Spark plug gap - Why so big? - Z06Vette.com - Corvette Z06 Forum
 
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post #1 of 9 (permalink) Old 08-04-2003, 01:49 PM Thread Starter
Slythetove
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Spark plug gap - Why so big?

I was working on a friend's modified 2002 Z06 this weekend, and changing his plugs. He was having a miss and I found one fouled and one heavily carboned (#7).

When I checked gap they were between .055 and .058 on NGK TR55 plugs.

MTI did loads of headwork and he has headers / full exhaust all the bolt ons. He's made a best of 441 rwhp, so it's pretty heavy mods. I think he's running about 11.5:1 compression. Sorry I don't have the exacts, but from what he says that's pretty close.

Anyway... in the 2003 Cobras most guys like myself are running about .040 on the plugs (NGK TR6), and the modded guys over stock boost are running sometimes as low as .035 on the Denso Iridiums IT 20 or 22. Running a gap of .060 like you guys are from stock would never work. It would blow out way too easily.

So why such a large gap on the 'vettes? Don't you guys worry about blowout once you have heavy mods?

I put the new ones in at .045 (ACDelco was only available). The miss was cured, and I'm thinking he should go with Denso IT 20 at about .040.

Am I way off? Why or why not?

Thanks in advance.
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post #2 of 9 (permalink) Old 08-05-2003, 01:55 PM Thread Starter
Slythetove
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Nobody knows why the 'vettes run such a large gap?

Am I in the wrong forum? Just need some input here guys.
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post #3 of 9 (permalink) Old 08-05-2003, 03:03 PM
DJWorm
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The out put of the individual coils is relatively high and the resistance of the wires is relatively low....so there is a pretty high powered spark available....there for you can have a bigger gap.

The big gap and high output helps the "fast burn" characteristics of the head and aids flame front travel. Ergo increased HP and Tx.

Although the coils are ugly....thay are so good that no aftermarket Co. has been able to produce a better one(s).

I just went to one of my reference books to make sure I knew what I was talking about and in fact "This sytem delivers 100% more amps at the plug", thats 2X the energy, than a previous and comparable coil with long plug wires.

Now....if you Turbocharge, Supercharge or increase the compression....then you may need to shorten the gap slightly.

Last edited by DJWorm; 08-05-2003 at 03:13 PM.
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post #4 of 9 (permalink) Old 08-05-2003, 03:07 PM Thread Starter
Slythetove
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Thanks for the reply. He's definitely running increased compression.

He says about 11.5 : 1

MTI spent 40 hours hand working his heads.

Do you think .045 is about right at that compression?
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post #5 of 9 (permalink) Old 08-05-2003, 03:28 PM
DJWorm
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My gut is telling me that 11.5:1 NA would work fine wiith 0.050.

That is if you are using a quality gasoline. In that engine I would make sure I was running Sunoco Ultra 94 on the street and for track work I would run the Sunoco GT100 unleaded race fuel.

Not only is the GT100 higher octane but has a better race additive package, is oxygenated and has a better vapor pressure.

I would also drop in a bottle of Chevron Techron fuel additive and FI cleaner every 10,000 miles.

If he is fowling plugs I would consider looking at the plug heat range and timing.

I would also run Magnecor KV8.5 Race Wires and Beru Silverstone plugs at the very least. These plugs are Silver tipped which is actually better than iridium or Platinum. Nology has them.

I might also consider the Nology wires for this car, but only after I tried the Magnecor.

I just saw a new reference on their website for the Nology "Hot Wires" which dyno'd a +11 HP on a stock LS1.....results released in July Corvette fever. That's right +11 HP on just the wires.

www.racegas.com
www.nology.com

Last edited by DJWorm; 08-05-2003 at 03:40 PM.
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post #6 of 9 (permalink) Old 08-05-2003, 03:31 PM Thread Starter
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He's running some race gas mix. I think 1 part race to 3 parts 93 octane. I'll get more specifics.

There was only one semi fouled, and the number 7 was extremely carboned.

I'll try to get some pics.

Thanks for the info so far.
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post #7 of 9 (permalink) Old 08-05-2003, 06:10 PM
Black_Magic
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I was running NGK TR55 @ .055 with no problems.

I added Blower and started getting spark blowout bigtime (misfires). Switched to a cooler plug TR6 @ .035 and now everything in the spark area is COOL.

Just pulled plugs after 300 miles and all burning (light gray) equally.


Click on images below for more info

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post #8 of 9 (permalink) Old 08-05-2003, 11:26 PM
Jason99T/A
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If your friend is running 11.5:1 compression, I would definitely look into running the NGK TR6 plugs gapped at .045". In all the motors in my Trans Am, this is where I have run them at with no issues. I would definitely swap to the cooler TR6 plug in that application.

Jason
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post #9 of 9 (permalink) Old 08-06-2003, 06:24 AM Thread Starter
Slythetove
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That's pretty much what I was thinking, but wanted to check with you guys.

Anyone else?

Thanks for the replies also.
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