Cummins 4BTThe 3.9-liter Cummins 4BT is an enigma among diesel engines. It's an excellent engine and has powered many things you've no doubt seen along your travels. Like many diesel engines, the 4BT powered things other than roadworthy vehicles. Some folks have even used them to power their boats. In addition, the engine has been known to power other industrial and agricultural equipment along with buses, bread vans, and box trucks. Among the most well-known is the humble FedEx box truck, some of which have been known to run a Cummins 4BT. So what makes this engine so legendary? For starters, its applications are virtually endless. It can be used in equipment, boats, or road-going vehicles, and that alone makes it super useful. Despite its relatively meager power, the engine is also considered highly reliable and often used in engine swaps for all sorts of vehicles. The 16-valve version of the engine made 170 hp and 420 lb-ft of torque — not enough to win races, but plenty to scoot a box truck forward. The enigma part comes due to timelines. Cummins began making the engine in 1983. It received a major revision in 1998 to the 4BTA. Cummins still makes this engine today as part of its ReCon series of engines, but a lot of details from the 2000s onward are exceedingly difficult to find. Rest assured, if you have a boat or a woodchipper that needs an engine, this is a good engine to start with. Cummins ISB 6.7-literThe Cummins ISB 6.7-liter diesel is the final form of the Cummins diesel engine as of today. This 6.7-liter straight-six turbodiesel is the newest model in the Cummins B-series engine lineup, and has largely replaced the 4BT and 6BT in most applications. It was introduced in 2007, boasting a 13% increase in displacement and more modern diesel tech than the 5.9-liter 6BA. While Cummins still produces both engines, the ISB is the current flagship. Since it is a B-series engine, it shares a lot of the same benefits as the others. It's quite reliable, with many examples online having north of 300,000 miles and sometimes more. By most counts, the 6.7-liter is an overall improvement on the 5.9-liter's design, which is a rarity in the engine space. After all, it took Ford two tries between its 7.3-liter and 6.7-liter Power Strokes to get things right again. The ISB 6.7-liter is also used in a variety of vehicles from Dodge Ram trucks to the 2016-19 Nissan Titan XD Diesel. In short, the ISB 6.7-liter is good for the same reasons as the other two Cummins engines on the list. It's reliable, durable, and it has a variety of uses. Pair that with an impressive 420 hp and 1,075 lb-ft of torque, and you have a modern engine with tons of power that'll last you a long time. It's hard to beat that.
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