Originally Posted by ZeeOSix

They are identical except for the gap from the factory. TR-5 is at 0.040" and TR-55 is at 0.060" out of the box. I guess you could gap either one to 0.050" ... as a +/- 0.010" change in gap is the max that NGK Tech Dept recommends.

Here's my dilemma. I've got a 2002 Z06 with the LS6. Owner's manual says to use ACDeclo Platinum 41-947, which are at 0.060" gap. GM came out with a Service Bulletin (03D-J-171, dated Dec 12, 2003) that said new spark plugs have been released for the 1997-2004 Vette (LS1/LS6), which are ACDelco Iridium 41-985, and to gap at 0.040" due to the new iridium tip.

Seems everyone likes the NGK TR-55 spark plug. These come with a 0.060" gap which is what the original plug gap spec was for the OEM platinum plugs in my LS6.

You guys think it would be OK to run the TR-55 at 0.060", or should I reduce the gap to 0.050"?

Does the tip design have a bearing on the gap that should be used? - sounds like it. I've also heard that a larger gap makes the coils work harder and could shorten their life span - any truth to that?

Originally Posted by LS6427

The only plugs I've ever used in my engine, when stock or my 427ci....are TR55 or TR5...whichever ones the store had in stock at the time.

I gapped them both to .050........runs perfect.

Gaps are stressed a little too much. I've tried gaps from .038 to .060 and everywhere in between.........my 427ci ran 100% IDENTICAL in every way....gas mileage, performance, starting, etc......NO DIFFERENCE.

Only time gaps start to get important is when you start passing 650 RWHP and/or Forced Induction or Nitrous....high HP stuff. Otherwise....NORMALLY ASPIRATED......doesn't really matter. Anywhere from .038 - .060....same ****.

Originally Posted by ZeeOSix

Thanks for the input ... I'll probably re-gap my TR55s down to 0.050" from their original factory gap of 0.060".

What has me a little confused is why did GM really change the gap spec for the 1997-2004 LS1/LS6 from 0.060" to 0.040"? The GM bulletin says because of the use of a different style of plug. But NGK's website application look-up tool now shows the required gap for all their plug types for the LS1/LS6 to be at 0.040". Guess 0.050" sounds like a good middle range setting.

Originally Posted by chrysler kid

Tr5's are on the verge of being over gapped at .050 We had a set in our trans am gapped at .055 and they mis fired like crazy.

TR55's are what you want.

Originally Posted by chrysler kid

Tr5's are on the verge of being over gapped at .050 We had a set in our trans am gapped at .055 and they mis fired like crazy.

TR55's are what you want.

Originally Posted by ZeeOSix

TR5s and TR55s are exactly the same plug except the factory gap is different; which means the ground electrode leg is slightly longer on the TR55 to give an even gap across the center electrode.

TR55s are supposed to be factory gapped at 0.060" ... so wouldn't they mis-fire like crazy too? TR5s are supposed to be factory gapped at 0.040".

I measured the TR55s I have and they were all at 0.056" out of the box. Maybe I'll just go trade them for a set of TR5s since GM and everyone now recommends 0.040" gap for the LS1/LS6 and be done with it.