Which is better 5.9 or 6.7

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View Poll Results : Which would you have Cummins 5. You may not vote on this poll. Jonathan Ashbeck. The Cummins 5. The 6. Personally I'd rather have the 5. Plus, they sound like diesels like the Powerstroke 7. The 5. Last edited by Jonathan Ashbeck; at PM.. Originally Posted by Jonathan Ashbeck. Originally Posted by Nlambert. None of the inline 6'ers sound like a V-8 diesel.

If you are referring to the clackety sound you are used to hearing from the 5. Specifically direct injection mechanical or HEUI. While the HEVE sounds like the best of both worlds, it does have some reliability issues. The 5. Thanks to its increased stroke over the 5. Unfortunately, this means more cylinder pressure is present in the cylinders, which is the primary culprit for a surprisingly common problem on the 6. A lack of sealing area between the cylinders and water jackets due to the 6.

Engines that tow regularly are known to lift the head anywhere near the ,mile mark, while modified engines typically one much sooner. By comparison, head gasket failures were few and far between on the 5.

Nearly a decade into its production run, the 6. In the upper echelon of truck pulling and drag racing, several companies add sleeves to the cylinders, a deck plate up top to keep the tops of the cylinder bores from distorting and increase the stroke of the crank.

Sign up for more restomod content to add horsepower to your inbox. Similar Injectors While the injectors used in both the 5. The engine itself is also very different than the previous 5. The Cummins engine was the last to adopt variable geometry turbocharger technology. This turbocharger reduces emissions and improves drivability greatly. It also brings exhaust braking to the trucks. This exhaust brake or turbo brake feature improves stopping distance and can help dramatically increase brake life when used towing.

By aggressive driving and regular use of the exhaust brake however, problems can be significantly reduced. The whole fuel system was changed to make room for more power. Thankfully, the CP3 injection pump is used again, but it allows for slightly higher injection pressure, up to 26, psi. The injectors were also redesigned. The increased bore and stroke of the 6. Cylinder pressures are drastically higher than the 5. Cummins redesigned the cast-iron engine block, incorporating siamese cylinder bores.

Very little changes were made to the cylinder head. Because of the increased cylinder pressures, it is much more common to have head gasket failures on a 6.

Even so, head gasket failures are not a common occurrence on Cummins engines until driving hundreds of thousands of miles. All 6. Auto manufacturers were being pressured to make trucks more environmentally friendly, and they succeeded. Exhaust braking is an awesome feature to have when towing and it massively improves the capability of the engine. As far as common issues, the 6. With the increase, in-cylinder pressure comes significantly more head gasket failures.

When it comes to after performance, both engines have a ton of potential. Both of them are easily capable of making lb-ft of torque or much more. The newest Rans with the 6. For those who want big power out of their engine, the Siamese bore design on the 6.

At the peak of diesel racing, the 6. Many of the top racers in a truck pulling and drag racing, add sleeves to the cylinders, a deck plate up top and increase the stroke of the crank. Back to the original question of which one is better, it kind of depends on your use case.

If you think reliability is the most important feature of an engine, the 5. Of course, this article mostly omits the older 12v engines with fully mechanical injection systems which are known for being crazy reliable.