Not alot of guys running 20 psi on here. You're going to have to read the plugs, and figure out what works for your specific combo. If it were me, I'd start at a lower boost level, say 12 or 13 psi, dial that in, then slowly creep up on the 20 psi, adjusting as you go. Otherwise you run the risk of blowing your junk up, just because you set it up and ran it "the way the internet told you to". No matter how similar your setup is to somebody else's, just doesn't mean the same plug gap and heat range will work for you.

I'd compare building a brand new setup & throwing 20psi at it, and expecting it to work properly right out of the gate, the same as building a brand new setup for nitrous, and throwing a 300 shot at it on the first pass. Pretty good chance it's not going to work right. Something might even just blow up.

 

I was just wondering what the coil near plug ignition was capable of doing under boost. I don't know if it would even go as high as 20 psi, it might, and I wouldn't have any real reason for it. I would imagine I will run off the wastegate at 8 psi most of the time and probably not more than 12 psi or so on pump gas.

 

You will probably have to go to 0.028 or so for 20lbs. Its not really an issue because as density increases (read boost) flame speed increases.

 

From what I understand flame speed is very much a constant. That is the reason you need more ignition advance at higher rpm. Flame speed remains the same, but the engine is turning faster, so you have to start the fire sooner so that it ends at the correct time.
I think you mean flame propagation, which increases with turbulence caused by increased squish area, maybe other things. Maybe the increased concentration caused by boost increases flame propagation, if so that is something I didn't know before.
I might be wrong but I'm sure write purty, don't I?

 

That is true; increasing spark advance with RPM can extend the useful range of operation due to lower combustion time. However, if you have access to a spark table, pick any column and move downward. Notice how spark advance decreases with increasing load (or charge denisty, whatever it is mapped against). This is a product of the increase in flame speed with higher density. It is also why you can have very high spark advance at low load and be perfectly alright.

 

Here is the next question. Do I start wide and work to a narrower gap or start narrow and work to a wider gap? When you misfire NA its not big deal but what about when you are under boost? Same thing just more pronounced or are bad things going to happen to the engine?

 

Misfires like that will typically only happen at high rpm, in which case its not a big deal. Tighten the gap slightly and work from there until it goes away.

 

And you guys are going to recommend TR55s for this kind of application?

 

for that much boost, id start with a tr7 and have some tr6 on hand to test with.

 

A TR6 is colder than a TR5 and a TR7 is colder than a TR6 correct?