Horsepower is horsepower?

transamz9 wrote:

wilber1 wrote:
These discussions always result in comparing power and torque curves of normally aspirated gas engines to turbo diesels and making it about gas vs diesel. The diesels real advantage is efficiency, not how it makes power, particularly now that many gas engines are also using high pressure common rail direct injection.

When the subject of reliability comes up, it then becomes "ya but that would never work for long haul trucking". The goal posts keep moving. Who knows how reliable the gasser would be if it was built like a long haul diesel, but then you would have an engine that cost as much to build as the diesel but much less less efficient, so why would anyone do that.

With the present state of the art, efficiency is the diesel's ace in the hole over DI boosted gas engines, not how they deliver power.

It's kind of interesting that the compression ratios of Mazda's Skyactive world gas and diesel engines are the same 14:1. Who thought that would ever happen.

I don't think it's as much the efficiency of the motor as it is the available power in each fuel. The diesel is built heavier to withstand the power of the fuel not necessarily built for the long haul. Just so happens you get one with the other. Even the HD truck engines are built lighter than the long haul trucks because they don't produce as much power (torque)

When it comes to producing power, it's about cramming as much fuel and air into the engine as possible without destroying it. The DI common rail injection systems with their electronics and multi stage injectors which have made diesels so much quieter, can be used to regulate combustion chamber temperatures in gas engines, reducing any tendency to detonate and effectively increase the octane rating of the gas they are using. Combine that with other innovations such as combustion chamber design, variable camshaft and ignition timing, any ten year old ideas about what it takes to "run on pump gas" no longer apply. The rules have changed.

Go out to the strip and talk to the pimply kid with the laptop plugged into his OBD2 port. He'll tell you all about it.

Long haul engines are built stronger because they are expected to last longer under more stressful conditions. I don't think they produce more power and torque relative to displacement.