[revetec]

For a start, the image you posted was not of Australian origin as we are Metric over here and don't use lb/bhp-h.

Can you post a link to that whole article please?

As a note: The graph you posted means nothing without full explanation as far as the air/fuel ratio during the test. It is very rare to find consistent fuel mixtures across a load range to WOT. Most engines run in closed loop at around 14.7:1 up to around 50-75% manifold loadings, although most engines run around 13.5:1 towards the WOT setting and they are not in closed loop rather than "Open Loop". It is easy to run 14.7:1 at WOT on a dynamometer and get a good BSFC figure but if you have programed fuel injection maps on the dyno, as you get to WOT you program the map, to produce the top power figure. At WOT this is not as lean as 14.7:1.

If we were to use a consistent air/fuel ratio throughout the rev and load ranges, you are correct and the graph is accurate. The problem is that I was quoting a real engine in a vehicle situation and you posted a graph that I assume is running a consistent air/fuel ratio on a dyno. It is ok to argue this point and I suppose the misunderstanding is my fault for not explaining the issue in full.

Looking at your graph from 50% load and an air/fuel ratio of 14.7:1 it uses 0.425lb/bhp-h. At 100% load and using a common WOT mixture as rich as 13.5:1 it would use about the same amount of fuel. This is a common situation.

One thing I have found from setting fuel mixtures on a dyno is that once you put the engine in a vehicle you have to adjust the fuel mixtures to that vehicle a 14.7:1 or lean mixture at WOT produces a surge type feel, which is eliminated by richening the mixture up to 13.5:1.

You may or may not agree with me, but this is why all electronic fuel management systems go into "Open Loop" at high loading situations. If 14.7:1 was optimal at WOT, there would be no need for "Open Loop"

Anyways, I apologize for my WOT BSFC comments as I was commenting on the typical engine Map from an on road vehicle set up which we had and was discussed when I was going through independent testing. Typically, from 75% load to WOT the pumping loss changes are minimal while a typical on road engine's fuel mixture is en-richened.

As a further note: I just went to the Pattakon website and looked at the data logger. At WOT they were using an air/fuel ratio in the higher rev ranges about 12.5:1. Not knocking them at all, this is normal as I have stated above. I would also assume that they would be closer to 14.7:1 with lower load. This data log was definitely in a vehicle while the graph that was posted would have been on a dyno test at 14.7:1 or close to it.