Quote:
Originally Posted by racprops
OK;
"Old V8s were lucky to ever crack 20 mpg. But let's be charitable and use 20.
Let's also be charitable ('tis the season) and say we'll save 60%, or use 40% of the 20:
20 / .4 = 50 mpg
That's a long way from 80-120 mpg. In fact it's an exponentially long way.
There must be an error in my analysis.
A little help please!"
Well I have no real idea what old V8 got other that a 67 Mercury Cougar I had with all the silly hot rod stuff on it and found it got around 13MPG no matter what, city or highway, but I figured I had screwed it up.
And my 74 Chevy van which got 12 to 14MPG but it IS a Van and I normally drive fast..
NOW my newer cars get 29 MPG.
So take 30 MPG and get 3 times as much MPG and we are talking 90 MPG.
Seems possible to me.
What they did with old cars I cannot say.
Rich
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That is the concept you must start with. It is usually given as a percentage that represents the amount of fuel that is turned into actual mechanical power. Early carburetor equipped vehicles returned 18-22% of their potential fuel energy as mechanical energy at the crank. You cannot obtain more than 100%, I think that is plain. The rest of the energy is lost as coolant heat, exhaust heat and friction heat. Add that all up and you get your 100% of the fuel energy.
If your old Mercury was typical, and converted its fuel energy into mechanical energy at an 18% rate, and pulled down 13 mpg, you would more than double that mileage by using a Toyota Atkinson type engine which currently returns 38% thermal efficiency (TE). Your Mercury could get 26-27 mpg. How can one get higher thermal efficiency? Simply reduce the losses of heat energy to the coolant, out the exhaust and into overcoming friction. Reduce those losses and you will have more mechanical energy to spin the crank. If someone claims 100 percent efficiency, and they have heat in their coolant and out their exhaust and the oil pan is full of hot oil - they don't have 100% efficiency. To be exact, engineers will measure the heat and mass of those very things - coolant, oil and exhaust - to see what proportion of the fuel energy is being wasted and where. Now, remember, mileage is dependent on the vehicle too, not just the engine. Vehicle weight, aerodynamics , drive train losses and rolling resistance all measure in. Using your Mercury again, if you did manage to build the perfect engine and get 100% TE, you would pull down 100%/18% x 13 mpg = 72.2 mpg! That is quite impressive - if it were possible. But you and I know it is impossible to build that perfect 100% efficient engine.
So what can you do to get that 200 mpg? You can do what a member on this forum has already done - start with an efficient car and put an efficient engine in it. That car would be the Centurion. Do a search here on the forum and see a real 200 mpg capable vehicle. Yes, it is light, low, sleek and uses a small Kubota diesel with a TE of around 40%. Now, if the builder of the car chose to use anti-friction coatings and ceramic thermal coatings, he might gain another 5% in TE. In a vehicle that gets 20 mpg like my diesel pickup, that would be only 1 mpg. On the Centurion, that is 10 mpg! If you look at my post on another thread about Charles Pogue and his 200 mpg carburetor, that is essentially what he did to achieve his 200 mpg run. He had a specially modded car to use his carb and make the run. You will not get 100-200 mpg from an everyday car - certainly not your Mercury. Certainly not my Dodge Cummins.