and should are maximum
Where did you come up with this particular factoid? Are you just making it up? If not, how about a reference? For an Otto cycle engine maximum efficiency is achieved at wide open throttle at some rpm that depends on a lot of factors that include bore, stroke, valve train, induction system, exhaust system, compression ratio, etc., etc. None of this is related directly to the engine's red line. For pbuttenger cars, the red line is often arbitrarily set. For a performance engine it should be based on the power curve and mechanical limitations of the engine. In neither case is it directly related to the most efficient speed (although for industrial engines it is often set just past the power peak - no need to run an engine faster to create less power).
Go back to the reference in my previous post and tell me where the maximum efficiency is obtained.
Here are a bunch of curves for automotive based industrial engines (same site as before):
lowest BSFC is achieved at around 2000 rpm, but is pretty flat - lowest BSFC is achieved at around 1800 rpm - to 3600. - lowest BSFC is achieved at around 2200 rpm, but is pretty flat from there to 3400 rpm - BSFC is almost flat throughout the operating range - BSFC is lowest at around 2000 rpm - BSFC is lowest at around 2000 rpm - BSFC is lowest at 3600 rpm - BSFC is lowest around 3200 rpm (this is the same 4.0 as used in Explorers) - BSFC is lowest around 3200 rpm - BSFC is almost flat (LPG) - BSFC is lowest at 3500 rpm for the 2.5L V-6 and 3000 for the 3L V-6 - BFSC is lowest from 1600 rpm to 4000 rpm for the 1.8L and 3000 to 4000 for the 2.0L - BSFC is lowest at 2000 rpm for the 1.8L and 1500 and 2500 for the 2L - BSFC is lowest at 2500 rpm for the 1.4L and from 2700 to 3500 for the 1.6L
And even if your engine is most efficient at 3500 rpm at wide open throttle (which is entirely possible), this doesn't mean that you will get maximum fuel economy at the corresponding steady state speed. For a given rpm, efficiency will be less at part throttle. And at higher speeds the loads on the engine will be greater because of aerodynamic drag. So while you engine may actually be more efficient at 75 mph (where efficiency is defined as work out-energy input from the fuel), fuel consumption will be higher because you have to do so much more work to maintain 75 mph than 55 mph.. As your car's speed increases from 55 to 75 mph, aerodynamic drag more than doubles. There is no way the efficiency of any properly designed engine increases enough over this relatively small rpm range to compensate for this increase in load.
Based on the size, weight, and coefficient of drag for your car, I'd estimate the following power requirements for different speeds: Speed Engine HP mph Horsepower 45 20 50 22 55 25 60 29 65 33 70 37 75 42 80 48 85 54 90 61 95 68 plus 1 100 78 105 87
I'd estimate you BFSC would have to be around 0.26 lb-hp-hr to achieve 42 mpg at 75 mph. I doubt that your engine has this good a BSFC at part throttle. The EPA highway mileage for a 1995 4 cylinder Galant was 30 mpg. buttuming that the peak mileage was actually around 35 mpg at 55 (the EPA test does involve some starting and stopping which lowers the mileage), the BFSC at 55 would need to around 0.39 lb-hp-hr - a good, but believable number. I don't believe that the BSFC improves by 30% as the rpm and load increases on the engine as you go from 55 to 75 mph. Any decently design automotive engine will have a relatively flat BFSC in the normal operating range. I might be willing to believe that the BFSC increased by 10% or 15% over a 1000 rpm range, but not 30% over around 900 rpm. Just for grins I'll make the following estimate - , if your BFSC increases by 15% as you increase your speed increased from 55 to 75, your fuel economy should go from around 35 mpg to around 33.5 mpg, NOT 42 mpg. So this estimate implies that even if your engine was 15% more efficient at 75, than at 55, your fuel economy still decreased by over 4% because of the greatly increased power requirement to go 75 mph (as opposed to 55 mph). To maintain the same fuel economy at 75 mph as at 55 mph, your engine would need to be over 18% more efficient at 75 mph than at 55 mph.
I think your claims are based on some strange brew of wishful thinking, horrible measurements, and chickeneyed science. The fact that nobody (EPA, Consumer Reports, Car and Driver, etc.) achieve fuel mileage numbers for a Galant even close to your claims should make you think seriously about revising your fuel economy measurement methods. Sometimes when everyone else thinks your are wrong - you are wrong.
Regards,
Ed White
