[hightower99]

Originally Posted by revetec

2,000rpm, 450kpa BMEP, best BSFC 207g/kW-h
So how did we get such good fuel efficiency figures? It didn't come from the top end.

With only that single point it could be almost anything. Maybe at 2000RPM and 450kPa BMEP several variables come together to achieve the great BSFC. You can't tell me that it could have only been the bottom end design.

Originally Posted by revetec

I'll tell you something. If we were to put the X4 cylinder heads on a conventional engine we would be lucky to get a BSFC figure of 315g/kW-h or 26% efficiency.

How do you know? have you tried? If you did something like that it would be going in the right direction towards proving any advantage from your bottom end.

Originally Posted by revetec

The engine is port fuel injected like most vehicles so we can rule out the fuel system. Our intake and exhaust system is nothing special so we can rule that out. What is left? The bottom end which is our technology.

That is a highly simplistic list of variables. What about any synergy that exists in the system? What about all the variables like bore:stroke ratio, cam characteristics, oiling system, maybe the clearances in all the bearings in the engine approach absolutely perfect? My point is that because you only have the single point you cannot make any conclusions other than it is possible to achieve that efficiency with that engine under those very specific circumstances. If the bottom end is the major contributer to the fuel efficiency then your engine should be more efficient all the time. This is what you have to prove.

Originally Posted by revetec

If you can achieve a lower BMEP at any RPM range at a given output then the efficiency is greater. Let's say, If you are able to lower the average pressure in a cylinder and increase the transfer of that force to the output shaft then the output of the engine will be the same. Lower pressure in the cylinder is a result of less throttle opening and less fuel used.

BMEP =/= Avg. cyl. pressure. BMEP is normally calculated from torque being a function of torque and displacement. Therefore if you have a lower BMEP value and the displacement is the same then output must also be lower(for any given RPM because the torque is lower). Maybe you are actually talking about average cylinder pressure and not BMEP.

Originally Posted by revetec

Well before you enter further into this view, post a BSFC figure of the most efficient petrol engine you can find on the internet or any other source and quote where you got the figure from. The best conventional engine I could find has a BSFC figure of 245g/kW-h and the best I could find on any engine was a non-certified figure on the quasi turbine engine which they stated was tested at a BSFC of 225g/kW-h. A good automotive engine can have a BSFC figure of around 270g/kW-h or 30.3% efficiency.

I haven't been able to find much but there isn't much out there anyways. What I need to counter you is a single point where an engine produces similar (Gasp! maybe even better) BSFC ratings and I can't find that on the www.

Originally Posted by revete

The 2,000rpm point was measured as it is an RPM point that most engine manufacturers test at. The reason...This is the point that most of the time an engine operates in/through. Cruising on the highway and accelerating economically in city driving.

I certainly don't spend the majority of time at 2000RPM, besides isn't this an aviation engine? My point was you should make a full BSFC map for the whole rev range and most loads. This allows everyone to see that the engine is always going to be more efficient and that it isn't just a lucky setup.