[efnfast]

This was the answer I got from Mr. Haibeck

Hi Steve,

For high load operation I recommend a spark plug that is one AC heat range cooler than the OE plug. The best spark plug is the NGK TR7IX. Part number 3690.

It has a tapered seat. All LT5's are machined for both tapered and flat seat plugs. Carefully open the gap to .050"

Best of luck.

Marc