Detroit 6.5 or Cummins 12v

1987 GMC Jimmy said:

I think it depends on the year of Cummins 12V you go for. Earlier years are simpler but have more static components in terms of tunability (e.g. P Pump vs. VE Pump). They can still be turned into monsters, though. You’d have to do the 47RH for an auto or an NP4500HD for a manual. I think they came with a Getrag something or another manuals, too. There are certain blocks to watch out for and the KDP issue is another thing.

My brother has an ‘02 OBS Dodge 2500 with a 5.9 Cummins. What a piece of crap, wiring nightmare, jacked up truck. I used to want to undertake a Cummins swap but not anymore after being around this. It’s left a horrible taste in my mouth towards them. Maybe if I was around an older, simpler setup that wasn’t all hacked up wiring, hick exhaust, and crappy shifting, I’d like it better, but that truck’s been an awful, unreliable form of transportation in my opinion. I still like the 7.3 PowerStroke a lot, and I would do the conversion if that trail had been blazed enough. I don’t think it has, though.

It seems like you like the Cummins a lot, and there are a lot of good points to them. If I had reasonable exhaust, good sound insulation, an early motor with simple components, and a transmission that had fluid gear changes rather than throwing you around/jerking around, I would consider it. I’ll play devil’s advocate here and stick my neck out for the Detroits. Late model 6.2s would be a better starting point, and some people combine parts between the two for their motor builds. I value the simplicity of the GM diesels. At its core, the 6.2 is a very rudimentary NA, V8 diesel. Super easy to work on, super reliable, and the most plug and play thing you can go for. The 6.5 follows the same idea. I don’t think it could ever hold a candle to the Cummins in terms of performance, but it’s definitely possible to build it outside of its traditionally anemic state into one where its competent and can hold its own. It also depends on what you want to do with it.

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