My first 2wd Sapph used to eat a plug almost every time I drove it hard.

In the end it looks like the head had been skimmed far, far too much and it was therefore running quite high compression and perhaps I ran a touch too much boost also, so every time it was held flat in 4th & 5th it would just get hot and blow the plug apart.

Sounds like his car needs sorting, but at least it's the plugs that are the weak link and are blowing - if he was running NGK 9's the plugs would probably be fine but something more serious might fail

Edd