| Cold intake air and power VS fuel economy [message #193687] |
Sat, 22 December 2012 11:20  |
JohnL455
Messages: 4447
Registered: October 2006
Location: Woodstock, IL
Karma: 12
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Senior Member |
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We know that a colder intake air temp is better for maximum power, but not so sure about for maximum light part throttle mileage. Todays cars run at higher temp to try to squeeze efficiency. What I have noticed is that on my OBDII Cherokee with SFI, the instantaeous mileage highway figures are down in the winter with colder IATs. My stat and gauge confirm 195 operating temp, so it doesn't think it's cold coolant temp causing enrichment. My guess is the computer is adding some fuel to allow for the colder IAT and poorer vaporization? On my GMC I have the heat tube still connected and working to try to maintain faster warmup and less emmisions and hopefully better mileage. As we know at WOT it goes to colder oustide air anyway so it doesn't diminish max power. My crossovers are supposedly restricted (per Cinnabar standards) but not blocked. The only other thing I can put my finger on with the Jeep is that the winter blend fuels here give poorer highway mileage but don't know if that is the case or the opposite should be true. So... the question is on the GMC at light throttle cruise (maybe primaries at 30%)wouldn't the best mileage come with a constant 115 deg IAT at the carb for better vaporization allowing leaner jetting as oppose to wildly swinging IAT depending on the weather? On a hot day the ThermAc door should be wide open anyway and out of the picture.
John Lebetski
Woodstock, IL
77 Eleganza II
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| Re: Cold intake air and power VS fuel economy [message #193705 is a reply to message #193687] |
Sat, 22 December 2012 13:43  |
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John Heslinga
Messages: 632
Registered: February 2011
Location: Edmonton, Alberta, Canada
Karma: 4
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Senior Member |
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John:
My theory:
I believe your Jeep sequential fuel injection system uses a mass air flow sensor as one of the inputs to control fuel injector pulse widths. Colder air going through the sensor is more dense ( more O2 molicules) and the computer will increase the amount of fuel to compensate. I think the engineers expect the heat to do a better job of increasing the intake air temperature. As a consequence, It is not uncommon for the charts in a factory computer to increase fuel consumption slightly during cold intake air temperature conditions in winter. I'm not saying that this should be the case but is certainly more common than you would imagine.
You never really know what the strategy in the computer programming is used and looking into the "black box" can be pretty frustrating sometimes. In my Ford explorer for instance. The transmission (computer controlled) has a completely different shift strategy during cold weather. (who knew??)
Your carb in the GMC would not care about intake air temps and would make no adjustment according to intake air temperature. On the whole when cooler air entered the cylinder, it actually increased the compression ratio a tiny amount which gave a small performance gain, noticeable only by a slight increase in fuel milage over the long term.
I don't engineer them, I only fix them.
Best regards
John and Cathie Heslinga
1974 Canyonlands 260
455, Manny tranny and 1 ton, 3:70 LS,
Red Seal Journeyman, DTE, BEd. MEd.
Edmonton, Alberta
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| Re: [GMCnet] Cold intake air and power VS fuel economy [message #193709 is a reply to message #193705] |
Sat, 22 December 2012 13:55 |
k2gkk
Messages: 4452
Registered: November 2009
Karma: -8
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Senior Member |
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My '99 GMC Sierra 2500 (6.0 L), '02 Explorer, and '12 Flex
ALL have different shifting points when cold until warmed.
~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~
~~ ~ D C "Mac" Macdonald ~ ~~
~ ~ Amateur Radio - K2GKK ~ ~
~ ~ USAF and FAA, Retired ~ ~
~ ~ ~ Oklahoma City, OK ~ ~ ~
~~ ~ ~ "The Money Pit" ~ ~ ~~
~ ~ ~ ~ TZE166V101966 ~ ~ ~ ~
~ ~ ~ '76 ex-Palm Beach ~ ~ ~
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> To: gmclist@temp.gmcnet.org
> From: rbeeper@hotmail.com
> Date: Sat, 22 Dec 2012 13:43:46 -0600
> Subject: Re: [GMCnet] Cold intake air and power VS fuel economy
>
>
>
> John:
>
> My theory:
>
> I believe your Jeep sequential fuel injection system uses a mass air flow sensor as one of the inputs to control fuel injector pulse widths. Colder air going through the sensor is more dense ( more O2 molicules) and the computer will increase the amount of fuel to compensate. I think the engineers expect the heat to do a better job of increasing the intake air temperature. As a consequence, It is not uncommon for the charts in a factory computer to increase fuel consumption slightly during cold intake air temperature conditions in winter. I'm not saying that this should be the case but is certainly more common than you would imagine.
>
> You never really know what the strategy in the computer programming is used and looking into the "black box" can be pretty frustrating sometimes. In my Ford explorer for instance. The transmission (computer controlled) has a completely different shift strategy during cold weather. (who knew??)
>
> Your carb in the GMC would not care about intake air temps and would make no adjustment according to intake air temperature. On the whole when cooler air entered the cylinder, it actually increased the compression ratio a tiny amount which gave a small performance gain, noticeable only by a slight increase in fuel milage over the long term.
>
> I don't engineer them, I only fix them.
>
> Best regards
>
>
> --
> John and Cathie Heslinga
> 1974 Canyonlands 260
> TC4W "Too Cool For Words"
> Retirement Projects Galore
> Edmonton, Alberta
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| Re: [GMCnet] Cold intake air and power VS fuel economy [message #193720 is a reply to message #193709] |
Sat, 22 December 2012 15:30 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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Senior Member |
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Winter blend fuel has less BTUs than summer blend. Summer blend is required to be sold between May 1 and September 15th. California is an exception. They play by their own rules 12 months a year and I never bothered to look up what they do.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: [GMCnet] Cold intake air and power VS fuel economy [message #193738 is a reply to message #193733] |
Sat, 22 December 2012 19:12 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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Senior Member |
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| Matt Colie wrote on Sat, 22 December 2012 18:05 |
I hate to start this without a solid reference, but here we go.....
Yes, your fuel economy is less in winter.
It is not because of the cold intake air, but it is because of the cold air and cold road and cold tires and cold and lubricants and cold beer (not really, I just thought I should throw that in).
The cold intake air really does not affect fuel rate as BSFC (Brake Specific Fuel Consumption = Lbs/HP-Hr of standard fuel). It does affect everything else. Apart from the fact that the engine will take a little longer to warn up, there are all the other things that can consume power just because they are colder than they could be. Gear boxes are a big on this. That heavy lube that is common in those can about set up solid at below freezing temperatures. Even ATF gets more viscous.
Yes, Ken is correct that the winter fuel is lower BTU because they have to add butane to make it vaporize better.
Matt
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They also add Butane because it is plentiful and cheap for them.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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