Gas Mileage

[273]

I was reading an old thread on engine size and gas mileage, instead of bring it back from the dead I'll put my thoughts here

1st thing, lets assume for now most engines have same efficiency, it takes the same amount of fuel and air in a given amount of time to make a certain hp, (thats why hate the miss use of the phrase "No Replacement for Displacement" if anything it should be no replacement for bore size) but anyways.

2nd the cars performance should be decided even if it just enough HP to drive the car down the road at highway speeds and safely pull into traffic, but to me the minimum hp an abody should have is 200hp I always find peppier cars better on gas for me since I got a heavy foot . Most cars need 50-70hp to drive at highway speed (dependent on aerodynamics, weight and speed) so a stock slant six is barely adequate at about 110hp, so the minimum rear gear you can get away with is where your engine makes 70ish hp (remember it takes the same amount of fuel to make 70hp whether its a slant six or a 440 so either should get the same mpg if you could find high enough gears for the 440 but it would have acceleration of a /6). A 440 is gonna make it closer to idle where a slant six will make it closer to peak power. Gearing is the great equalizer when it comes to different displacements whether its performace or gas mileage.

Speaking of displacement and performance (hp) and gas mileage you probably want 0.7-0.8hp per cid cause for good mileage you don't want the peak power to high in the rpm band and anything under 0.7 hp per cid is pretty inefficient engine.

Energy can't not be lost or gain but only transfered from one state to another, no free lunch
Every mod you do to your car has trade offs, if you do it wisely you can get close to having your cake and eat it to. So I guess what im saying if built efficiency similar performance is gonna get similar gas mileage if built right whether you build a 273 or 440.

P.S. I got a 1980 Bronco that im fixing up hope to have it back on the road next year, its got a 400 in it and got 10 mpg when I parked it, I bought headers and performer intake and carb and went with a Comp 256 cam, could of went to 262 or 268 with out sacrificing any bottom end and gain 20-30hp and 500-1000 rpms but my truck will rarely see north of 4500 rpm and even a lost of 1/2 mpg over the 256 cam to me wouldn't be worth it.

 

[273]

I just read what I wrote it's a bit of a rambling mess

 

[Dart Sport 360]

LOL! um... what he ^ said....

 

[DionR]

Just a random thought, but doesn't internal friction play a part? I would guess that a motor that absorbs (or wastes) more hp to output 70 hp would get less mpg than a motor that used less hp to do the same thing.

So, if a 440 needs 50 hp to make 70 hp, in total it would need to make 130 hp to push it down the road. But if a 225 only needs 35 hp to make 70 hp, it would only require 105 hp to do the same thing. Since fuel = hp, the 440 is never going to be as efficient as the slant, provided they are both equally efficient at using the fuel they need.

 

[inkjunkie]

I was reading an old thread on engine size and gas mileage, instead of bring it back from the dead I'll put my thoughts here

1st thing, lets assume for now most engines have same efficiency, it takes the same amount of fuel and air in a given amount of time to make a certain hp, (thats why hate the miss use of the phrase "No Replacement for Displacement" if anything it should be no replacement for bore size) but anyways.

2nd the cars performance should be decided even if it just enough HP to drive the car down the road at highway speeds and safely pull into traffic, but to me the minimum hp an abody should have is 200hp I always find peppier cars better on gas for me since I got a heavy foot . Most cars need 50-70hp to drive at highway speed (dependent on aerodynamics, weight and speed) so a stock slant six is barely adequate at about 110hp, so the minimum rear gear you can get away with is where your engine makes 70ish hp (remember it takes the same amount of fuel to make 70hp whether its a slant six or a 440 so either should get the same mpg if you could find high enough gears for the 440 but it would have acceleration of a /6). A 440 is gonna make it closer to idle where a slant six will make it closer to peak power. Gearing is the great equalizer when it comes to different displacements whether its performace or gas mileage.

Speaking of displacement and performance (hp) and gas mileage you probably want 0.7-0.8hp per cid cause for good mileage you don't want the peak power to high in the rpm band and anything under 0.7 hp per cid is pretty inefficient engine.

Energy can't not be lost or gain but only transfered from one state to another, no free lunch
Every mod you do to your car has trade offs, if you do it wisely you can get close to having your cake and eat it to. So I guess what im saying if built efficiency similar performance is gonna get similar gas mileage if built right whether you build a 273 or 440.

P.S. I got a 1980 Bronco that im fixing up hope to have it back on the road next year, its got a 400 in it and got 10 mpg when I parked it, I bought headers and performer intake and carb and went with a Comp 256 cam, could of went to 262 or 268 with out sacrificing any bottom end and gain 20-30hp and 500-1000 rpms but my truck will rarely see north of 4500 rpm and even a lost of 1/2 mpg over the 256 cam to me wouldn't be worth it.

I just read what I wrote it's a bit of a rambling mess

Hope you are ready to duck.....when the / crew reads what is highlighted they will probably be gunning for you lol....

Maybe a bit rambling but it sorta made sense to me....

 

[CUDA69]

The larger, stronger and heavier drive train of the 440 car takes more HP to turn.

 

[273]

Just a random thought, but doesn't internal friction play a part? I would guess that a motor that absorbs (or wastes) more hp to output 70 hp would get less mpg than a motor that used less hp to do the same thing.

So,440 needs 50 hp to make 70 hp, in total it would need to make 130 hp to push it down the road. But if a 225 only needs 35 hp to make 70 hp,/6,,t would only require 105 hp to do the same thing. Since fuel = hp, the 440 is never going to be as efficient as the slant, provided they are both equally efficient at using the fuel they need.

I was taking it to the extremes yes the 440 extra weight of the engine and the internal reciprocating assembly, more internal surface area for friction, bigger more inefficient bore size will effect gas mileage compared to /6 or even a SB but I'm sure that the weight and aero of the cars a 440 comes in has more effect on gas mileage. But most people problably are deciding between /6, 318 or 360, but in reality I find theres not much mileage difference between non econo boxes bigger rear wheel drive cars I've probably own 60 or more cars and driven 40 or so on the road, I'm not much of a highway driver and I find most get 15 mpg plus or minus 3 mpg, my 5th Ave gets 15, my cab a Crown Vic get 16, my 5.9 jeep gets 12.5 mpg, even the half a dozen 2.2 cars I've own didn't get to much over 20 mpg, and the dozen of /6 cars I've own were no better than any 318 I've driven.

I guess what I was trying to say is if you built an NA /6, 273, 318, 360 or even a 440 to the same performance level 0-60, quarter mile or whatever, you'll end up with similar mileage, plus with the average engine choice we got for an abody you'll be lucky to see anything over 20 mpg in town even car manufacturers with all there technology are having a hard time get much more out of abody size cars.