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Old 09-04-2007, 01:58 PM   #1
XtremeVette
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Default Spark Plug Gap?????? 40? 50? 60?

Ok what is up with the spark plug gap for the LS1 engines. I have an 02 and right off of advance autoparts website lists like 3 different gaps for the same car! Depending on maker it can be .040, .050, or .060

A little advice here....I am going to go with the AC Delco Iridium's and they say, they come pre gapped at .040

Thanks Guys
Jeff
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Old 09-04-2007, 02:04 PM   #2
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The AC Delco 49-145 Iridium plugs are CORRECTLY pre-gapped at .040 so check them, but they should all be fine.

The Irridium plugs use a smaller gap than the Platinum plugs did. They work great.
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Old 09-04-2007, 04:36 PM   #3
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what about NGK TR55? whats the proper gap for those? and whats teh stock gap size?
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Old 09-04-2007, 04:37 PM   #4
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I believe the last digit of the NGK part number is the pre-gap. I think it is 0.055 but don't quote me on that. The first "5" is the heat range. It is also a copper plug.
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Old 09-04-2007, 04:41 PM   #5
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I recently put the iridium plugs in my 02 Coupe. Everyone here said they come gapped at 40, mine were 44 but I put them in and it runs great. Here's my question. I always thought the biggest gap the ignition system could handle was best. My old ones were 60 and the new ones 44. I can't tell any difference. Any ignition experts want to jump in here?
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Old 09-04-2007, 04:42 PM   #6
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Default Iridiums are .040 but check them anyway

Quote:
Originally Posted by BlackZ06 View Post
The AC Delco 49-145 Iridium plugs are CORRECTLY pre-gapped at .040 so check them, but they should all be fine.

The Irridium plugs use a smaller gap than the Platinum plugs did. They work great.
You have the right answer but the wrong part number. It ends with either 185 or 195. need a price check here at aisle 2. BIGHANK
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Old 09-04-2007, 06:16 PM   #7
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Quote:
Originally Posted by vettenuts View Post
I believe the last digit of the NGK part number is the pre-gap. I think it is 0.055 but don't quote me on that. The first "5" is the heat range. It is also a copper plug.
That's the correct gap for the TR55s.
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Old 09-04-2007, 09:32 PM   #8
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I put Iridium 41-985 plugs in my 2000 vett.
I don't know if the plugs are the same for the 02.
They do come pre-gapped at .040, but I have read they should be gapped at .042. Is this true?

I also put red performance wires in my. I am very happy. I did make a difference.

Good Luck
C T 00
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Old 09-04-2007, 09:38 PM   #9
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The plug gap is determined more by coil output than anything else. If your ignition system can handle a larger gap and therefor put out a more robust spark, go for it. The coil will only put out enough spark to jump the gap, no more.

The LS1 ignition can handle a larger gap. The denso plugs I pulled had a gap of .060+. I put the AC iridium plugs in my 01 and opened the gap to .050. The car runs perfect.
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Old 09-05-2007, 02:37 AM   #10
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Quote:
Originally Posted by Chevy Guy View Post
The plug gap is determined more by coil output than anything else. If your ignition system can handle a larger gap and therefor put out a more robust spark, go for it. The coil will only put out enough spark to jump the gap, no more.

The LS1 ignition can handle a larger gap. The denso plugs I pulled had a gap of .060+. I put the AC iridium plugs in my 01 and opened the gap to .050. The car runs perfect.
Note that the AC Delco website (and other references) tell you NOT to change the gap from the factory set .040 (web reference below)

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Originally Posted by bighank View Post
You have the right answer but the wrong part number. It ends with either 185 or 195. need a price check here at aisle 2. BIGHANK
Goes to show what happens when I don't put on my reading glasses and type before my first cup of coffee .... 41-985 is the correct number ... from the AC Delco website .... http://198.208.187.182/internet/Vehi...e=25&part=7212

Quote:
Originally Posted by Plasticfan View Post
I recently put the iridium plugs in my 02 Coupe. Everyone here said they come gapped at 40, mine were 44 but I put them in and it runs great. Here's my question. I always thought the biggest gap the ignition system could handle was best. My old ones were 60 and the new ones 44. I can't tell any difference. Any ignition experts want to jump in here?
I'm not an expert ... but I did stay at a Holiday Inn last night .... the gap is determined by several things .....

The larger the gap the higher the voltage needed to "jump" it ... which means the coil needs longer to generate the required power. If you had a 10 foot gap, you'd need to generate a thunderbolt to jump it ... by going with a smaller gap, the spark fires closer to the time the PCM requests it.

In the "old" days a larger gap meant a "better" (hotter) spark to light off the fuel/air mix. Today, engines run much "hotter" than before. The fuel is very close to lighting off even before the spark is fired. It doesn't take much to start the fuel burn, so a smaller gap is sufficient.

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Old 09-05-2007, 09:20 AM   #11
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Good info !!
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Old 09-05-2007, 10:47 AM   #12
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Quote:
Originally Posted by BlackZ06 View Post


I'm not an expert ... but I did stay at a Holiday Inn last night .... the gap is determined by several things .....

The larger the gap the higher the voltage needed to "jump" it ... which means the coil needs longer to generate the required power. If you had a 10 foot gap, you'd need to generate a thunderbolt to jump it ... by going with a smaller gap, the spark fires closer to the time the PCM requests it.

In the "old" days a larger gap meant a "better" (hotter) spark to light off the fuel/air mix. Today, engines run much "hotter" than before. The fuel is very close to lighting off even before the spark is fired. It doesn't take much to start the fuel burn, so a smaller gap is sufficient.

Thanks, BlackZ06. That explains a lot (I need to find one of those Holiday Inns ). Sometimes I keep my mind busy by dreaming up all kinds of weird questions about car stuff. Part of the problem is my experience is mostly with older vehicles. Do you remember magnetos in race cars?
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Old 09-05-2007, 01:13 PM   #13
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Quote:
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Thanks, BlackZ06. That explains a lot (I need to find one of those Holiday Inns ). Sometimes I keep my mind busy by dreaming up all kinds of weird questions about car stuff. Part of the problem is my experience is mostly with older vehicles. Do you remember magnetos in race cars?
LOL ... Sure do .... quick funny story ... a couple of years ago a friend-of-a-friend invites us to take a flight in his single engine Piper Comanche. He opens the engine cover to do his pre-flight, and I'm looking over his shoulder when ... WTF ... are those TWO magnetos in there? He laughs and says "you're the first non-pilot I've met who knew what those are". Apparently magnetos are still common in the piston engine aviation business ... who'd a thunk it ???

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Old 02-20-2008, 12:21 PM   #14
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Originally Posted by Last C5 View Post
That's the correct gap for the TR55s.
Whats the difference in the NGK TR55 and the NGK TR55s?

Any?
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Old 02-20-2008, 02:16 PM   #15
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Quote:
Originally Posted by MACKASH View Post
Whats the difference in the NGK TR55 and the NGK TR55s?

Any?
"TR55s" I meant a set of the TR55 plugs, the s was just a plural.
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Old 02-20-2008, 06:53 PM   #16
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I put in a set of NGK TR55 in my LS1 Firehawk and they work great. At first I thought oh man that gap is too big but I didn't have a good gap or feeler gauge so I just put them in and it works great.
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Old 02-20-2008, 07:20 PM   #17
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Speaking of spark plugs, I removed one of my plugs for inspection this past weekend, as my car has some 59,000 miles on the clock. The wear appeared neglible but I noticed that the plug was non OEM. I purchased my '99 FRC in '01 with about 18,000 so, evidently, the previous owner changed the plugs.

Now the interesting part. The plugs are: NGK PTR5C-13. I have not seen this show up as a recommended plug? Is this perhaps an obsolete plug designation?

Thanks,

Jason
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Old 02-21-2008, 01:58 AM   #18
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Quote:
Originally Posted by j curtiss View Post
Speaking of spark plugs, I removed one of my plugs for inspection this past weekend, as my car has some 59,000 miles on the clock. The wear appeared neglible but I noticed that the plug was non OEM. I purchased my '99 FRC in '01 with about 18,000 so, evidently, the previous owner changed the plugs.

Now the interesting part. The plugs are: NGK PTR5C-13. I have not seen this show up as a recommended plug? Is this perhaps an obsolete plug designation?

Thanks,

Jason
According to NGK you have a
P = Premium Platinum
T = tapered seat
R = Resistor type
5 = heat range about the same as the TR55
C = Special design firing end
13= plug gap of .052

If it's not a recommended plug, it's sure close.
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Old 02-21-2008, 07:17 AM   #19
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Thanks there "Last C5" - very informative.
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Old 03-03-2008, 11:40 PM   #20
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Quote:
Originally Posted by j curtiss View Post
Speaking of spark plugs, I removed one of my plugs for inspection this past weekend, as my car has some 59,000 miles on the clock. The wear appeared neglible but I noticed that the plug was non OEM. I purchased my '99 FRC in '01 with about 18,000 so, evidently, the previous owner changed the plugs.

Now the interesting part. The plugs are: NGK PTR5C-13. I have not seen this show up as a recommended plug? Is this perhaps an obsolete plug designation?

Thanks,

Jason
Check this out:
http://forums.corvetteforum.com/show....php?t=1771192
He was the original owner of a '99 FRC and it had the NGK PTR5C-13 plugs in it, too.
I just changed the plugs/wires in my daughters' '99 coupe we bought in 2003 with 40K miles and they were...NGK PTR5C-13 spark plugs.
Obviously, GM used those plugs for OEM installation, I'm sure the previous owner didn't replace the plugs in your car or ours. Now for the best part, he had 110K miles on his plugs and we had 118K miles on ours and they still looked good...if I had known they were in such good shape, I would have left them alone until at least 150K miles maybe 200K. The original spark plug wires are the "spiral core" design with very low resistance and were also in excellent shape. As the miles pile up on this car, it's becoming more and more apparent that it's an easy 200K mile engine with only oil and filter (air and oil) changes. I change the oil strictly IAW the DIC and never before. Yours is still a baby at 59K miles.

PS Yes, we've had the harmonic balancer (once) and oil pressure switch (twice now as of last month) issues and I replaced the water pump and idler pulleys/tensioners last September. Only $400 in engine repairs in almost 120K miles is excellent as far as I'm concerned.

Last edited by glass slipper; 03-03-2008 at 11:59 PM.
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Old 03-03-2008, 11:40 PM
 
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