Will This Improve Gas Mileage?

[Willie]

Hello all. First post in these parts. Looks like there's tons of experience present and accounted for. Maybe someone knows the answer to my issue.

I'm trying to increase the MPG I get from a 1996 GMC Suburban 5.7L (350cc), 4x4 with 84,500 miles. A friend of mine, who is a do-it-himselfer auto guy, told me that by placing a K&N air filter kit (not just the filter but removing alot of the stock supply line and replacing with a less restrictive air supply line), installing a 1" throttle body spacer, and totally replacing the stock exhaust (2 or 2.5" at present) with a 3 or 3.5" exhaust with hi-flow catalytic converter and muffler, that I could improve my gas mileage to get 20MPG in the city! Does anyone have experience with knowing this to be possible? Right now I get 13MPG city and about 16/17 HWY. If these suggestions are possible, that would be a killer savings in city-type driving--well worth the $500 to $600 dollars in cost for the long run. My buddy stated that he and a guy he worked with, did the very same thing to a 1996 Suburban a couple of years ago and the end result was the super gas mileage that I mentioned. However, before spending that kind of money, I'd like more input from others. Thanks alot....

 

[Kestas]

If it was that easy, the auto manufacturers would be building them that way. Auto makers are always looking for ways to squeeze another 0.1 mpg out of a vehicle.

I doubt you'd get THAT drastic of an mpg increase with that plan. In his previous episode he and his buddy may have done other things at the same time such as a tune-up. People who make these improvements often do other regular "tune-up" jobs at the same time and completely ignore the fact that these simple jobs may have had the most impact on getting better mileage.

For example, replacing the exhaust system may have required new O2 sensors. If the old O2 sensors were bad or lazy, then most of the mileage gain could have been from the new O2 sensors.

 

[theguru]

Doing this work I would think would improve fuel economy and performance, but, I doubt that it would be anything like the increase suggested, unless the standard exhaust/ air intake are really poorly designed, which is probably not the case, eg a 1" exhaust. If you got more than 10% improvement I would be surprised.

People are willing to spend money to get a fuel economy improvement and yet they can get it for free. Just drive with with less pressure on the pedal and no hard exceleration.

[ January 21, 2004, 07:07 PM: Message edited by: theguru ]

 

[SteveD2]

Yes, that will improve your mileage. Certainly not to 20mpg in a suburban! It could increase it by 1-2mpg though, and you'll have more power. I got about 4mpg better on my old jeep by removing the muffler, installing a cone filter, and replacing the mechanical fan with an electric one - something you might also want to think about. The reason auto manufacturers don't do this stuff is because they have other restrictions to meet - noise. It will certainly be louder, but in my opinion sound much better.

Another thing, manufacturers have a certain amount of HP they want to get, and that's what they aim for. They don't usually try to get the most out of the displacement...

 

[pacem]

>> Right now I get 13MPG city and about 16/17

This mileage is right on the money!

In such a big and heavy vehicle, that's as good as it gets. F150 with a 351 engine gets worse than that. I have a vehicle with 350 chevy engine and it gets 20, but it is lighter, more aerodynamic and 2WD.

Bigger MPG reducers are O2 sensors and EGR valve. Beyond that, a complete tune up is good. If you really want optimum mileage, a new engine would help. I doubt even that will bring you into 20mpg range.

P.S. Driving as close to your idea RPMs is the solution. where torque and hp intersect. Anything above that, you are wasting gas.

Your rear axle gear is a contributor. You want a low number, like 3.08, 3.23, not something like 4.10 or 3.73 - which are only good for towing, but terrible for grocery-getting and every day driving.

3.55 is a good compromise.

[ January 21, 2004, 09:21 PM: Message edited by: pacem ]

 

[Robbie Alexander]

I can get you to the number... but cant tell you how!

Do what you are, but it may not give you all you hoped... ADD this:
Remove the FAN clutch and ADD ($$$$$) an electric fan, that's ought to add a couple MPG right there.

Then after you do that... Go to a Motor oil WITH a HIGH abount of MOLY in it and give that a shot, you may see an additional 1-2 mpg there if lucky

 

[Willie]

What I can't understand is how come some 35 foot motorhomes get around the same MPG as a light-duty truck? I think the manufucturers are up to something wacky when a 6,000lb truck can't get 20MPG. Probably they're in bed with the oil producers and refineries.

I think my contact is sincere about his previous experience. However, I'll confirm that nothing else was modified or updated to get the gas mileage to improve. Again, anything that could possibly increase gas mileage by 46+% is worth looking into a little.

From my understanding, the Japanese makers can get the same HP and much better MPG from a 6 cylinder. Does anyone know how they do it?

 

[Mike_dup1]

If it sounds to good to be true, it most likely is!

I don't know where you heard a 35 ft motor-home gets good mileage? My neighbor had one and he could not get 10 mph going downhill on a windy day.

[ January 22, 2004, 01:55 PM: Message edited by: Mike ]

 

[JohnnyO]

You wouldn't get 20 mpg in a 'Burban 4x4 going downhill with the engine off.

 

[jeepzj]

I think A/T tires also decrease gas mileage. I had Goodyear Wrangler AP whcih are all-season then switched to Michelin LTX A/T tires and my MPG dropped at least 1-2mpg.

 

[n8wvi]

Wow! I used to get up to 8MPG, but that was in a '93 Freightliner!
I think it's funny that people will do nearly ANYTHING to get better fuel mileage, but when I set my cruise control to the speed limit on the freeway, EVERYONE passes me. Am I the only one that sees the irony in this?

Dave (1997 AllWheelDrive, All-the-time, 31MPG)

 

[VaderSS]

quote:

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Am I the only one that sees the irony in this?

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No...

At least once a month I see someone on the Impala forum saying, "How do I get better mileage?"

You tell them that you can get 17 city and 25 highway, IF you drive VERY conservatively and keep your stock or midly modded car in a perfect state of tune. They then say, "but what if I put headers, big exhaust, super plugs, run premium, put gadgets on..."

The answer; well IF you drive VERY conservatively...

Otherwise, get a different vehicle, one that has higher fuel economy ratings...

If a '96 Suburban COULD get 20 MPG city without VERY expensive and complicated tech that YOU would have had to pay extra for, such as regenerative braking, it would have got 20 MPG from the factory. Can you imagine the sales coup that would have been? I can see it happening in a few years with "hybrid" techology, aka regenerative braking. It will be mandated, and WE will be paying for it.

TANSTAAFL...

 

[SteveD2]

Another thing to think about, my cherokee is a 6 cylinder and weighs about 3500lbs. It also gets about 18mpg.

I'd say you're already doing pretty good for a big *** truck with a big *** V8.

 

[Robbie Alexander]

quote:

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Originally posted by n8wvi:
Wow! I used to get up to 8MPG, but that was in a '93 Freightliner!
I think it's funny that people will do nearly ANYTHING to get better fuel mileage, but when I set my cruise control to the speed limit on the freeway, EVERYONE passes me. Am I the only one that sees the irony in this?

Dave (1997 AllWheelDrive, All-the-time, 31MPG)

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When I go the Posted limit I always get WORSE MPG.
Yesterday I went about 600 MIles and most of it was at 90-95 MPG and I got about 26.???
Today I traveled about 300 Miles and averaged on the expressway 85-105 got 25.???
The day before yesterday I traveled about 300 Miles and got about 24.??? MPG and averaged around 80ish
Day before I get 23.888---999ish mpg because I was traveling around 70-80
Hummmmm
Leadfoot saves me money!

 

[VaderSS]

quote:

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When I go the Posted limit I always get WORSE MPG.

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Why are you driving the posted limit? What is your attitude when driving slower? Are you running into heavier traffic? Getting into the throttle and brakes more?

My car has a direct connection between speed and fuel consumption. 65 with very light traffic will get me 25 MPG. That's from a 4550Lb(with me, gas and luggage) 350 powered road hog. Increase that to 75 and it drops to 24. 85 puts it at 22. 95 drops it to 18. I ain't complainin'

Those figure are out the window if I'm running RFG. Knock 15-20% off...

[ January 22, 2004, 10:15 PM: Message edited by: VaderSS ]

 

[Gary Allan]

quote:

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My car has a direct connection between speed and fuel consumption.

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Vader is right. No if, ands, or buts about it. It's not rocket science to figure out that the losses due to wind resistance increase the faster you go. This is an immutable law of physics ...you can't "wish" this away. The only difference to you is how the wind impacts your particular vehicle. My 99 Jeep Wrangler 4.0...it's a brick ..the best mileage is achieved (on average) in suburban/rural driving at speeds around 45 mph ...hit the highway ..and you get 17 from a 3200 lb vehicle.

Now I've had vehicles that didn't seem to care how you drove them. My mothers 88 Corsica 2.0 got around 26 all the time. I kinda think that the auto consumed so much power that the converter sappped any fuel economy in slower driving ..while the resistance sapped it in light speed driving. On the other hand ...by placing an egg (figuratively) between my foot and the gas pedal ..I've gotten a 2.8 Citation to get 35 mpg ...a 78 BMW 320i to get 30 mpg (it ran like crap afterwards) ..and the Chevette to get over 40 while their typical mileages were much lower. I must admit, however, that the most gains from this technique was with carberated engines. Perhaps modern injected engines tend to not allow you to "fool" them into added economy.


Now if you really want to complain about mileage. My 02 jeep 2.5 can get 22 in sensible highway driving mixed with "casual" suburban/semi-rural driving. My daughter, driving the same vehicle in her daily "rounds" (she's 18), ...brings this down to 12.5

...which is what I typically got with my 78 454 C20 pickup.

 

[K-Man]

Willie, please understand that I mean no offense, but I have wondered for some time why people get a huge vehicle and then complain about the poor fuel economy and want to know how to improve it.

Gas ain't gonna be cheap in the US forever. Some doomsayers are calling for gas to hit $3.00/gallon as early as this summer! Some experts in the oil field are claiming that worldwide oil production is about to peak--if not this year, then in the next few years--before beginning a steady decline as we run out. One new book, The Party's Over, makes this point. It's time for people to make more rational vehicle choices on their own. The day is coming, I'm sorry to say, when government bureaucrats will decide what we can drive based on true need. I seem to see too many big SUVs and pickups driving around with no load and with only a driver, typically chatting on a cell phone in city traffic.

If you've got a legitimate use for the hauling and off-roading capabilities that your Suburban has, fine. But if you got the vehicle for vanity or simply because you like driving something big, then please consider getting something a bit--or a lot--smaller. This is a better long-term fix than trying to decrease the fuel consumption on what is inherently a very thirsty vehicle.

 

[VaderSS]

quote:

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My 02 jeep 2.5 can get 22 in sensible highway driving mixed with "casual" suburban/semi-rural driving. My daughter, driving the same vehicle in her daily "rounds" (she's 18), ...brings this down to 12.5

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Yup, for a vehicle in good tune, the driver is the biggest factor in fuel economy. People don't want to believe that though. Everyone believes they he/she is the best driver in the world.

I've proven it to myself many times. If I attempt to squeeze the most mileage I can out of my car, I am typically awarded with 15-25% better fuel economy, practising energy conservation(using the brakes as little as possible and never getting over 1/2 throttle) and staying at or below the posted speed limit. I prefer to drive it like I stole it though.

 

[ZR2RANDO]

You can hook up an in-dash vacuum gauge, driving by the gauge will make you a more conservative driver and get you some better gas mileage. Usually the high performance mods just allow the engine to perform better..(and use more gas doing it..duhh).
do tuneups when needed, lighter wt oil can give better fuel economy, sometimes at the expense of engine longevity though. Winter time driving can give worse gas mileage just due to colder intake air (but gives more engine efficiency according to calculations though)..over the years I have noticed better gas mileage in summer with most of my vehicles, even with the AC on..
You bought a Suburban, they were not made for good mileage, they are heavy and have gear ratios made for towing heavy loads which they do very well. Enjoy the vehicle for what it is designed for, and buy a little yap-yap car to get good mileage...its hard to get a vehicle that does both things very well...