Spark Plug Interesting Find

[BRIAN]

In my ever ending quest to extract an extra MPG out of my Suburban I found the following interesting info. The truck has every ignition piece replaced including the distributor with a DUI distributor. I did a quick test with about 5 different sets of plugs. First I noticed that each MFG has A different length that extends into the chamber which did not really seam to effect the running condition. Next I noticed a annoying sparatic miss with several of the sets of plugs. I pulled out my trusty OHM meter and was very surprised with my findings. I checked the resistence between the tip and the top of the plug. Besides the resistence being all over the board comparing different MFG'S I noticed that the exact MFG and model plug differed in resistence at a signicant level. Actually Bosh Platinum where the worst in the group. In a group of 8 that were boxed in groups of 4 the readings were incredibly bad anywhere from 3.4? to 8.6?. NGK had the lowest overall in the low 3's but were also different plug to plug. I then purchased a set of Autolite Platinum plugs (set #6) and was amazed. Every plug in the group of 8 were between 4.53 and 4.87. I started the truck and could not beleive the idle with ZERO other adjustments made. The tach is as steady as my Benz. Not a miss or hicup at all. Not bad for a truck with over 100k. I know a long ramble but hey if you have a free afternoon check out your plugs you might be surprised what you find. I also swapped the lower resistence plugs onto the cylinders with the longest plug wire routing to attempt to even it out even more. Hopefully I will be into 11-12mpg???

[Rick Dorion]

Interesting. I wonder if the Autolites would be consistent from batch to batch. Great info. Now I have something else to measure! I'm surprised at the effect though given the resistance of the wires themselves? I wouldn't have thought a few more ohms would matter. When you say 3.4, is the scale 1 or 100 or 1000?

[deadcarny]

I installed some basch 4 plugs in my lt1 car a few years ago and it ran noticably worse than with old plugs! I replaced them with AC Delco Rapidfires and it ran terrific. when I started using Nitrous, I always ran NGK or Autolite (depending on how quick I needed them since Autolite were available at wal-mart). Neither the NGK or the Autolite gave me any problems like the bosch did before! It was strange how a $1 plug was better than a $5 one. the expensive might last longer, but is it worth it if the car runs more efficiently with the cheap ones? you will definately save a lot more money with the cheaper plugs and better fuel efficiency!

Great info, Brian!

[gen3bu]

this is kind of off topic but oh well-
on the autolite platinums, is the outer porcelin as short as the bosch (header clearance)?

thanks
kevin

[malihoochie]

My Father is meticulous with darn near everything, and has put low resistance plugs w/ higher resistance wires for decades. I used to tease him - but his cars have always run hard. It proves that it does pay to sweat the details.

[gmachinz]

I did quite a bit of research a few years back on various spark plugs and the ones that I liked the best were NGK U-groove plugs. The multiple ground electrode plugs are purely gimmicky and they run worse on Cadillac Northstar engines than any other plug I've ever seen-it sends out random and multiple cylinder mis-fires codes as soon as you start the car! The reason they run so bad are two-fold: 1.) You have up to three other "hot-spots" for the engine to mis-fire from directly off the plug, and 2.)-electrical current follows the path of least resistance-so if one ground strap has a little more corrosion build-up thna the rest, that is where the spark is going to reach to. So their claim of consistent firing with multiple electrodes flies in the face of proven electrical data. I like NGK's in my race motors and AC Rapidfires in everything else-I only drive GM stuff anyway. I have yet to test the Denso Iridium versions yet,though-they're about $12 each though....yikes! -Jabin