I have been dealing with gas motors almost my entire life, but this diesel thing is new to me. I understand the basics, igntion under compresion, no throttle body, fuel amount regulates rpm/power delivery.

My question is, and this may sound dumb, but a diesel is a four stroke, right??? My buddy says it is a 2 stroke. I think differently, who is correct???

 

There is actually a 2-stroke and a 4-stroke diesel engine just like gassers. The Cummins is a 4-stroke. Im sure someone else will be able to give a little more info on this!

Edit: I actually found this link helpful for some of the basics of diesels...

http://auto.howstuffworks.com/diesel.htm

 

I've some first hand experience with Detriot 6-71 engines in medium duty trucks. The 71 series is a 2 cycle diesel that's been around for quite a long time.

In this design, there are intake valves in the head has usual, but no exhaust valves. Exhaust goes out some ports around the sides of the near bottom of the cylinder sleeve. The 71 series is always supercharged to the best of my knowledge. The supercharger is required to blow fresh air in the top of the cylinder via the intake valves and force the exhaust out through the bottom ports. Everytime the piston is at the top, there is an injection event and power stroke. So you get perhaps a bit more power out of the same cubic inches as it fires twice as often as a 4 stroke. Its been a few years, but I don't remember this engine being real good on fuel economy or that great on power.

Eventually my dad traded up to a rig with a Cummins. Seemed to have a lot more torque and it was way more reliable. I saw the insides of the 671 a bunch of times when we had to overhaul them. I never saw the inside of the Cummins.

I remember some way high EGTs on the Detriot. We basically drove and shifted them by the pyrometer more than the tach or speedo. Again, its been a lot of years since I drove one, but I seem to recall pyrometer almost equaling the tachometer when you were pulling any load at all. On the 671, the EGT we were measuring would be pre-turbo as compared to the Cummins in our Dodges.

In my not real informed opinion, you want a 4 cycle. Like the Cummins in the Dodge.

 

Most Detriots are two strokes and they make huge power and have the jump of a highly tuned gas motor but pull of a diesel. They are very tough with less mooving parts and are used in buses, boats and heavy trucks. In the marine world of fast boats Two stroke diesels are king.
Nick named Screaming Jimmys!