We have probably been through this about a million times on this forum, but could someone please tell me what the best plugs are to use on my LT1. I always try to use at least 93 octane, but occasionally I have to use 92. The highest grade would be 100 lowlead (avgas) and as I don't have cats, there is no problems. The other thing I need to know is if I can bump the time without using a chip. I was a Ford person until the Vette came along, so that is really all I have to go by. Thanks for the help. :confused:

 

I would suggest you stick with the AC Delco's.
I'm the original owner of my '86 Vette, and I have never had a reason to go to another plug type.
I shift my gears at 6200 RPM, and change them out, about every 10K miles.
I do have an MSD-6AL Ignition Box...so I know this helps too.
What I've liked the most over the years, is how all 8 plugs read the same, in both appearance, and electrode burn.
I did have some concerns when I installed a set of Trick Flow Heads back in 1995...but the AC Delco's are still reading the same. :yesnod:

John

 

Either AC Delco or NGK.

 

:nonod: :nonod: I would highly recommend you do NOT use the stock AC Delco plugs that came with your '94. Unlike earlier years, the later C4s used AC double platinum plugs. Unfortunately, the little platinum "pucks" on the ground electrode like to disappear. One of my original plugs was missing its puck after less than 30k miles. On a replacement set, 6 of the 8 plugs were missing their pucks within a similar amount of mileage. These are supposed to be 100k mile plugs. :mad :

I would recommend any of the following: NGK TR55VX (platinum), NGK TR55iX (iridium), Denso IT16 (iridium, but $$), RapidFire 12s (a step cooler than stock), or a "regular" (i.e. non-platinum) plug if you want to save a few $ don't mind changing them.

You'll find that changing the plugs the first time is a B*tch 'cause you have to bond with the engine and learn the secret handshake before it'll tell you how to contort your arms, hands, and tools :D Even then, it'll still take an hour or two to change them.

 

1. AC Delco Rapidfire #14, $3.99 each at Autozone, or I know a guy selling them for ~ $10.49 + shipping for a set of 8 new in box. He's in Witchita KS

2. NGK TR55ix Iridium (NGK part #7164) $5.84/ea @ O'Reilly Auto Parts

3. Denso IT16 Iridium, ~ $10/ea on eBay (too costly for me but great plugs)

4. AC Delco 41-906 ~ $5.99/ea at Advance Auto parts or Autozone these are the OEM double platinum plugs.


Of the above, I would try the AC Rapidfire #14's. there is a product review on them from Hib Halverson, if you look in the forum product reviews:
https://www.corvetteforum.com/review...=461&TopicID=2

 

I run NGK TR6's and have no problems, I needed a cold plug for spray but I have no trouble with them :D

 

The original equipment AC dual platinum plugs commonly drop their rock hard electrodes into the combustion chamber. This can cause cylinder scoring and it adds about 0.030" spark gap which beats the heck out of the "already-weak" Optispark. Experienced GM LT1 mechanics see pucks missing all the time. I was missing several at 38K miles. My advice is to try a different premium plug. Autolite Pro's are very similar in quality & design but do NOT drop electrodes.

I would recommend an extended life double (full) platinum plug because the job is an SOB & swapping plugs can damage the ignition wires and ruin your weekend. Don't be fooled by single iridium or single platinum designs. Center electrodes and adjustable grounding electrodes BOTH erode which widens gap and results in wearout.

note:
-The AC Rapidfire #14 is a nice plug, but not extended life.
-The NGK with it's iridium center electrode has a conventional non-iridium grounding electrode that will erode just like any other $1.75 "single platinum" plug.

The Rapidfire and Iridium plugs are excellent choices, if you change plugs every 15K miles.

The Autolite Titanium Pro plugs are full (double) platinum AND they have a unique titanium coating that will NOT bond to the aluminum head threads which can cause thread damage or tear-out and helicoil nightmares. Tough to find...but at $5.80 ea, cheap insurance. Titanium does not migrate like anti-seize and it won't damage oxygen sensors. The LT1 part is Autolite ATI-606

http://www.monarchproductsinc.com/autolite.htm#order


[Modified by Rick93Z07, 9:22 AM 2/22/2003]

 

Very good/accurate advice given in regard to the A/C Delco plugs...they are garbage. :mad At 25,500 miles, mine were pulled for a tune-up, and at least 6 of the 8 were missing the pucks.

The shop that did the work put A/C Delco's back in the car :nono: . Well, after getting the story straight about what was going on with these plugs (thanks to the Corvette Forum), I am going to pull them and install the NGK TR55VX plugs before it leaves the garage for Spring driving. I have put 1,000 miles on the new A/C Delco plugs since the tune-up, but it would not surprise me if pucks were missing already.

I'll also be doing compression testing to see if there is any damage from these crappy plugs. They are not worth the risk, and I would NOT recommend that you install them in your car. :bs

 

When I removed the AC Platinum's at 27k when I bought the car, all still had their pucks. I put in a new set of the same, then learned of the puck dropping issue. I recently removed them after 6K miles and all still had their pucks. I put in the NGK TR55ix's at that point. I picked up a pair of the rapidfires cheap to try out sometime.

 

FWIW, I have never had any problems with the original single electrode Bosch Platinum plugs. I know they don't seem to be popular on this forum, but never any problems for me.

 

The stock AC Delco's work fine for me.

 

When I bought my vette last year it had the Bosch platinum tips installed in it too. They were trashed so much by people in here I replaced them with standard NON platinum tip AC Delcos...I could feel a definite difference and it wasnt a good one. I kept the Bosh plugs and will put them back in when I get the time. :blueangel:

 

I just pulled the original AC Delcos out of my 92 last weekend, all pucks were intact at 59,600 miles. The guy I bought the car from said they were the original plugs... but I tend to doubt that. I have had the car since about 33k miles, and it was the first time I changed the plugs, so I can tell you that this set lasted at least around 27k.

Changing plugs in the LT1s is a snap.... just jack the car up, remove the wheel, then remove just the back part of the inner-fender well. This allows you perfect access to 7 of the 8 with just a long 3/8 extension, a universal, and the socket. I only had to be a contortionist for the back one on the passenger side. I figured this out because I had to remove the fender well on the passenger side to get the hood popped after a broken hood cable.

I used Bosch platinums, and they are fine so far. :yesnod: