Ok Ross and Ted,
I've been thinking about this.... and I read part of one of the articles L Adamson provided, where it said that two engines producing the same HP at the same RPM, would produce the same torque.
Given my two comparisons: my 300 hp gas suburban vs my 300 hp Diesel pickup - and the Cat powered heavy haul rig vs the same rig with a 550 hp Chevy -
Are you saying that if I were to create some type of optimal gearbox for the gasoline engine - a torque multiplier -, then run the engine at the RPM required to achieve rated hp (300 or 550 in these examples), that the gas-powered rig would pull the same load up the same grade at the same speed as the diesel does? If that's what you're saying, then I think I get it. Not a very practical or reliable thing to do, but doable in theory I suppose, leaving efficiency and power loss from the gear train out of the discussion.
Let me know if I'm thinking straight. It would not make me a convert to the SI Gospel Fellowship, but I may be starting to understand what you're trying to tell me
Kurt
I'm glad you kept an open mind through all of this discussion. This shows you REALLY DO want to understand the concept. Nobody expects you to convert to SI engines. What you have achieved in both your 9 and at Bonneville is very impressive in my mind. I'm a firm believer in driving and flying what turns your crank. Clearly you love diesels which is fine by me.
Getting back to the discussion, in fact, just putting a 3 to 1 gearbox aft of the 502 atmo Chevy would allow it to do almost the same job as the 928 inch turbocharged CAT engine running 40 psi boost. The Chevy would output around 1700 lb./ ft. to the main transmission. As Ted pointed out, it is not going to last anywhere near as long as a 2900 lb. giant loafing along at 1500 rpm and part load and it needs to be kept within a narrow upper rpm band.
Ted hits on the other points about design and intended application well. The CAT is practical for heavy duty truck use but would be a poor choice for a Lancair IVP for instance, just as the Chevy would be a poor choice for the semi.
Ted reiterates my stance on CI, torque etc. My whole objection to people stating that CI engines have superior torque merely because they are diesels just rubs me the wrong way because it is simply not true. Modern turbo diesels have high torque because they are heavily boosted, simple as that. If we apply even half the boost pressure to the same size, same stroke SI engine, we'll always have both more torque and more hp as we can see in any of the examples. HP does the work, not torque.
People continually compare a 6.5L turbo CI engine to a 6.5L atmo SI engine and come to conclusion it has more torque and even more hp in some cases- well of course it does since it is running 2-3 atmospheres of boost- a no brainer. Add even one atmosphere of boost to the same SI engine and it will trounce the diesel in both respects. The SSC Aero is an example of what relatively low boost does to a well designed 6L class production SI engine- 1200/1200 hp and torque is far in excess of any comparable size diesel running even double the boost pressure.
No one disputes the superior BSFC of CI engines. When this can be combined with low weight, longevity and comparable cost to SI engines, they make a fine choice for aircraft. The weight part does not matter much in road use and I'd be the first to admit that some of the modern turbo CI engines in auto and truck use today work very well and are vastly different and better from the stuff available 20-25 years ago. Diesels continue to intrigue me, I don't hate them- well maybe the smell part but even that has pretty much gone away lately.
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