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65 mph at 1400 rpm

Discussion in 'The Garage' started by Big GMC truck, Apr 3, 2006.

  1. Big GMC truck

    Big GMC truck Registered Member

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    Just installed my tach and was shocked at my low rpms, 1400 rpm at 65 mph. Is this wrong or do I just have really high rear end gears? The truck is a 1984 K1500 305 TH700R4 4wd with 31 inch tires. How high of a gear ratio was offered in 1984.
     
  2. Masiony

    Masiony 1/2 ton status

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    welcome to the smog/economy mindset of GM through the early 80's. you probably got 3.08 gears.
     
  3. redneckdude

    redneckdude 1/2 ton status

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    sounds liek 3.08s to me. Mine was spinnin amazingly low too in OD with 33s and 3.08s. just install a set of 5.13s and some 40" tsls, itll put you where it needs to be.
     
  4. Big GMC truck

    Big GMC truck Registered Member

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    So this explains my poor acceleration, or lack thereof. I always thought that there was something wrong with the engine. I replaced the engine, cat, and carburetor without noting much performance gain. Redneckdude, what rpms did you do at 65. You would think that this low rpms would equate to hybrid gas mileage, but it doesn't. My 305 gets about 11 city and 17 highway. Was 3.08 the lowest, numerically?
     
  5. Muddytazz

    Muddytazz 1 ton status

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    nope, i've seen 2.42's :eek1:
     
  6. Masiony

    Masiony 1/2 ton status

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    that sucks, my 85' while driving 300 miles with a tired crappy running q-jet'd 305 while having probably about 1600+ lbs in the back (had my 60/14FF, 205 and a few more parts in it), still got 10, and that was in drive not OD.
     
  7. 1985_K5_Silverado

    1985_K5_Silverado 1/2 ton status

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    I turn a hair under 1900rpm at 65mph in overdrive (700R4, 3.73 gears, 31-inch tires). The stock engines back then were also anemic. Mine rolled out of the factory with a 305 that was rated at 160 HP and 235 lb-ft torque! The 350 wasn't much better that year.

    Luckily, small block Chevies :bow: are probably the least expensive crate engines around, bang-for-the-buck-wise. Does WA do smog tests?
     
  8. Masiony

    Masiony 1/2 ton status

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    yeah on the smog. every two years. mine was also had 3.73 in it, maybe part of a factory tow package? and yep on the motor swap. im going TBI 350 here shortly, hopefully i wont have to run that 305 on the trail.
     
  9. Russell

    Russell LB7 Tahoe Status Premium Member GMOTM Winner

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    My 2wd 77 short stepper spins at 2200 rpm at 60 mph (700r4, 3.73, 27" tires) Absolutely perfect combo, my truck gets about 20 mpg at that speed :D
     
  10. Grizz84

    Grizz84 Registered Member

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    I feel your pain, its sucks to think that my '05 Colorado with a 2.8 4 banger has more hp and almost as much torque as my '84 K5.
     
  11. 1985_K5_Silverado

    1985_K5_Silverado 1/2 ton status

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    Yeah, back in '85, they were playing catch-up with every kind of clobbered-up, half-ass way to get gas mileage up and emissions down. Grabbing at straws it seemed.

    20 lbs of truck for every lb-ft of torque! 30 lbs of truck per HP! It's enough to make an old, reformed street racer cry. You'd have the gas pedal flat on the floor just to get out of your own way. It'd be like driving a 1960s VW bus. I believe one Bronco vs Jimmy shootout road test from the early 80s had both doing a 1/4-mile in around 19 seconds and 0-60 in 15 seconds or thereabouts. Very lame.

    Nowdays, the seem to roll full-size trucks off the line with about 300 HP and about 350 lb-ft torque, and that's not bad at all for most light truck buyers.
     
  12. roadnotca

    roadnotca 3/4 ton status

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    65?? But officer, its not off the choke yet.:haha:
     
  13. Drey

    Drey 3/4 ton status

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    My K10 would get better mileage in 3rd pulling my small trailer then it would by itself in OD
     
  14. Big GMC truck

    Big GMC truck Registered Member

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    I wonder why it gets better fuel economy turning higher rpms.
     
  15. Russell

    Russell LB7 Tahoe Status Premium Member GMOTM Winner

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    If the engine is lugging to move the vehicle, it isn't nearly as efficient if it is happying applying a little bit of effort to keep the vehicle moving. Nor is the engine efficient if it is revving way up at higher speeds.
     
  16. dyeager535

    dyeager535 1 ton status Premium Member

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    Yes, which is one of the reasons you'll note that 350 and 305 economy is almost exactly the same in these trucks. 350 just isn't working as hard to keep you moving. 305 is theoretically going to need less gas at the same RPM with no load than a 350, but our trucks are nowhere near "no load" lol. 305's were underpowered even for the big cars, but they hung on for quite some time.

    I get the same economy with no OD, 3.42's, and a 350 than I did with OD, 3.08's, and a 305.
     

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