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Old 01-21-2008, 02:20 PM   #1
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Turbocharging for FE

it may sound strange but a light pressure turbo system may provide a fuel savings. I am currently researching a LPT system for my wagon. My research has shown that a low (2-5 psi) boost turbo system will keep the transmission in lock up on hills resulting in a small improvement in FE. If I end up with the same FE and a touch better freeway performance I'll be fine with that. Having the car downshift to 3rd and even 2nd to make hills is ridiculous.
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Old 01-21-2008, 07:02 PM   #2
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You aren't alone in thinking that turbos can improve FE. Lots of auto manufacturers are going in that direction as well.

A quick tip though, is that if you can manage (ie, if traffic allows) it, you should try to coast up the hill as much as possible. Get going fast on flat ground, and then coast up the hill as far as possible. If absolutely necessary, you can downshift, but your momentum might be able to tackle some of the smaller "bumps in the road."
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Old 01-22-2008, 04:30 AM   #3
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A properly matched turbocharger (meaning one designed to provide boost at LOW rpm) will usually provide better efficiency. It usually also helps to change the gear ratios to a taller gear with a low rpm turbo.

Unfortunately, most guys want power and they size the turbo for high rpms and high power. This will drain your gas tank faster too.
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Old 01-22-2008, 05:03 AM   #4
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turbo's definately are handy to improve FE, the main advantage is that they can get more power out of a much smaller engine block.

Fiat for example is currently developeing a 2 cylinder 0.9L turbo engine that should output between 90 and 110 hp... i'd love to put that in my car... less weight more power...
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Old 01-22-2008, 06:04 AM   #5
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I can't help but notice you're trying to keep the auto trans from downshifting too early. Perhaps the problem isn't a lack of power, since most auto trannies will shift to an easier gear around 2/3 throttle, which means there's more throttle and slightly more power already there.

I'm getting good FE out of my turbo car by staying out of boost. I'm very familiar with the operation of my car, and it will begin to run rich even when making low boost. I tried leaning it out at the onset of boost, but it just knocks at that point. So I tried reducing ignition timing at that point to reduce knock and power dropped noticeably. Timing has more of an effect on power than A/F ratios, and running a richer A/F ratio lets me use more timing.

Have you thought about using adjustable cam gears to improve low end power? MetroMPG has a good thread about swapping the cam in his metro.
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Old 01-22-2008, 10:22 AM   #6
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the problem with this car is that it is heavy and has a smallish 4-cyl (3400lb and a 2.2l) with just 135hp. it really needs a bunch more torque to move the car effectively. on the freeway I come to a slight rise and I am down on two or even three gears to get over it, this is at 65-70mph. If a low pressure turbo system will make enough differenc that I only need one lower gear than I will see some improvement. Trust me 6500 at 65mph is NOISY!!!
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Old 01-22-2008, 10:42 AM   #7
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3400lbs is indeed quite hefty for an engine with as little power as that de-tuned Ecotec... Have you looked into a transmission controller? You may just want to control the gears yourself, this may alleviate some of your downshifting problem (stay in higher gears at the expense of "performance" maybe?)

Look here at the transmission controller: http://awshifting.com/index.html

It may be a good first step for you and you should definitely be able to improve your fuel economy using it. A turbo is going to be an expensive and complicated endeavor, just remember that.
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Old 01-22-2008, 11:01 AM   #8
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turbo is easy on this engine trans control isn't and the site you posted doesn't cover any gm transmissions. But thanks anyway.
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Old 01-22-2008, 02:08 PM   #9
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Quote:
Originally Posted by philip1 View Post
the problem with this car is that it is heavy and has a smallish 4-cyl (3400lb and a 2.2l) with just 135hp. it really needs a bunch more torque to move the car effectively. on the freeway I come to a slight rise and I am down on two or even three gears to get over it, this is at 65-70mph. If a low pressure turbo system will make enough difference that I only need one lower gear than I will see some improvement. Trust me 6500 at 65mph is NOISY!!!
Oh wow, I didn't realise your power to weight ratio was that bad. OTOH it's nice to see someone actually opt for the base engine instead of the ultra gashog option. Since you're climbing hills, weight reduction will make a bigger difference on your car.

How about a small shot of nitrous for the hills?
If the guys at Mythbusters can come up with a JATO for their car I don't see why you couldn't use one, too!
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Old 01-23-2008, 06:32 AM   #10
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Quote:
Originally Posted by philip1
on the freeway I come to a slight rise and I am down on two or even three gears to get over it, this is at 65-70mph. If a low pressure turbo system will make enough differenc that I only need one lower gear than I will see some improvement. Trust me 6500rpm at 65mph is NOISY!!!
I have a feeling you might get a good bump in FE with a slight adjustment to your speed. Would the trans hold a higher gear if you kept the speed around 55-60mph on the uphills? WOT at high rpm is will really suck down the gas.
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