[enkeivette]

Originally Posted by Vettezuki

I love empirical observation. But, uh, don't we need mpgs at the theoretically most effecient speed and compare to some other base point, like 55mph? This also means you need a fixed moderate length test loop and vaguely similar conditions (temprature, humidity). Take it up to this level and I'll participate with my 5 very different cars.

Should I control head winds too?

[Vettezuki]

Originally Posted by enkeivette

Should I control head winds too?

You should control what you can control.

[enkeivette]

We'd have to empty the entire tank at a specific speed to get accurate results.

Besides, I'm not trying to convince anyone that pulling the most vacuum (gas engine) will provide the best economy, I'm already convinced of that. I'm just trying to find an average for the speed at which these cars pull the highest vacuum.

[Vettezuki]

Originally Posted by enkeivette

We'd have to empty the entire tank at a specific speed to get accurate results. . .

Nope. Fill the tank SLOWLY with the nozzle fully inserted. Stop after the first kick off. Run a loop (e.g., 50 - 100 miles). Fill up the SAME WAY AT THE SAME PUMP. The difference between this method and fully draining the tank would be nominal, maybe even better because a motor can run out of fuel while there's still fuel in the tank depending on the shape of the tank and location of the pump.

[BRUTAL64]

Originally Posted by enkeivette

We'd have to empty the entire tank at a specific speed to get accurate results.

Besides, I'm not trying to convince anyone that pulling the most vacuum (gas engine) will provide the best economy, I'm already convinced of that. I'm just trying to find an average for the speed at which these cars pull the highest vacuum.

That's highest vacuum at lowest possible RPM. Just in case you forgot.

[enkeivette]

Ben, true true.

Glenn, true true.

[st-evo-9*corn fed-8urvet*]

when u say highest vacuum what do u mean because say in an NA car the vacuum number would increase say giving u 15 vacuum...which in that case woudl be the highest. and in my case the highest vacuum number would be 1-0 seeing as how turbos force air in illiminating vacuum and creating BOOST!!

ill just toss in my results for my "highest vacuum runs"

the vacuum where i start to feel power and can maintain speed on a flat road is
10-9 vacuum and the air/fuel ratio on my car reads 18.1-17.6:1 at that vacuum the speed will usually get me to 65 on a flat road.

the highiest vacuum for me which is 1-0 vacuum can excellerate me on a flat road to 103mph at 16.1:1 air/fuel ratio.


so ya now define higher vacuum so i can be on ur page!

[enkeivette]

Originally Posted by st-evo-9*corn fed-8urvet*

...the vacuum where i start to feel power and can maintain speed on a flat road is
10-9 vacuum and the air/fuel ratio on my car reads 18.1-17.6:1 at that vacuum the speed will usually get me to 65 on a flat road.

<- This is what I'm talking about, the highest numerical vacuum. Are you sure you get the highest vacuum at the lowest speed of 65? Not 60 or 70? If so, I'll add it to the list.

My motor is boosted too, I see the best vacuum (or highest) around 10 or 12" off the top of my head.

[enkeivette]

Wanted to post another clarifying thought about the vacuum theory.

As Sean mentioned, a throttle blade is a restriction. When it comes to efficiency it would be best to be at WOT, this is one of the reasons diesel engines get such good mileage. But, for a gas engine, more throttle equals higher cylinder pressure (due to more air flow) which causes a higher demand for fuel... So although the engine is less efficient with the throttle closed, there is less fuel consumption, and that's primarily what we're concerned with here.

So how do we measure fuel consumption without doing it directly? We look at the vacuum guage, the higher the vacuum reading, the less the throttle is open and therefore the less fuel is being metered with the air. Because the vacuum guage is actually reading the restriction, the negative pressure which relates consequently to lower cylinder pressures and once again, less fuel consumption necessary to match the air being sucked in.

So, if the vacuum guage does not read the highest number possible while cruising, this means that the throttle is open more feeding the engine more air, and yes more fuel, to maintain speed. There is a greater need at lower rpms, (where the engine is making less power) for increased cylinder pressures to maintain speed.

Was that good, did that all make sense? I think I've said most of this before, just trying to be more clear.

[st-evo-9*corn fed-8urvet*]

oh ya crystal ass clear!!!

so ya after my tune my highest vacuum is 10-9 in numerical value which yields me about 65mph at on cold nights or cold weather in general

but this is only because of my tuning. a stock evo would probably hit 50-60mph

and if u look at just about every stock tune out there

there fuel areas read at 14.7 in the idle and cruising cells in relation to engine load and rpm.

this is because 14.7 is the air/fuel ratio that is perfect for best emissions....all cars i have seen that have installed a wideband o2 air/fuel ratio monitoring system will read at 14.7 no matter where u are in the cruising area of ur stock tuned factory map

so in essence u arent really gonna yield to much better gas milage by letting off the throttle because the car is always gonna compensate the afr and make it 14.7:1 which most cars to get the best fuel efficiency there afr needs to be at 15.8:1 to 16.1:1 on petrol based fuels.