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mpg gain story...read on....hot air intake idea
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fixityourselfer Offline
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Post: #1
mpg gain story...read on....hot air intake idea
I purchased my 98 volvo s70 T5 turbo sedan a year and a half ago.
car is supposed to run on premium fuel only, and i've been using 87octane only,cuz i said what the heck regular gas is expensive enough, and i wasn't seeing any loss in mpg or performance with the 87.( as judged against the one time that i used some premium)

mpg #'s for highway driving were as follows:
(these #'s are for NO TRAFFIC situations, use of cruise control, a/c off, and no passengers. tests were carried out many times over long streches of road. also, these #'s are +/- 1mpg or so, cuz sometimes i'd have variations of +/- .5-1 mpg. maybe due to weather or weight in car)

#'s come from vehicle's computer which i have tested against the gas pump #'s and is very accurate.
tires almost always 36psi. sometimes a drop higher38 but difference 36-38 is very small . below 36psi, mpg falls.

55mph=34mpg.
65mph=32mpg.
70mph=29.5mpg.
3 passengers and 75mph=25-27mpg(car's epa rating is 25 hwy)

so i've got a pretty good idea of what my car does.

but i'd been having a problem with the engine shuddering (on takeoff from a light etc.) and mechanic told me its due to buildup in the intake manifold area due to 87oct. in a high performance engine. Mechanic said "go back to premium and the junk will burn off "
so i began using premium for the first time in a year and a half, and half a tank into my first premium fill-up the shudder was gone.
here came my surprise: later that same day i was back on the highway,(am pretty sure I was doing 55mph, i don't drive less then that on a highway) and was doing 37 mpg for a 30 mile stretch (until my exit came) with the a/c on, (which always robs my car of a few mpg's) ....not only that but one of my FRONT tires had a tiny leak and only had about 23 psi...which robs my car of mpg's too! (past experience of going below 36psi in a front tire always hurt the car's mileage.)
come to think of it, had the a/c been off and the front tire up at the proper 36psi i'd have gotten 40+.

Driving north from NYC I was not going downhill.

I'm guessing it happened as part of the process of the computer recognizing a new fuel, and was adjusting.

i do not think this new gain will last long, time will tell. but one thing is clear: if the car can do 40mpg with no mods and NOTHING (as in "NOTHING") done to it, it should be able to keep it up by fooling the computer alone. just efie. no additives, and no hho either.

additives to the gas , or HHO should only help on TOP of the 40mpg that should be possible with an efie alone, no?

please feel free to chime in, and please feel free to agree or disagree with my philosophy!
(This post was last modified: 05-13-2009 12:19 PM by fixityourselfer.)
05-07-2009 10:27 PM
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Alttech Offline
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Post: #2
RE: mpg gain story...read on
DO NOT install an EFIE without an HHO system!! You WILL damage your engine by running it too lean.
As far as the better mileage with the higher octane, it makes sense, gas contains octane, benzene, hexane, toluene, xylene, and some others. The higher octane, in theory, doesn't get completely burned in the combustion process, and is dumped out the exhaust. The O2 sensors reflect the lower oxygen levels in the exhaust, and the ECU compensates by reducing the amount of fuel delivered. I would try the lower octane gas along with the homemade octane booster that I told you about in the other post, I would bet that you will see similar results. (along with the abscense of the shuttering)
05-08-2009 04:30 AM
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Mika Offline
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Post: #3
RE: mpg gain story...read on
The mpg savings with higher octane comes from _more_ complete burning, not less. Higher octane rating means that the fuel can handle more compression pressure without explosing before ignition spark (detonation). Ecu and the knock sensors notices if you use higher octane, and advances timing. The most advanced timing without detonation means most completed burn, and most power for the amount of fuel.

But, I agree, don't EVER use efie without hho, especially on a turbocharged engine like yours. You will ruin your engine for sure.
05-10-2009 07:01 AM
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fixityourselfer Offline
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Post: #4
RE: mpg gain story...read on
thanks alot for the replies guys, i really appreciate it.

i read on smartgas.com (which seems NOT to be a scam site) that a warm air intake will increase fuel economy. he says to modify the intake so it will take air from a warm area such as the radiator area instead of the grille, or the cool wheel well.

So i thought of bypassing my intercooler. if i modify the turbo-to-intercooler hose to go straight to the intercooler-to-throttlebody hose, i should have a jet of hot air , as the air has just gone through the piping-hot turbo.(or run the turbo-to-intercooler hose straight to the tb..same idea) easy mod,the turbo-to-intercooler hose really is not far away from the tb.
I can also modify the intake to take air from a hot spot too, and the already-warm air will be further heated when passing thru the turbo area.

if it causes a small loss of hp i don't care, if it would bring a good mpg gain i would do it.
what do you guys say?
05-10-2009 09:38 PM
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Mika Offline
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Post: #5
RE: mpg gain story...read on....hot air intake idea
It doesn't make any sense to me. Cooler air is denser and because of that, it has much more oxyxen in it (more efficient burn), and is also a lot safer to your engine. It's there for a reason.
05-11-2009 06:09 AM
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Alttech Offline
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Post: #6
RE: mpg gain story...read on....hot air intake idea
Mika,
If you have a more complete burn, wouldn't the O2 sensors pick up on this and add more fuel due to the change in oxygen levels? This is what we are fighting with the HHO systems and compensating with the EFIE's. Octane has a vapor point of 258 degrees. Under compression, it is higher, and if you have a higher octane grade, it takes longer to burn, or increases the burn time. There comes a point where a high octane is a waste, because the piston has passed the critical crank angle and is on its way back down. A prolonged burn time will also increase the chances of burning a hole in the top of the piston. Here is an article that explains it: http://chemistry.about.com/gi/dynamic/of...octane.htm


As far as the hotter air, it's a well known fact that colder air and fuel give more horsepower. Hotter air and fuel will provide more efficiency. (with a loss of power) There are more oxygen molecules in colder air, you are correct, but with hotter air (with fewer oxygen molecules) the ECU is expecting to inject less fuel to maintain the targeted AFR ratio. This is also where we can adjust the IAT settings to lower the lean limits. But you have to be careful, because it will also retard the timing.
With the turbo, you could install a tee between the turbo (or intercooler) and the throttle body. On the open leg of the tee, install a check valve and a small air filter. Mount the air filter someplace where it will have hot air. Under normal driving conditions, the engine will draw from the path of least resistance, the new air filter inside the engine compartment. When the turbo spools up and boost is created, it will close the check valve, and draw from the stock setup, preventing detonation.
Just a suggestion.
05-11-2009 07:28 AM
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fixityourselfer Offline
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Post: #7
RE: mpg gain story...read on....hot air intake idea
(05-11-2009 07:28 AM)Alttech Wrote:  Mika,
If you have a more complete burn, wouldn't the O2 sensors pick up on this and add more fuel due to the change in oxygen levels? This is what we are fighting with the HHO systems and compensating with the EFIE's. Octane has a vapor point of 258 degrees. Under compression, it is higher, and if you have a higher octane grade, it takes longer to burn, or increases the burn time. There comes a point where a high octane is a waste, because the piston has passed the critical crank angle and is on its way back down. A prolonged burn time will also increase the chances of burning a hole in the top of the piston. Here is an article that explains it: http://chemistry.about.com/gi/dynamic/of...octane.htm


As far as the hotter air, it's a well known fact that colder air and fuel give more horsepower. Hotter air and fuel will provide more efficiency. (with a loss of power) There are more oxygen molecules in colder air, you are correct, but with hotter air (with fewer oxygen molecules) the ECU is expecting to inject less fuel to maintain the targeted AFR ratio. This is also where we can adjust the IAT settings to lower the lean limits. But you have to be careful, because it will also retard the timing.
With the turbo, you could install a tee between the turbo (or intercooler) and the throttle body. On the open leg of the tee, install a check valve and a small air filter. Mount the air filter someplace where it will have hot air. Under normal driving conditions, the engine will draw from the path of least resistance, the new air filter inside the engine compartment. When the turbo spools up and boost is created, it will close the check valve, and draw from the stock setup, preventing detonation.
Just a suggestion.

do you mean that my original idea of hooking the pressurized hose coming from the turbo directly to the TB should not be done ? is it a risk to the engine? (thanks alot for the responses everyone, i really appreciate them)
(This post was last modified: 05-14-2009 03:46 PM by fixityourselfer.)
05-12-2009 04:40 PM
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Alttech Offline
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Post: #8
RE: mpg gain story...read on....hot air intake idea
I would recommend the tee method, this will ensure there will be no problem under heavy acceleration. Chances are that your idea would be fine, but I don't want to be the one responsible if something goes wrong. You aren't going to see tremendous gains with just this though. But you will see some.
05-12-2009 06:29 PM
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Mika Offline
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Post: #9
RE: mpg gain story...read on....hot air intake idea
Ok, Alttech 1 - Mika 0 Smile .
05-13-2009 11:13 AM
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fixityourselfer Offline
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Post: #10
RE: mpg gain story...read on....hot air intake idea
as i mentioned earlier, the mpg gains that i saw when i switched to premium fuel did not last. the higher mileage i spoke of was a byproduct of the computer seeing a new fuel. computer got used to new fuel and went back to original mileage.

i just completed several 36 mile road tests to determine if 3oz acetone/10g gasoline will help my car.

first test was to see what the car will do over a particular piece of highway. 18 miles west, and 18 east to compensate for any downhill.

did test. got results. put in acetone. let it all settle and tried test. no gain. reset computer and tried again several days later. no gain.

car is well in tune, and tire pressures etc. all the same during all testing.

conclusion: acetone does 0 for my car.
car continues to get 35 highway @55mph, and 37-38 on humid days.

am wishing to break the 40 mpg #.

can anyone give positive feedback on hot air intake idea? am a bit reluctant in fear i may damage the motor someway or other.
(This post was last modified: 05-13-2009 12:25 PM by fixityourselfer.)
05-13-2009 12:10 PM
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