timing on a 1970 350LT-1

Discussion in 'Engine Topic' started by 1hot1970, Oct 2, 2011.

  1. 1hot1970

    1hot1970 Veteran Member

    Messages:
    118
    Likes Received:
    0
    Joined:
    Sep 23, 2011
    Location:
    Lancaster, Pennsylvania
    Just fired up my brand new rebuilt 1970 350LT-1, and after breaking in the cam for a 30 min period, I changed the oil readjusted all my valves and fired it back up to set the timing, dwell, and carb. When I was setting my timing to 8 degrees as per factory setting with the vaccum hose off the distributor my timing mark on the crank periodically flucuates not staying in one steady rythm?? Does anyone know what causes that?? I did set my dwell to 30 and they are saying anywhere between 29 to 31 is the factory setting. I adjusted my idle speed air mixture screws but the timing still flucuates. Is there an actual procedure on what should be adjusted first to last?

    The engine seems to be running very strong, smells a little on the rich side!!! but maybe the idle screws need adjusted again!!! is there a proper way to adjust them??

    And lastly how do you set your total timing ?? I hear different people saying to set your total timing the engine will perform much better!!! I never heard of that ... I know this was a lot of information but if someone could give me some advise I would greatly appreciate it.
     
  2. Pfrederiksen

    Pfrederiksen Veteran Member

    Messages:
    609
    Likes Received:
    0
    Joined:
    Feb 21, 2011
    Location:
    Edmonton,Canada
    Curious, why would you run a points ignition in this day and age?
     
  3. muscl car

    muscl car Veteran Member Lifetime Gold Member

    Messages:
    22,285
    Likes Received:
    1,058
    Joined:
    Jul 8, 2001
    Location:
    SoCal High Desert
    i've got a 70 LT1 motor in my camaro running 11.1:1 comp and my timing is 23 initial/38 deg total all in by 3k rpm
     
  4. 1hot1970

    1hot1970 Veteran Member

    Messages:
    118
    Likes Received:
    0
    Joined:
    Sep 23, 2011
    Location:
    Lancaster, Pennsylvania
    I wanted to keep it pretty much all original
     
  5. 1hot1970

    1hot1970 Veteran Member

    Messages:
    118
    Likes Received:
    0
    Joined:
    Sep 23, 2011
    Location:
    Lancaster, Pennsylvania
    How do you set that ?? all in by 3K, My motor is the same as yours, but I am running the original 2110 intake, 4555 carb, with the original LT-1 vaccuum advance distributor, can you give me some pointers in making my engine perform to its peak?
     
  6. Gary S

    Gary S Administrator Lifetime Gold Member

    Messages:
    23,108
    Likes Received:
    1,105
    Joined:
    Apr 14, 1999
    Location:
    Bismarck, North Dakota
    A properly set up points ignition will run as well as any properly set up factory HEI ignition, and likely more reliable than any aftermarket electronic ignition. Points ignitions are higher maintenance, but very reliable because they are very simple. If the engine doesn't run right with a good points ignition, changing ignition to something else won't help.
     
  7. Pfrederiksen

    Pfrederiksen Veteran Member

    Messages:
    609
    Likes Received:
    0
    Joined:
    Feb 21, 2011
    Location:
    Edmonton,Canada
    Fair enough. That's why I asked. Never spent any time with them.

    P
     
  8. spicewood1

    spicewood1 BANNED

    Messages:
    1,936
    Likes Received:
    0
    Joined:
    Jul 16, 2001
    Location:
    NC
    I run a similar timing setup as listed above on mine too. I like to run a lot of initial timing and have a smaller advance curve total.

    You have to modify the cams and their travel slot to get it this way. A certain amount of advance is built into the factory weights and slot and it cannot be altered any other way. Mine seems to like 36 degrees total and I like about 18 static. All in by 2500 or so. The factory curve was in the vicinity of 8 static and 25 to 30 more in the advance curve all in by about 4000. (way too late)

    And yes, the timing mark jumps around a bit on the timing light. Its all due to actual timing flutter or "scatter" caused by the oil pump shaft pulses, clearances in the original cam gear, and dizzy shims, and even slight fluctuations in your timing light itself.
     
  9. COPO

    COPO Veteran Member Lifetime Gold Member

    Messages:
    18,928
    Likes Received:
    1,264
    Joined:
    Sep 15, 1999
    Location:
    Ontario, Canada
    I'm running with 36* total advance on my 70 Z28 LT-1. I ran with Pertronix for years before it died by mimicking a carb problem when the engine got to operating temp. It did finally die. I ran points again for a couple of years then decided to try out the Crane XR-1 module with a built in rev limiter.

    [​IMG]
     
  10. warped

    warped Veteran Member Lifetime Gold Member

    Messages:
    3,212
    Likes Received:
    1
    Joined:
    Oct 20, 2003
    Location:
    Sitting in my command bunker waiting for the zombi
    There are several things you have to consider here. Your primary concern seems to be timing, so to put things a bit simpler, total timing is just the sum of your initial and the distributor's mechanical advance. This is independant of any advance the vacuum can adds in.


    All timing changes should be done with the vacuum advance disconnected and plugged. To get the total mechanical advance in by the 3000 rpm mark, you have to adjust the way the distributor brings the advance in. this is done by changing and/or modifying the weights and springs in the distributor. The easiest way to do this would be to find an old timer with a Sun distributor machine. the distributor is placed in the machine and the curve can be set there once rather than fiddling multiple times with the weights and springs then testing if you don't have access to a machine. However, since points type distributors have not been around for quite a while and the electronic type can't use the same machine, finding someone with the machine and know how to use it properly is not going to be easy.

    I think a lot of the fluctuation you are seeing in your timing is due to the overlap of the cam, causing erratic vacuum readings. this is normal for an LT1 solid lifter cam, so you have to do the best you can to get your initial readings where you want them. Idle mixture is also affected here. The best way to set it is to use a vacuum gauge attached to manifold vacuum. Adjust each mixture screw to give the highest vacuum level. You may have to go from one to the other a couple of times to get it perfect. Good luck.
     

Share This Page