> That doesn't sound right. Diesels are 2-stroke engines similar to bike engines except that they have an intake valve. They need exhaust back pressure to properly scavenge the cylinder, otherwise excess gas (and raw fuel) would go through without burning.
I don't know what you've been smokin', but the 4 stroke deisels and two stroke diesels I saw when I was a USMC wrench are nothing like you describe. They act exactly like a 2 or four stroke gasoline engine, except that they are usually a 20:1 compression ratio (or higher), and directly inject the fuel when the spark would normally fire.
All engines usually need a certain degree of back pressure to simplify tuning. Appropriate back pressure can amplify the exhaust wave from the header length, making the scavenging more effective. Too little back pressure, and the wave isn't strong enough to do anything. Too much, and the engine can't breath.
That's why bikes with large diameter straight pipes usually run poorly at lower RPM -- too little back pressure to help with scavenging.
J
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