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One last timing question, then I'll leave yall alone

Discussion in 'The Garage' started by 78Suburban, Oct 13, 2005.

  1. 78Suburban

    78Suburban 1/2 ton status

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    I know I know, you could write a book from all the posts I've made about this, and certainly write a book from all the messenger conversations I've had about timing... :bow:

    one more question.. I have the timing light right now.. i've retarded it to 10 degrees before TDC... the factory recommeded 8*..... It seems to be running really well right now.. my question is: Would 10 degrees before TDC be less apt to detonate with regular fuel than 8 degrees? if so, I'm gonna leave her where she is, because I run regular, and its running pretty sweet right now.

    PS: will the engine being up to operating temperature make a big difference in the timing readings? (Its not completely warmed right now, I'm very paranoid about melting my borrowed light's wire)

    :bow: :bow: :bow: :bow: :bow: :bow: :bow:
     
  2. mrk5

    mrk5 The Sticker Guy Moderator Vendor GMOTM Winner Author

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    The higher you go, the more likely it WILL detonate.

    I think you should at least have the motor at 165* before setting the timing. If the choke has the high speed idle on, it will affect you timing because it may be pulling some mechanical advance. So at least make sure the choke is fully pulled off.
     
  3. 78Suburban

    78Suburban 1/2 ton status

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    so, I would be a little on the safer side being at 7* BEFORE top dead center?
     
  4. mrk5

    mrk5 The Sticker Guy Moderator Vendor GMOTM Winner Author

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    If you don't get any knocking at 8*, leave it there. There shouldn't be any normal reason why the factory spec wouldn't work. If for some reason that is too much initial timing, you'll know when you take it for the first test drive. Accelerating up a on-ramps is a good place to test it.

    Up here living at an elevation of 5000ft, I run my advance a 14*. So 8* doesn't sound like much to me.
     
  5. 78Suburban

    78Suburban 1/2 ton status

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    I'm just paranoid because what's left of the emissions sticker says to run at least 91 octane fuel..... I think I will go on a test drive with 10 degrees... I'm thinking about leaving it on 10, because that's what its on now, and it seems to run better than it did before I had the dizzy out..
     
  6. Russell

    Russell LB7 Tahoe Status Premium Member GMOTM Winner

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    Ignore that emissions sticker :) Be bold, and tune that engine to run its best by fiddling around.

    I ran my old 355 up to 16 degrees before it started pinging, and then set it back to 15 degrees and left it there for a long time.

    Different engines will allow more or less timing, it depends a lot on your compression ratio, plugs, coil etc etc. My old 355 was a low compression motor, so it was less prone to pinging, and actually benefitted a ton by having the initial timing set up high like that. My emissions sticker stated that I should have mine at 8 degrees too, but it ran terrible compared to where I sat it all the time.

    My new higher compression 355 on the other hand, can only go up to 13 degrees before it starts pinging, according to my ECM.
     
  7. 78Suburban

    78Suburban 1/2 ton status

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    UPDATE: I decided to clocker her right onto 8*.... I drove it around and it ran great! I checked the timing one more time once the engine was fully warmed up, and it was still right on the money...

    This was a learning experience, and I cant thank yall enough :bow: ... no I can proudly say that I know how to set the initial timing on a motor...

    My water and oil gauges both worked flawlessly.... now all I have to do is wire up the ammeter and tach, and I know how to wire the tach...

    I AM one happy camper, finnaly something I have done has gone right :D :p:
     
  8. rcamacho

    rcamacho 1/2 ton status

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    Timing curves

    There are a lot of online articles available on how to optimize ignition timing. Without knowing your specific compression ratio or air/fuel ratio the best way is by trial and error.

    http://www.hotrod.com/techarticles/43300/

    In general chevrolet V-8 engines can take 32-36 degrees of total centrifugal advance. Initial advance can vary significantly depending upon personal preferences and idle tuning. Vacuum advance should be limited to 10-15 degrees if centrifugal is 30+.

    Personally,
    I'm running 14 degrees initial advance and 32 degrees total centrifugal on my HEI. Vacuum advance is limited to 15 degrees to eliminate light throttle pinging. This is on a 402 BBC, mild hydro roller cam in a fs blazer.
     
  9. theperfectgarage

    theperfectgarage 1/2 ton status

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    10 deg. is more apt than 8. Whats your elevation ?
     
  10. CustomChevy

    CustomChevy 1/2 ton status

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    no write it all up and take some pretty pics. Make a nice tech article and post.
     

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