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Unread 06-18-2009, 05:10 AM   #1
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Default Fuel Economy: Throttle vs RPM?

Which should always be lower? I have a 4-speed automatic, but it powers way different because of my Turbo I put in it. I used to get 23/26MPG City/Highway with my '92 turbo, and this '89 turbo get's about 16/20MPG City/Highway. the 1989 740 turbo and the 1992 940 turbo were not much different from each other. The only real engine difference was the Mitsibushi TD05 in the '92, and the Garrett T3 in the '89. Bot got around 17/19MPG City/Highway. (my mods increase the fuel economy).
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Unread 06-18-2009, 06:20 AM   #2
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On most vehicles, and especially a vehicle with FI staying in the lower RPM's will have better overall fuel economy. Staying out of boost should have a considerable positive affect on your fuel economy, but then again that isn't very fun.

I have noticed that with my jeep if I drive like a granny with an egg beneath the pedal (Which is very hard for me to do) my jeep will shift at 2.5k RPM's, and I get around 14 city (New 02 sensor helps a ton). If I accelerate like I want to from every stop, the jeep shifts at around 3k-3.5k RPM's, and I get 8-10 city.

I'm not the greatest at keeping track of my fill ups, but I have manged to correctly figure out my fuel economy a few times, and I have noticed that I save a noticeable amount of money if I drive conservatively.
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Unread 06-18-2009, 02:19 PM   #3
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Throttle position and load % matter more than RPM. You can cruse at 5k up a hill and use less fuel than you would with the pedal on the floor at 2k rpm... The higher the load on the motor, the more fuel is dumped in the engine.

If you have ever driven a turbo car, you can actually drive at 6k rpm and not be in boost, as long as you dont load the motor, but as soon as you start to go up a hill, or try and accelerate, boost will build quickly as you supply more fuel (pushing on the throttle).
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Unread 06-18-2009, 07:18 PM   #4
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As a rule of thumb, you should try to keep the vacuum as high as possible.

Your turbo car should have a vacuum/boost gauge. This is the best indicator of fuel consumption. Try driving without going into boost.

High vacuum requires a lessor throttle opening and a lighter load. Increase the load (pressing the right foot down) will drop the vacuum and fuel mileage. Keeping the load light may require a bit more RPM but will consume less fuel overall.

Your vacuum gauge is your friend.
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Unread 06-19-2009, 02:31 AM   #5
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Quote:
Originally Posted by Mr Car Guy View Post
As a rule of thumb, you should try to keep the vacuum as high as possible.

Your turbo car should have a vacuum/boost gauge. This is the best indicator of fuel consumption. Try driving without going into boost.

High vacuum requires a lessor throttle opening and a lighter load. Increase the load (pressing the right foot down) will drop the vacuum and fuel mileage. Keeping the load light may require a bit more RPM but will consume less fuel overall.

Your vacuum gauge is your friend.
I used to make it a game to try and stay out of boost. lol Its a fun and useful way to learn how to drive much more efficiently. IMO, all cars should come with a vac, or boost gauge. People could learn how to drive more efficiently with them.
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Unread 06-19-2009, 02:57 AM   #6
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So, I can accelerate faster if I shift manually, and not hit turbo. Should I do it? I think I'll test it out. Maybe stay in auto with the overdrive off...
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Unread 06-19-2009, 02:59 AM   #7
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Hmmm...I usually make a game of it and try to see if I can maintain the most boost for longest. Maybe that's why I'm getting 18 mph in my Regal. It's so much fun though!
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Unread 06-19-2009, 05:55 AM   #8
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I know it's bad for the tranny, but revving up in Neutral at a stop sign, then popping it in gear at 4k.... screeeeeeeecccchhhh! (White Smoke)
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Unread 06-26-2009, 04:37 PM   #9
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looks like i was somewhat wrong. I got 10MPG on my paper route just driving normally (granny), and 10 using "manual" (granny also). However.... If I accelerate fast to JUST BELOW the white line on the turbo gauge, I get 16MPG on my route.
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