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454 mileage

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by Blazer79, Apr 17, 2001.

  1. Blazer79

    Blazer79 1/2 ton status

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    As you may already know, I just got a 454. My best highway mileage with my current 350/Edelbrock Q-jet/Performer intake/Flowtech Headers/TH350/3.07 gears/31" tires is 11.2 mi/gal. Can anybody running one tell me how much should I expect? I'll be using the same setup, except Tri-Y headers instead of the Flowtech Afterburners. My theory is that it should improve a bit because of the added torque.

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  2. tRustyK5

    tRustyK5 Big meanie Staff Member Super Moderator GMOTM Winner Author

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    I would count on a mileage drop...more torque but also 104 more cubes to fill.

    Rene

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  3. dyeager535

    dyeager535 1 ton status Premium Member

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    Stole this off the 73-87 chev/gmc truck list. i'm sure the guy won't mind though....

    "
    &gt; any suggestions of where I should tune a tranny up to work at this
    &gt; point? 60 MPH comes out at approx 2000 RPM, with my current tire/axle
    &gt; setup ( about to change, cause one of the tires exploded last night
    &gt; from 7 years of being parked... prolly 33x10.50-16.5) or should I just
    &gt; replace the THM 400 with a NV4500 and call it even? ( or SM465/torque
    &gt; splitter/saturn overdrive etc)

    Thats a combination isn't going to be easy to sort out using wrecking yard
    parts- there just arent any really tall axle ratios availible for the full
    floating differentials. You can look at using a low stall converter to help
    keep it connected and let it lug a little. If you have anywhere near that
    kind of HP and torque you are pretty much confined to using a THM 400 or a
    heavy duty manual transmission. The THM 400 will use less gas all things
    being equal because the pump in the THM 400 takes less effort to operate
    than stirring up the thick oil in the four speed with the countergear does.

    Theres a few things will be conspiring against fuel economy on your truck-
    throttling losses arent too bad at 2000 rpm even on a 454 but will sure go
    up fast as you increase speed. The other main issues are rolling drag on big
    tires is enormous (one reason I decided to skip the Big Dooley conversion)
    and its a heavy truck and if its lifted has a lot of frontal area besides
    (big tires really hurt here too) so its not what you'd consider a real
    economy truck. The cam you're using actually is probably hurting economy as
    much as anything, as it is making a tremendous amount of power at much too
    low a speed to be useful unladen, and you might get better economy with a
    cam with a little less bottom end, seeing as you're stuck with a 2000 rpm @
    60 mph figure. Just the normal car 454 cam for 1971-'75 might work well, or
    even retarding the timing of your present cam with an offset key 4 degrees
    or so.

    That aside, theres room for improvements in a few areas. Get the narrowest
    highest pressure radial tires you can live with for one. A lower stall
    converter is another prospect, and a jetting the carb lean enough that 60-65
    mph takes about 18-19" Hg will make some improvements for you. You may need
    to rejet the secondaries a little richer to compensate for wide open
    throttle to make up for the lean primaries. Make sure the float level is
    low, idle mixtures are 1/2 turn lean, and the secondary air valve stays
    closed in flat road driving at 70 mph. Quite a few secondaries are beginning
    to partly open at 60-70 mph on trucks like yours which just murders fuel
    economy. As I'd posted a few months back, rich main jetting also allows
    cruising with the engine at such high vacuum from the small throttle opening
    that it draws fuel from the idle ports as well which is wasted.

    As far as transmission weakness, dont feel too nervous about the automatics.

    One of my favourite automatics ever is the Chevrolet Turboglide, which was a
    delicate little three speed with a five element switch pitch converter they
    sold in 1957-'61 cars. They were disasterously weak, but Really Cool Junk.
    In the 1959 cars, Chevrolet made a lot of changes to improve durability. I
    have a '59 Chevy sales training film showing the Proving Grounds tests of
    the 'improved' version.

    It features a '59 Impala convertible (top down) with a 348 engine (small
    409) and Turboglide, and two guys with white lab coats, one holding a big
    brass fire extinguisher.

    The test is to open the engine full throttle and make ONE HUNDRED shifts
    between "Drive" and "Reverse" at full throttle. This you have got to see.
    About the forth shift, the tires catch fire and the guy with the
    extinguisher gets to work putting them out. After 100 cycles have been
    completed, they let the car cool a few minutes idling, and then repeat the
    series again 100 more times. And again, until about 600 full throttle shifts
    have been done. The transmission is then disassembled for inspection.
    Naturally, the parts look fine.

    Anyhow, thats the standard test, I have no idea how they keep the driveshaft
    in the car myself, but the transmissions are pretty stout, if a Turboglide
    didnt grenade, you have little to fear from a THM 400. GM ran a similar TV
    ad about ten years ago featuring a Cutlass FWD with the tires on fire you
    may recall.

    If I remember right, you're in AZ, and I'll be down there in a few weeks,
    maybe I could visit and see the Suburban myself! You can check out the 16
    mpg 454 3+3 while you're at it;-)


    Dorian
    My K5 and Chev/Olds tech/links page: <A target="_blank" HREF=http://www.dorianyeager.com/index2.html>http://www.dorianyeager.com/index2.html</A>
     
  4. thatK30guy

    thatK30guy 1 ton status Premium Member

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    Whats everybody bitching about the 454 mileage for??? ANYTHING over 10 is fantastic for a big block.
    My 85 K30 has a steel crank, 260 Comp Cam, Hedman headers, TH 400, and 4.10 gears on 35" tires. I get around 5 to 6 mpg!!!!!!!!!!!!!!!!!! In the last 5 years since I have owned this truck, I have only put on 24,000 miles on the truck. Why, you ask? Because who can afford the gas for it?!?!?!?!
     
  5. Blazer79

    Blazer79 1/2 ton status

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    That's a very interesting post, dyeager. I do know that I'll never get any Sentra style mileage on my Blazer because of aerodynamics and heavy tires. I'm just hoping I can stay in 3rd gear most of the time now.

    I'm wondering why does this guy say that the cam is hurting economy because it's making tremendous amount of power at much too low a speed. I don't know what cam they were talking about, but a cam with lots of power in the low end is what I'd use for 60mph @2000rpm (pretty much what I'm running). Don't you think? Why would a cam with a little less bottom end make you get better economy?

    I'd love to see that video. Do you think my TH350 will hold with the 454 if I add a tranny cooler? I'm sure it wouldn't live through that kind of test, though.

    What is a 454 3+3?

    Thanks.

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  6. Blazer79

    Blazer79 1/2 ton status

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    You're scaring my K30guy. 5-6mpg!!![​IMG]!!! Are you a heavy foot? Is that on the highway? I get down to 6-7 mpg in heavy traffic with my 350. Thank God it's not a daily driver.

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  7. thatK30guy

    thatK30guy 1 ton status Premium Member

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    LOL!!! [​IMG] My 5-6 mpg is NOT heavy foot driving!!! Thats the mileage I get on both highway AND city driving!!! Cant figure that one out. [​IMG]

    4x4 3+3 stands for the crew cab version, 3 passengers front and rear.
     
  8. dyeager535

    dyeager535 1 ton status Premium Member

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    I'd have to say that he mentions the cam hurting because it was designed specifically for low end, and wasn't making enough power up high, maybe. I might find fault with his theory there, but with the mileage he is running, he can't be all wrong.

    Just for an example, with a 204/214 .429/.452 lift cam in a SBC 350 (with vortec heads, 750 carb, manifolds, 9.5 compression) starts out at 400ft lbs of torque at 2000RPM, and keeps that (perfectly flat) until 3000RPM. HP never gets above 275 though, and thats what keeps your vehicle moving. TQ gets you moving, HP keeps you moving, and that may be where he figures the less agressive cam is hurting.

    If I change the cam to a street/strip cam, the HP increases to 327, but at 5500RPM! Definitely not useable in most cases, especially trucks.

    I think a WELL BUILT 350 would hold up to a 454 no question, especially if you weren't really hard on it, IE burnouts on pavement, low stall converter, etc.

    Dorian
    My K5 and Chev/Olds tech/links page: <A target="_blank" HREF=http://www.dorianyeager.com/index2.html>http://www.dorianyeager.com/index2.html</A>
     
  9. prjt_blzr

    prjt_blzr 1/2 ton status

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    For what it is worth.....I have a 455 Buick in my blazer with 3/4 ton running gear, 4.10's and 35" BFGs. I get 10MPG at 6,000 ft elevation and almost 12 at sea level. My K30 has a 450HP 454 and it does about 9.5MPG ( I run it hard ) and averages about 7MPG towing 8,500LBs up and down the passes in CO.
     

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