I received this email a while ago asking whether there would be a big sacrifice in power when using NA precups in a turbo'ed engine.

I am building up a Turbo 6.5 corresponding to your fuel economy buildup article. Are we going to see a follow up on that soon? I am held up at the pre cup stage to see how that works out. I am getting so many nay sayers that tell me I will sacrifice too much power if I go with the early style pre cup.

Thanks in advance, -TMiller

Back in late 1991, Motor Trend did a comparison test between a Banks turbocharged 6.2L diesel and a brand new 1992 model-year 6.5L turbodiesel. The Banks TD outperformed the new 6.5 by a little.

If maximum power is more important to you, go with the TD precups. If better fuel economy and nearly as much power sound like a good compromise, go with the NA precups.

Jim

I would also add that NA 6.2's have routinely produced low 20's for fuel economy. A 6.2L GMC that I drove for over 200,000 miles would routinely deliver 22-24 mpg, with an all-time high of 27. High teens are more common in carefully driven and high geared 6.5TD's. If precups don't explain the difference, let me know what you think does.

The fuel economy project is still on. Member Gordon Marks recently donated a complete serpentine set. Still debating whether to run an electric rad fan or go with an engine-driven fan. I'm leaning more toward electric, since this is about ultimate 6.5 fuel economy.