NGK TR55 spark plugs
Team Owner
Joined: Feb 2001
Posts: 27,254
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From: Short Hills, NJ
You may be thinking of the NGK TR6 plugs? Often used for nitrous and FI applications.
They're in my LS1 Z28 and they will be what goes in my LS2 C6 when the time comes as well. 
They're in my LS1 Z28 and they will be what goes in my LS2 C6 when the time comes as well.
Safety Car
Joined: Jun 1999
Posts: 3,570
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From: Austin, Singapore, Kuala Lumpur, Houston, Dallas, Hong Kong, Elgin, etc.. Texas
My LS2 with a Lingenfelter head/cam has the TR55. These were recommended by 21st Century Muscle Car. There was a thread a few months ago discussing the TR55 vs. TR5.
The difference is the TR55 is designed for a ~.060 gap while the TR5 is ~.040 gap. The GM specs for the LS2 shows the spark plug gap is .040.
I was confused by the NGK website which incorrectly listed the TR55 for the 2005 Corvette. I emailed NGK and they said the website was wrong. It should be the TR5 gapped at .040.
The difference is the TR55 is designed for a ~.060 gap while the TR5 is ~.040 gap. The GM specs for the LS2 shows the spark plug gap is .040.
I was confused by the NGK website which incorrectly listed the TR55 for the 2005 Corvette. I emailed NGK and they said the website was wrong. It should be the TR5 gapped at .040.
Race Director
Joined: Mar 2005
Posts: 11,549
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From: Southampton NJ
yes the tips are none to break off, the first rule of thumb when racing is to check your plugs and gap frequently, that plugs tr55ix are for the long haul. the tr55 is a cheaper to buy plug, so cheaper to replace more often, i gap at 35
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Safety Car
Joined: Jun 1999
Posts: 3,570
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From: Austin, Singapore, Kuala Lumpur, Houston, Dallas, Hong Kong, Elgin, etc.. Texas
FYI:
Here is what NGK wrote me regarding the gap procedure:
You do not want to change the gap on a plug more than about .008" from where it was factory set (welded) unless you will be changing the plugs every weekend (like in drag racing applications).
What happens is once the gap is moved beyond this point the inner surfaces between the electrodes will not be parallel and so the rate of misfires will increase and plug life will deteriorate very quickly. If you wanted a gap of only .035" you should use the TR5 plugs which would come factory set to .039". The TR55 plugs are factory set to .059". Hope this helps, thank you.
Best regards,
Brandon Peeler
Technical Support Representative
Team Owner
Joined: Feb 2001
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From: Short Hills, NJ
Race Director
Joined: Mar 2007
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From: Missouri City Texas
Interesting...didn't know that.
I always ran TR55s in my firebird and they were great. Switched to TR6s when I sprayed it and they were great too.
I'll be putting NGKs in the C6 when I swap the plugs out (probably in the next couple thousand miles....at 25K on the clock)
I always ran TR55s in my firebird and they were great. Switched to TR6s when I sprayed it and they were great too.
I'll be putting NGKs in the C6 when I swap the plugs out (probably in the next couple thousand miles....at 25K on the clock)
Safety Car
Joined: Jun 1999
Posts: 3,570
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From: Austin, Singapore, Kuala Lumpur, Houston, Dallas, Hong Kong, Elgin, etc.. Texas
According to the NGK technician communication I received, if you want a ~.040 gap use the TR5. For a ~.060 gap, use the TR55. Their advice also was not to vary more than .008 from the spec.
Last edited by Mez; Aug 27, 2008 at 11:39 PM. Reason: fix mistake
Safety Car
Joined: Jun 1999
Posts: 3,570
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From: Austin, Singapore, Kuala Lumpur, Houston, Dallas, Hong Kong, Elgin, etc.. Texas
It depends. The factors to consider are the other ignition components and engine mods. The physics are the denser the combustion chamber gases are, the more resistance thus the more volts/amps is necessary to get a spark across the gap. That is why its recommended to reduce the gap a few thousands when engine mods are done such as heads/cam, NOS, supercharger, or turbo when no other changes are made to the ignition system.
A car that runs fine at .040 but starts to misfire at .060 gap may be because of the increase in resistance and there is not enough volts/amps being delivered to the plug to jump the gap. There also maybe enough volts from the coil but there maybe leakage somewhere else in the high voltage circuit (wires). Electricity takes the path of least resistance. So an engine that runs fine at .040 gap may start to miss at .060 gap because of leaky spark plug wires to ground. Or the coil is not able to produce enough voltage to jump the gap.
In my case, I regapped the TR55 to .055 which was within design spec of the plugs. The car runs fine and according to NGK, this is ok. Otherwise, I could use the TR5 gapped at .040.
A car that runs fine at .040 but starts to misfire at .060 gap may be because of the increase in resistance and there is not enough volts/amps being delivered to the plug to jump the gap. There also maybe enough volts from the coil but there maybe leakage somewhere else in the high voltage circuit (wires). Electricity takes the path of least resistance. So an engine that runs fine at .040 gap may start to miss at .060 gap because of leaky spark plug wires to ground. Or the coil is not able to produce enough voltage to jump the gap.
In my case, I regapped the TR55 to .055 which was within design spec of the plugs. The car runs fine and according to NGK, this is ok. Otherwise, I could use the TR5 gapped at .040.
Le Mans Master<br><img src="/forums/images/ranks/5k-6k.gif" border="0">
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St. Jude Donor '08-'09
If I'm reading this right, a bigger gap is better as it provides a better start to the flame front prior to combustion. However, at some point the current can't jump the gap. That becomes the limiting factor.
If I got that right, I'd run TR55 at .060 and if I got misfires, I'd look at my wires and coils before giving up and going to a smaller gap.
Is that right?
If I got that right, I'd run TR55 at .060 and if I got misfires, I'd look at my wires and coils before giving up and going to a smaller gap.
Is that right?
Safety Car
Joined: Jun 1999
Posts: 3,570
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From: Austin, Singapore, Kuala Lumpur, Houston, Dallas, Hong Kong, Elgin, etc.. Texas
If I'm reading this right, a bigger gap is better as it provides a better start to the flame front prior to combustion. However, at some point the current can't jump the gap. That becomes the limiting factor.
If I got that right, I'd run TR55 at .060 and if I got misfires, I'd look at my wires and coils before giving up and going to a smaller gap.
Is that right?
If I got that right, I'd run TR55 at .060 and if I got misfires, I'd look at my wires and coils before giving up and going to a smaller gap.
Is that right?
In my research, I have yet to find any controlled tests that show the power difference between a .040 and .060 plug gap with all else being equal.
In my opinion, if there is a power difference, it would be almost unmeasurable. The more important issue perhaps is which gap has the least amount of misfires under the conditions the engine operates (coil output, wires, RPM, load, NO2, Supercharger, etc..)
There is also the consideration of emissions and fuel economy. In the mid 1970's, GM had to comply with new emission standards and went to the HEI ignition system, catalytic converters, EGR, lean mixtures so the plug gap went from .035 to .060. Remember, these engines were still running carburetors and no computer controls. The mixtures under light throttle were leaner and the bigger gaps probably help to reduce misfires. So, I am not sure it really has much of a power increase on today's unmodified stock engines.
Is there an automotive engineer out there that can shed some professional insight here?
Drifting
Joined: Feb 2007
Posts: 1,844
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From: Alpharetta Georgia
I have TR55's in mine. I wouldn't be worried so much about running these plugs on our cars. My Evo only had 2 coils that distributed power to 2 cylinders. It ran on 23psi daily and the spark plugs were a couple of heat ranges colder w/ a gap of .035. I never had any spark blow out issues with that car. Everything on the Vette's ingintion system is better and to back that up, I have had no issues at 477whp w/ spark blow out w/ my TR55's