P&G not helpful in Saturn SL2

[Project84]

Keep in mind fellas, my average probably won't get much higher than what it is because I rarely drive 100% highway....

at best, I probably average 20% highway each tank, my last fillup, the 38.xx was nearly 70% highway.

My 100% city mileage seems to have momentarily capped off at 31.

[Wingmn]

I've read through this entire thread and wanted to post my numbers up. I have a 93 SL2 Auto - and I've managed to consistently get 37-38MPG going to and from work (11 miles 1 way). I can't seem to get past that 38mpg point though, seems like without doing some real mods I won't get past it. Anyone have any suggestions? I've posted my fill ups for this entire year - I did get 41mpg 1 time, but that was a special circumstance.

No Scanguage - I have to rely completely on tank average MPGs.. I've had this SL2 since 1996, and have actively tracked my mileage since 2004.

If anyone has any suggestions to get past that 38.8 MPG ceiling I've hit I would welcome the advice. Thanks!

[s1120]

Originally Posted by Project84

I have complete confidence that if I was doing all highway, I'd be seeing 36 to 37 MPG. My best highway mpg to date was 33.xx mpg to Louisville and back w/ windows up, A/C used the entire trip, tires at door jamb spec (26 front 28 rear I think?) one passanger, cruise control used the entire trip, and ambient temp was 90*F both ways. That was 2 years ago when the car had all kinds of bugs and before I knew about hypermiling. My best mixed tank back then was 27 mpg...

Advance to today, my most recent mixed tank was probably 90% city and got 31.xx mpg. That's 4mpg improvement over 2 years ago. Even though it's not realistic, lets just say I get 4mpg improvement on my best highway tank, that would land a solid 37mpg.

Till I read this I thought you had some real problems. My Wifes 94SL2 auto got 31-32 with her driving. Pedel to the floor, 75+mph etc!!

Have you had the temp sensor changed??? They are problemmatic, and cause lower MPG. Its cheep, and knowing they have a problem, you might want to toss one in there. Oh and make sure your T stat is good. You should be a tick under 1/2 way on the temp guage when warm.

Bolth of those had went bad on mine, and the MPG tanked!!!!

[Wolfcollar]

Would somebody please explain to me how an HAI helps FE? Cold air is more compresses, putting more air into the engine and causing a higher ompression ratio. Cold fuel burns at a faster rate, giving you more power. PLEASE tell me where the notion that a hot engine runs better? It's a standard of mechanics, auto and diesel, to make the air cold in order to provide more power and economy.

[Jay2TheRescue]

Cold air is more dense, and has more oxygen, so therefore the computer is going to have to increase the fuel injector duty cycle to keep the air/fuel ratio at the proper level. When using an HAI, your power goes down, but your mileage goes up.

[bobc455]

Wolfcollar-

You are thinking in terms of making the most HP from a given displacement. For this, you want things as cold as possible so you can cram as much into the cylinder as possible. That works for generating horsepower.

However, remember from your HS chemistry days that the hotter a chemical, the faster a reaction will take place. So if you can get the air/fuel combustion to take place more quickly (by having hotter air and fuel), that essentially gives the reaction more time- and the more time, the more of a chance you have to complete the combustion reaction. This is how you extract the most energy from a given amount of fuel (and therefore maximize efficiency).

Generating horsepower is about maximizing volumetric efficiency, however generating best gas mileage is about maximizing combustion efficiency.

Make sense?

-Bob C.

[GasSavers_Erik]

One of the reasons why a gasoline engine is less efficient than a diesel is because it takes a lot of energy to produce and maintain a partial vacuum behind the throttle butterfly valve.

Using a hot air intake means that less air/fuel gets into the engine, which means you have to open the throttle wider to do the same amount of work which means a lower level of efficiency robbing manifold vacuum is generated.

Not: Running the throttle wide open is not a good idea since most ECU's will richen the mix up under those conditions.

Less vacuum is the same concept behind why pulse and glide works on most vehicles.

[Wolfcollar]

You make sense on some points but I still don't understand how lower power could possibly increase mileage. Cold air does not only increase HP, it maximizes torque over the greatest range. High torque allows for more efficient acceleration. You don't want to lessen the amount of gas/air in the engine. It forces you to get into the throttle more, causing you to leave your high torque range in favor of your high HP range--not good for gas. The whole idea behind a turbo is forcing more air into the engine. Yes, it forces more fuel in with it, but the torque as well as horsepower gained cause a higher efficiency gain than the added fuel in the cylinder causes loss. Cold air broadens your torque range, giving you more area in which to accelerate at high efficiency. This is one of the reasons why not only are semi trucks turbocharged, they have an intercooler, to cool air entering the engine.

[8$PG]

Under most driving conditions you are using little power and throttle. This is inefficient because of the large pumping losses. Hot air in the intake reduces the pumping losses but makes the engine less efficient at wide open trottle loosing some maximum power instead. It's a tradeoff. The best way would be to have two intake channels and shifting between them depending on the power requested. Even diesels use preheating of air intake to increase efficiency but I can't explain the reason why this works. Maybe it has something to do with how the fuel is vaporised when injected into the pressurized cylinder. Even pre-heating the fuel is benefitial.

[bobc455]

Remember that for maximum MPG, you want to use the smallest amount of fuel as possible - and, since you want to maintain a constant A/F ratio (14.7), as little air as possible.

A turbocharger helps you cram more air into the engine, but that isn't what we're after! We want as little air as possible.

And, what we're really trying for is to extract the maximum amount of energy from that small amount of fuel.

Start thinking in those terms, and you'll understand better.

-Bob C.