Author Topic: more power = better fuel economy  (Read 14713 times)

Offline Irish_Alley

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more power = better fuel economy
« on: July 25, 2009, 02:04:48 AM »
OK i had water in my oil not a lot but had some so i changed my intake gasket fix it i think for now. but while i had it apart i put a elderbrock performer intake and a carb spacer i think 3" well all is fine till i go to fill up and calculate my mpgs its usually around 7-8 more at 7 than 8 but this time it was around 10. i was like whatever i must of did something wrong so next time i filled up " a couple days later" it was around 9 but that was after letting my wife drive it and then leaving the lights on and killing my battery then letting it idle for a while to let the battery charge back up. now i would expect and it make sense more power would give you better economy since the engine doesn't have to work as hard to get moving but 3 mps that blew me out of the water.
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Online VileZambonie

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Re: more power = better fuel economy
« Reply #1 on: July 25, 2009, 08:26:33 AM »
7 mpg isn't very good at all. You probably removed some carbon and got your timing set better.
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Offline choptop

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Re: more power = better fuel economy
« Reply #2 on: July 25, 2009, 05:00:24 PM »
Any ime you increase the efficiency of a motor, the mileage should improve as well. It just makes sense. But if you build an engine that easily produces 400hp + and drive it to where it uses those horses, then the mileage wont be great. Sounds like you fixed some other problems that needed attention anyway. 7-8 isnt good.
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Offline gold84gmc

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Re: more power = better fuel economy
« Reply #3 on: July 25, 2009, 10:12:45 PM »
7-8 mpg's isnt that about normal for one of these trucks?
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Offline 69byrd

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Re: more power = better fuel economy
« Reply #4 on: July 25, 2009, 10:25:07 PM »
I know alot of guys with these trucks who are lucky to get 10mph, but alot of that has to do with there driving habits.
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Offline Irish_Alley

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Re: more power = better fuel economy
« Reply #5 on: July 25, 2009, 11:21:27 PM »
i had this engine in my 86 4x2 1/2 ton it was getting about 13. then once i dropped it in my 79 it got 7-8 with out any changes. i could of fixed a couple problems that i didn't know about but as far as i could tell there were no signs of any problems except for the water in the oil and that had just started. and my driving habits are about the same cause i never wanted to pull another motor again lol or at least prolong it as long as i can.
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Offline gold84gmc

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Re: more power = better fuel economy
« Reply #6 on: July 26, 2009, 06:15:19 AM »
ya i dont exactly baby my truck so i probably get about 7
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Offline Captkaos

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Re: more power = better fuel economy
« Reply #7 on: July 26, 2009, 10:22:54 AM »
My 81 K10 (with a 4 speed) got 12mpg all the time, this was with a 350 Crate.

Offline gold84gmc

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Re: more power = better fuel economy
« Reply #8 on: July 26, 2009, 02:58:14 PM »
i got the original 350 with 101k miles all original and a th400 tranny all original and i dont know what the gear ratio in the axle is but its the 9 1/2" 14 bolt...its not exactly in the best shape.....would my engine be better or worse than a 350 crate?
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Offline TexasRed

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Re: more power = better fuel economy
« Reply #9 on: July 26, 2009, 04:33:07 PM »
Yikes, am I naive to hope for high 18 or 19's with a 383 and a 700r4?

My 305 with th350c got about 18-19 with the original quadrajet. On the highway, City was like 13-16mpg. Closer to 13 with A/C.

Offline gold84gmc

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Re: more power = better fuel economy
« Reply #10 on: July 26, 2009, 06:21:41 PM »
Yikes, am I naive to hope for high 18 or 19's with a 383 and a 700r4?

My 305 with th350c got about 18-19 with the original quadrajet. On the highway, City was like 13-16mpg. Closer to 13 with A/C.

how did u get 18-19 mpg with a carb? i must be beating on my truck too much lol
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Offline choptop

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Re: more power = better fuel economy
« Reply #11 on: July 26, 2009, 08:31:32 PM »
Ive gotten 18-20 mpg with a 305 and carb. My 86 GMC is getting 18-19 mpg, Big Red gets about 14, but with 35's I dont expect any better. I have had several others that got this similar mileage. I havent had any of the 4x4s or 3/4 ton up trucks do it, but thats to be expected. Ive even got 20 out of my 51, so I dont think its a crab thing. One thing to take into consideration is most of us have different driving areas. Mine is mostly flat. The wifes 01 get better fuel mileage at 75 than it does at 65 becaus the taller tires set the gears to high. But at 75-80 mph the engine is around 2200-2300 rpms and likes it there.
 But, like I said the terrain is different. We are flat, and most highway driving is 70-80 mph. I know alot of areas hardly ever see speeds above 55mpg, and have twists and turns with hills. That needs to be considered when comparing notes on fuel mileage with eachother.
  Altitude, and fuel type are considerations as well. We are about 2500ft above see level ( Or close, Im  not sure) so mileage difference will be different in Denver. We also dont have any methanol fuel that I know of, and Ive heard that methanol mixed fuels are notorious for poor fuel mileage.
  That being said, if you live in an area that requires alot of start and stopping and hill climbing, I dont see the mileage being to good.
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Offline gold84gmc

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Re: more power = better fuel economy
« Reply #12 on: July 27, 2009, 08:09:45 AM »
would a 350 be much different in mpg's than a 305? some of these trucks got around 18 then how come the late 90's trucks with fuel injection couldnt get any better...my dad used to have a 97 gmc 1500 with a 350 vortec and it only got about 16-18 mpg's. and the terrain in maine isnt exactly flat so there are quite a bit of hills
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Offline eventhorizon66

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Re: more power = better fuel economy
« Reply #13 on: July 27, 2009, 01:29:09 PM »
These trucks are lighter than any later model chevys and wouldn't even come close to meeting today's crash safety tests.  The only reason I mention the crash safety is the frame is largely resposible for this and I believe our trucks are the last that had full C-channel frame rails (contributing to the lighter weight).
« Last Edit: July 27, 2009, 01:31:15 PM by eventhorizon66 »
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Offline SUX2BU99

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Re: more power = better fuel economy
« Reply #14 on: July 27, 2009, 03:11:17 PM »
For sure, much lighter. I weighed mine at the track recently and it was 4040 lbs and that's with my 270 lbs in it. I think I read that the Ford Lightnings were close to 5000 lbs. Mine seems like it gets attrocious mileage but I only have one saddle tank in it so that's like 15 gallons. But even with the cam, heads and other performances parts done to my motor, it still got 14 mpg on a mostly-highway tankfull back in May. I was pleasantly surprised.

Todays trucks are terrible for mileage. 30+ years of technology progress and they get the same mid-teens they always did. BUT, the flip side is more power, better driveability and more weight they are hauling around all while producing cleaner emissions. The LS-series motors are better than the 1st-gen SBC they replaced though. The 2 Dakota R/T's I had with their injected 360's got 12-16 mpg and the 96 GMC 1/2-ton my friends dad had with the Vortec 350 would have a hard time getting better than 12mpg. The 2003 Tahoe 5.3 we had wasn't too bad. It would get high-teens I would say. Mid-high teens. The 05 Magnum R/T I had with it's 5.7 HEMI would get about 21mpg on my weekly commute. I think the best it ever got was about 26-27. It was a porker though at 4400 lbs!
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