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Chevy V-8 question

Discussion in '40- & 55-Series Tech' started by 1Fine40, Sep 12, 2003.

  1. 1Fine40

    1Fine40 Rust Buster SILVER Star

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    Recently replaced my heads on a 350. Old ones cracked. Got some rebuilt units from a reputable shop with same casting numbers as old ones. Added roller tip rocker arms. Set up hydraulic lifters using method of rotating each cylinder in turn to TDC, then rotating pushrod between fingers until it was snug, then add a half turn of preload. After getting the mill together, and adjusting timing etc., it seems to have very little low end. :( Before the head cracked, it was very torquey....Did I set up the rocker arms incorrectly? :-\ They are 1.5 ratio units like the stockers they replaced....I think. Any Chevy guys want to set me straight?? The rig runs smoothly, just no bottom oomph!

    Ideas??
     
  2. Gumby

    Gumby Supamod Staff Member s-Moderator

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    If your rockers open too fast and too much, or the valves are too big, you will loose on the bottom. The good news is you gain on the top with the right cam.
    I'm installing 305 TBI heads on the 350 in my T for exactly the opposite effect.
     
  3. 1Fine40

    1Fine40 Rust Buster SILVER Star

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    Hmmmm, then maybe the valves are opening too far. Maybe I need to back off the preload some..... ::)

    The valves are not big ones. 1.73 intake and 1.60Ex is what I think they put in. I didn't measure before I installed the heads. But, I do have an invoice w/ part numbers, so I can call and check.
     
  4. dinkleberry

    dinkleberry

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    If the casting #'s are the same then the valves should be the same. I would say you have different ratio rockers.
     
  5. Gumby

    Gumby Supamod Staff Member s-Moderator

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    [quote author=1Fine40 link=board=1;threadid=5216;start=msg40862#msg40862 date=1063468093]
    Hmmmm, then maybe the valves are opening too far. Maybe I need to back off the preload some..... ::)

    The valves are not big ones. 1.73 intake and 1.60Ex is what I think they put in. I didn't measure before I installed the heads. But, I do have an invoice w/ part numbers, so I can call and check.


    [/quote]
    No, don't back off the pre-load. If they are too tight, you will have compression problems when the engine heats up. Then your engine will run very poorly. Since that's not the case, I wouldn't think that's the problem. I was suggesting that the rockers were the wrong ratio or the cam was wrong.
    Sorry I was unclear. :-[
     
  6. 1Fine40

    1Fine40 Rust Buster SILVER Star

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    :eek: Oh, O.K., thanks for that clarification. Perhaps the stockers (rocker arms) were less than 1.5?? I'm not sure what they were. I do know they were worn and needed to be replaced. The stamped steel roller tip units seemed to be a good choice. I guess I'll need to go to the shop and talk to them some more about the options. :-\
     
  7. 1Fine40

    1Fine40 Rust Buster SILVER Star

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    :-[So, I feel stupid....but I'll admit what I found is better than what I expected to find. The stamped steel roller tip rockers are just fine at 1.5 ratio. Stock was 1.43, so this is a small improvement. Preload was adjusted correctly. Timing was set o.k. too at 10 deg. BTDC. But the auto choke on the carb was not set up right.... :-* It is amazing that a simple thing like the choke rod length can make a huge difference in how the engine responds when not fully warmed up. Runs like a whole different beast now!