Dismiss Notice

Welcome To CK5!

Registering is free and easy! Hope to see you on the forums soon.

Score a FREE t-shirt and membership sticker when you sign up for a Premium Membership and choose the recurring plan.

Hi compression vs low compression vs fuel quality?

Discussion in 'The Garage' started by moturbopar, Apr 24, 2006.

  1. moturbopar

    moturbopar 1/2 ton status

    Joined:
    Feb 9, 2005
    Posts:
    387
    Likes Received:
    0
    Location:
    mesa az
    Ok the title might be confusing but I do not know which would be better. I am puting a new rebuilt 350 in my work truck. The problem is I am considering doing a few mods to help performance and hopefully fuel economy. The most important question and the one that is most important is would I be better off running higher compression (64cc heads) and run 91octane or run lower compression (75cc=8.5-1) and 87 octane. I am wondering which would be cheaper in the long run more mpg and higher priced fuel or less economy and cheaper gas?
     
  2. 4X4HIGH

    4X4HIGH 1 ton status Premium Member GMOTM Winner

    Joined:
    Dec 14, 2001
    Posts:
    22,062
    Likes Received:
    69
    Location:
    Pleasanton, CA.
    Never run high compression in trucks or you will end up with detonation no matter what grade fuel you try using. Stick with a compression ratio of between 8.5:1/9.0:1 for best drivability and you will also gett better mileage since it won't be detonating and working against itself.
     
  3. moturbopar

    moturbopar 1/2 ton status

    Joined:
    Feb 9, 2005
    Posts:
    387
    Likes Received:
    0
    Location:
    mesa az
    For high compression I was thinking 9.5 for max, and vortec heads since they have a good combustion chamber, I forgot to mention that:doah:
    Anyways I am leaning to the low compression (8.5) engine anyways, since it will be cheaper to build and I know I can run cheap gas, which I can get anyplace.
     
  4. dyeager535

    dyeager535 1 ton status Premium Member

    Joined:
    Dec 13, 2000
    Posts:
    26,980
    Likes Received:
    189
    Location:
    Roy WA
    You want as much compression you can run (without problem) with the lowest fuel grade available, since you are talking about *economy*. Obviously there are a few variables, (cam, fueling, etc) but Vortecs have no problem running at 9.0+ on 87 octane if tuned right. (which is always going to make a difference)

    Manufacturers are up around 10:1 on 87 IIRC in some applications, so higher is possible, but not likely on an iron headed 350.
     
  5. steve_kibbe

    steve_kibbe 1/2 ton status

    Joined:
    Feb 4, 2004
    Posts:
    2,895
    Likes Received:
    2
    Location:
    Spartanburg, SC
    What kind of milage are you wanting to achieve? You can swap in a 6.2 and get 17+ all day long, just might take a few minutes to get there:D

    Then you'll have 18:1 or so:wink1:
     
  6. MTMike

    MTMike 1/2 ton status

    Joined:
    Feb 10, 2005
    Posts:
    2,992
    Likes Received:
    0
    Location:
    Billings, Montana
    My engine was built for mud racing by the previous owner. It has 10.5:1, Vortec heads, moderate cam and I have to run 91 octane w/ the vacuum advance disconnected to keep it from pinging. Even then I get 4-6mpg

    If you're looking for economy, keep the compression in the ~9:1 range.
     
  7. 4X4HIGH

    4X4HIGH 1 ton status Premium Member GMOTM Winner

    Joined:
    Dec 14, 2001
    Posts:
    22,062
    Likes Received:
    69
    Location:
    Pleasanton, CA.
    The only way this is possible without detonation is with FI and an ECM to control everything. Manufacturers are up to as much as 11:1 but like i said, this is with FI and all the sensors monitoring everything.
     
  8. Chevy305

    Chevy305 6 Lug 14bsf Status Premium Member GMOTM Winner

    Joined:
    Jan 23, 2006
    Posts:
    11,230
    Likes Received:
    488
    Location:
    New Hampshire
    I vote for the 64cc heads.

    More power equals less lugging and you don't have to be on the gas as hard to get to where you are going.

    I say go for more compression!
     
  9. crometooth

    crometooth Registered Member

    Joined:
    Aug 21, 2004
    Posts:
    14
    Likes Received:
    0
    I'm running a 350 with Vortec heads and about 10:1 compression. I don't have any serious problems with 87 octane. Course, the cam makes the difference, you need some overlap if you are going for higher compression.

    If I had to do it again I would stick with 9:1 or so. If turbo or a blower is in your future then 8:1 might be a better choice...
     

Share This Page