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Old 07-19-2011, 05:50 AM   #1
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Hello!

Hello all. im phill and i drive a 08 chevy cobalt 5 speed.

my journey is kind of odd compared to most of you. currently i have lots of bolts on for power, as well as a tuned ecu to make use of them. they do all increase my engines volumetric efficiency which will help with mpg.

but...I also race which is my number one priority.

im not trying to get 60+ mpg but a few more would help

as of now i get pretty decent mileage i can average around 38 on the highway.

i plan to partial block my grille and i like the idea of extending my stock air dam. my goal is better aero with keeping it stealth.

i also have a few questions. i was reading about Pulse and glide, and i dont really know the specifics about it. how fast or slow should i accelerate? and should i try to only accelerate on flats or down hill?

Thanks everyone and im excited to see what differences i can make in my mpg!!
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Old 07-19-2011, 06:20 AM   #2
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Re: Hello!

Welcome.

For P&G, determining exactly how it works best for you is trial-and-error. It depends on your car, your route, and your traffic. My 2008 VW had very short gears, plenty of torque, and an engine that ran most efficiently with WOT at low RPM. My roads involve lots of small rolling hills. My traffic gets impatient and I get offended when they tailgate; I also prefer not to be in anybody's way. I can't afford speeding tickets. As such, what worked best for me was to pulse at WOT in high gear uphill, then glide downhill. It used my engine efficiently and kept my speed pretty steady near the speed limit, keeping my climbing speed up and my descending speed down.

In addition to P&G, there's plenty of other strategies. For example, if you know there is a red light ahead in the distance, don't wait until you're closer to get off the gas. Instead, immediately get off the gas (and neutral coast if you're into P&G), and perhaps even use the brake, in an attempt to arrive at the green light carrying as much speed as possible.

Another, significantly more exciting and fun, is carrying your speed through turns. I'm going to guess that you already do that one.

If you ever decide to have a dedicated race car and a high-efficiency commute car you may want to review which bolt-ons effect your efficiency in which ways; sometimes common knowledge is wrong (often based on obsolete conditions or strong marketing). As well, volumetric efficiency is only one component of fuel economy. Among the bolt-ons that do increase efficiency, almost none can ever pay for themselves in savings (if your motivation for saving fuel is to save money).
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Old 07-19-2011, 07:23 AM   #3
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Re: Hello!

yea i already drive pretty efficiently. 55 is my favorite number wither the speed limit is 45 or 60 lol. but i do also realized there is a time and place for everything. im not going to impede traffic if its busy but if there is not much traffic and plenty of room ill do 55.

but yes i tend to take corners much faster than others and in theory that helps my mileage a bit.

but thanks alot man. i guess ill just try and try for the pulse and go.

i do wish i could have a dedicated race and efficient daily but at this current time its not really an option. the class that i race in is Street Touring in SCCA so its deff a class for DD's in fact 90 % of the cars i race with are dailys.

so my cars got to pull dual duty lol.
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Old 07-19-2011, 07:24 AM   #4
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Re: Hello!

also on the p&g note. is coasting in neutral better than in gear? i hear two different things. 1 that it is because you go further and 2 its not because you use gas to idle as opposed to none in gear.
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Old 07-19-2011, 08:27 AM   #5
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Re: Hello!

P&G without neutral (I called it Pulse & DFCO) was worse than steady driving in my 2008 VW, and logically it would be worse in any car. All those extra engine revolutions aren't free. The distance you "coast" in gear (actually engine braking, even if not enough braking to feel it) is not as far as the distance you coast in neutral. Although you use fuel to keep the engine running, you only need enough energy to run it for fewer revolutions.

If your car is tuned for racing then it might have DFCO (Deceleration Fuel Cut Off) disabled anyway. In that case you use more fuel while engine braking than coasting, regardless of distance.
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Old 07-19-2011, 08:32 AM   #6
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Re: Hello!

ok so ill do it in neutral. i figured that would be better but i just wanted to make sure.
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Old 07-19-2011, 11:21 AM   #7
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Re: Hello!

Welcome. You'll find pulsing to be a lot more effective if you monitor engine load with instrumentation like a Scangauge or Ultragauge. You want to pulse the engine in its best BSFC range, and seat-of-the-pants doesn't come close to doing that. As for gliding, do it as much as possible. Most drivers still have their foot on the gas half a block from red lights and stop signs. I'm gliding to those stops 3-4 blocks away.
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Old 07-19-2011, 12:23 PM   #8
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Re: Hello!

wow those are expensive. i wonder if my obd2 scanner has these ability's already.

but thanks, im excited to see what i can do with this pulse and glide method.

it just seems odd to me that its more efficient. but if it is it is.
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Old 07-19-2011, 12:54 PM   #9
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Re: Hello!

There are multiple concepts at work that make P&G more effective.

One, which I mentioned earlier, is fewer engine revolutions. Each revolution brings friction loss and reciprocating loss, among others.

Another is operating in a better BSFC (volumetric efficiency) range without wasting any of the resulting energy.

Cheap OBD2 scanners do not have the ability to display live data. The cheapest way I know to get live OBD2 data is the $60 UltraGauge.
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Old 07-19-2011, 12:58 PM   #10
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Re: Hello!

my obd2 is no cheap one. dropped a decent amount of money on it. but if it turns out it dosent have the ability then i guess the ultragauge will be the way i go.
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