This is my suggestion, tighten up the spark plug gap to .025 and watch you voltage meter on the dash. My car used to have this problem and I determined it happened whenever I hit WOT from a hard launch at the strip. For some reason stock alternator would quit charging when the engine quickly accelerated in first gear. The voltage would drop to the high 11's and the engine would miss at high RPM. As soon as the engine would shift gears and drop RPM the miss would go away. To fix the problem I tightened the spark plug gap to .025 and the miss went away. So if my quirky alternator would quit charging at WOT high RPM first gear acceleration it would not misfire. Just in case someone asks the obvious question of why didn't you fix the alternator the answer is I would replace the stock piece of junk and within a few weeks the same issue would happen on WOT high RPM acceleration in first gear. I eventually replaced the stock alternator with a CS-144 and the voltage drop problem is gone for now.

My guess was the higher then stock cylinder pressures of the modified engine and the .040 spark plug gap combined with the voltage drop when the alternator cut out was creating a condition where I did not have enough secondary spark energy to jump the spark plug gap.

If you do some research on the subject you will find recommendations for spark plug gaps that suggest .040 gap for stock engines .030 for modified high performance street engines, .025 for nitrous engines.

 

THANK YOU!!!!! I have not tried this but it makes sense. I have a brand new race alt on the shelf I can put in the car. I have my alts built, single wire, low idle kick on, high amp with top of the line parts for my airboat because of all the amp draw. Keep your fingers crossed guys!!! With any luck I will be back at the track this Friday whooping Ford Mustangs.

 

We changed out the alternator and the car has WOKE up big time. Sometimes you cant see the forest for the tree in front of you I guess. We took it to a road by the house and made 8 passes with it. This has been killing me and I feel like a weight has been lifted off my shoulders.


Thank you guys, thanks to everyone who tried to help me with this problem.

 

Glad you found it!! I would still however check and clean the ground to the engine. A bad ground will make it harder for your plugs to fire and the lifting engine makes sense. It might be that the new alt is giving it enough ump to fire under load and hiding the real issue. Just a thought

 

Good deal i have only seen 2 bad altenators do this in 35 years or racing but when it does it is madening it will make you crazy. It really is the zebra in a herd of horses kind of problem and intermitent one too. Glad you found it and bet your times will get with the program now!
dave