I understand its a unit of measurement to judge engine life, but googling “Mrev” and “Mega Rev” and “Mega Rev lifespan” gave me nothing, so what exactly is one mega rev and how does it relate to the life of an engine?
one megarev = one million of revolutions
its set like that as since the engine is on a dyno it cant be calculated in kilometers or miles ect - say 400 million revs is equivilant to 250,000km? i dont actually know that but its a guesstimate
also @ Kubboz - awesome avatar! Screwie Lewie is back! 
I don’t see there being a real way to determine exactly how far even 1 million revolutions would take you , considering there’s no transmission differential or tires attached to the motor , and there’s no real way to determine how someone will drive their car, someone with a lead foot could easily reach 1 million revs long before a more tentative driver. I mean you could make a guess based on typical car design (and forgive my units of measure) where cruising speed is about 55-60 mph running about 1800- 2250 rpm . MRevs in the end is a way to state how long an engine can go without the guesswork as to what the engine will be attached to or whose driving it.
This! Its a way of comparing how long each engine will last, independant of what gearing its attached to, like fuel economy you’ll only get the final statistic once its in a car 