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MPG / octane

Discussion in 'The Garage' started by bear76, May 14, 2006.

  1. bear76

    bear76 1/2 ton status

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    Came across somthing on the web a few days ago about octane and mpg. It said (opinion) that they went from 15mpg to 19mpg by switching from 87 to 93 and adjusting the timing. This was a 89' Sub with 350. Any merit to this?
     
  2. 79k20350

    79k20350 3/4 ton status

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  3. sled_dog

    sled_dog 1 ton status

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    plus the PCM can't change timing as it wants to. If you start to detonate and it tells the timing to dial back to 0* advanced, well say you bumped it forward 4*, now you are sitting at 4* instead of the 0* the PCM wants it at. I really don't think this a good idea. Who is getting 15mpg out of their 89 350 burb? haha, mine got 10 on a good day. I found a $700 way to improve gas mileage and still run on 87... its called a 95 Saturn...

    There are a lot of people buying 93 octane nowadays, my only thought is they either expect it to treat their car better(less repairs) or think they are getitng better mileage. Someday I'd love for someone to explain to me how making less power and running a fuel your engine wasn't meant to run is improving things.
     
  4. diesel4me

    diesel4me 1 ton status Premium Member

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    milage may vary..

    On an older carbureted rig with higher compression ratio you could gain a few MPG's by advancing the timing more and using higher octane fuel....Sled Dog already explained why newer rigs with computers will gain nothing,and perhaps even use more fuel!..not to mention the extra cost of premium gas..

    One thing I did notice recently...used my moms dodge caravan to bring my sister home a few days ago,a 65 mile ride each way..it had a half a tank of gas from the last time it was filled a month ago,the "older" gas without methanol in it..it used the usual 1/4 tank each way..

    Then I fill the tank with the "new" gas that now has up to 10% methanol,and it used 3/4 of a tank to do the same trip as before!..I did get stuck in traffic while a wreck was cleared off the highway for about 10 minutes,and it was raining this time..but I swear this new fuel burns faster than the other gas did,and its NEVER used that much gas to do that ride in any weather condition..I know it needs a tune up (never had one,its a 93,and has 66,000 miles)..but it runs great,and I dont think the engine is to blame..

    I think they know this new gas will give LESS mpg,and we will have to buy more even sooner than ever!:mad:
    ...also,my 79 C10 runs like dog doo when cold on this new brew..it spits back thru the carb,and I have to choke it with the hand choke longer than I ever did with the older fuel in order to keep it from bogging on acceleration during take offs when its still cold. I used to be able to turn the choke off 100% as soon as I left my driveway..now it takes a couple of miles before I can do it,and it guzzles more gas than it ever did..:mad: ..its a conspiracy to get carbed vehicles off the road if you ask me..I bet methanol will eat the zinc castings in my Edelbrock ,and any other carb if you run it long enough..all the gas they make now is designed for EFI vehicles..I can only imagine what it will do to lawn mowers and other small engines carbs and engines..:doah:
     
  5. 71 Blazer

    71 Blazer 1/2 ton status

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    I saw an article on 60 mins about people in Brazil using 85% ethanol, and although it was cheaper than gas they burned it faster. I don't know to much about it but my 71 Blazer hasn't been giving me any problems.
     
  6. mostwanted

    mostwanted 1/2 ton status

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    We have a 1991 3/4ton Sub. 4x4 with a GM 350 crate motor with about 8kmiles. We get about 15-16 mpg combo highway and city streets. BTW, it has a chip and flowmaster exhaust. Run it on 91 octane.
     
  7. 79k20350

    79k20350 3/4 ton status

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    The equation to figure out the mileage without ethanol is simple...(this is just rough but close...)

    100% ethanol would require fuel to air mixture of 1:7
    Gasoline is 1:14

    So twice as much alcohol to do the same as gas...10% of your fuel burns twice as fast so 10/2=5.

    So roughly youll get 5% worse mileage with gas containing 10% ethanol
     
  8. diesel4me

    diesel4me 1 ton status Premium Member

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    suspicion confirmed!

    Thanks!,,now I know its not just ME thinking it was drinking gas faster!..

    I have a book on "Alternative Fuels"...it shows how to build stills to make alcohol motor fuel...and the last chapter goes into great detail on how to drill out the jets in a carb to make it run the same as gas with alcohol.(did you know carb jets can EXPLODE if drilled with a power drill?:eek1: --they say use a hand powered drill only!)---and how to use an electric fuel pump to squirt gas down the carb throat for "cold starting"...so I suppose after wasting money to build a still,spend all day cooking mash,and making alcohol,you'll only succeed in burning it faster than gas,and probably not save a dime in the process!:doah: ..you'd be better off DRINKING the moonshine,and staying home!..:p: :D
     
    Last edited: May 14, 2006
  9. big83chevy4x4

    big83chevy4x4 3/4 ton status

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    with the motor in my truck (higher compression than stock and a fairly big cam) with 87 i got horrible millage, around 6 or 7 mpg. with 93 i get 12-13, i did nothing with the timing, but i had it set fairly advanced to begin with.
     
  10. Thunder

    Thunder 3/4 ton status

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    I get 18 MPG highway no problem as long as I keep it under 70.. I run my 89 K5 4* advance with a .050 plug gap & preimum fuel. But I also have a bunch of other mods for fuel mileage& low end torque.
     

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