I installed Bosch Plus-4 plugs on my '97 GTP years ago and noticed a significant decrease in KR (hooked up an Autotap with a friend monitoring it as I drove) over the stock plugs. I have a 2000 GTP now and was considering using them again, but the local Pep Boys actually has a note in their parts system that says "FOR NORMALLY ASPERATED ENGINE ONLY" and wouldn’t sell them to me - any ideas why the change?

I've been out of the GTP arena for a while and haven't heard anything about the NGK Iridium plugs - would these be considered a top-end plug? How about plug wires? Any suggestions would be appreciated.

pardon my ignorance here fellas...I'm assuming that "KR" has something to do with spark knock or preignition...what exactly is "KR" standing for?

This came up a few weeks ago. Your best bet is just to use OE plugs and wires. The updated AC plug for your car is an iridium, which is what all the newer ones are getting when built. I wouldn't mess around with anything else.

KR= knock retard. Microphones placed in the block listen for a frequency associated with knock. When the PCM sees that frequency it starts retarding the timing effectively taking power away. Too much KR and your mods are useless. CAI/FWI, 180 and colder Tstats, colder range spark plugs, free'r flowing exhaust, Inter cooling all help to prevent the dreaded KR. To see just how much KR you are currently experiencing you'll need either the autotap or LS1m scanner.

thanks for the informative answer...I can see how this would be a huge issue with a pressure fed engine...so in reference to the earlier post, you're saying that multi prong plugs actually increase the chances of detonation thereby giving you a greater KR?...which means bigger power loss due retarded ignition timing.

AC Delco's 41-101 sell for $6. ea.

exacta mundo!!! Most people run the Autolite 104s(one heat range colder)($1.99 a pair at walmart)To help with the dreaded KR. Only bad thing is you gotta pull em every oil change and recheck the gaps as the copper tends to wear easy.

Now here's the magic question: What's the best gap?

I changed mine to the AC-Delco iridiums that the new ones come with and I kept the factory gap - .60

does anyone use any kind of platinum plug with a standard gap? I think the platinum plugs would wear longer.

People run anywhere from 55 to 60 for the gap. As for the platinums. Most platinum plugs have small pieces of platinum on the electrode and cathode. The platinum pieces could create hot spots causing knock retard for us S/C'd peeps tryin to run a smaller pulley.

Hey guys...how about the new NGK non-iridium V-Drive plugs with the "V" cut into the resistor..are these any good?..do they actually lower the energy required to fire the plugs?..what will I be gaining here in the way of fuel efficiency or gas mileage??..