RPM questionThoughts?

Discussion in 'Engine Topic' started by JD Z, Oct 31, 2017.

  1. JD Z

    JD Z Veteran Member

    On a 1980 Z28 with a 350. From what I can tell it has updated roller cam, headers and a Holley 750 carb. The car gets up well and 1st - 3rd is quick. Gettting to 4,800 RPMs is pretty fast and easy. It’s a new to me car and I feel it can go farther. Are there any obvious risk points in RPM that I should be concerned or cautioned at?

    I think the owner put a Holley 750 because he was expecting higher RPM, or why the 750? Would you generally expect 6,500 is an OK RPM? I would like to give it a good run, but don’t want to blow something. Thoughts?
     
  2. JD Z

    JD Z Veteran Member

    At 5,000 it feels like it has qiute a bit more. The redline on the tach has me shifting.
     
  3. SRGN

    SRGN Veteran Member

    167
    46
    Feb 20, 2009
    Central NJ
    Hard to make recommendations without knowing what parts are in the engine. Do you have any information about the cam, valvesprings, and bottom end?
     
  4. JD Z

    JD Z Veteran Member

    Hydraulic Roller Cam, edelbrock manifold and hedman heads is all that was written, so I don't know how deep the previous owner went. The car runs great and has really good power from my memory of the original 80z. The 750 carb got me thinking. That really would only be put on if the owner felt they needed max power at higher RPM's...I think. All other research suggest a 650 would be right for the car.

    The car is from MA and is in fantastic condition. No rust to speak of, even the underside looks good. The owner(s) had good respect for the car so I'm thinking they spent good time working on the motor. Would you put a hydraulic roller cam in without doing anything else to improve the engine?
     
  5. JD Z

    JD Z Veteran Member

    I'm wondering if on occasion I take it to 5.5k or even 6k will there be probable problems. The times I would likely do this and be interested are 10 times or less per year and only on 0-70 shots. Not long term RPMs.

    My gut gets queezy looking at the tach redline of 5K. The factory orange is at 4,700 and red at 5,000. The previous owner put some work into the engine and it feels there is plenty of going past 5K. Not sure how far but I think I can sense it from the pull and feel.

    Looking for words of caution/comfort from experience in the group. No promises I understand. Thanks guys.
     
    Last edited: Nov 4, 2017
  6. 8pack

    8pack Veteran Member Lifetime Gold Member

    1,810
    14
    Aug 29, 2007
    Pittsburgh, PA
    People often oversized their carb. They think bigger is better. You are right that a 650/70 is probably all ththe carb you need for that engine. So don’t guess at your redline based on carb size. I suppose you could take it and get it put on a dyno and see where it starts to fall off. They should be experienced enough to help figure out your redline.
     
  7. 80sz

    80sz Veteran Member

    2,153
    143
    Feb 2, 2014
    Buffalo,n.y.
    With out specs it hard to say whats safe. wind her out and be risky , its a rush! 6000 rpm is when Id get little squirmy with a cast crank. My 355 buzzed to 6500 with cast crank and never broke.
     
  8. BonzoHansen

    BonzoHansen Administrator Lifetime Gold Member

    Well, you'll never really know because you don't know the cam specs. heads matter too, not sure what you have. Hedman is headers (exaust) not heads.

    A hydraulic roller is great and does not need other changes. mild factory engines had roller cams. its presence does not mean wild setup. the cam specs still matter. Same with the intake, there are different intakes with different performance.

    Your tach red line is no longer relevant, that was for the stock engine.

    If it worries you stop at 5k. you aren't racing. the 600 will probably limit things to 6000 rpm or less, at least regarding making power
     
  9. cadillac_al

    cadillac_al Veteran Member

    512
    33
    Apr 22, 2015
    Maine
    Do you have dual exhaust or single exhaust with catalytic? I'll rev a stock 350 to 5500 rpm with no worries, 6000 if it will do it. A 350 Chev should be safe to 6k imo.
     
  10. Coadster32

    Coadster32 Veteran Member Lifetime Gold Member

    1,185
    41
    Oct 2, 2013
    Milford,CT
    Just big picturing it here...If you're happy with the current performance, and hit 5500-6000 occasionally, and don't hold it there, I wouldn't worry about it. If you feel you're leaving some on the table, you can see if the carb is tuned correctly for your setup, look into timing, etc., which isn't extremely difficult, and very cost effective. I agree, people do tend to oversize their carbs for street use. Your engine will only pull whatever cfm's it needs, elsewise you are just keeping the fuel bowls where they should be. FWIT...I have a 383 motor, street car only, with a 600cfm carb on it. With a wideband sensor attached after adjusting the jetting a bit, I'm reading 12.6% at WOT up to 6200. This tells me my carb is ok. If it was too small, my readings would be lean. Street use doesn't negate a bigger carb.
     
    JD Z likes this.

Share This Page