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Thread: My DIY LT1 24X 411pcm upgrade.

  1. #1
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    Default My DIY LT1 24X 411pcm upgrade.

    Hi guys.

    I'm doing a 24X conversion using a 411 PCM on my LT1 96 TransAm.
    I'm building the crank and cam reluctor wheels. I'm a machinist by trade so building the parts is the fun in it for me. I know I can buy everything I need to do the change over but I like making my own parts.

    The plan is to turbo charge the LT1 and tune it with EFILive.
    I have a LS1 on the engine stand and I have used a piston stop and degree wheel to find true TDC so I can see the relationship between the cam and crank reluctor wheels and sensors.
    One of my questions is if I miss the crank reluctor wheel to sensor alignment by a degree or 2 and I command
    20* of timing and my timing light shows 22* is there a place in the EFILive software to offset this so the commanded timing matches what I see with a timing light?
    Or should I build in some adjustment into the sensor bracket?
    Last edited by LT1; December 12th, 2015 at 05:19 AM.

  2. #2
    Joe (Moderator) joecar's Avatar
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    Quote Originally Posted by LT1 View Post
    ...
    is there a place in the EFILive software to offset this so the commanded timing matches what I see with a timing light?
    ...
    I don't see any place for such an offset.

  3. #3
    Joe (Moderator) joecar's Avatar
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    This may be of interest to you (I don't know what the timing was):

    Click image for larger version. 

Name:	CKP CMP waveform relationship.png 
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  4. #4
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    Thanks for posting that, very valuable info.
    I will build in some adjustment so my commanded timing matches what my light shows, that's easy to do.
    As fare as the accuracy of the 1X cam signal is concerned in relation to the 24x crank signal I can't see it being very critical.
    If it were people couldn't degree there cams and motors with high mileage with badly worn timing chains would set codes and not run very well. I've owned a few trucks with 300K+ miles that ran great. I know GM has a "target" to set off the cam sensor in relation to the crank but there are so many things that change the relationship the target window must be quite large.

    If I'm missing something please feel free point me in the right direction.

  5. #5
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    I would do the 58x E38/E67. you get better idle quality and a faster ECU .... if you are going to do this, might as well do that...
    "All that is needed for the triumph of evil is that good men do nothing..."

  6. #6
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    Those ECM's are defiantly upgrades over the 411 unit. I have a couple of reasonse for going the 411 route.
    I didn't want to tackle the DBW throttle body on my first time with tuning a factory ECM. I'm sure I'll have my fair share of bugs just changing over the LT1. The other reason in my son owns a stock 02 Z/28. If I get to lost I can plug up to his car and compare things.

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