Oh, well. I doubt it's because he puts the power on too soon, they suffer with quite bad turbo-lag, and as a result (unlike the supercharged 'Marinediesel' version from sweden) it's hard to make it work until the RPM's are up.
I marinised an Automotive 21.3:1 CR GM 6.5, but only to 240 hp, single turbo from a Volvo AQAD41 motor, no intercooler.
Used it in a single engine 26 Extreme (Ring 26). It only did 47 mph, but was very reliable, and VERY economical, using under 3 imp galls/hour average, usually cruising at around 40mph.
That's about £2.50/hour back then, absolutely unheard of at the time. Did 2000 miles in one season, then sold it to a friend who did another 1000 miles or so, without a single problem.
He re-engined the boat with a 315 Yanmar after that, as he wanted more speed, he sold the motor to a Bayliner owner, who continued to use it.
I think the answer is to not be too greedy with the amount of power you try to extract.
Peninsular do indeed make a twin turbo 400hp model, but i'm not sure whether the motor is really strong enough for that.
"I Agree with everything you say really!" - John Cooke to Jon Fuller - 26-01-2013