POWER Vs MPG!!

I made a similar argument about gears giving better MPG and everyone said i was crazy. Obviously on the open highway it won't be so, but the way i see it is around town if you're easy on the gas and don't wind out every gear, a higher gear ratio just lets the engine move the car with less effort which should equal better MPG.

More RPM = More Air = More Fuel Consumed.

This is subjective of course.

I will say, I gained a +3 better MPG average after adding AFR cylinder heads, Performer Intake, and FTI custom camshaft.

I did not even ask for gas mileage. The engine did not have to work so hard with the factory top-end pieces, and got around easier, and more efficiently.

To get the best MPG possible on both carb & EFI cars, buy a vacuum gauge and watch it like a hungry hawk. If you learn to
drive the car and keep the manifold vacuum high, you will get some surprisingly good MPG figures. Thumper’s heads with
high port velocities and a roller cam with small overlap and fast ramp rates will provide the performance. That way you
can have a car with some real acceleration and not hurt your wallet on a regular basis.

in my car with all my mods i barely have to press the throttle to drive around normally.

Foxfan88 said:

in my car with all my mods i barely have to press the throttle to drive around normally.

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That's exactly my point with the gears aspect..i can literally cruise around town at 1500 rpm and not lug the engine...you can't do that with 3.08s. As stated before, more RPMs equal more fuel consumption...the key is just staying out of the gas and down on the RPMs.

my motor made 272/316 years ago and knocks down mid 20s (25-26 all day) on the highway.

85_SS_302_Coupe said:

That's exactly my point with the gears aspect..i can literally cruise around town at 1500 rpm and not lug the engine...you can't do that with 3.08s. As stated before, more RPMs equal more fuel consumption...the key is just staying out of the gas and down on the RPMs.

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This isn't always true. It's kinda hard for me to explain but I'll try. There is a sweet spot for automobiles. It's at the point where, as Mike said, the vacuum is highest. This will vary from car to car but it's never at the lowest RPM. My F-150 will get better mileage at 55 MPG than 45 MPG. The engine doesn't lug along trying to move the truck as hard at 55 as it does at 45 because the engine is further into the torque band at the higher RPM.

My mileage did go up when I swapped the factory 3.08 for 3.55 in my truck.

I don't really care about the Mustang since it's not a DD. I could park it tomorrow and it wouldn't make a difference other than the pleasure I would miss out on.

I think my supercharged Cobra gets 18MPH in the city. And it runs 12's spinning Nitto Drag Radials. Needless to say, I'm happy.

My car gets ish for gas mileage..

between 18-19mpg on the highway with stock 2.73's and stock engine (save for full exhaust). I'll be doing a set of thumpers soon, and i have an explorer intake and some 3.55's in the garage. I'm hoping this helps with the MPG's

I've thought about these things a bit, and here are a couple of my observations. Take 'em or leave 'em.

- High overlap cams = more power (n/a), but gas mileage suffers
- Numerically lower gears (as long as they're kept within reason) = better gas mileage
- Shooting for a cruising AFR (read: at low load) of 15.0-15.5 seems to strike a perfect balance between engine manners/responsiveness and mpg.

It is my opinion that freer flowing heads, intake, air-filter, headers, etc... increase volumetric efficiency which directly improves fuel mileage. Another technique to increasing fuel mileage and HP is bumping up compression (static and/or dynamic), which increases an engine's thermal efficiency.

In my stock C5 Corvette, I've observed that as long as the engine isn't at a lugging RPM (which highly depends on cam profile), lower RPM is typically better for fuel mileage. This seems true all the way down to about 40ish mph were the vette drops below 1000 rpm in 6th gear and begins to lug. At this point, going up steeper inclined require too much throttle.

Something to keep in mind is that an engine's tune, especially in regard to the commanded AFR, is heavily dependant on load. If you're at 100% load, even at low RPM, the computer will richen the fuel mixture significantly to decrease the risk of detonation. So at a lugging rpm, it is usually better to downshift into the previous gear.

These are just my opinions/ observations, and I have not conducted extensive studies on the matter.

FWIW, though most will likely think I'm full of crap, I have managed a best of 38.79 mpg from my C5 corvette over the 2nd half of a 660 mile road trip from FL to OH. A large portion of that part of the trip included driving through the hills of tennesee and kentucky. My strategy was to leave the windows up, vents on instead of A/C, manually control the throttle, stay in neutral while on downhills steep enough to maintain speed, and stay between 45 and 60 mph (45 going up hills, and usually around 55 on the flats. Of course on downhills, I'd pull the car out of gear and let it go to any speed without braking. The driver's information center reported a mpg on that trip of 36.x mpg, but I calculated 38.79 by measuring the gallons of fuel into the tank and dividing the mileage driven by it. Before anyone calls BS, I am willing to put my money where my mouth is and prove that I can do it again.

I believe that the best thing that the corvette has going for it is the 6th gear in its tranny (.5:1). With 3.42 rear gears, that makes for an astounding overal gear ratio of 1.71. Compare that even to a 5.0s 2.73 gears with a .675 5th gear, which is still 1.84.

My turbo car made 762 rwhp, but also got over 20 mpg with 3.73s and a 5 speed tranny. I couldn't get any more accuracy at the time without an odometer. I had to use my gps navigator for the rough mileage. I think that a couple very helpful factors that allowed me to do so well included my ability to lean the car at cruise with my Big Stuff 3, and the fact that my camshaft has low overlap, which is actually -2* at .050".

Chris

I get 20-21 mpg around town which is a couple higher than when I had 3:08 gears. On the highway I get 26-27 mpg. No complaints here.

Mustang5L5 said:

I could care less about gas mileage now It's all about power!!


Granted I do get a chuckle when i see someone delete their EGR, o2's and all their emmissions junk and then ask what CAI will give them better gas mileage

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I have cats and a smog pump, but when i built my car i didn't install the EGR sensors and tubes. My car was orginally a 4 banger so i have no canisters in the fenders, all that i'd have to add. I mean i could, it would just take alot. I wonder if that is the route cause of my lower mileage

tmoss said:

I get 20-21 mpg around town which is a couple higher than when I had 3:08 gears. On the highway I get 26-27 mpg. No complaints here.

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Tmoss are you running an EGR system?


I'm planning on getting a set of thumpers and having you port my explorer intake. I'm hoping that helps with both power and MPG.

Yes, I run an EGR system - had to smog until this last year.