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Re: lowest reasonable highway rpm for a 440?
[Re: 360view]
#1058358
08/21/11 03:35 PM
08/21/11 03:35 PM
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Joined: Aug 2006
Posts: 247 DuPont, Washington
DZJim
enthusiast
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enthusiast
Joined: Aug 2006
Posts: 247
DuPont, Washington
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Quote:
Prior to adding the OD you could try a few 'real world' experiments by adding a vacuum gauge connected to the intake manifold then driving in top gear at 1700 rpm at whatever mph the current ratios give, up a progression of ever steeper hills, to increase load on the engine.
When the vacuum drops below the 6 to 8 inches of Mercury level, you are getting out of the operating region of good fuel economy.
You can estimate your horsepower load at different speeds and grades of hills using the stuff found in this article;
http://web.archive.org/web/20061123075351/http://www.etrucker.com/content/downloads/ccj0302.pdf
notice it is in pdf format
Although the article is focusing on big trucks, the same applies to cars climbing hills
This admittedly old (1960s) but 'universal' BSFC graph from the Taylors at MIT for engines shows the 'island' of good fuel economy:
Notice the bottom line of the graph is not rpm but 'average piston speed' in feet per minute which you get by converting your stroke from inches to feet, doubling it since it goes up and then down once per each revolution of the engine shaft, then multiplying by rpm
I didn't crunch through the above, but looks like good info.
Depends...
Cam, carb, manifold, heads? Grade; uphill even a tiny bit makes big difference. Wind, a little headwind makes a difference. Aerodynamic drag is proportional to the speed squared. 55 mph with 15 mph headwind is 70 mph for drag purposes. Big difference in drag. Tire type and pressure. Steel on steel is good e.g. railways. Obviously can't do that with your car, but you get the idea. Wheel alignment. Fluid viscosities in trans and axle, synthetics?.
I got a 250cc on/off road bike w/6spd trans. Torque below 4,000 rpm is negligible. It'll cruise along just fine at 55 mph in 6th until I hit a little uphill; have to downshift right away.
Almost same with my Corolla 5spd. BB MOPAR torque is a different story.
My $0.02
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