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Thread: 454 will not start help!!! Opinions needed!!!

  1. #1
    Junior Member SHOW GUEST
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    454 will not start help!!! Opinions needed!!!

    I have a stock short block 454. I have 781 large oval port heads that I had ported an 2.19 in, 1.88 exh valves added an milled .020 . The cam is a 629 lift with 260 duration at .050( cam specs http://www.compcams.com/Cam_Specs/Ca...?csid=459&sb=2 ) The car will not start, it trys but just will not run. I did compression test showing 90 psi?? I know thats very low, cause of cam or flat top not going to work? :?:

  2. #2
    Senior Member RACING JUNKIE
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    First thing i would check is cam timing, if you have multiple keyed timing gears it may not be set on the right combination. The compression is way too low even for flattop pistons. It should have 160 to 200 lbs. of cranking compression even with that cam.

    JMO

    Zip.

  3. #3
    Senior Member RACING JUNKIE
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    I agree with Zip. One time I put a cam in one that was otherwise all stock and decided to advance it 4 deg...didn't degree it and I didn't do it at the cam I used the key on the crank pully. That thing never would fire.Not even close.I finally put it back to "straight up" and it fired immediately....I guess the cam was probably already ground with advance in it to begin with.

  4. #4
    Senior Member DYNO OPERATOR
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    Has it run with the current setup, or are the heads & cam something new?

  5. #5
    Junior Member SHOW GUEST
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    I put the cam in straight up dot to dot.
    Yes the car ran fine before tear down, ran 8.16 in 8th with stock motor. I just had the heads done then added the 629 lift cam. The car will try to run but only after I pump the gas million times.

    The motor turns over fast like theres no compression, same as it did when no plugs where in? I did notice when I kept double checking to make sure it was on compression stroke, there was hardly any pressure blowing out the cycl like it should.

  6. #6
    Senior Member MASTER BUILDER
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    If you are running he 781 heads w/119cc chambers and a flat top piston, your compression should be around 8.5:1 and on the cam specs it calls for a 11:1 for this cam. Is it possible that the cam is too big and your bleeding off what little cylinder pressure that there is? This is a pretty stout cam for a flat top engine. JMO.

  7. #7
    Senior Member RACING JUNKIE fla1976's Avatar
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    Won't start

    I would adjust the valves again. Sounds like they are too tight and bleeding off compression.

  8. #8
    Senior Member DYNO OPERATOR
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    I agree with tcarda. With that cam, the intake valve closing a 79 degrees after BDC, you have an effective stroke of 2.70 inches. If you only have a static compression of 8.5:1 your dynamic compression is going to be about 5.86:1. Something to think about.

    TS1955

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    Senior Member RACING JUNKIE
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    Re: Won't start

    Quote Originally Posted by fla1976
    I would adjust the valves again. Sounds like they are too tight and bleeding of compression.
    x2

  10. #10
    Senior Member SENIOR BUILDER
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    did you put new lifters in? if so are they hyd? the valves might be to tight due to not pre oiling the lifters? JMO
    if something goes wrong there is always the cooler!!!


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