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80 mph at 3000 rpm's good?

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by chaka454, Apr 17, 2002.

  1. chaka454

    chaka454 1/2 ton status

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    80 mph at 3000 rpm\'s good?

    Am I running too high RPM'S I'm doing 80mph at 3000rpm's is this good? I'm running 35's with 410's and a 4" lift, I was driving my moms 2000 Tundra with over drive I was going 80 and took the overdrive off and it jumped from 2800rpm's to 38 almost 3900rpm's so that leads me to believe that I'm not too bad what do you guys think?
     
  2. kpanza

    kpanza 1/2 ton status

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    Re: 80 mph at 3000 rpm\'s good?

    3000 rpm cruising speed for a truck small block 350 is about the limit if you want it to last a while...the Tundra's overhead-cam, high tech motor is a higher revving motor than your 350. A constant 3000 rpm seems a bit high to me...and of course I don't drive the big behemoth at 80 mph either! That would get scary in a hurry! /forums/images/icons/smile.gif

    When towing, and in Drive (not Overdrive), I try to keep the revs in the 2600-2900 range at the most (about 65 mph or so)...
     
  3. Esteban86K5

    Esteban86K5 1/2 ton status

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    Re: 80 mph at 3000 rpm\'s good?

    <blockquote><font class="small">In reply to:</font><hr>

    I don't drive the big behemoth at 80 mph either! That would get scary in a hurry

    <hr></blockquote>

    That's about the right speed where my truck just begins to smooth out. (Well my speedo says like 90 something since it isn't accurate) but my RPM's are only about 2700. And it feels like glass at that speed. When I go any slower I feel/hear all kinds of WIERD noises and vibrations. Anything below 65 and above 80 is good for me./forums/images/icons/wink.gif
     
  4. wheelnut46

    wheelnut46 1/2 ton status

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    Re: 80 mph at 3000 rpm\'s good?

    55-65 is about it for me. I can watch the gas guage move at 65+. I havent seen 80 mph is a LONG time.
     
  5. barbastard

    barbastard 1/2 ton status

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    Re: 80 mph at 3000 rpm\'s good?

    I've got 36's with 4.56 and NO OVERDRIVE (thanks to my TH350) and I turn about 3000 doing "cruising speed" on the freeway. I haven't yet determined what exact speed I'm at due to my speedo being way off...it says I'm going about 85-90. However....if that's the case....I've never been passed so much doing "90". I estimate I'm doing about 60, maybe 65. I'm really not going to be able to cruise much past that though...the little 350 wouldn't like it. It's going to make those long drives to the mountains a LOT longer!!! You didn't mention what tranny you've got...I'd be curious. But it sounds like your RPM is just about right.
     
  6. 79Beast

    79Beast 1/2 ton status

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    Re: 80 mph at 3000 rpm\'s good?

    I would say that you want your normal cruise speed to fall into the lower end of your powerband. This will be your call because you know the specs of your engine. I cruise at 2200 doing 65-70 (with 44's, 4.10s, SM465). I plan to go lower on the gears one day. To me, I sounds like your speed / RPM is fine....especially considering the hassle to change anything.
     
  7. wayne

    wayne 3/4 ton status

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    Re: 80 mph at 3000 rpm\'s good?

    3000 rpm's at 80 is not bad. I have 4:56's and 35's but hardly ever get into overdrive.
     
  8. ChevBlazin

    ChevBlazin 1/2 ton status

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    Re: 80 mph at 3000 rpm\'s good?

    barbastard. Just a thought. Your spedometer will be off when you get larger tires and do not re-gear your truck. However, 36" tires and 4.56 gears is about the same as stock tire to gear ratio (right??) so your spedometer should be pretty accurate within a few mph I would think. If you dont have one, find a buddy with a GPS and check your speed with that, works great.
     
  9. chaka454

    chaka454 1/2 ton status

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    Re: 80 mph at 3000 rpm\'s good?

    I have a TH350, hmmmmmm I guess i'm gonna try to keep it under 2800 just to be on the safe side, thanks for the info.
     
  10. DesertDueler

    DesertDueler 1/2 ton status

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    Re: 80 mph at 3000 rpm\'s good?

    Well my Jimmy has 35s(really measure 34") 4.56s and I have OD. I am around 2600 rpms at 80 mph. There is nothing wrong going over 80 in a big truck /forums/images/icons/smile.gif
     
  11. BowtieBlazer

    BowtieBlazer 1/2 ton status

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    Re: 80 mph at 3000 rpm\'s good?

    3000 for me is 72-73 mph with 31's SM465 and 3.08's in the rear. I'd like my 3000 to be about 80! I like to keep my motor around 2800...I'd think long drives at anything between 2600-3200 won't kill a 350 anytime prematurely.
     
  12. 90K5

    90K5 1/2 ton status

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    Re: 80 mph at 3000 rpm\'s good?

    Theoretically, 4.56's and 35/36's is close to stock. So are 4.11's and 33's...Thats what I have, and mine is way off...says 25 when going 20, so about 50 when goiung 40, if it went to 100, I'd be going 80. I've had the needle buried and looked at the speedometer on newer Suburbans and stuff, because I know where all the numbers are on the gauge, and they usually say something in the 70's. If you actually do the math, 3.73 is closer to stock for 33's and 4.11's for 35's.
     
  13. BOWTIE

    BOWTIE 1/2 ton status

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    Re: 80 mph at 3000 rpm\'s good?

    3000 is what i hit when cruising around 65, that's in drive. with the overdrive i'm at about 2400 to 2500. that's with 5.13s and 39'' boggers.


    ric
     
  14. Jay73K20

    Jay73K20 Registered Member

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    Re: 80 mph at 3000 rpm\'s good?

    If you do the math, take your known values which is 3000 rpm, 4.10 gearing, 1:1 transmission gear, 35" tire and 5280 feet is one mile. (3000/4.10=731.71 rpm for the axles) (35*3.14=109.9 circumference in inches) (109.9*731.71=80414.93 inches per minute) (80414.93/12=6701.24 feet per minute) (6701.24/5280=1.27 miles per minute) (1.27*60=76.2 miles per hour). If you had a lockup converter that was locked up at the time you took the reading like a TH350C or a manual transmission then the answer would be accurate. If you don't have a lockup converter then you have to account for converter slop, which could be 10 to 15 percent. So 3000 engine rpm which is felt on the torque converter would only equal 2550-2700 driveshaft rpm. Conclusion, you are not doing 80 MPH at 3000 RPM with those components that you mentioned.
     

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