Wellllll...I'm guilty of not data logging the last run as my laptop battery went dead. I may go back to the drawing board where my car ran 9.06...it was with NGK R5671a-7 plugs gapped at .028, 20 degrees total timing, boost at 20 psi and running VP 110.
What are your thoughts on spark plug selection? brand, heat range, and gap for boost over 20 psi? Also, what are your thoughts on fuel with an 8.5 to 1 motor and 20+ psi boost?
Thanks for your input!
I'm not going to be much help with plugs or gap. I can throw any plug with the correct reach and thread in my cars and never really see a difference. Same with gaps. If they close up it might start missing, or if the tips get way too wide it will miss, but other than bad plugs I just don't have problems. I run the coldest plugs that do not foul with the correct reach and base and try to avoid resistor plugs.
Right now I use NGK R5671A-8 set at .030-.032 in either my 11:1 compression turbo motor or in the 9:1. I run around 25 psi in either. Neither is plug or gap critical. I've run Autolite AR3934, NGK BCP7ES, or even RC9YC Champions in a pinch. Both engines are over 1000 at the tires.
I run Renegade pro 120+ at 23-24 degree timing in the high compression motor because I'm scared of knocking. I run about the same timing with C16 in the low compression engine. It doesn't matter if I swap between fuels, the MPH and ET stays about the same. I just worry less with the 120 plus in the higher compression engine because it has a hard street alloy style piston. The piston wasn't my choice, they came with the engine.
All of my stuff was tweaked on a dyno, where we could listen for knock and see what happens. I just advanced timing until horsepower stopped increasing and made sure it was not rattling.
I don't think any of this helps you or means anything. You really have to find out why your engine started missing. You really need to get data logs, and a dyno session is really worth it. Just put some good radial street tires on it. Dyno's will heat up and eat up soft compound tires or slicks.
The way my engines behave is the power comes up a good bit every few degrees advance if they are retarded too much, then power abruptly stops increasing with more advance. As soon as I don't see more than a percent or two increase, I stop advancing timing. It is a heck of a lot better doing this on a dyno.
I run about 12.5 AFR in the low compression motor and 11.5 AFR in the high compression, mostly because I am afraid of detonation with the pistons in the high compression motor. The low compression motor made a few percent more power at 12.5 mixture. I didn't even try that on the other one, I just left it at 11.5 for safety.