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Old 04-14-2009, 10:14 PM   #1
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Default Turbos and MPG

This discussion is from a local Mazda forum I grace with my presence every now and then..
My posts are in red.

Does anything this guy is saying make sense to anyone?
to keep my car at 0 on the boost gauge you would have to be slightly accelerating at all times.. And it seems to me, that the more vacuum the motor is creating the less effort the engine is putting forth, less exhuast = less spool right?
Am I correct in thinking this or should I just shutup?
Quote:
Originally Posted by arashi_nero
when you're on the highway, it's not that hard. the best place to have your turbo is at 0 (no vac and no boost), supposedly that's where you get the best gas mileage with a turbo.




Physics Injection: with turbocharged vehicles and gas mileage, the engine will compensate for the increased air being compressed into the engine with more fuel. Your ecu is constantly trying to maintain the perfect air/fuel ratio (i think its 11:1 but i may be wrong). So if your turbo is spooling, you are throwing more air in, and hence more fuel being dumped in to compensate.

Simple equation:
Less air in aka. less boost
MPG > Boost
More air in aka. more boost
MPG < Boost

Quote:
Originally Posted by kibert
Weird I've always thought you got the best MPG with more vacuum, that way the engine is working to spool the turbo.. I'll have to research that.

Due to simple combustion engine mechanics, the more work an engine has to do, the more fuel it needs to complete the task. Having increased vacuum means that the engine is working more.
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Old 04-14-2009, 10:17 PM   #2
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More vacuum = less air

Less air = less fuel
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Old 04-14-2009, 10:19 PM   #3
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ding ding ding..
I dont see why that's so hard to accept
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Old 04-14-2009, 10:44 PM   #4
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it depends on AFR, vac, and RPM. All the turbo does is add parasitic back pressure. 0 will not keep accelerating your car, at some point the drag will equal the acceleration and cancel it out.
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Old 04-14-2009, 11:30 PM   #5
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That happens around 100-110mph.

Not that I've tested that or anything.
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Old 04-14-2009, 11:32 PM   #6
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Quote:
Originally Posted by TrickerZ View Post
...at some point the drag will equal the acceleration and cancel it out.
And at that point, I'm sure you'll be getting stellar MPG...
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Old 04-14-2009, 11:39 PM   #7
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Quote:
Originally Posted by TrickerZ View Post
it depends on AFR, vac, and RPM. All the turbo does is add parasitic back pressure. 0 will not keep accelerating your car, at some point the drag will equal the acceleration and cancel it out.
+1 but 0 vs. drag end nearby 120 mph. +-15 inHg enough to cruise in the 1.8, looking at the boost/vacuum gauge can know if it suits to downshift on a hill climb for better MPG
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