![]() ![]() If you are going to tell people who know what they are talking about that they are talking rubbish, might be wise to know what on earth you are talking about first - especially when every single piece of factual data would seem to indicate you are very wrong. which isn’t a surprise as Diesel engines are more efficient. In fact, surprise surprise, there wasn’t a single diesel that was even close to the petrol, they were all way more efficient. So Qbhoy - you asked for ONE engine, I’ve just given you four (it’s the same for every single VP diesel as well). So 20 litres per hour per 100 HP produced, or just 74% of the consumption.ĭ4 300hp - 54.8 lph at wot - so 18.2 litres per hr for each 100hp or just 69% of the fuel use of the petrol. Same website, for the Mercruiser cummings diesel of 320 HP (so significantly more) it uses 71 lpg (or the 200hp - which has way more torque of course) 49.6 lpg.Īn even better example - Volvo Penta D4 260 HP - so similar size, same power (masses more torque of course) at wot producing 260 HP. Sadly he isn’t able to grasp that because his engine is under a very light load at 2000 rpm, it doesn’t use masses of fuel - however at that point it may only be producing 100hp - simply put, at its peak power of (from memory 260/270 HP) it will be burning about 70 litres per hour at WOT according to MerCruiser 3.0 Fuel Consumption 135 HP | Test & Specs | 181 mpi/tks (need to scroll through to 5.0 mpi) I don’t think there will ever be a spark ignition gasoline engine that will get within 20% of the efficiency of a compression ignition Diesel engine - ever. I don’t think I can top MapisM’s table as the perfect, and accurate, solution to the question “which is more efficient”. From this however, he has managed to deduce that petrols are more efficient than diesels - a bit like, “if all dentists wear jeans sometimes, then everyone who wears jeans must sometimes be a dentist” kind of logic.įor a small lightweight boat, a petrol may (for blasting around) be the right choice - it doesn’t follow however that it is more “efficient”. It's obvious that the vesselview screen that he posted previously is totally irrelevant, because we don't know how many of those 300 hp the engine was producing, at an RPM which is surely way below WOT.Ĭlick to expand.From memory he has a small light boat with a big MPi propped to give 60mph top end so that does allow him to plane at lower than usual rpm. Let's hear from him if he thinks that this number makes sense. He said that he has a 300hp petrol engine, which according to the previous table should burn 99 L/hr (0.33 * 300) at its max rated power. ![]() I'm genuinely curious to hear if he also finds that the table works for him. ![]() Not to mention my funny feeling that the generic table might well be more accurate than the manufacturer's specs.īut as I said, I'm not pretending that QBhoy takes my word for it. Of course MPI, direct injection, and many other tricks all contributed to improve the fuel efficiency of petrol engines over the years - as well as others factors did with diesels, anyway.īut none of these factors, neither alone nor all together, can circumvent physics.įor this reason, if you take the following table, which is obviously generic and based on averages, and you compare it with the specs of ANY engine, you will be surprised to see how valid the approximation is.ĭon't take my word for it, give it a try.Ĭlick to expand.Goes without saying that I wouldn't have posted the table if it weren't that I already know it's generally very accurate.įWIW, my 800hp turbo diesel engines burn 162 l/h according to the manufacturer's specs, and 168 according to the previous table (0.21 * 800). There are actually slight variations on that, because some engine manufacturers use the weight rather the volume of fuel, and you can either use kW or hp to measure power, but this is just hair splitting.Įssentially, it's meant to measure the amount of fuel that one engine burns for each unit of power produced.Īnd the crux of the matter is that there are physical reasons why even the worst diesel engines are, and will always be, more fuel efficient than the latest and greatest petrol engines. See, the point is that there's only one commonly accepted definition of fuel efficiency of internal combustion engines, and it's the Brake-Specific Fuel Consumption, aka "BSFC". It's when you jumped in the conclusion that petrol engines are "more fuel efficient" than diesel engines, that you dug the hole in which you are now.Īnd from where, as the old saying goes, you'd better stop digging. They wouldn't sell as hot cakes if they weren't. QBhoy, you don't need to convince anyone that modern outboards are good. ![]()
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