[revetec]

Originally Posted by hightower99

Well that is simply not true as there is a certain BMEP that is needed to achieve any given output at any given speed for any given displacement.

Don't get peak performance/output confused with peak efficiency, which you are. A higher BMEP produces more outright performance but the lower the BMEP for a given output provides a greater efficiency. One thing you are not factoring in is the manifold load of the engine at that BMEP figure point.

Originally Posted by hightower99

I spend most of my time on roads with 80km/h speed limits on roads that aren't straight and flat for several km. I would say that the average RPM that my engine sees is somewhere over 3000RPM maybe 3500RPM. I am rarely able to cruise for more than about 1-2 minutes and then I will be cruising at about 2200-2500RPM.

Try changing up a gear or buy a car that is more modern. Most cars I have driven is at around 2,000rpm at 100kph in 5th or 6th gear BTW: My car with a 5.7litre V8 and auto trans sits around 1,500rpm at cruise 100kph.

Originally Posted by hightower99

Edit: I just realised that there is no WOT full rev BSFC figures... I would really like to see that because there is a little bit of that sort of info on the WWW to compare it to.

This is because an engine is most efficient at around 3/4 load and from 3/4 to full throttle the performance gain is not great, but there is a higher fuel consumption. So the figure at full throttle is rarely used or quoted.

Originally Posted by hightower99

Now that you have a good starting point the goal should be to increase specific power (which will also increase power density) without increasing the BSFC figures.

It's the same result as maintaining power and decreasing BSFC figures. Fuel efficiency is all about how much fuel you use to produce each kW per hour. It all comes down to matching an engine to an application. Depending on the vehicle's requirements, you adjust the engine's capacity and characteristic to the vehicle along with final drive and transmission ratios so as the vehicle drives with the best fuel efficiency at the point it will be driven mostly. The standard quoted tests are highway and city cycles.

Take your car for an example. If we were to change your final drive ratio to provide a 100kph cruise whereas you engine is operating at 2,000rpm, the result would be?

Another point I can add is that if we were to use our engine in a power generator type application. The engine will operate at one specific speed. A lower BSFC will provide less fuel consumption per kW-h which makes it more economical to produce electricity from this powerplant regardless of the efficiencies in other RPM ranges. A huge market for us.