well, i got this off ebay for like 25 bucks for all 4. not bad. i guess Denso came pre-gapped for my 5th gen prelude, which uses the IK20, according to Denso's site. so i didn't worry about gapping, installation was a breeze...having the special "spark plug lug" is like a dream. Performance wise, i can't really say anything, gas mileage, i may have gained like 1 or 2 mpg at the most. the only thing noticeable is that it's harder to stall now? idling is better... I was sorta hopin for my mpg to go up, but 1 or 2 is tops I guess...but if ur thinkin about them...think of it as adding 1 or 2 mpg to ur car for around 25 bucks, not bad, saves u $$$ in the long run.