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How high should I rev my engine?

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by Blue85, Sep 9, 2002.

  1. Blue85

    Blue85 Troll Premium Member

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    I only found bits and pieces on this in old posts.

    I have a Goodwrench 350, 4-bolt mains that is pretty much the way it came out of the crate. How hard is it on the engine to be in the 5000-5500 rpm range for a couple of seconds?

    Where do I get into danger of bending a valve or pumping up the lifters or something else?

    During normal driving I keep it under 3500. Ocassionaly, I'll shift it up at 4200 or so. I'm just trying to get a feel for where I start being really hard on the engine and where I am in danger of blowing it up.
     
  2. dyeager535

    dyeager535 1 ton status Premium Member

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    More than anything, I think the RPM is dependent on the valve springs.

    Stock springs, I'd be *guessing* around 45-5500RPM the valves will start to float, and you won't be doing any good doing that. I've taken mine up to 4500 before, and its pretty worn.

    There is nothing inherently wrong with the SBC to limit RPM to X-rpm, it just really depends on the springs, and whether or not you are even making any power at that high of RPM. In case others reading don't know, you need to shift OVER the RPM's where peak power is made, or you bog the engine down on the shift. (I guess theoretically, shifting so that the next shift puts you into the high-low end of your power band would be ideal)

    Just a rough guesstimate, I'd pick 4500 as a good upper end.
     
  3. mudhog

    mudhog THEGAME Staff Member Super Moderator

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    my 350 starts loosing power at about 4200-4500 rpm so i generaly dont take it over 4500rpm
     
  4. Blue85

    Blue85 Troll Premium Member

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    Right, mine feels the same way.

    But for maximum performance, assuming no danger to the engine, you don't want to shift until your torque at the output of the transmission would be greater in 2nd gear than it currently is in 1st. This means going past the torque peak and past the power peak. If your 1st gear is 3:1 and your 2nd gear is 2:1, then you want to stay in 1st until you hit the rpm where the torque band is down to 2/3 of what it is at 2/3 of that rpm. From the few torque curves that I've seen that are representative of a mild 350, this rpm would be around 5500. Maybe I'm wrong about that?
     
  5. Diesel Dan

    Diesel Dan 1/2 ton status

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    The stock auto trans in my '74 malibu did a 1-2 shift @5500 rpm. I've always tried to run mine up to 5500, providing they didn't fall off the powerband too much. This was for boggin/racing. Basically I use 5500 as a stock redline.
     

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