I increased gas milage
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Northstar Engines and System Technical Discussion Discussion, I increased gas milage in Cadillac Engine Technical Discussion; I got looking at the air cleaner system on my STS and came to realize that the factory system was ...
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    first sts is offline Cadillac Owners Member
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    Talking I increased gas milage

    I got looking at the air cleaner system on my STS and came to realize that the factory system was very restrictive so I went about making a less restrictive one out of parts laying around the shop, an air filter from Discount auto $25.00 and a reducer from the hardware store $3.00 that is used on sewer lines and some flex tuging from somewhere.....I travel about 7 miles to work 5 days a week making 2 stops along the way, most of the time my mileage will show a decline in MPG over the week of travel to and from work. Since I made this system the milage has a tendency to go up rather then down. Nice to see this happening also the car seems more responive like its BREATHING easier, will be making a 500 mile trip this coming weekend hope to see higher than 22.5mpg avg.no other changes were made to the car.

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    Ranger's Avatar
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    Re: I increased gas milage

    A less restrictive air filter may help MPG on a carburated engine but will not affect MPG on a fuel injected engine. Fuel is metered by the PCM and is not affected by air flow. You'll get the same fuel flow with no air filter as you will with a very dirty clogged one.

    Also if you look under the air box you'll see the PCM. It was placed there so as to be cooled by intake air. If it overheats, it will be a costly experiment.

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    first sts is offline Cadillac Owners Member
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    Smile Re: I increased gas milage

    My PCM is inside the car under the dash I can't imagine any PCM being in the engine compartment there is way to much heat there BUT I MAYBE WRONG I'm not any kind of expert

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    Re: I increased gas milage

    the PCM on my fathers '99 GTP is in the airbox too... for cooling....

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    eldorado1 is offline Cadillac Owners Connoisseur
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    Re: I increased gas milage

    Quote Originally Posted by Ranger
    A less restrictive air filter may help MPG on a carburated engine but will not affect MPG on a fuel injected engine. Fuel is metered by the PCM and is not affected by air flow. You'll get the same fuel flow with no air filter as you will with a very dirty clogged one.
    I disagree. Here's why. If you substitute the 3" intake plenum for a drinking straw, you will detrimentally affect the power of the engine. Same thing with a dirty air filter. You won't "feel" it, but a dirty air filter may be stealing 5... 10hp. And possibly as much as 5mpg. You're correct in saying that fuel is metered by the pcm, and for the 96+ models, the pcm looks up the amount of fuel needed in a table. The input for that table being the air flow through the MAF sensor. X airflow needs Y injector pulsewidth. In the earlier models, it was "guesstimated" by manifold vacuum and TPS position charts. In either case, if the PCM calculated you needed a 4ms pulsewidth, and the o2 sensor is showing rich (which would be the case if you weren't getting the amount of air the PCM *THOUGHT* you were... i.e. dirty air filter), it will start "learning", and cutting back on fuel... and hp. Hope that makes sense, and no flames intended... Hope I didn't come off that way

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    Re: I increased gas milage

    No flames taken and you did not come off that way. I used to think that way too. What I posted was from the master himself. I'll see if I can find it and post it.

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    Re: I increased gas milage

    I increased my gas mileage by at least 10% simply by switching from 87 octane to 93 octane. According to the dashboard computer I was getting 15.0 to 15.5 miles per gallon in city driving on 87. When I switched to 93 octane it has gone up to and stayed at 17.0 to 17.5 miles per gallon in city driving.

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    eldorado1 is offline Cadillac Owners Connoisseur
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    Re: I increased gas milage

    Quote Originally Posted by Ranger
    No flames taken and you did not come off that way. I used to think that way too. What I posted was from the master himself. I'll see if I can find it and post it.
    Actually, the more I think about it, the more I think you're correct... With a dirty air filter, you'll get better gas mileage since it will be compensating for less air. New air filter = more hp+more fuel. I even said that above... dirty air filter = less fuel Ahh well...

    I should also mention that this is only below whatever the cutoff for WOT is. I think it's like 60% throttle or there'bouts. At WOT, it doesn't have any "learning cells" that lean/richen the a/f that I am aware of.

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    first sts is offline Cadillac Owners Member
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    Smile Re: I increased gas milage

    I had already replaced the original airfilter with a K+N filter placed in the "box" this filter has been there for most of the time I have owned the car and the milege figures are based on this type filter....I went out to eat last night and drove on the interstate about a 80 mile round trip when I left the house the AVG. was reading 19.5 when I got back to the house the AVG. was now 23.4 this is up from the normal 22.5 that I normaly get...Is the fact that the air cleaner is now getting its air from a cool spot under and away from the engine have any thing to do with this increase in milage ???? I know that when I put a simaler system on my Buick Turbo a increase in proformance was noted at the track...Thanks for all the great comments....Robert of Hurricane alley.........Does anyone know of anyone how can make computer chips for this car ??????? I make them for my Buick but this is a different type of chip which I have no equipment for

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    Anthony Cipriano is offline Cadillac Owners Fanatic
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    Re: I increased gas milage

    The PCM was moved to the air box in the underhood mounting location starting with the 1996 Northstars. Prior to the 96 models the PCM was under the dash. It's extremely unlikely that a cobbled up air induction system got any better fuel economy for several reasons:

    1. The production system on the 95 is actually very free flowing and is not a restriction to HP or fuel economy. it is capable of flowing plenty of air to the engine even at full throttle and 6500 RPM much less at part throttle and low RPM driving to work for fuel economy. Prove it to yourself by putting a vacuum gauge on the intake and monitoring the intake vacuum with and without the air cleaner. The readings will be the same.

    2. Since 99% of your driving is at part throttle and at very low air flows, the amount of air moving through the system during that mode of operation (which is the mode you are interested in when fuel economy is being measured) is extremely low. Far lower than the capacity of the production air cleaner. Since the system is flowing well below its maximum flow capability there's no way the system is restricting air flow and as a result there's no way it would improve fuel economy by modifying the system. There's just no engineering reason or justification for improved fuel economy with a lower restriction system.

    3. Carbureted engines tend to run richer and richer as the air filter gets dirtier and dirtier - which causes a restriction to the air flow. Speed density fuel injection systems (like the one that is on that 95 Northstar), however, do not get richer with a dirtier aircleaner. The speed density system simply looks at the manifold pressure (via the MAP sensor) and computes the correct amount of fuel. Even if the air cleaner were plugged solid and barely flowing any air the engine would run fine as the correct air fuel ratio would be delivered and the fuel economy would not be affected. The engine would lose power at full throttle as the air cleaner would be the major restriction ( or the "throttle" in the system) but the air/fuel ration would not be affected. Since the air flow at part throttle and idle would be so low that it would not likely "see" the restriction of the air induction system neither the air/fuel ratio nor the engine performance would be affected.

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    Re: I increased gas milage

    There are so many variables to gas milage that you can get just about any result you could want if you play around long enough. Millions if not billions of dollars have changed hands in the quest for better milage with the latest economy gimmick. The list is endless. One trip with results different than the last does not mean a thing. Carefully conducted and repeatable tests conducted in the laboratory can fool you just as badly. Because of the requirements of the CAFE tests and the like if a few pieces of ABS pipe would make any difference at all you would find miles of it under the hood of your car.

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    an01sts is offline Cadillac Owners Fanatic
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    Re: I increased gas milage

    There are many variables that will affect average mpg. If you catch or miss a red light, have to back down or accelerate in a merge, air temperature, humidity, and air pressure all affect average mpg.

    I have no clue but doesn't your car have cold air pickup as factory deisgn? I reduced restriction at the intake of my air box, giving the induction system more flow, and a signifigant increase in power. I haven't documented before/after, but it seems that my mileage has decreased with the additional flow in the air box.

    I, also, have no clue as to how all this computer managed stuff works, but the age old rule says that if you increase flow, you decrease mileage. Notice that Corsa, in all its claims, never mentions increased mileage becuse it's a no brainer that it decreases mileage.

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    Anthony Cipriano is offline Cadillac Owners Fanatic
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    Re: I increased gas milage

    Quote Originally Posted by an01sts
    There are many variables that will affect average mpg. If you catch or miss a red light, have to back down or accelerate in a merge, air temperature, humidity, and air pressure all affect average mpg.

    I have no clue but doesn't your car have cold air pickup as factory deisgn? I reduced restriction at the intake of my air box, giving the induction system more flow, and a signifigant increase in power. I haven't documented before/after, but it seems that my mileage has decreased with the additional flow in the air box.

    I, also, have no clue as to how all this computer managed stuff works, but the age old rule says that if you increase flow, you decrease mileage. Notice that Corsa, in all its claims, never mentions increased mileage becuse it's a no brainer that it decreases mileage.

    Fuel economy is a concern when the engine is operating at a heavy throttle condition. Cruising down the interstate at 10% of the power it could make so increasing the flow POTENTIAL of the system does not decrease the fuel economy. It just wont help it. The throttle blades are restricting the flow through the engine so severely that things like a cleaner air filter, cold air induction, more open exhaust, etcetera - just do not have an effect on the fuel economy. Vendors that sell the parts want you to think they do but they don't.

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    eldorado1 is offline Cadillac Owners Connoisseur
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    Re: I increased gas milage

    So you're saying... that if you removed the stock air crap, and attached a 1/2" hose as the "air intake" (same as a caked-up-dirty air filter, and effectively restricts the throttle to like 10%) , that it wouldn't get better gas mileage?

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    Anthony Cipriano is offline Cadillac Owners Fanatic
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    Re: I increased gas milage

    Quote Originally Posted by eldorado1
    So you're saying... that if you removed the stock air crap, and attached a 1/2" hose as the "air intake" (same as a caked-up-dirty air filter, and effectively restricts the throttle to like 10%) , that it wouldn't get better gas mileage?
    You're taking things to an extreme to prove a point. First, even a caked up dirty air cleaner element will flow a lot of air. Plenty of air to run the engine at part throttle down the highway. If the engine is fuel injected as described, then the caked up air cleaner will not cause the engine to run rich even if it were to be the restriction.

    You might be surprised at how much air can flow thru a 1/2 hose or you might be surprised at how little throttle opening is required to cruise along the highway when "fuel economy" is a concern. Yes, you could probably use a 1/2 inch hose for an induction system if all you did was cruise along measuring fuel economy.

    The air cleaner system is designed to flow the maximum amount of air the engine needs at max power/max RPM with an allowance for dirt build up. In the case of the Northstar that would be full throttle, 6500 RPM with the air cleaner 25% blocked. That is how much the production system is designed to flow. But, under those conditions, fuel economy is rarely a concern or consideration. That is why I say that, under conditions that most people are concerned with fuel economy, the air induction system is WAY oversized and presents no possibility for a fuel economy improvement.

    The fuel injection system computes the correct amount of fuel based on measured mass air flow rate and/or the inlet manifold absolute pressure. It doesn't care where the restriction that is "throttling" the engine is so if it's that 1/2 hose the engine will run correctly at that maximum power level. It'll make a lot less power (compared to the production system) but wont run rich or anything and it'll still get good fuel economy up to the power level allowed by the 1/2 hose. You won't have reserve power for accelerating or anything, though.

    Put a vacuum gauge in the inlet system and watch the vavuum level measured. If there is no vacuum then there is no restriction. You wont see any vacuum up to WOT and high RPM and even then only a tiny bit indicating the system is flowing adequately for that power level. Tape a 1/2 hose into the inlet and see how much the engine will accelerate and drive the car with no vaccum showing on the vacuum gauge. You'll be surprised.

    That "stock air crap" is designed to flow for maximum power, keep dust intrusion into the system to a minimum, keep water out so the engine does not hydrostatically lock, provide cool air, stifle induction roar, etc. It's not exactly "crap". A lot of engineering goes into the system that you must not appreciate. I suspect it does a few things you don't even know about.

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