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What follows is based on some fact, some observation, and hard experience. Take it as you like, but here are a few tidbits that might help distinguish the different Detroit Diesel engines.

The different sizes break down like this:

  • DD 8V71
  • DD 8V92
  • DD 6V92

Diesel8V71 Means a V8 (8 valves), 71 cubic inches per cylinder. It is also known as a 71 series engine.

The 92 Series Engines are based on the 71 Series. The differences are found in the power output. Naturally the larger cylinder size allows more compression to build up thus providing more overall power. The 92 series engines also make considerably more power due to the turbo and make better fuel economy by around 10%.

Same general thoughts as 8V92, although a bit less power. Still more power than the 8V71.

When comparing the different engines from a power output standpoint, in general, the 6V92 makes about 10% more power than the 8V71, while the 8V92 about 40% more than the 8V71.

The down side is the 92 has a "Wet Sleeve" construction and tends to not like sitting. In general, diesel engines like these like to run!

To counteract this they require careful cooling system care. There are test kits to track this.

These engines should not be idled, Target a 3 minute warm up or until air pressure is up, three minute cool down and shut it off. (If its over hot three minutes after it cools off on the gauge) Run the correct 40 weight diesel oil. 30 weight if under freezing. Not 15w40 unless nothing else is available.

For decades running Detroit Power, the 92 series rarely runs until overhaul with out a serious internal failure, while the 71 series seems to be more reliable in this area.

These three engines are running various large vehicles everyday. They have been battle-tested, so-to-speak, over many decades and have proven their mettle.

(This article is written using extracts from Bubba the Bus Tech posts in our forums).

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