theadmiral94

Hello all,

What gap do you use for these plugs?

Consider the following:

Original AC/Delco 41-906's (Platinum) call for 0.050".

NGK Website and manuals for TR55ix (iridium tip) specify 0.044" for our Vettes.

NGK website specifies and my plug gap gauge confirms the TR55ix are shipped with a gap of 0.059".

Confusing though is that the NGK website within their FAQ's advises "NGK doesn't recommend adjusting the spark plug gap < or > .008"."

So, whereas one might be inclined to reduce the gap from 0.059" to 0.044", that would almost double maximum adjustment recommended (i.e. 0.015 vs max of 0.008)?

Also supportive of the 0.044" gap, if I were instead replacing the plugs on our 2000 LS1, which originally called for AC/Delco 41-952 (platinum) and a 0.060" gap, with the currently specified AC/Delco plug, 41-985 (iridium), AC/Delco's website strongly specifies a 0.040" gap (i.e. "do not deviate from preset gap 0.040" "). Also NGK specifies the TR55ix with the 0.044" gap for the 2000 LS1.

Further supportive of the 0.044" gap is the NGK TR55ix (iridium) plug has a 4.6k ohm resistance, versus one old AC/Delco 41-906 (platinum) plug has 1.6k ohm resistance. Obviously, A smaller gap would be required with a higher resistance plug. Though, I must say the difference is much more than I would have expected, at least it is not the other way around, as it could overheat the coil.

So, what gap do you use?

And yes, I know I could use the TR55's, but I choose to use the ix's to get additional mileage out of the plugs (as I am not interested in removing the wheel or moving the ASR more often than needed).

BTW, Have you checked your spark plugs lately?

I never expected to find this -- 3 spark plugs on the passenger side were loose (able to turn them out by hand), oddly #8 was almost ok (perhaps the previous owner's 'mechanic' did not change that one).

Luckily, the head's threads seem ok. Also I expect to find loose ones on the driver's side too (based on a ticking noise and exhaust smells).

Further, I am hopeful that once the new plugs are installed and torqued properly (11 ft lb), the engine temperature will also be cooler.

I will post a follow-up on this issue once I complete everything.

theadmiral94

Hi All,

Last night I also sent an inquiry to NGK tech via their website, and am happy to report they were very responsive , and have already exchanged a few email's this morning.

They advised the following:

Set the gap at 0.050" to 0.051".

Honor their recommendation NOT to alter the gap more than 0.008, as it WILL cause mis-alignment and could cause faster plug wear, misfiring and poor performance, and raise the required voltage to fire the plug.

The difference in resistance between NGK and AC/Delco can be disregarded as it has very small effect on the output at the air gap.

Lastly, there may be a change on their website as to the recommended gap for the TR55's, as the 0.044" gap mostly applies to their ""laser series plugs (as they) are only offered in a 0.044" gap out of the box and are not recomended to be adjusted as the small center electrodes are easily damaged, and so that customers will not want to try and adjust or regap that series plug".

redwing76

Thats pretty interesting, but why NGK's?

I used Autolite standards. Good for 100k.
I use Autolites cuz they're a hotter plug than AC's, but AC's have always worked well also.

I do use platinums if its a OEM app.
Otherwise its a standard plug.

I know its the in-thing not buy American, but I do anyway.
Got any data to show that NGK's will outperform the factory OEM plugs?

theadmiral94

Hi Redwing,

Picked NGK's based on many other forum members touting them.

Also, I wanted Iridium, and AC/Delco does not have an Iridium plug for the car.

Reasons for Iridium are: the platium 'pucks' come off the AC/Delco Platinum plugs (have evidence of at least 1 out of 4 doing that), for our 2000 Pontiac TransAm and 2000 LS1 Vette, GM issues a service bulletin changing the recommended plug from Platinum to Iridium (possibly due to the pucks coming off too).

Honestly, I did not know they were made in Japan until after I bought them, as I too prefer to buy American.

As to performing better, no data, only other members on the Forum and all plug manufactures touting Iridium as better than Platinum.

Strick

I set my NGK IXs to .050 4 years ago and they seem to be running just fine.

redwing76

Good luck with them brother.

theadmiral94

Hi All,

update -- I started to worry about the difference in resistance between the OEM AC/Delco 41-906 and the NGK TR55ix, so I actually went to buy the AC/Delco's, but decided to test their resistance first.

I was surprised to find a new AC/Delco 41-906 had a resistance of 3k-3.5k ohms.

That is a substantial drop in resistance (over 50%) on plugs with only about 25k miles).

Further, the quality of the AC/Delco plugs bothered me (metal filings and some platinum pucks on the ground electrode was mis-aligned).

So, I am staying with the NGK's, and already have half of them in (the driver's side).

BTW, changing the driver's side plugs were almost the easiest I have ever done, once I removed the 3 bolts (1 in the car frame and 2 through the wheel well) and one electrical plug from the ASR unit and swung it (with cables still connected) out of the way.

theadmiral94

Hi All,

OK, all plugs are in and I did a 45 minute test drive last night. There is a definite improvement, power seems smoother, and mild reving of the engine seems quieter as if all cylinders are now firing evenly.

Further, coolant temperature now seems more steady and doesn't rise as much as before in same circumstances (e.g. at at light, at full temp of 194, only rose to 205, oil temp went only to 212, and both dropped to 194 and 204 respectively, after 4 miles more of driving at 40-50 mph).

How much of this is the NGK plugs versus the AC/Delco, and how much is just plugs properly gapped and torqued (i.e. no longer 3 loose plugs), is anyone's guess, but at least with the NGKs, I do not have to worry about loosing any of of their 'pucks'.

Regarding installation.

The driver side, after swinging the ASR out-of-the-way, IS VERY EASY. I was even able to get my 2' long 1/2" drive torque wrench on each plug with just a straight 3/8" driver 5/8" spark plug socket, 3/4" long 3/8" extension and the 1/2" x 3/8" drive adapter. Torque is 11 ft lbs (albeit I set it for 12 ft lbs to compensate for a slightly loose socket and a cheap torque wrench).

The passenger side is actually the more difficult side.

The forward most plug (#2), was relatively easy, in only required using the socket with a built in single knuckle swivel.

Plug #4 and # 6 were easy, and was able to use the straight socket on them.

All the above were easily torqued with a 2' long 1/2" drive torque wrench (remember to increase torque wrench setting 1-2 lb fts when using a swivel -- e.g. on plug # 2 I set wrench at 14 lb fts).

Plug # 8, now that's another story because of the air handler/ac/blower 'box' and the extra long bolts on the fuel line bracket and dip-stick bracket.

It requires small hands (which I thankfully have) and at maximum a short 3/8" drive ratchet and a straight 3/8" drive 5/8" socket.

To torque, would require a small 3/8" drive torque wrench (which I do not have nor could find easily). So, I 'guessed' the torque, after doing the other 3, to hopefully give me a feel for the correct torque.

So in summary, if you have done spark plugs on at least 2 cars in the past, do not fear, this car is no worse than most v8's.

Paul Workman

Plugs on the LT1...

Moving the ASR out of the way helps a lot on the driver's side.

#8 is a bitch from the top, no matter what. But, from underneath it is a piece o' cake - relatively speaking. (I wouldn't attempt to do it any other way!)

FWIW,

P.

oknahs

I just bought Bosch no gap plantinum plugs. Any idea on how they work on a LT1?

helphos

Hey, I know it's been three years since your post, but thanks for the tip on getting to No. 8 from under the car. I'm changing my plugs today -replacing the AC's with Bosh Platinum +4s. Looking at No.8 from above is scary.

I plan to take off the fender panel on the drivers side to do the odd ones. I'm assuming there are no tricks to getting it back on.
(Are any of the drivers side plugs easier from underneath?