[aardvarcus]

With regards to the turbo, I know this is counter to popular opinions on the subject, but the BSFC numbers I have been able to find in some published military papers between turbocharged and naturally aspirated 6.5L show better BSFC numbers at peak levels but not across the spectrum. The numbers I have seen at low to moderate power outputs weren't significantly different.

Doing the modifications listed should greatly reduce the steady state power requirements to roll down the road so most driving time should be at low levels of fueling, which in a 6.5L engine would result in very high air to fuel ratios. In this scenario, I don't think extra air will help increase efficiency since the air to fuel ratios should already be very high.

If I was using a lower displacement engine thus decreasing the air volume or did not do any load reduction thus using more fuel where the typical air to fuel ratios were lower, I think the turbo would be a better fit. Anyway if I end up dissatisfied with natural aspiration, I can always add a turbo and do a real A-B comparison.

Edit: To be clear I am not making blanket statements above, I understand how a turbocharger typically increases efficiency and how a smaller diesel engine with turbocharger would be more efficient than a larger naturally aspirated engine to make the same power. I would rather have a 3.25L engine running 14 psi boost than my 6.5L (3.25L at two atmospheres ingests the same air as 6.5L at one atmosphere). However since I want to use the 6.5L platform but reduce the load required, I don't think the turbo will benefit that scenario.