The Dodge Challenger Message Board

Eddie, i think you might be the resident plug expert. Could you please let me know what you think of these plugs. I drove my 360 Chal to Sydney and back from the West coast (10,000km). I had the car dyno'ed in Sydney and the Thermoquad rejetted as it was a touch lean on the secondary jets. These pictures are of 3 different plugs taken on the return trip. I kept a steady cruise of 70mph for about 20minutes and then at that speed, cut the engine and coasted to a stop. I was told this was the best way to accurately determine the cruise mixture reading on the plug. They seem very clean to me, they still have a reddish tinge which may indicate a slight richness? I am not sure. Most of the colour is a light grey. Because of this i leaned out the cruise mixture 2 more turns. Fuel at the time was premium unleaded - 95 octane.

I would say you are either too lean or the plug is too hot.

Tha looks like a hot plug to me. Try a colder one and see if the colour improves.

Timing might be too far advanced too.

Not to bad but as Dave says it's a bit 'Hot' I see some specks on the insulator on the last pic? What is the timing total with vac. adv. disconnected at say 3500 RPM's? If you look at the ground strap carefully, you will see a distinct firing line on the ground strap,, it should be near the 'elbow' of the strap. If it's near the base/threads it's overadvanced. Near the tip/electrode area it's too late. I wouldnt change plugs until you sure the timing is where you want it too be. If it's centered near the 'elbow' or radius on the ground strap, then I would change to a colder plug as Dave says. But overall,,Ive seen a LOT worse!! Good job of almost getting it tuned to near perfection Steve But carbs suck--Injectors Blow!!

Guys thanks heaps for the analysis. If you reckon it is too lean, then its even leaner now as i leaned off the cruise screw (that very small screw in the centre of the TQ). As you know from the previous post, i thought i had too much advance. By my timing light, with 16deg initial it showed 30deg at only 1500rpm and well over 36 at 3000. That is without vac advance. So for the whole trip over i ran no vac advance. Bit sluggish off the mark but didn't seem to worry it. In Sydney the fellow who built my TQ convinced me to put the vac advance back on for the trip back because i was complaining of the poor fuel consumption and he said it should improve it. It was a bit more lively off the mark but fuel consumption only improved about 5%. I got a worst of 14.9, best of 19.2 and average around 17-18mpg. I didn't recheck the timing after i connected it, but i did back off the initial about 4 degrees. It has about 40+ total now. I will not be recurving that dizzy until i put the 340 back in. But i intend to run MSD anyway.

Ed, that firing line you are talking about... i am not sure if it is what i have arrowed in the photos? These plugs are taken out after coming back and some stop-start and slow driving. Look how red they are. The one on the far left was quite wet too.

As for plug heat range, they are NGK BP5ES. A 6ES or EY will be colder. However i was told that a warmer plug better helps combustion of leaner mixtures? Anyway, if the line in the pictures is what you are talking about, then it is near the electrode, and therefore too retarded by your opinion. This is hard to believe with around 40 degrees of total!

You should see a clear line half way down the ground strap right on the 90 degree bend where the strap is a different colour above to the one below.

I have had to switch to a colder NGK 6 to get my plug colour right in my high performance 440. There are some clear marks on my plugs last I looked. I will pull one out and take a picture.

Better still. I just remembered this was here.

http://www.4secondsflat.com/Spark_plug_reading.html

Thanks that's a very helpful burst on plug analysis. I see what they mean. I will have to have a closer look at the earth straps on all of them now. Amazing that so much can be seen just from the plugs. I wonder how old that site is - ie i was interested to see if they still sell that book they are advertising.

Yeah Don is still going.