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Carwhisperer 11-12-2015 03:47 PM

BSFC data top speed vs cruise
I'm trying to accumulate some data to make some problems for some of my students. The premise of the problem is that you can take rated horsepower and rated top speed and use that to estimate horsepower at cruising speed. The assumption is that power is proportional to velocity^3.

Then, if you can find data for fuel consumption and power used at that speed you can calculate BSFC. Then, check to see if it is inline with expectations or data for that engine. I tried it with a Ferrari F355 and came up with 21hp needed to cruise at 70mph. I had some data that suggested 22mpg and came up with a BSFC of around 0.9 lbs/hp/hr, which is pathetic, but Ferrari is not known for it's engine efficiency at cruising speed. Yes, I know that BSFC is usually not very good at part throttle operation.

EPA fuel mileage data aren't very useful because highway mpg are not really cruising. They have acceleration and deceleration built into the cycle with an average speed of 48mph.

At any rate, if you can supply the following data for any car/engine combo, I'd appreciate it:

Engine size
Rated HP
Top Speed
Cruising speed
mpg at that cruising speed

If you knew the actual horsepower needed for that cruising speed that would be icing on the cake.

some_other_dave 11-16-2015 12:05 AM

Here's as close as I know of:

Steady State Speed vs Fuel Economy results - CleanMPG Forums


JRMichler 11-16-2015 01:02 PM

There are several threads on coastdown testing. Coastdown tests provide hard numbers for the power to move the vehicle as a function of speed.

The actual engine power is higher because of driveline friction and accessory loads.

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