# Gas Mileage Calculations **URL:** \ **Category:** Factual Questions\ **Created:** [May 23, 2003, 7:03am UTC](https://boards.straightdope.com/t/gas-mileage-calculations/176986 "2003-05-23T07:03:55Z")\ **Posts on this page:** 6\ **Page:** 2
**Author:** ![Tuckerfan](https://avatars.discourse-cdn.com/v4/letter/t/eada6e/32.png) [@Tuckerfan](https://boards.straightdope.com/u/Tuckerfan)\ **Post date:** [May 26, 2003, 2:32am UTC](https://boards.straightdope.com/t/gas-mileage-calculations/176986/21 "2003-05-26T02:32:21Z")
> [@](#): > > \*Originally posted by RJKUgly \* > **That 32 GPH has to be a max flow rate, not a real world average.** I think you’re right about that, but the pump has a fuel return line, so it maybe that the pump’s _always_ pushing that kind of fuel load to the carb, and what’s not needed is simply sent back to the tank. So, perhaps the question is, “What’s the real world average for a car like the one I’m planning on converting?” ---
**Author:** ![JimOfAllTrades](https://avatars.discourse-cdn.com/v4/letter/j/ba8739/32.png) [@JimOfAllTrades](https://boards.straightdope.com/u/JimOfAllTrades)\ **Post date:** [May 26, 2003, 4:05am UTC](https://boards.straightdope.com/t/gas-mileage-calculations/176986/22 "2003-05-26T04:05:23Z")
> [@](#): > > \*Originally posted by Tuckerfan \* > \*\*So, perhaps the question is, “What’s the real world average for a car like the one I’m planning on converting?” \*\* Hmmm, not sure, but maybe I can add a data point. My buddy’s dad had a big Chrysler (a 300?) in the 70’s, and it seems to me it got around 12 mpg. Given that, your fuel consumption would be about 1 gph at parking lot speeds, and around 7 gph at freeway speeds. But 12 mpg for a sedan isn’t all that hot these days, so you’d probably want to do a little better than that. Get it down to 4-5 gph with enough power to push the car at freeway speeds, and you’re at least in the ballpark. ---
**Author:** ![Tuckerfan](https://avatars.discourse-cdn.com/v4/letter/t/eada6e/32.png) [@Tuckerfan](https://boards.straightdope.com/u/Tuckerfan)\ **Post date:** [May 26, 2003, 12:44pm UTC](https://boards.straightdope.com/t/gas-mileage-calculations/176986/23 "2003-05-26T12:44:22Z")
> [@](#): > > \*Originally posted by RJKUgly \* > \*\*Hmmm, not sure, but maybe I can add a data point. > > My buddy’s dad had a big Chrysler (a 300?) in the 70’s, and it seems to me it got around 12 mpg. Given that, your fuel consumption would be about 1 gph at parking lot speeds, and around 7 gph at freeway speeds. > > But 12 mpg for a sedan isn’t all that hot these days, so you’d probably want to do a little better than that. Get it down to 4-5 gph with enough power to push the car at freeway speeds, and you’re at least in the ballpark. \*\* Well, depending upon the year, a Chrysler 300 was the same thing as a Newport except for trim and a few options. The engines in them ranged from a 318 to a 440 with a 4 barrel carb. 12 MPG sounds a little low for milage compared to the one I had in high school, but not horrifically low. I have managed to find some formulas which should help shed some light on the matter, but I’m too tired at the moment to do the necessary char mapping to be able to post them. I’ll do it later today, if I can find the time. (Assuming the board can handle the coding, which I’m not sure that it can.) ---
**Author:** ![Tuckerfan](https://avatars.discourse-cdn.com/v4/letter/t/eada6e/32.png) [@Tuckerfan](https://boards.straightdope.com/u/Tuckerfan)\ **Post date:** [May 26, 2003, 10:23pm UTC](https://boards.straightdope.com/t/gas-mileage-calculations/176986/24 "2003-05-26T22:23:46Z")
Okay, I’ve got the formulas and some stats for the Chrysler engine, and some more info on the Tesla turbine (TT), if I can get some help crunching the numbers I’d be most appreciative. And, apparently the symbol font’s been turned off, so what I’m going to do is put the Greek name of the symbol in brackets like this: [Omega]. The first set comes from _ **La Locomotive A Vapeur** _ by Andre Chapelon. He doesn’t give much explaination of the formula, intending that for a 2nd edition which was never published. He writes > [@](#): > > it is the cross section [Omega] of gas area through the tube bank and the ratio 1/d=1/4XS/[Omega] of _the Length_ L _to the diameter_ d _of the tubes_ which controls the functioning of the locomotive boiler from the viewpoints of _power_ and _efficency_. (emphasis in the original). The second set comes from a series of articles on building the TT that appeared in the _Home Shop Machinist Magazine_ from Sept. 01 to June '02. The optimum runner speed for the TT is a peripheral velocity of about 750 ft/sec. The given formula for figuring out the theoretical performance of a TT is: T=6[Pi][Mu]VR(R[sup]2[/sup]-r[sup]2[/sup])/2H Where T= Torque in N-m (Newton-meters) [Mu]=1.79X10[sup]-5[/sup]Ns/m[sup]2[/sup] V= the peripheral velocity of the disk in m/s R=The radius of the disk in m. r=The radius of the central hole in the disk in m. H=1/2 the disk spacing in m. (In the above formula, [Mu] is the dynamic viscosity of the fluid. The value I have is for air as I don’t have the value for steam handy.) This gives the torque produced by 1 side of 1 disk. The outside of each end disk apparently are capable of providing sealing and do not generate any power. I am planning on using an 18" dia. turbine, with a 7" center hole, with a total of 6 disks spaced 0.031" apart for a total of 10 power producing sides. The author of the article on the TT built a smaller turbine which was predicted by this formula to yield a HP of 0.096, but in use he got 0.14 HP out of the TT using [120 psi](http://bbs.homeshopmachinist.net//Forum1/HTML/000318.html). The information I can find on the Chrysler 383 engine I’ll be replacing is somewhat contradictory, but some of it comes from police car data sheets, so that might explain it. The gross HP is listed on [this site](http://www.allpar.com/squads/engines.html) as 290 and the gross torque is listed as 390. The fuel economy I can find is 10 MPG. From what I’ve been able to gather the standard psi of a steam car’s boiler is 400. I’ve just stumbled across another [site](http://www.angelfire.com/mi3/gmpr/ptbc.htm) which might have some figures for the TT, but I haven’t had a chance to do a lot of poking around on it yet. So is this enough, you think? Or do I need more data? If so, what? ---
**Author:** ![Tuckerfan](https://avatars.discourse-cdn.com/v4/letter/t/eada6e/32.png) [@Tuckerfan](https://boards.straightdope.com/u/Tuckerfan)\ **Post date:** [May 27, 2003, 8:05am UTC](https://boards.straightdope.com/t/gas-mileage-calculations/176986/25 "2003-05-27T08:05:07Z")
Just realized that I forgot something. [Jay Leno’s Doble](http://popularmechanics.com/automotive/sub_coll_leno/2003/5/a_case_for_steam/) has a boiler which contains some 525 feet of tubing, which appears to be about 1/2 an inch in diameter, I plan on using a Doble-style boiler since they seem to be the best designed. Leno’s article about the car is pretty interesting, though he doesn’t mention the kind of mileage the car gets. ---
**Author:** ![sailor](https://avatars.discourse-cdn.com/v4/letter/s/a587f6/32.png) [@sailor](https://boards.straightdope.com/u/sailor)\ **Post date:** [May 28, 2003, 3:10pm UTC](https://boards.straightdope.com/t/gas-mileage-calculations/176986/26 "2003-05-28T15:10:19Z")
As I said in the other thread and repeated in this one, what you need to determine is the specific consumption of the engine: grams of fuel per kwh delivered. A larger diesel has a specific consumption in the 180 - 200 g/kwh range. The (tiny) yanmar in my boat has a specific consumption of 280 g/kwh. I do not know what the specific consumption is for gasoline engines but I am guessing it may be somewhat lower. In any case, the thing is that you would need to achieve a specific consumption under 250 g/kwh or better just to be in the same league as regular cars. That is what you need to determine. Build a motor that is efficient in converting heat into mechanical energy and the mileage will take care of itself. [Previous page](https://boards.straightdope.com/t/gas-mileage-calculations/176986.md?page=1)