[texan]

My bad, that's what I get for not finishing sentences. What I meant to say is that peak cylinder pressure has far less meaning to overall power output than mean cylinder pressure. I of course agree completely with mike in that it's the cornerstone of parts strength design, thank for the clarification.

To illustrate my point further, take readings from a test NA engine. Then add a moderate amount of nitrous injection to the mix, and watch the peak cylinder pressure skyrocket for an attendent moderate increase in power output (if the engine is making 150hp, a 75hp shot of nitrous can nearly double peak cylinder pressure). Now instead add a turbocharger to the mix and double power output to 300hp, you'll notice that peak cylinder pressures only increase to about 150% of NA levels (assuming no detonation). The point being: nitrous accelerates burn rate drastically and has as such has a large effect on PCP, but a smaller comparative effect on mean pressures. Standard forced induction, however, does not drastically increase burn rate and therefore has more of an effect on mean pressures than peak pressures, by way of mainting high cylinder pressures further into the power cycle. Late cycle pressures are often nearly triple what they were in the NA engine when running significant amounts of boost, while peak pressures dont even double.

Ps- Mike, didn't you transpose those MEP values relative to the compression ratio? Simple Otto cycle thermodynamics indicate that higher CR also equals better pressure ratios. Or am I just that thick when it coms to diesel power tuning?