Spark Plug Misfire???

Two weeks ago, I did a few test passes with my car... Ran great except for the traction sucked...

At the time I was running NGK R5671A-7 plugs gapped at .025

I had always run a -9 in my other cars because they are much easier to read, and I figured I would swap back... The -7's were given to me with the heads.

We went to the track yesterday with the -9's all gapped at .025 with nothing else changed.

Warmed up the car in the pits, pulled it up to the burnout box and as I brought the RPMs up it seemed to have somewhat of a miss... Didnt really think much of it. Staged the car, and went to make a pass... The thing missed like crazy... It only 60 footed a 1.37 compared to the usual 1.08 range. I got out of it after the shift to 3rd.

Went back to the pits, pulled the plugs and only one plug had any cadmium burned off of it... A couple looked like they were firing, but 4 of the cylinders looked like they didnt even fire. By the sounds of it, they wernt.

We went to put the -7's back in the car, but broke the starter and couldnt run for the rest of the day, so we wernt able to ensure that was the problem.

I am running a 498" BBC, Blown Alcohol, 20 to 25 pounds of boost, 10.7 to 1, with a 7-al2... I know I should have more spark, but it is what I have right now.

Does it sound like the plugs were the problem, and why would the colder plug not fire?

 

So you are saying the car was running fine before? Someone correct me if Im wrong, but 25 sounds like way too much gap. I have only heard of 14-18 on the gap....just a thought

 

I was thinking that was a pretty big gap... That is what NGK suggested, so I gave it a try...

But yeah, ran fine with the hot plugs... They may have had slightly less gap than 25, but pretty close

 

I would start there, that ignition may really struggle jumping that gap under pressure....Do you have a flowmeter on the car? A fat tune up will also cause this, i just went thru that.

 

plugs

We too run the NGK 5671's only we run the -10. We tried the -7 and -8's and both times had the same problem youre having. Popping and banging. Once we even blew the ceramic off a couple of them. We gap our stuff between 18 and 20. We tried to run the 7AL-2 and had no luck. Had to switch to a MSD10. Made a HUGE difference.

 

FYI lower the # hotter the plug, 10 colder than 9, we gap at .015.