I am switching out My bosch plugs I researched and purchased NGK XR5IX they are pre gap at 0.35 I run a 8.71 blowin 440 @ 9.5-1 compression, full MSD ignition including wires I would like to leave the 0.35 gap but have seen a few who have increased it to 0.40 or larger opinions please if your running a high performance big block. I produce over 700 hp and it runs great but its time for a plug change.

 

The ProPower or HVC coils or MSD don't care if you run .035 or .040
What might determine the gap is if the boost is blowing out the flame?

I would stay with whats been working as to not loose your base on the way the motor runs.

Remember... The more Boost... The smaller the gap needs to be....

I'll talk about going the other way...

But if your looking to go out side, Stepping the gap up to .040 or .060 might use up a little more KV from the coil. Play with some jetting and timing, and see if you can change one end or the other the way the engine runs for your liking...

Just food for thought....
Just so you know.... I love Blown Cars....