-energy ignition also allowed larger plug gaps. All the while this was happening, something else happened. Something that no one seems to have really noticed as the real culprit when the issue of factory type plugs being used with nitrous comes up. We’d like to clue you in.
Quite often, a factory type, wide-gap projected plug will produce a misfire condition after only a few seconds of nitrous use. The misfire is not due to the heat range. The misfire occurs because the ground strap of the spark plug becomes a glowing ember because it is too long to dissipate the extra heat produced by a nitrous-accelerated burn condition. The correct fix for this phenomenon is to replace the plugs with one that has a shorter ground strap. By doing this, you will shorten the path for the heat being absorbed by the ground strap. You can use the same heat range, you just have to find a non-protected nose plus with a shorter and preferably thicker ground strop.
If you only change the heat range of the spark plug to a colder heat range, you may very well still have the misfire problem. Since the length 0f the ground strap is the cause the misFire, a colder spark plug may have the same length of ground strap as the hotter plug you replaced it with.
Spark plug gaps should generally be .030” to .035”. Never try to gap a plug designed for an .060” gap down to .035’. Find the correct non-projected nose plug designed for an .035” gap.

[east TX Muscle cars]

get a plug made for nitrous or boost. one were the tip sets down into the plug more.
gap them to 35 for what your wanting to do.

[skittleoncrack]

I looked at the autolites and they weren't what i thought they were. The ground strap was way too long on them. I wish I could find a set of NGK V-Powers or the NGK Racing Competition Plugs but from my understanding there are no NGK plugs of any kind for LS3s.

[tylerSS]

Originally Posted by skittleoncrack

I looked at the autolites and they weren't what i thought they were. The ground strap was way too long on them. I wish I could find a set of NGK V-Powers or the NGK Racing Competition Plugs but from my understanding there are no NGK plugs of any kind for LS3s.

There are alot of NGK plugs for the LS3...actually i think most f/i guys are runnning NGK's.....look up the NGK BR7EF....thats what nitrous outlet recommended to me for a 150 shot

[Graham@N]

Originally Posted by tylerSS

There are alot of NGK plugs for the LS3...actually i think most f/i guys are runnning NGK's.....look up the NGK BR7EF....thats what nitrous outlet recommended to me for a 150 shot

Correct.

I also like to steer people away from Autolite's in nitrous street cars unless they themselves are sure there tune is 100% dialed in. This involves more than 2* per 50hp and then what a wideband tells you.

Which Autolite are you running?

[JANNETTYRACING]

Originally Posted by skittleoncrack

I just got some new plugs for my car. I couldn't find the NGK's I wanted anywhere so I settled for Autolite Copper I just wondered how much gap would be recommended.

I'm going to use the plugs for track only and use iridium for daily driving. I have an LS3 with K&N CAI, Cat Delete, Mufflers replaced with glasspacks, and a Nitrous Express 150-shot. Nitrous tune is set for 11.7 WOT AFRs. I'm thinking .35ish from what I've researched.

Why not just switch to the ZR1 Plugs and run them all the time?

[Graham@N]

Originally Posted by JANNETTYRACING

Why not just switch to the ZR1 Plugs and run them all the time?

What plugs come stock in the zr1?

[JANNETTYRACING]

Originally Posted by Graham@Nitrousoutlet

What plugs come stock in the zr1?

Colder version of the Stock LS3 plugs, AC-41-104

[Graham@N]

Originally Posted by JANNETTYRACING

Colder version of the Stock LS3 plugs, AC-41-104

I would not use that plug in a nitrous application. That is an AC equivalent of the Tr6 that NGK offers. While it was the plug to use at one time there are simply better option on the market now that are the same price and attainable at the same locations.

The AC-41-104 is a projected tip plug which is something we never run in a nitrous application regardless of the size shot, but especially once you go to upwards of 100hp worth.

Also that I would want a 7 heat range for that amount of nitrous.

While you can run the AC-41-104 and the TR6 in a nitrous application, the same tuneup with the correct plug (IMO) will open up the tuning window and also might save parts in the event of an issue or too aggressive a tuneup.