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HT4100 4.1, 4.5, 4.9 Discussion, Techheads, answer me this: in Cadillac Engine Technical Discussion; Most of the older ones relied on the manifold for ground. They added an external ground to some to help ...
  1. #16
    ewill3rd is offline Cadillac Technician
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    Re: Techheads, answer me this:

    Most of the older ones relied on the manifold for ground.
    They added an external ground to some to help signal problems but I mainly meant the ones without heaters.

  2. #17
    the recluse is offline Cadillac Owners Connoisseur
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    Re: Techheads, answer me this:

    Quote Originally Posted by drewsdeville View Post
    Averaging 21mpg around town and a personal best of 27.2 on the highway (I drive it quite conservatively), I'm assuming that the car never plays games like this.
    The 4.9 I put together averages 23.5 to 25 mpg around town and 30 to 32 hwy. I'm running new Bosch O2's and my motor idles at 192 to 195 degrees (where the thermostat is rated). I can't imagine that a motor that hot would throw the O2 sensors out of loop...would it?

  3. #18
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    Sevillian273 is offline Cadillac Owners Connoisseur
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    Re: Techheads, answer me this:

    Quote Originally Posted by the recluse View Post
    The 4.9 I put together averages 23.5 to 25 mpg around town and 30 to 32 hwy. I'm running new Bosch O2's and my motor idles at 192 to 195 degrees (where the thermostat is rated). I can't imagine that a motor that hot would throw the O2 sensors out of loop...would it?
    Thats seems like unusually high city mileage.. what injectors are you running?

  4. #19
    the recluse is offline Cadillac Owners Connoisseur
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    Re: Techheads, answer me this:

    MSD Competition 19#'ers

    I've always loved the gas mileage the car has had to offer, but it seems to run better now that I've gutted the cat, port and polished the heads, tweaked the the throttle body, added a velocity stack, gasket matched and ported the intake, and gasket matched the exhaust manifolds...

    Next I would love to work on the intake box, it seems way too restrictive...

  5. #20
    Sevillian273's Avatar
    Sevillian273 is offline Cadillac Owners Connoisseur
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    Re: Techheads, answer me this:

    Oh I forgot it was a 4.9.... I was going to tell you that the 19's were too large and make the fuel data center inaccurate. The 19's in my 4.5 made my car display 21.6mpg when in fact I was getting 15.

    How did you make a velocity stack and is it before or after the TB? I started making a dual runner setup similar to the one on fieroaddiction.com but never finished it...

    http://www.fieroaddiction.com/caddy49a.html

  6. #21
    the recluse is offline Cadillac Owners Connoisseur
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    Re: Techheads, answer me this:

    Quote Originally Posted by Sevillian273 View Post
    How did you make a velocity stack and is it before or after the TB?
    It's an old school after the TB stacker plate that I made out of Corian (dense countertop material). I didn't want to mod the intake (cut into the intake to equalize flow between plenums), so I made a riser and cut out between the middle holes to accomplish the same thing. I also tapered the TB ports above and below the butterflies and opened the manifold to match. I wish I had access to a dyno to find out what it really is putting out, but i definitely feel a difference in throttle and passing gear. It'll burn 180' trail

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