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Old 06-21-2007, 05:45 PM   #1
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Turbo FE?

I know that turbos behave completely different than other cars, at least in the way of fuel milage.

Standard cars, Go easy on the acceleration, but use as high a gear as possible, and depress the throttle as much as possible without revving high. (Wider throttle=less resistance ect...)

Problem is, that turbo cars, if I have the throttle low, and floor it, I start getting into a boost condition, which sucks more gas, right?

I'd heard from some people that it's best to have minor turbo "boost" that will keep the vacuum/boost level at 0.

What is the best way to get fuel milage out of a turbo car? Is it better to go 65 and have the EGR and the turbo spooling the vac down to 0, or is it better to go 55 and have less wind resistance?
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Old 06-21-2007, 06:19 PM   #2
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the boost only helps with acceleration. that hold true for performance and fuel economy.

also the more throttle for better fuel economy in the low rpm range holds true because it is best to get to the top gear as quickly as possible so that you have the least amount of combustions per rotation of the tire.

these principals hold true whether the car is turbo or not

the advantage of having forced induction is the extra power out of smaller displacement. more power meaning faster acceleration, and from a fuel economy standpoint, less combustions spent in the lower gears.

with that said i will address your last question. it is almost always better to go as slow as reasonable in the cars top gear. there are not any cars out there that get better mpg at 65 than 55.
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Old 06-21-2007, 07:23 PM   #3
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The disadvantage of having forced induction is that if you have a throttle that is open any significant amount, you don't just get the extra fuel used from the higher revs you might hit. The turbo shoves more air into the motor, and therefore more fuel.

A turbo that is at WOT at 2500 RPM uses WAY more gas than cruising at 3000rpm. Depending upon boost levels, it could be more than twice the gas.

Therefore, I can't have do the "half throttle at 1500 is better than a quarter throttle at 2000" Because at that half throttle, I'm boosting 5psi, And shoving 30% more gas into the motor than I would if I was at quarter throttle and not boosting at all.
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Old 06-21-2007, 07:26 PM   #4
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Perhaps Landspeed will chime in. I believe his car has a turbo.
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Old 06-22-2007, 05:06 AM   #5
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Boost is VERY addicting and will ultimately lead to much less mpg. LOL!
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Old 06-22-2007, 11:53 AM   #6
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My car does indeed have a turbo

If you have a petrol turbo, you need to make sure you have a boost gauge.

Then, you assume that a tiny little bit below '0' vacuum is equal to full throttle, and halfway between idle and the '0' vacuum is equal to half throttle.

On my car, when I go to boost at low RPM you get a tiny bit more power, but the fuel usage more than doubles (goes from 4.4 to 1.5 on my uncalibrated SuperMID).

If you really want to get good FE on a turbo car, get a wideband lambda sensor, so you can see when the car starts enriching the mixture. The 'half throttle' position I talked about above is where my car starts enriching the mixture, so there is no point going above that.

If you look at my gaslog, you will see that turbo cars can get good FE . If I drive even a bit of the time on boost, my FE goes to less than half - it just drinks fuel with little benefit (other than the fun of boost). I have just realised that my car has two of the brakes dragging a bit - and have been for ages, and despite this, I am getting good MPG over the EPA!.

The advantages of the turbo are that, you are using 'waste' energy to force the air into the engine (even when at 'half throttle' as described above). This means that you are wasting less energy dragging the air into the engine. Another advantage is that, the turbo makes the air move faster into the engine, so you use less throttle to get the same vacuum. If the air moves faster then it will be more turbulent so might give better fuel mixing. If nothing else, the fact that you get the same vacuum with the throttle plate more closed (because the turbo is pushing air against the throttle plate), means you get the air forced through a narrower opening so it is more turbulent.

On the official tests, my car gets better economy than the 1.8 non-turbo, despite the fact that my car enriches earlier (as it is turbo), and also is lower compression.
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Old 06-22-2007, 03:06 PM   #7
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Let's hear DRW.
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Old 06-23-2007, 10:07 PM   #8
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Quote:
Originally Posted by Biffmeistro View Post
The disadvantage of having forced induction is that if you have a throttle that is open any significant amount, you don't just get the extra fuel used from the higher revs you might hit. The turbo shoves more air into the motor, and therefore more fuel.

A turbo that is at WOT at 2500 RPM uses WAY more gas than cruising at 3000rpm. Depending upon boost levels, it could be more than twice the gas.

Therefore, I can't have do the "half throttle at 1500 is better than a quarter throttle at 2000" Because at that half throttle, I'm boosting 5psi, And shoving 30% more gas into the motor than I would if I was at quarter throttle and not boosting at all.
i think you are missing my point. is 2500rpm the lowest shift point??? and if you are going to be burning gas anyway what does it matter how much is burnt in a short period if in the end you end up burning less????

of course you are going to burn less fuel just maintaining speed than you will be accelerating. that is why it is best to accelerate as best as the car allows in the lowest rpms possible. if you had read my post more carefully maybe you could have learned...
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Old 06-23-2007, 11:42 PM   #9
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>>if you had read my post more carefully maybe you could have learned...

Jeesh, lighten up. And consider the possibility that the corollary is true.
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Old 06-25-2007, 06:52 PM   #10
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Quote:
Originally Posted by lca13 View Post
>>if you had read my post more carefully maybe you could have learned...

Jeesh, lighten up. And consider the possibility that the corollary is true.
what corollary? we are speaking pretty subjectively... either way there isnt a car that gets better mpg at 65 than 55 given all other variables are made constant. also if you are shifting at 2500 you are definitely not shifting at the lowest rpm. i dont think the corollary implied is able to be proven. although i have no intention of disproving it

i didnt mean to make it seem like i was getting heated, i just get annoyed when people disagree with me just because i am not telling them what they want to hear.
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