# Air vs fuel consumption **URL:** \ **Category:** Maintenance/Repairs\ **Created:** [June 15, 2015, 7:16pm UTC](https://community.cartalk.com/t/air-vs-fuel-consumption/90289 "2015-06-15T19:16:56Z")\ **Posts on this page:** 8\ **Page:** 1
**Author:** ![rocketman](https://avatars.discourse-cdn.com/v4/letter/r/eada6e/32.png) [@rocketman](https://community.cartalk.com/u/rocketman)\ **Post date:** [June 15, 2015, 7:16pm UTC](https://community.cartalk.com/t/air-vs-fuel-consumption/90289/1 "2015-06-15T19:16:56Z")
I was listening a another car talk kind of show (no, not this Car Talk) it was a local show. Anyway, someone was discussing how much air is used vs. fuel in an 11 to 1 compression engine, and he said it was 11 gallons of air to one gallon of fuel. I always believed it to be a heck of a lot more than that. Comments? Rocketman ---
**Author:** ![texases](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/texases/32/862_2.png) [@texases](https://community.cartalk.com/u/texases)\ **Post date:** [June 15, 2015, 7:26pm UTC](https://community.cartalk.com/t/air-vs-fuel-consumption/90289/2 "2015-06-15T19:26:53Z")
You’re right, it’s a mass ratio, not a volume ratio. The ‘stochiometric’ ratio (enough air to burn all the gas, but no more) for gasoline is about 15:1. It has nothing to do with compression ratio, either, so that person was doubly mixed up! ---
**Author:** ![Mustangman](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/mustangman/32/44130_2.png) [@Mustangman](https://community.cartalk.com/u/Mustangman)\ **Post date:** [June 15, 2015, 9:13pm UTC](https://community.cartalk.com/t/air-vs-fuel-consumption/90289/3 "2015-06-15T21:13:03Z")
A perfect ratio is called stoichemetric and it is 14.7 to 1, theoretically. More air say 16:1 is lean and less say 13:1 is rich. Rich makes more power up to about 12.7:1 depending on lots of things but makes lots more pollution. Compression ratio is how much the piston squeezes the air/fuel mixture, or these days air only in direct injection engines, as the piston goes from the bottom dead center to top dead center. ---
**Author:** ![MG-McAnick](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/mg-mcanick/32/188_2.png) [@MG-McAnick](https://community.cartalk.com/u/MG-McAnick)\ **Post date:** [June 15, 2015, 9:45pm UTC](https://community.cartalk.com/t/air-vs-fuel-consumption/90289/4 "2015-06-15T21:45:51Z")
The fuel ratio of 14.7 **:** 1 is by the weight or mass of the air, not the volume of the air. Figure that a 232 CID engine displaces almost exactly a gallon. Once each cylinder has completed its intake stroke, a gallon of air has been drawn in. Obviously that’s not enough air to burn 1/11 of a gallon of gas. ---
**Author:** ![BillRussell](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/billrussell/32/3179_2.png) [@BillRussell](https://community.cartalk.com/u/BillRussell)\ **Post date:** [June 15, 2015, 11:52pm UTC](https://community.cartalk.com/t/air-vs-fuel-consumption/90289/5 "2015-06-15T23:52:35Z")
1 gallon of gasoline weighs 6.073 lb multiply by 14,7 to get 89.27 lb of air. Density of air varies with temperature and pressure, but I’ll use 0.0765 lbm/ft3 (sea level and at 15°C) to get 1167 cubic feet, which is 8730 gallons So (if my math and physics are correct) 1 gallon of gasoline requires 8730 gallons of air. ---
**Author:** ![asemaster](https://avatars.discourse-cdn.com/v4/letter/a/5f9b8f/32.png) [@asemaster](https://community.cartalk.com/u/asemaster)\ **Post date:** [June 16, 2015, 12:33am UTC](https://community.cartalk.com/t/air-vs-fuel-consumption/90289/6 "2015-06-16T00:33:14Z")
It’s a good thing 80% of the air that goes into an engine comes right out of the tailpipe otherwise we’d have an air shortage along with water and gas shortages. ---
**Author:** ![the\_same\_mountainbike](https://avatars.discourse-cdn.com/v4/letter/t/c89c15/32.png) [@the\_same\_mountainbike](https://community.cartalk.com/u/the_same_mountainbike)\ **Post date:** [June 16, 2015, 3:17am UTC](https://community.cartalk.com/t/air-vs-fuel-consumption/90289/7 "2015-06-16T03:17:31Z")
It’s a good thing he’s so wrong. A 5 litre engine running at 5,000 rpm inhales 12,500 litres (3,300 gallons) of air every minute. If it inhaled 1 gallon of gas for every gallon of air, it would be inhaling 275 gallons of gas every minute. Man, would you need a BIG gas tank! And for anyone checking my arithmetic (PLEASE check my arithmetic!), remember that it only inhales every second rotation. ---
**Author:** ![George\_San\_Jose1](https://avatars.discourse-cdn.com/v4/letter/g/e5b9ba/32.png) [@George\_San\_Jose1](https://community.cartalk.com/u/George_San_Jose1)\ **Post date:** [June 16, 2015, 4:27am UTC](https://community.cartalk.com/t/air-vs-fuel-consumption/90289/8 "2015-06-16T04:27:16Z")
If you want to do a little puzzler, try modeling gasoline as a long string of … C-H2 's … , which an individual segment reacts with the oxygen in air as CH2 + (3/2) O2 = CO2 + H2O * * * See if you can calculate the air to fuel ratio (by mass) using the respective atomic masses, approximately as C 12 O 16 H 1 And that the percentage (by mass) of O2 in air is 21% . [![](http://term2chemace.wikispaces.com/file/view/periodic_table_complete.png/209988558/800x470/periodic_table_complete.png) ](http://term2chemace.wikispaces.com/file/view/periodic_table_complete.png/209988558/800x470/periodic_table_complete.png) > **[Calculate the mass percentage of oxygen in dry air?](https://answers.yahoo.com/question/index?qid=20101112140832AAE3aJ4)** > > Air is a mixture of several gases. The 10 most abundant of these gases are listed here along with their mole fractions and molar masses. > Component Mole fraction Molar...