So ive been wondering what makes a diesel more torqey than a gasser, i mean how does it work, what makes it get same hp but different tq?

 

I believe it has to do with the fuel... Diesel doesnt explode, it burns, thus it pushes the piston down through the whole stroke, creating lots of torque. where a gas burner explodes and shoves the piston for the first 1/4 of the stroke or so and from there its just carrying its initial momentum, the quickness of the exploding gas makes the hp higher. I could be way off though.

 

Well; that is a really big question depending on how technical you want to be, but the basic answer goes like this:

Primarily it is the difference in combustion process which generates the higher torque numbers in a diesel engine. Essentially because the diesel engine runs a substantially higher compression ratio, and modern diesels are all supercharged in one way or another (most commonly with a turbocharger) the cylinder pressures during combustion are correspondingly higher which translates to larger forces on the crankshaft, which means more torque.

Also bear in mind when looking at engine dyno results to look at where the peaks occurred. Then rpm nuimbers for diesels are radically different than gassers. A diesel to gas comparison is not an apples to apples comparison at all, there are too many factors that are totally different.

 

short answer: long crank throws.

Long answer: Thermodynamics. The Diesel cycle is different in the thermodynamics than the Otto (gasoline) cycle. The diesel cycle works in what's called "constant pressure heat addition" and the Otto cycle works in "constant volume." What that means is that the Diesel cycle adds heat (which translates into pressure) across a wider portion of the crank stroke than does the Otto cycle. Using supercharging simply increases the pressure inside the cylinder at all times, but gives you a higher peak pressure as well.

How well this works in real life is largely dependent on actual engine cylinder and crank geometry. Most indirect-injection diesels thermodynamically work very closely to an Otto cycle in real-world thermodynamics (intentionally, by design). When you get closer to a real-world Diesel cycle, you run into problems like poor cold weather performance and starting. You also start running into high-speed running problems, since at high speeds the Otto and Diesel cycles start looking very similar on a Pressure-Volume diagram (they look very different at low speeds). The Diesel cycle starts losing a great deal of efficiency over certain RPM's when the engine has been optimized. Which is part of the reason why you never see big-rigs running high-RPM engines.

Clear as mud?

-blaine

 

Thanks guys, ive wondered that for a while just never thought to ask!